The rs356182 variant sits approximately 19 kilobases downstream of the SNCA gene¹¹ SNCA gene
Alpha-synuclein (SNCA) is the first gene linked to Parkinson's disease and encodes a protein that forms the pathological hallmark of PD — Lewy bodies, in a brain-specific regulatory region marked by H3K27Ac histone modifications. This variant is one of the most statistically significant genetic associations with Parkinson's disease²² This variant is one of the most statistically significant genetic associations with Parkinson's disease
With a meta-analysis p-value of 1.85 × 10⁻⁸², rs356182 ranks among the strongest non-coding PD risk variants, consistently identified across multiple large-scale genome-wide association studies³³ multiple large-scale genome-wide association studies. The G allele increases PD risk with an odds ratio of 1.34 to 1.47⁴⁴ odds ratio of 1.34 to 1.47 depending on the population studied, and is robustly represented at approximately 37% frequency globally.

What makes rs356182 particularly interesting is that it doesn't follow a simple story. The risk allele (G) increases your chances of developing Parkinson's, but if you do develop the disease with GG genotype, you're more likely to have a tremor-predominant form with slower motor progression⁵⁵ tremor-predominant form with slower motor progression compared to the more aggressive postural instability and gait disorder (PIGD) phenotype. This paradox — higher disease risk but milder disease course — reveals the complexity of how this variant influences neurodegenerative processes.

The Mechanism

rs356182 resides within a genetic enhancer active in brain tissue, and the protective A allele creates a binding site for the transcription factor FOXO3⁶⁶ transcription factor FOXO3, while the risk G allele disrupts this binding. The traditional assumption was that this variant simply modulates alpha-synuclein levels, since it's near the SNCA gene. However, breakthrough CRISPR studies have revealed a more nuanced picture⁷⁷ breakthrough CRISPR studies have revealed a more nuanced picture: the protective A allele promotes normal neuronal differentiation and actually increases SNCA expression, while the risk G allele impairs neuronal development and reduces SNCA expression. This is counterintuitive — you'd expect higher alpha-synuclein to be worse for Parkinson's risk.

The resolution to this paradox likely lies in timing and context. The risk G allele appears to compromise dopaminergic neuron development during embryonic neurodevelopment⁸⁸ embryonic neurodevelopment
The effects manifest during fetal brain development, creating a diminished dopaminergic neuron population, leaving fewer neurons to spare when age-related degeneration begins decades later. Meanwhile, in adults who already have PD, having the GG genotype (which reduces alpha-synuclein expression in the cerebellum) may slow the accumulation of toxic protein aggregates, explaining the slower motor progression observed in clinical studies⁹⁹ slower motor progression observed in clinical studies.

The Evidence

A large case-control study in 2,205 Han Chinese participants¹⁰¹⁰ A large case-control study in 2,205 Han Chinese participants
Cheng et al. SNCA rs356182 variant increases risk of sporadic Parkinson's disease in ethnic Chinese. Journal of the Neurological Sciences, 2016 found that the G allele was significantly overrepresented in PD patients (OR=1.470, p=2.3×10⁻⁸), with the GG genotype showing the strongest association (OR=1.620). This replicated findings from Caucasian populations, establishing rs356182 as a cross-ethnic risk factor.

A multi-site study of 810 Parkinson's patients¹¹¹¹ A multi-site study of 810 Parkinson's patients
Cooper et al. Common variant rs356182 near SNCA defines a Parkinson's disease endophenotype. Annals of Clinical and Translational Neurology, 2017 demonstrated that the GG genotype correlates with more tremor-predominant motor symptoms and predicts a 1-point per year slower UPDRS-III motor score progression. The variant was also associated with decreased SNCA expression in cerebellar tissue (p=0.005), suggesting region-specific effects on gene regulation.

The most mechanistically revealing study¹²¹² The most mechanistically revealing study
Prahl et al. The Parkinson's disease variant rs356182 regulates neuronal differentiation independently from alpha-synuclein. Human Molecular Genetics, 2023 used CRISPR to create precise hemizygous deletions at rs356182 in dopaminergic neuron cell models. Transcriptional profiling revealed that hundreds of genes involved in neurogenesis and axonogenesis were differentially expressed based on the allele present, with only minimal overlap with genes affected by SNCA knockout. This suggests rs356182 confers PD risk largely through mechanisms independent of alpha-synuclein levels.

A comprehensive meta-analysis¹³¹³ A comprehensive meta-analysis
Pihlstrøm et al. A comprehensive analysis of SNCA-related genetic risk in sporadic Parkinson disease. Annals of Neurology, 2018 identified rs356182 as one of at least three independent association signals at the SNCA locus, demonstrating that multiple genetic mechanisms at this locus contribute to PD risk in a non-redundant fashion.

Practical Implications

While there's no gene therapy or drug that specifically targets rs356182, the mechanisms it influences — neuronal health, oxidative stress, mitochondrial function, and dopamine system integrity — are all modifiable through lifestyle interventions. The evidence is strongest for aerobic exercise and antioxidant support.

Regular aerobic exercise demonstrates neuroprotective effects in Parkinson's models¹⁴¹⁴ Regular aerobic exercise demonstrates neuroprotective effects in Parkinson's models, improving mitochondrial function, reducing oxidative protein damage, and boosting neurotrophic factors like BDNF and GDNF in the substantia nigra. Exercise activates the Nrf2-ARE antioxidant response pathway, upregulates endogenous antioxidant enzymes, and may help preserve the dopaminergic neuron population that could be developmentally compromised by the G allele.

Dietary antioxidants — particularly beta-carotene and vitamin E¹⁵¹⁵ beta-carotene and vitamin E — have shown inverse associations with PD risk in prospective cohort studies. While these studies weren't stratified by rs356182 genotype, the biological rationale is sound: alpha-synuclein pathology generates oxidative stress, and individuals with variants affecting SNCA-related pathways may benefit more from antioxidant support.

For those with existing Parkinson's disease, knowing your rs356182 genotype may offer prognostic information. The GG genotype appears to predict a slower, more tremor-dominant course, which generally has a better prognosis and responds well to dopaminergic medications. However, this is population-level data — individual disease trajectories vary enormously based on other genetic factors, environmental exposures, and treatment responses.

Interactions

rs356182 is one of multiple independent SNCA risk variants. Other key variants include rs356219 (located in the promoter region) and rs356165, though these show minimal linkage disequilibrium with rs356182¹⁶¹⁶ these show minimal linkage disequilibrium with rs356182, meaning they segregate independently and can combine to increase risk additively. Individuals carrying risk alleles at multiple SNCA positions show incrementally higher PD susceptibility.

