rs1799941 — SHBG

Promoter region variant affecting sex hormone-binding globulin levels, with the A allele increasing SHBG by 15-25% and influencing free testosterone and estradiol bioavailability

See your personal result for SHBG

Upload your DNA data to find out which genotype you carry and what it means for you.

Upload your DNA data

Works with 23andMe, AncestryDNA, and other DNA test exports. Results in under 60 seconds.

SHBG Promoter Variant — The Hormone Bioavailability Regulator

The SHBG gene on chromosome 17 encodes sex hormone-binding globulin11 sex hormone-binding globulin
a liver-produced transport protein that binds testosterone and estradiol in circulation. Only 1-2% of testosterone and estradiol circulate as "free" bioactive hormones — the rest is bound to SHBG (44%) or albumin (54%). By controlling how much hormone is bound versus free, SHBG acts as a master regulator of sex hormone activity throughout the body. The rs1799941 variant sits in the promoter region just upstream of the SHBG gene and directly influences how much SHBG protein the liver produces. This variant is particularly important because low SHBG levels are strongly associated with metabolic syndrome, type 2 diabetes, PCOS, and cardiovascular risk22 low SHBG levels are strongly associated with metabolic syndrome, type 2 diabetes, PCOS, and cardiovascular risk, while genetically higher SHBG levels may protect against these conditions — though with some unexpected trade-offs.

The Mechanism

Rs1799941 is a G-to-A polymorphism located in the regulatory promoter region of the SHBG gene on chromosome 17p12-p1333 regulatory promoter region of the SHBG gene on chromosome 17p12-p13. The proximal promoter of SHBG contains binding sites for hepatocyte nuclear factor 4-alpha (HNF4A), which activates SHBG transcription44 hepatocyte nuclear factor 4-alpha (HNF4A), which activates SHBG transcription. The A allele appears to enhance promoter activity, leading to increased SHBG production by liver hepatocytes. In population studies, each copy of the A allele increases serum SHBG levels by approximately 7-12 nmol/L55 each copy of the A allele increases serum SHBG levels by approximately 7-12 nmol/L, with AA homozygotes showing 15-25% higher SHBG than GG homozygotes. Because SHBG binds testosterone with 5-fold higher affinity than estradiol, changes in SHBG levels disproportionately affect testosterone bioavailability — more SHBG means more testosterone gets locked up, reducing free testosterone even when total testosterone remains normal.

The Evidence

The largest study of rs1799941 is the Tromsø Study, which genotyped 5,309 Norwegian men and followed them for cardiovascular events, diabetes, cancer, and mortality66 Tromsø Study, which genotyped 5,309 Norwegian men and followed them for cardiovascular events, diabetes, cancer, and mortality. Men with the AA genotype had 14.7% higher total testosterone and 24.7% higher SHBG compared to GG homozygotes, but crucially, free testosterone levels did not differ significantly between genotypes. The SNP was not significantly associated with myocardial infarction, type 2 diabetes, cancer, or mortality, suggesting that the A allele's protective effects on SHBG may be offset by reduced free testosterone bioavailability77 the A allele's protective effects on SHBG may be offset by reduced free testosterone bioavailability.

A pediatric metabolic syndrome study in Turkish children found the opposite direction of effect88 pediatric metabolic syndrome study in Turkish children found the opposite direction of effect — having at least one A allele associated with a 3-fold increased odds of metabolic syndrome (OR=3.09, p=0.006). Paradoxically, in control subjects the A allele increased SHBG levels (as expected), but in metabolic syndrome cases there was no association between genotype and SHBG, suggesting the mechanism through which rs1799941 affects SHBG is disrupted in metabolic disease.

A study of 212 young obese males investigated rs1799941 and hypogonadism risk99 study of 212 young obese males investigated rs1799941 and hypogonadism risk. The A allele was associated with higher SHBG (AA genotype showed +12.45 nmol/L) but lower free testosterone (AA showed -18.52 pg/mL reduction). Importantly, the A allele increased the risk of presenting hypogonadism compared to normal free testosterone hypogonadism (OR=2.54). This reveals the double-edged nature of the variant — higher SHBG is generally metabolically protective, but if SHBG rises too high, it can reduce free testosterone to levels that trigger hypogonadal symptoms, especially in obese individuals.

In 558 women with polycystic ovary syndrome (PCOS), rs1799941 genotype was independently associated with SHBG levels after controlling for BMI, insulin resistance, and hyperandrogenism1010 558 women with polycystic ovary syndrome (PCOS), rs1799941 genotype was independently associated with SHBG levels after controlling for BMI, insulin resistance, and hyperandrogenism. However, the SNP was not associated with PCOS status itself, suggesting it influences SHBG levels but doesn't directly cause PCOS. This is consistent with the understanding that PCOS is driven more by hyperinsulinemia and hyperandrogenism than by SHBG genetics.