Beyond SNCA, gene-gene interactions have been documented between rs356219 (a related SNCA variant) and variants in LRRK2 and GAK genes¹⁷¹⁷ gene-gene interactions have been documented between rs356219 (a related SNCA variant) and variants in LRRK2 and GAK genes, suggesting that SNCA-pathway risk is modified by other Parkinson's genes. While specific studies haven't examined rs356182 in combination with LRRK2 or GBA variants, the biological pathways overlap — LRRK2 affects alpha-synuclein neurotoxicity and GBA mutations compromise lysosomal degradation of alpha-synuclein. Individuals with multiple risk variants across these pathways likely face compounded neurodegeneration risk, though the precise combined effects remain under investigation. Similarly, in carriers of LRRK2 mutations, the SNCA rs356219 variant modifies age of onset by approximately 4 years¹⁸¹⁸ in carriers of LRRK2 mutations, the SNCA rs356219 variant modifies age of onset by approximately 4 years, suggesting that SNCA variants interact with other PD genetic risk factors to influence disease timing and phenotype.

SLC19A1, known as the reduced folate carrier (RFC1), is the principal gateway through which folate vitamins and antifolate drugs enter cells. Every cell in your body depends on RFC1 to import the folate it needs for DNA synthesis and methylation. The same transporter is exploited by two major drug classes — antifolate chemotherapies (pemetrexed, methotrexate) and antifolate antibiotics — to enter their target cells. A variant in the second intron of SLC19A1, rs3788189, has emerged in pharmacogenomics studies as a modifier of how well these drugs work and whether side effects are likely.

The Mechanism

rs3788189 sits in intron 2 of SLC19A1 at chromosome position 21:45,516,669 (GRCh38). The gene lies on the minus strand, so the plus-strand T/G polymorphism corresponds to C/A on the coding transcript. This variant has also been annotated in the literature as IVS2(4935) G>A (intron 2, 4,935 bases into the intron). As an intronic variant, rs3788189 does not directly change the amino acid sequence of the RFC1 protein, but intronic variants can alter pre-mRNA splicing¹¹ pre-mRNA splicing
Intronic sequences contain branch points, polypyrimidine tracts, and splice enhancer/silencer sequences that regulate how exons are joined, create cryptic splice sites, affect mRNA stability, or alter transcriptional regulation through intronic enhancer elements. The exact molecular mechanism by which rs3788189 influences RFC1 expression or function has not been characterized, but the pharmacogenomics signal is consistent with functional consequences in folate and antifolate transport.

Note that rs3788189 is distinct from the well-characterized G80A coding variant (rs1051266, p.His27Arg), which is already in the GeneOps database. These are independent variants in the same gene with different functional implications.

The Evidence

The clearest pharmacogenomics signal comes from two small but consistent studies in patients receiving pemetrexed²² pemetrexed
Pemetrexed (Alimta) is an antifolate used for non-small-cell lung cancer and mesothelioma; it enters cells via RFC1 to inhibit folate-dependent enzymes, a modern antifolate chemotherapy that uses RFC1 for cellular uptake.

In a phase II perioperative study of 38 NSCLC patients receiving cisplatin plus pemetrexed, the TT genotype at rs3788189 was associated with improved disease-free survival³³ TT genotype at rs3788189 was associated with improved disease-free survival
Dy et al. J Thorac Oncol 2014 (p=0.0821), suggesting patients with two copies of the reference T allele derived greater benefit from pemetrexed-based chemotherapy.

In a larger pharmacogenomic study of 136 lung cancer and mesothelioma patients receiving pemetrexed/platinum⁴⁴ 136 lung cancer and mesothelioma patients receiving pemetrexed/platinum
Corrigan et al. Pharmacogenomics J 2014, rs3788189 was among three SLC19A1 polymorphisms independently associated with overall survival, supporting the hypothesis that this intronic variant influences RFC1-mediated pemetrexed transport.

A meta-analysis of 16 publications covering 1,510 patients on pemetrexed or gemcitabine identified SLC19A1 IVS2(4935) G>A — corresponding to rs3788189 — as a predictor of grade 3+ leukopenia in American patients⁵⁵ SLC19A1 IVS2(4935) G>A — corresponding to rs3788189 — as a predictor of grade 3+ leukopenia in American patients
Zaïr & Singer, Pharmacogenomics 2016. This hematological toxicity signal suggests that the G allele may be associated with impaired RFC1-mediated pemetrexed transport efficiency or altered folate competition during treatment, leading to differential drug exposure in bone marrow progenitor cells.

The evidence base is limited — most studies are small, the mechanism is not characterized at the molecular level, and no clinical guidelines (CPIC, DPWG) currently exist for this variant. The evidence level is therefore rated emerging.

Practical Actions

For people with GG or GT genotypes who are candidates for pemetrexed or methotrexate treatment, sharing this pharmacogenomic result with their oncologist or rheumatologist provides potentially useful context — particularly given the leukopenia signal in the meta-analysis. Pemetrexed requires standard folic acid and vitamin B12 supplementation before each cycle regardless of genotype (per prescribing protocol), but this variant may influence monitoring intensity.

From a nutritional standpoint, since RFC1 is also the main folate transporter, this variant may modestly affect baseline folate transport efficiency. The G allele may be associated with slightly altered intracellular folate availability, though this has not been studied in nutritional contexts independent of antifolate chemotherapy.

Interactions

The most clinically significant interaction is with the coding variant rs1051266 (G80A, p.His27Arg) in the same gene. rs1051266 reduces RFC1 transport function through a structural change in transmembrane domain 1; rs3788189 may additively affect transport through an independent regulatory mechanism. Carriers of risk alleles at both sites within SLC19A1 may have more pronounced impairment.

The folate pathway interaction extends to MTHFR (rs1801133 C677T, rs1801131 A1298C): if MTHFR activity is reduced AND RFC1 transport is impaired, intracellular methylfolate may be doubly compromised, amplifying the importance of methylfolate supplementation over synthetic folic acid.

Pain and the medications used to treat it are profoundly personal. The same opioid dose that barely touches one person's pain may overwhelm another's reward circuits. Part of that individual variation is genetic — and some of it traces back to the chromatin architecture of pain-relevant genes themselves. rs3791033 is an intronic variant¹¹ intronic variant
A change within a non-coding region of a gene, located within intron 8 of KDM4A at position c.1163+387 on chromosome 1 in KDM4A, a histone demethylase that regulates which genes are switched on or off in the brain's pain and reward systems. The C allele was identified as one of only two genome-wide significant variants for problematic opioid prescription use in one of the largest studies ever conducted on opioid genetics.

The Mechanism

KDM4A (lysine demethylase 4A²² lysine demethylase 4A
Also known as JMJD2A or JHDM3A; the gene encodes a JmjC-domain Jumonji family demethylase, OMIM 609764) removes trimethyl marks from histone H3 at lysines 9 and 36 (H3K9me3 and H3K36me3). These marks are repressive — regions of chromatin bearing them are condensed and transcriptionally silent. By erasing these marks, KDM4A opens chromatin at specific gene promoters and allows transcription to proceed. At pain-relevant loci and in dopaminergic reward circuits — where H3K9 methylation status tightly controls gene expression — variation in KDM4A activity can shift the transcriptional landscape of pain processing and opioid reward.

rs3791033 lies in an intron, so it does not alter the KDM4A protein sequence. Its effect is likely regulatory: altering splicing efficiency, intron retention kinetics, or binding of regulatory RNA-binding proteins, any of which could modulate KDM4A expression levels in relevant tissues. The mechanism by which this specific intronic change influences opioid use behavior remains under investigation.

The Evidence

Sanchez-Roige et al. (2021)³³ Sanchez-Roige et al. (2021)
PMID 34728798, Molecular Psychiatry, N=132,113 European-ancestry 23andMe participants, ~21% cases conducted a GWAS of "problematic opioid prescription use" — defined as using prescribed opioids not as prescribed — as a proxy phenotype for opioid use disorder risk. Among 132,113 participants, only two loci reached genome-wide significance (p ≤ 5×10⁻⁸): rs3791033 near KDM4A and rs640561 near LRRIQ3. The genetic correlation between this phenotype and clinically diagnosed opioid use disorder was rg = 0.64–0.80, validating the proxy approach. Additional genetic correlations were found with alcohol dependence (rg = 0.74), chronic pain, depression, and insomnia — consistent with the known comorbidity structure of opioid misuse.

The study did not report specific odds ratios or beta coefficients for the lead variants in the abstract, which is a limitation. The finding represents discovery-level evidence: genome-wide significant in a large, well-powered study, but requiring replication in independent clinical cohorts with direct OUD diagnosis and functional follow-up.

Contextualizing the biology, Holen et al. (2023)⁴⁴ Holen et al. (2023)
PMID 37252880, Addiction Biology, ~15,756 OUD cases and ~600,000 psychiatric controls identified 14 novel OUD loci using a cross-disorder conditional FDR approach, including DRD2, FURIN, and MHC region — establishing shared genetic architecture between OUD and major psychiatric disorders. KDM4A's epigenetic regulatory role connects this variant to the broader landscape of transcriptional dysregulation in addiction neuroscience.

Practical Actions

The C allele of rs3791033 signals higher individual susceptibility to problematic opioid use — using opioids in ways that deviate from prescribed instructions, which is an early behavioral marker for developing opioid use disorder. This does not mean opioid medications should never be used; rather, it suggests heightened vigilance when opioids are prescribed for pain management.

CC homozygotes carry two copies of the risk allele and face the greatest concern. Discussing genetic risk explicitly with treating physicians allows for proactive steps: careful dosing titration, shorter prescription durations, preference for non-opioid first-line analgesics where clinically appropriate, and early monitoring for signs of dose escalation or dependence. CT heterozygotes carry an intermediate signal worth noting, particularly for anticipated longer-term opioid exposure (post-surgical recovery, chronic pain management).

Non-opioid pharmacological alternatives include NSAIDs, COX-2 inhibitors, anticonvulsants (gabapentin, pregabalin), SNRIs (duloxetine for neuropathic pain), tricyclic antidepressants for neuropathic and central sensitization pain, and topical agents (lidocaine patches, capsaicin). Interventional options — nerve blocks, spinal cord stimulation — are worth earlier consideration in surgical and chronic pain contexts for individuals with elevated genetic opioid risk.

Interactions

rs3791033 has been studied as an independent locus. The GWAS that identified it found a second significant hit at rs640561 near LRRIQ3, though these are on different chromosomes and are not in linkage disequilibrium. The broader opioid use disorder genetic landscape overlaps with OPRM1 rs1799971 (the A118G variant, the best-studied opioid receptor variant, which alters mu-opioid receptor binding affinity) — though rs3791033 and OPRM1 act through distinct mechanisms (epigenetic regulation vs. receptor function) and both may contribute independently to overall opioid response phenotype.

When scientists began systematically scanning the human genome for type 2 diabetes risk, one of the first and most consistently replicated signals landed on chromosome 10q23 — near two genes with seemingly different jobs: HHEX¹¹ HHEX
Hematopoietically Expressed Homeobox — a transcription factor that acts as a master switch for organ development, including the pancreas and IDE²² IDE
Insulin-Degrading Enzyme — a metalloprotease that degrades insulin and amyloid beta peptides. The SNP rs5015480 sits in this locus and is in complete linkage disequilibrium (r² = 1) with the primary association marker rs1111875, meaning the two variants are inherited together as a single functional unit in nearly all human populations.

The Mechanism

HHEX encodes a homeodomain transcription factor expressed in the liver, thyroid, and — critically — the developing pancreas. During embryogenesis, HHEX is required for proper formation of the ventral pancreatic bud; mice with HHEX knockout fail to develop a normal pancreas and show profound defects in insulin-producing beta-cell mass. In adult beta cells, HHEX continues to regulate genes involved in beta-cell identity and function, including insulin gene expression programs.

The C allele at rs5015480 (and the linked C allele at rs1111875) is associated with reduced HHEX expression in pancreatic tissue, which translates into diminished beta-cell function and reduced first-phase insulin secretion in response to glucose. IDE, located nearby, degrades secreted insulin — variants that alter IDE expression or activity could further modulate circulating insulin levels, though whether IDE or HHEX is the causal gene remains an active area of investigation.

The Evidence

This locus was identified simultaneously by multiple landmark GWAS in 2007, cementing its status as one of the most robustly replicated T2D signals in the literature.

The Sladek et al. 2007 GWAS³³ Sladek et al. 2007 GWAS
Sladek R et al. A genome-wide association study identifies novel risk loci for type 2 diabetes. Nature, 2007 tested 392,935 SNPs in a French case-control cohort and identified the IDE-KIF11-HHEX locus as one of four novel T2D risk regions, together with TCF7L2 replication.

The Scott et al. 2007 FUSION study⁴⁴ Scott et al. 2007 FUSION study
Scott LJ et al. A genome-wide association study of type 2 diabetes in Finns detects multiple susceptibility variants. Science, 2007 confirmed HHEX among validated T2D susceptibility loci. Combined analysis across the FUSION, DGI, and WTCCC/UKT2D cohorts yielded an odds ratio of 1.13 (95% CI 1.09–1.17)⁵⁵ 1.13 (95% CI 1.09–1.17)
Scott LJ et al. Science, 2007 per C allele (p = 5.7 × 10⁻¹⁰), with a risk allele frequency of ~0.52 in controls. The effect is modest but genome-wide significant and highly reproducible across European, East Asian, and other populations.

Zeggini et al. 2008⁶⁶ Zeggini et al. 2008
Zeggini E et al. Meta-analysis of genome-wide association data and large-scale replication identifies additional susceptibility loci for type 2 diabetes. Nat Genet, 2008 placed HHEX/IDE among 10 established T2D loci, each conferring allelic odds ratios in the 1.1–1.2 range.

Takeuchi et al. 2009⁷⁷ Takeuchi et al. 2009
Takeuchi F et al. Confirmation of multiple risk loci and genetic impacts by a genome-wide association study of type 2 diabetes in the Japanese population. Diabetes, 2009 confirmed the HHEX association in a Japanese cohort, demonstrating the cross-ethnic stability of this signal. Notably, the T allele (the protective variant) is far more common in East Asian populations (~82% frequency vs ~42% in Europeans), which may partly explain differences in T2D genetic architecture across ancestries.

Practical Implications

The HHEX/IDE locus acts primarily through the insulin secretion axis — specifically impaired beta-cell development and reduced first-phase insulin release. Unlike variants that primarily affect insulin resistance (PPARG, ADIPOQ), HHEX risk carriers have beta cells that are constitutively less efficient at responding to a glucose load.

The single most actionable implication is protecting beta-cell reserve through dietary patterns that minimize demand on the insulin secretory apparatus. This means limiting glycemic spikes — not through generic "healthy eating" but through specifically timed, lower-glycemic-index meal patterns that match the reduced first-phase insulin capacity of HHEX C-allele carriers.

Post-meal glucose monitoring and periodic HbA1c checks are particularly informative for this genotype, because the impaired first-phase insulin response is precisely what blunts early post-meal glucose suppression and progressively loads beta-cell reserve over decades.

Interactions

HHEX rs5015480 operates through the insulin secretion pathway, distinct from the insulin resistance pathway. Carrying risk alleles at both this locus (impaired secretion) and at TCF7L2 rs7903146 (impaired Wnt-mediated beta-cell function) compounds T2D risk through converging but independent mechanisms. Similarly, co-inheritance with SLC30A8 rs13266634 (zinc transporter affecting insulin granule crystallization) further loads the insulin secretion pathway. Individuals with risk alleles at multiple secretion- pathway loci should give highest priority to metabolic monitoring and glycemic-load management.

The SRD5A2 gene encodes steroid 5-alpha-reductase type 2, the enzyme that converts testosterone to 5-alpha dihydrotestosterone (DHT)

— the most potent androgen in the body. This conversion is critical in the prostate, hair follicles, and skin. The V89L variant (rs523349) is a missense single nucleotide polymorphism resulting in a valine to leucine substitution at codon 89 that reduced SRD5A2 enzyme activity . The L allele (coded as C in 23andMe data) is extremely common, carried by

54.8% of Asians, 30.4% of whites, and 23.1% of African Americans .

The Mechanism

The valine-to-leucine substitution at position 89 sits in a functionally important region of the enzyme. Biochemical studies¹¹ Biochemical studies
Makridakis et al. demonstrated functional differences between variants show that the L variant produces about 30% less DHT from testosterone compared to the V variant. This reduced enzyme activity means that individuals with LL genotypes produce less DHT throughout their lifetime, while those with VV genotypes maintain higher DHT production. The heterozygous VL genotype shows intermediate activity.

Because DHT is the primary androgen driving prostate growth, hair follicle miniaturization in male pattern baldness, and sebum production, this variant has wide-ranging effects on androgen-mediated physiology.

The Evidence

The relationship between V89L and disease risk is complex and ethnicity-dependent:

Prostate cancer:

A 2010 meta-analysis of 25 studies (8,615 cases, 9,089 controls) found that V89L polymorphism could play a low-penetrant role in prostate cancer risk among Europeans , with an OR of 1.11 (95% CI 1.03-1.19) for carriers of at least one L allele.

However, a comprehensive meta-analysis found that prostate cancer was not associated with V89L overall (OR = 0.99, 95% CI: 0.94, 1.05) . The European-specific risk appears modest and was significantly associated with increased prostate cancer risk in men aged ≤65 (OR 1.70, 95% CI 1.09-2.66 for LL vs VV) .

Interestingly, one large French study found that the low-activity V89L variant is associated with an increased risk of aggressive prostate cancer , suggesting that chronically lower DHT levels may paradoxically increase risk of high-grade tumors. This finding helped explain controversies observed in finasteride chemoprevention trials.

Benign prostatic hyperplasia (BPH):

SRD5A2 rs523349 (V89L) polymorphism showed no significant role in BPH occurrence in total analysis, but its reducing and increasing effects on the disease risk were reflected in Caucasian and other-ethnicity subgroups, respectively . In Caucasians, the L variant appeared protective (OR 0.47, 95% CI 0.24-0.93), while in Asian populations it increased risk (OR 2.74, 95% CI 1.27-5.92).

Male pattern baldness: Studies have been inconsistent.

Genetic association studies of 5 alpha reductase genes SRD5A1 and SRD5A2 in 828 families failed to show an association between these genes and male androgenetic alopecia , despite the clear role of DHT in hair loss and the efficacy of 5-alpha-reductase inhibitors as treatment.

Metabolic effects:

Metabolic syndrome develops more frequently in testicular cancer survivors homozygous or heterozygous variant for SNP rs523349 in SRD5A2 , with patients with lower testosterone levels (<15 nmol/l) and a variant genotype showing a high prevalence of metabolic syndrome (66.7%) .

Practical Implications

The main clinical relevance of this variant lies in pharmacogenomics and understanding individual androgen physiology:

Finasteride response: Finasteride works by inhibiting 5-alpha-reductase type 2.

Substantial pharmacogenetic variation was observed among the mutants, with finasteride inhibition varying 60-fold depending on the variant. Studies suggest²² Studies suggest
Genetic variation affects drug binding affinity that individuals with different SRD5A2 genotypes may respond differently to finasteride treatment for BPH or male pattern baldness, though clinical dosing guidelines do not yet account for genotype.

Prostate health monitoring: Men of European descent who carry the L allele, particularly those over 40, may benefit from more vigilant prostate cancer screening, given the modest increase in risk and association with aggressive disease. However, the effect size is small enough that this should not override standard screening guidelines.

Understanding DHT-mediated effects: If you have LL genotype, you produce less DHT throughout your life. This may contribute to less severe male pattern baldness, reduced prostate enlargement with age, but potentially different metabolic patterns. The VV genotype maintains higher DHT production, which may manifest as more robust androgen effects.

Interactions

The SRD5A2 V89L variant interacts with rs9282858 (A49T), another variant in the same gene.

The effects of compound heterozygotes and haplotypes composed of homozygotes for the common V89L variant plus one rare heterozygous mutation were determined , showing that the V89L–A49T haplotype demonstrated the highest affinity for finasteride compared with other haplotypes . Individuals with both variants may have substantially different enzyme kinetics and drug response.

The HSD3B2 gene (encoding 3-beta-hydroxysteroid dehydrogenase) also influences androgen metabolism.

Most of the prostate cancer risk associated with the intron 3 HSD3B2 short allele was confined to the SRD5A2 89L variant subgroup , indicating that combined genotype analysis may better predict risk than either variant alone.

When you lose weight through a calorie-restricted diet, your HDL-cholesterol levels can shift in complex ways — and your ABCG1 genotype at rs692383 appears to determine how much HDL-c you preserve during that process. ABCG1¹¹ ABCG1
ATP-binding cassette transporter G1, a membrane pump that moves cholesterol and phospholipids from macrophage cell membranes onto mature HDL particles — the second step in reverse cholesterol transport after ABCA1 initiates HDL loading is one of the body's primary cholesterol efflux transporters. Located on chromosome 21q22.3 and expressed in macrophages, liver, and many other tissues, ABCG1 loads surplus cellular cholesterol onto mature HDL particles, funneling it back to the liver — a central step in preventing foam cell accumulation and atherosclerotic plaque formation.

The rs692383 variant is an intronic variant in ABCG1 at chromosome 21, position 42,215,064 (GRCh38). It does not alter the ABCG1 protein sequence but sits within a region where intronic variants can influence gene expression, splicing efficiency, or regulatory element responsiveness to metabolic signals. What distinguishes rs692383 is its documented interaction with calorie-restricted dietary conditions: the G allele at this position is associated with better preservation of HDL-c levels during weight-loss dieting.

The Mechanism

The precise molecular mechanism by which rs692383 modifies ABCG1's response to calorie restriction is not yet established. However, ABCG1 transcription is regulated by liver X receptor (LXR)²² liver X receptor (LXR)
a nuclear receptor activated by oxysterols and dietary lipid signals; once activated, LXR drives expression of ABCG1, ABCA1, and other cholesterol homeostasis genes. During calorie restriction, circulating lipid profiles shift substantially: fatty acid mobilization increases, HDL remodeling accelerates, and ABCG1 activity modulates how efficiently cholesterol is transferred to and from HDL particles.

An intronic variant in this regulatory context could influence how strongly the ABCG1 gene responds to these dietary metabolic signals — for instance, by altering an enhancer element or splice site that controls expression levels under conditions of negative energy balance. AA homozygotes may have a less robust ABCG1 response during calorie restriction, resulting in less efficient cholesterol recycling through HDL and a net decline in circulating HDL-c. G allele carriers appear to maintain ABCG1 efflux activity more effectively under these conditions, preserving HDL-c levels even while losing weight.

The Evidence

The primary evidence comes from a study by Teixeira et al. (2020)³³ study by Teixeira et al. (2020)
Teixeira MD et al. Is it possible ABC transporters genetic variants influence the outcomes of a weight-loss diet in obese women? Genetics and Molecular Biology, 2020 examining 137 obese women following a nine-week calorie-restricted diet (−600 kcal/day). G allele carriers showed a significantly lower reduction in HDL-c compared to AA homozygotes (p=0.043), and this association remained significant after correction for multiple testing in the longitudinal analysis. A secondary finding — association between the AA genotype and lower BMI in the post-diet period — did not survive multiple-testing correction.

The evidence base for rs692383 is currently at the emerging level: a single study with a modest sample size (137 women), focused on one specific context (obese women undergoing calorie restriction), with no independent replication to date. The biological plausibility is solid — ABCG1 is a well-characterized HDL efflux transporter — but the specific effect of rs692383 on HDL-c during dieting requires confirmation in larger and more diverse populations.

The global G allele frequency is approximately 0.46, with substantial population stratification: ~31% in Europeans, ~76% in Africans, and ~46% in East Asians. This variation means the population-level relevance of this finding differs markedly by ancestry.

Practical Actions

For AA homozygotes (~29% of people globally, ~47% of Europeans): calorie-restricted dieting may reduce HDL-c more than expected. This does not mean weight loss should be avoided — the metabolic benefits of appropriate weight management outweigh a modest HDL-c dip in most cases. However, tracking HDL-c before, during, and after a weight-loss intervention gives personalized data on whether this genotype-specific response is occurring. If HDL-c falls substantially during dieting, specific interventions can offset this effect: regular aerobic activity is one of the most potent HDL-raising strategies, EPA/DHA supplementation modestly supports HDL remodeling, and niacin (extended-release) raises HDL-c specifically — though it should only be considered under medical supervision.

For G allele carriers (AG or GG): HDL-c appears more resilient during calorie restriction, which may provide a cardiovascular advantage during weight-loss periods. Standard dietary monitoring is appropriate.

Interactions

ABCG1 at rs692383 is one of three independent ABCG1 variants in this database. The rs4148102 variant modifies LDL-c response to high-PUFA diets, and the rs57137919 promoter variant alters ABCG1 expression in macrophages and is associated with altered HDL-c and LDL-c levels at baseline. Together, these three variants define distinct aspects of ABCG1 biology: promoter regulation, dietary PUFA response, and HDL-c dynamics during calorie restriction. Carrying risk alleles at multiple ABCG1 variants may compound impairment in reverse cholesterol transport, though no study has directly examined the rs692383 × rs4148102 or rs692383 × rs57137919 interaction.

Adiponectin is one of the body's most potent insulin-sensitizing hormones, secreted by adipose tissue and acting on the liver and muscle to reduce fat accumulation and improve glucose handling. Its actions depend entirely on two receptors: AdipoR1 and AdipoR2¹¹ AdipoR2
AdipoR2: adiponectin receptor 2, encoded by ADIPOR2 on chromosome 12p13.33. Primarily activates PPARα signaling in liver and adipose tissue, enhancing fatty acid oxidation and suppressing glucose production. rs767870 sits in intron 6 of ADIPOR2, and the G allele at this locus has been linked to impaired receptor signaling, elevated liver fat content, and increased type 2 diabetes (T2D) risk in replicated studies across European populations.

The Mechanism

ADIPOR2 encodes a seven-transmembrane receptor with intrinsic ceramidase activity that converts ceramide — a pro-apoptotic and insulin-antagonizing lipid — into the cytoprotective sphingosine 1-phosphate. When adiponectin binds AdipoR2, the receptor activates PPARα²² PPARα
PPARα: peroxisome proliferator-activated receptor alpha, a nuclear transcription factor that drives expression of fatty acid oxidation genes, particularly in liver cells, which then transcribes genes for β-oxidation, reducing ectopic fat and hepatic triglyceride output. Independently, AdipoR2 activation engages AMPK³³ AMPK
AMPK: AMP-activated protein kinase, the cell's central energy sensor; activation inhibits glucose production (gluconeogenesis) and stimulates glucose uptake to suppress hepatic glucose production.

rs767870 is located in intron 6, 20 nucleotides downstream of the codon 650 splice junction (HGVS: NM_001375363.1:c.650+20G>A). As an intronic variant, it does not alter the encoded protein, but intronic variants commonly affect splicing efficiency, mRNA stability, or the binding of intronic regulatory elements — all of which can reduce receptor abundance at the cell surface. Less functional ADIPOR2 means weaker PPARα induction per unit of circulating adiponectin, attenuating the receptor-mediated reduction of liver fat and hepatic insulin resistance.

The Evidence

The primary genetic evidence comes from a Caucasian case-control study⁴⁴ Caucasian case-control study
Vaxillaire M et al. Genetic analysis of ADIPOR1 and ADIPOR2 candidate polymorphisms for type 2 diabetes in the Caucasian population. Diabetes, 2006 of 2,876 French subjects. Among three ADIPOR2 SNPs showing nominal T2D association, rs767870 was the one replicated in an independent dataset, reaching OR 1.25 (95% CI 1.07–1.45, p=0.0051) in the pooled meta-analysis. The G allele — the minor allele at ~15% frequency in Europeans — is the risk allele.

The metabolic consequences extend beyond T2D susceptibility. A Finnish multi-cohort study⁵⁵ A Finnish multi-cohort study
Kotronen A et al. Genetic variation in the ADIPOR2 gene is associated with liver fat content and its surrogate markers in three independent cohorts. European Journal of Endocrinology, 2009 found rs767870 significantly associated with liver fat content measured by proton magnetic resonance spectroscopy (¹H-MRS) in Finnish subjects, with the association validated in two further cohorts via gamma-glutamyltransferase and fasting triglyceride levels — both accepted surrogate markers of hepatic fat. This places rs767870 in the liver-fat category alongside rs738409 (PNPLA3) and rs58542926 (TM6SF2), though with more moderate effect.

A Greek cross-sectional study⁶⁶ A Greek cross-sectional study
Halvatsiotis I et al. Genetic variation in ADIPOR2 is associated with coronary artery disease and increased ADIPOR2 expression in peripheral monocytes. Cardiovascular Diabetology, 2010 found significantly different rs767870 genotype distributions between CAD and non-CAD individuals (p=0.017), with heterozygous carriers showing worse endothelial function (lower flow-mediated dilatation) and higher intima-media thickness — early markers of atherosclerotic burden.

The evidence is rated moderate: the T2D association was replicated within the same French study across independent cohorts, and consistent pleiotropic effects on liver fat and vascular phenotypes suggest genuine biological activity at this locus. However, rs767870 has not appeared in the largest T2D GWAS meta-analyses (DIAGRAM, UKBB), likely reflecting its moderate effect size (OR ~1.25) and ~15% MAF, which give it limited power in studies not specifically focused on ADIPOR2.

Practical Actions

For AG and GG carriers, the main levers are those that directly amplify adiponectin signaling or compensate for impaired PPARα induction: omega-3 fatty acids (EPA/DHA) are independent PPARα ligands that partially bypass the receptor step; aerobic exercise robustly raises plasma adiponectin and upregulates ADIPOR2 expression in muscle; and reduced saturated fat intake lowers the ceramide substrate that impaired AdipoR2 ceramidase activity handles less efficiently.

Liver fat monitoring is particularly actionable: serum ALT and gamma-GT provide inexpensive early signals of hepatic fat accumulation that can guide dietary intervention before overt hepatic steatosis develops.

Interactions

ADIPOR2 acts in the same adiponectin signaling axis as ADIPOR1 (rs1044498), which primarily signals through AMPK rather than PPARα. Carriers of risk alleles at both receptors face a doubly attenuated adiponectin response — reduced AMPK activation (AdipoR1) and reduced PPARα induction (AdipoR2) — potentially producing greater combined insulin resistance than either variant alone. A compound action for the combined genotype is warranted if rs1044498 risk alleles are also present.

PPARG rs1801282 (Pro12Ala) is a functional variant in the PPARγ gene that affects adipogenesis and adiponectin secretion upstream of ADIPOR2 signaling. Carriers of the Ala12 (G) allele at rs1801282 tend to have higher circulating adiponectin but greater adipose tissue (more substrate for the receptor). The combined effect of elevated adiponectin (PPARG Ala12) and impaired receptor (ADIPOR2 G allele) has not been characterized in a single published study but represents a plausible pathway interaction for compound action design.

The SPINK5 gene encodes LEKTI¹¹ LEKTI
Lympho-Epithelial Kazal-Type Inhibitor, a 15-domain serine protease inhibitor expressed in skin, thymus, and mucosal surfaces; it acts as the primary brake on kallikrein proteases that drive epidermal desquamation, the protease inhibitor central to skin barrier integrity. Genetic variants across SPINK5 have been associated with atopic dermatitis since the landmark Walley et al. study²² Walley et al. study
Gene polymorphism in Netherton and common atopic disease. Nat Genet, 2001 identified the gene's role in common allergic disease. rs2303065 sits in exon 13 of SPINK5 and changes the codon for histidine at position 396 from CAT to CAC — a synonymous substitution that does not alter the LEKTI protein sequence (His396=).

The Mechanism

The c.1188T>C change at rs2303065 does not alter any amino acid in LEKTI and has no known direct functional consequence on protease inhibitor activity. ClinVar classifies this variant as benign based on submissions from multiple independent clinical testing laboratories with no conflicts. The T allele's clinical relevance arises entirely from its physical proximity to the functional rs2303067 variant³³ rs2303067 variant
SPINK5 p.Lys420Glu, 843 bp downstream in the same exon 13 region; Lys420 increases furin-mediated cleavage of the LEKTI D6–D7 linker, impairing the potent D6–D9 inhibitory fragment and elevating KLK5/KLK7 kallikrein activity in the skin. These two variants are in tight linkage disequilibrium within the exon 13 risk haplotype: the T allele of rs2303065 and the A (Lys420) allele of rs2303067 are inherited together more often than chance would predict.

The consequence of impaired LEKTI function — the mechanism tagged by this haplotype — is well characterised: KLK5 and KLK7 kallikreins run with reduced inhibition, cleaving desmoglein-1 and accelerating corneodesmosomes breakdown, increasing transepidermal water loss. Simultaneously, elevated kallikrein activity upregulates TSLP⁴⁴ TSLP
thymic stromal lymphopoietin, a cytokine that polarises dendritic cells toward Th2 immune responses and initiates the atopic sensitisation cascade in keratinocytes, lowering the threshold for IgE-mediated sensitisation to environmental allergens.

The Evidence

The rs2303065 T allele was among seven of eight SPINK5 polymorphisms found to be significantly associated with atopic dermatitis in a Japanese cohort of 124 AD patients and 110 healthy controls by Kato et al.⁵⁵ Kato et al.
Association of SPINK5 gene polymorphisms with atopic dermatitis in the Japanese population. Br J Dermatol, 2003. This finding was extended by Nishio et al.⁶⁶ Nishio et al.
Association between polymorphisms in the SPINK5 gene and atopic dermatitis in the Japanese. Genes Immun, 2003 using transmission disequilibrium tests, which confirmed SPINK5 haplotype-level association with AD but not asthma, and noted cross-ethnic consistency.

A large European analysis by Weidinger et al.⁷⁷ Weidinger et al.
Analysis of SPINK5, KLK7, and FLG polymorphisms and eczema risk. J Allergy Clin Immunol, 2008 (2,774 AD cases, 10,607 controls) found that SPINK5 variants showed only modest association at the population level, primarily through maternal transmission — a finding consistent with an LD proxy effect that varies in strength across populations with different haplotype structures. Because rs2303065 tags rather than causes the LEKTI impairment, the magnitude of its association with AD depends on how tightly it co-segregates with the functional rs2303067 variant in a given population — an LD parameter that differs between Japanese, European, and African cohorts.

The overall evidence is best classified as moderate: replicated across independent Japanese cohorts using different statistical methods, with a plausible mechanistic explanation via LD, but attenuated in large European studies and with no independent functional pathway.

Practical Actions

Because rs2303065 has no protein-altering effect, its actionability derives entirely from the underlying LEKTI pathway impairment it tags. Carrying the T allele — particularly in homozygous form — signals an increased likelihood of also carrying the risk haplotype at rs2303067. The practical implications are the same as for impaired LEKTI activity: supporting the skin barrier proactively, identifying allergen sensitisers that exploit a more permeable barrier, and monitoring for early atopic features in childhood.

Interactions

LD relationship with rs2303067: This is the primary interaction. Carriers of the TT genotype at rs2303065 are enriched for the Lys420/Lys420 (AA) genotype at rs2303067, the directly functional variant. For users who have results for both SNPs, the rs2303067 result provides the mechanistic information; rs2303065 provides LD-based corroboration.

SPINK5 × FLG variants: SPINK5 haplotype risk and filaggrin (FLG) loss-of-function variants operate through parallel mechanisms — protease over-activity vs. structural scaffold loss — and their effects on AD risk appear additive rather than synergistic, as documented in the Weidinger 2008 analysis.

The SNCA gene¹¹ SNCA gene
Alpha-synuclein (SNCA) was the first gene linked to Parkinson's disease; it encodes the protein that forms the pathological hallmark of PD — Lewy bodies contains multiple independent risk variants. rs356219 sits approximately 9 kilobases downstream of SNCA in a regulatory region that controls how much alpha-synuclein protein the cell produces. Unlike rs356182 — which acts through neuronal differentiation pathways — rs356219 works primarily by upregulating SNCA gene expression: carriers of the G allele have measurably higher alpha-synuclein levels in blood and specific brain regions. This is the variant's defining characteristic, and it makes rs356219 one of the most actionable SNCA risk markers because elevated alpha-synuclein is directly tied to aggregation, Lewy body formation, and dopaminergic neuron death.

The G allele has been consistently identified as a risk factor across twelve or more independent case-control studies spanning European, East Asian, and South American populations, making it one of the most robustly replicated common SNCA risk variants²² one of the most robustly replicated common SNCA risk variants.

The Mechanism

rs356219 functions as a regulatory variant³³ regulatory variant
A variant that alters gene expression rather than protein sequence; these often reside in promoters, enhancers, or 3′UTR regions in the 3′ region of the SNCA locus. The G allele alters the activity of this regulatory element in a direction that boosts SNCA transcription. Studies in CD45+ blood cells⁴⁴ Studies in CD45+ blood cells
Circulating immune cells express SNCA and can serve as a peripheral proxy for central nervous system expression confirmed that individuals carrying the G allele have significantly elevated SNCA mRNA levels and higher alpha-synuclein protein concentrations compared to AA homozygotes. Similarly, plasma alpha-synuclein is elevated in G-allele carriers in a dose-dependent additive manner⁵⁵ plasma alpha-synuclein is elevated in G-allele carriers in a dose-dependent additive manner, suggesting each additional G allele incrementally raises the ambient level of this aggregation-prone protein.

The downstream consequence is straightforward: more alpha-synuclein means a higher probability of misfolding, oligomer formation, and ultimately aggregation into the insoluble fibrils that kill dopaminergic neurons in the substantia nigra. This dose-response model explains why GG homozygotes show earlier onset and more rapid cognitive decline than AG heterozygotes, who in turn show higher risk than AA individuals.

The Evidence

The seminal genetic association study⁶⁶ The seminal genetic association study
Mata et al. SNCA variant associated with Parkinson disease and plasma alpha-synuclein level. Archives of Neurology, 2010 enrolled 1,956 PD patients and 2,112 controls and identified rs356219 as the most significant SNCA marker (OR 1.41, 95% CI 1.28–1.55; p=1.6×10⁻¹²). Crucially, the study also measured plasma alpha-synuclein in a subset, demonstrating that the risk allele correlates with higher protein levels — establishing a plausible dose-response mechanism.

A Chinese Han population study⁷⁷ A Chinese Han population study
Pan et al. SNP rs356219 of the alpha-synuclein gene is associated with Parkinson's disease in a Chinese Han population. Parkinsonism & Related Disorders, 2012 (403 patients, 315 controls) found OR 1.88 (95% CI 1.27–2.78) for variant genotypes, with GG homozygotes comprising 42.2% of PD patients versus 32.4% of controls. A follow-up Chinese study of 685 patients ⁸⁸ Li et al. SNCA rs356219 variant increases risk of sporadic Parkinson's disease in ethnic Chinese. Am J Med Genet B, 2013 confirmed these findings with OR 1.81 (95% CI 1.54–2.13; p=5.71×10⁻¹³) and documented earlier age at disease onset in G-allele carriers.

A 2025 systematic review and meta-analysis⁹⁹ A 2025 systematic review and meta-analysis
Common SNCA genetic variants and Parkinson's disease risk. International Journal of Molecular Sciences, 2025 across 27 studies found rs356219 demonstrated the strongest risk association of any common SNCA variant, particularly under the recessive model (OR 1.69, 95% CI 1.49–1.92). Under the allelic model the overall OR was 1.35 (95% CI 1.22–1.50).

A 2021 systematic review¹⁰¹⁰ A 2021 systematic review
Pedersen et al. A systematic review of associations between common SNCA variants and clinical heterogeneity in PD. npj Parkinson's Disease, 2021 covering 58 studies confirmed that the most reproducible clinical association for any common SNCA variant is rs356219 and earlier age at onset of PD. A Brazilian cohort study ¹¹¹¹ Campelo et al. Variants in SNCA gene are associated with PD risk and cognitive symptoms. Front Aging Neurosci, 2017 found that GG homozygotes with PD showed OR 5.74 (95% CI 1.42–23.21) for cognitive impairment, and a Scandinavian longitudinal study confirmed that GG genotype associates with faster annual cognitive decline as measured by MMSE.

A gene-environment study¹²¹² A gene-environment study
Lucchini et al. Metal exposure and SNCA rs356219 polymorphism associated with Parkinson disease. Front Neurol, 2020 of 432 cases and 444 controls in an industrially exposed Italian region found that the homozygous risk genotype alone confers OR 2.03 for PD, and that metal exposure independently adds further risk — with a directional (though not statistically significant) interaction suggesting carriers face compounded hazard when exposed to manganese and other neurotoxic metals.

Practical Actions

The central mechanism — elevated alpha-synuclein due to higher SNCA expression — shapes the specific interventions that make sense for G-allele carriers. The goal is not to lower risk of developing any disease, but to slow the aggregation of the excess protein that this variant produces.

Coenzyme Q10 targets several mechanisms directly relevant to alpha-synuclein toxicity¹³¹³ Coenzyme Q10 targets several mechanisms directly relevant to alpha-synuclein toxicity: mitochondrial complex I dysfunction (the primary energy failure in PD), oxidative stress that promotes alpha-synuclein misfolding, and neuroinflammation. The ubiquinol form is preferred for absorption. Coffee and caffeine have shown consistent neuroprotective associations in PD¹⁴¹⁴ Coffee and caffeine have shown consistent neuroprotective associations in PD, including evidence that caffeine reduces the toxicity of alpha-synuclein oligomers and restores autophagy — the cellular process that clears misfolded protein aggregates.

Reducing exposure to neurotoxic metals is particularly relevant for this variant: manganese specifically promotes alpha-synuclein overexpression and aggregation, and the gene-environment interaction data for rs356219 support avoiding occupational or environmental manganese/heavy metal exposure. Pesticides containing manganese compounds (maneb, mancozeb) are a specific concern for agricultural workers.

For those who develop PD, knowing the rs356219 genotype may inform prognosis: GG homozygotes face higher risk of cognitive decline and should discuss early cognitive monitoring with their neurologist.

Interactions

rs356219 is distinct from and independent of rs356182 (another SNCA risk variant already profiled in this database). These two variants reside in different linkage disequilibrium blocks and likely confer risk through different mechanisms — rs356182 acting through neuronal differentiation, rs356219 through SNCA expression levels. Carriers of risk alleles at both loci may face incrementally higher cumulative PD susceptibility.

The most clinically significant interaction is with LRRK2 G2019S, the most common dominant PD mutation. In LRRK2 G2019S carriers, the rs356219 G allele shifts age of onset approximately 4 years earlier¹⁵¹⁵ In LRRK2 G2019S carriers, the rs356219 G allele shifts age of onset approximately 4 years earlier (AG+GG carriers: mean onset ~58 years vs AA carriers: ~62 years; p=0.006). Individuals who carry both LRRK2 G2019S and rs356219 G risk alleles represent a high-priority group for early monitoring and preventive intervention.

rs356165, another 3′-region SNCA variant, co-occurs with rs356219 in some studies and may contribute additional independent risk, though its LD relationship with rs356219 varies by ancestry.

The SLC19A1 gene encodes the reduced folate carrier (RFC1), the primary mechanism by which folate moves from the bloodstream into your cells. Without efficient RFC1 function, intracellular folate levels fall — even when blood folate appears normal. The rs3788200 variant sits in intron 2 of SLC19A1 and has no direct effect on protein structure, but it serves as a reliable molecular tag for the same haplotype as rs1051266, the well-studied G80A coding variant that directly reduces folate transport kinetics.

The Mechanism

rs3788200 is an intronic variant that does not itself change amino acid sequence. Its biological relevance comes from its position in the genome: it is in very strong linkage disequilibrium¹¹ very strong linkage disequilibrium
LD r²=0.98 — the two variants co-occur nearly perfectly across populations with rs1051266 (G80A, p.His27Arg), which directly alters transmembrane domain 1 of the RFC1 transporter protein and reduces folate uptake into cells. Carrying the G allele at rs3788200 therefore marks the same genetic background as carrying the T allele at rs1051266: reduced folate transport capacity.

The Evidence

A 2023 Italian cohort study Bugianesi et al. Biomedicines, 2023²² Bugianesi et al. Biomedicines, 2023
Impaired Function of Solute Carrier Family 19 Leads to Low Folate Levels and Lipid Droplet Accumulation in Hepatocytes genotyped 756 individuals (452 NAFLD cases, 304 controls) and found rs3788200 significantly associated with non-alcoholic fatty liver disease (p=0.003). The G allele was associated with higher NAFLD risk, while the A allele was protective (0.6-fold decreased MAFLD risk). The LD with rs1051266 (r²=0.98) confirmed these two variants represent the same functional haplotype — impaired SLC19A1 transport reduces intracellular folate, dysregulates hepatic lipid metabolism genes, and promotes lipid droplet accumulation.

A family-based transmission disequilibrium test O'Byrne MR et al. Birth Defects Research, 2010³³ O'Byrne MR et al. Birth Defects Research, 2010
Association of SLC19A1 genes with meningomyelocele in 610 families found rs3788200 significantly associated with meningomyelocele risk (p=0.0195). Only 37 of 97 informative transmissions passed the G allele to affected offspring — fewer than expected — suggesting the G allele on its own shows a complex pattern, with the intronic variant's effect mediated through its LD relationship with the coding variant rs1051266.

A 2022 Chinese pharmacogenomics study Cen H et al. Pharmacogenomics and Personalized Medicine, 2022⁴⁴ Cen H et al. Pharmacogenomics and Personalized Medicine, 2022 of 104 rheumatoid arthritis patients on methotrexate found rs3788200 G-carrier status (AG+GG) associated with significantly better EULAR treatment response (RR=1.45, 95% CI=1.04–2.01, p=0.03). This seeming paradox — the G allele associated with reduced folate transport yet better methotrexate response — is mechanistically coherent: methotrexate enters cells via the same RFC1 transporter, so the G-tagged rs1051266-T haplotype may affect drug accumulation dynamics differently than folate in the context of pharmacological dosing.

Practical Implications

The clinical significance of rs3788200 runs parallel to rs1051266. If you carry the G allele, your folate transport efficiency is likely reduced, making adequate dietary and supplemental folate more important. Methylfolate (5-MTHF) is the preferred form — it is already in its active state and may be transported more efficiently than synthetic folic acid. Monitoring homocysteine provides a functional readout: elevated homocysteine signals that methylation is falling behind, potentially due to limited intracellular folate availability.

If you are prescribed methotrexate (for rheumatoid arthritis, psoriasis, or other conditions), your SLC19A1 genotype at this locus may influence how the drug accumulates in your cells. Inform your prescribing physician of this variant; dosing and monitoring protocols may benefit from adjustment.

Interactions

rs3788200 is in strong LD (r²=0.98) with rs1051266 and the two should be interpreted together — they report on the same underlying folate-transport haplotype. The combined effect is amplified when MTHFR variants (rs1801133, rs1801131) are also present: impaired methylfolate production (MTHFR) combined with reduced folate import (SLC19A1) creates a more significant bottleneck in the folate-methylation cycle than either variant alone. rs1888530, another SLC19A1 intronic variant (intron 5), showed even stronger meningomyelocele association in the O'Byrne 2010 study and may tag a partially distinct haplotype within the same gene.