Practical Implications

For carriers of the AA genotype, higher baseline SHBG production is generally protective against metabolic syndrome and insulin resistance. However, this comes with caveats. In obesity, the AA genotype may paradoxically increase hypogonadism risk by binding too much testosterone, leaving insufficient free testosterone for biological action. For women with PCOS, the variant influences SHBG levels but doesn't override the strong suppressive effects of hyperinsulinemia on SHBG — insulin resistance will drive SHBG down regardless of genotype. The GG genotype produces less SHBG baseline, which in lean individuals may optimize free testosterone availability, but in metabolic syndrome states this lower SHBG exacerbates the condition by allowing more free androgens to drive insulin resistance.

From a clinical standpoint, rs1799941 genotype helps explain why some individuals have relatively high or low SHBG despite similar metabolic profiles. AA individuals may benefit from monitoring free testosterone rather than total testosterone1111 AA individuals may benefit from monitoring free testosterone rather than total testosterone, particularly if obese, as their high SHBG can mask functional hypogonadism. GG individuals with low SHBG should be screened more aggressively for metabolic syndrome markers — fasting insulin, glucose, triglycerides, and waist circumference — as they are at higher baseline metabolic risk.

Interactions

Rs1799941 frequently interacts with other SHBG gene variants, particularly rs727428 and rs6259 (Asp327Asn), which also independently influence SHBG levels. Rs727428 and rs1799941 together account for significant variance in SHBG levels in PCOS women1212 Rs727428 and rs1799941 together account for significant variance in SHBG levels in PCOS women, with compound effects observed when both variants are present. Additionally, the (TAAAA)n pentanucleotide repeat polymorphism in the SHBG promoter modulates the strength of rs1799941's effect — shorter repeats enhance promoter activity, amplifying the A allele's SHBG-raising effect. Beyond the SHBG gene, this variant's effects are modified by metabolic state — obesity, insulin resistance, and hepatic steatosis all suppress SHBG production through downregulation of HNF4A, potentially overwhelming the genetic effect of rs1799941. Thus, lifestyle factors (weight, exercise, diet) and metabolic health status significantly modulate the penetrance of this variant.

Genotype Interpretations

What each possible genotype means for this variant.

GG Standard SHBG Producer Normal

Baseline SHBG production with normal sex hormone bioavailability

The GG genotype represents the baseline SHBG production phenotype. Population studies show GG individuals have SHBG levels that are 15-25% lower than AA homozygotes, but this is not inherently pathological — it simply reflects the ancestral state. The key clinical implication is that GG individuals are more metabolically vulnerable to SHBG suppression from obesity, insulin resistance, hepatic steatosis, and inflammatory states. Low SHBG (<20 nmol/L in men, <30 nmol/L in women) strongly predicts metabolic syndrome and type 2 diabetes risk. In the absence of metabolic disease, the GG genotype allows for optimal free testosterone bioavailability, which is favorable for muscle mass, libido, bone density, and energy levels. However, if metabolic dysfunction develops, the lack of the A allele's protective SHBG boost means lower SHBG and more free androgens, which paradoxically worsens insulin resistance in a vicious cycle.

AG Intermediate SHBG Producer Intermediate

Moderately increased SHBG production with balanced effects on sex hormone bioavailability

The AG genotype shows a clear dose-response effect — one copy of the A allele produces an intermediate SHBG level between AA and GG genotypes. Regression analyses show the AG genotype associates with approximately +3 to +7 nmol/L higher SHBG and a modest reduction in free testosterone (approximately -9 pg/mL) compared to GG. This typically doesn't reach clinical significance in healthy-weight individuals but may become relevant in obesity or with aging. The metabolic implications are generally favorable — modest SHBG elevation provides some buffering against metabolic syndrome risk without substantially impairing free testosterone bioavailability. In PCOS women, the AG genotype associates with moderately higher SHBG levels independent of obesity and insulin resistance, which may slightly mitigate hyperandrogenism severity.

AA High SHBG Producer High

Higher SHBG production increases bound sex hormones, reducing free testosterone and estradiol bioavailability

The AA genotype represents the highest SHBG-producing variant. Studies show AA individuals have SHBG levels approximately 12-25 nmol/L higher than GG individuals, translating to 15-25% higher circulating SHBG. Because SHBG binds testosterone with approximately 5-fold higher affinity than estradiol, the impact is particularly pronounced on testosterone bioavailability. In the Tromsø Study of over 5,000 men, AA genotype was associated with 14.7% higher total testosterone and 24.7% higher SHBG, but free testosterone did not differ significantly from GG. This creates a clinical paradox — labs may show normal or even high total testosterone, but functional testosterone activity may be reduced. In obese males, this genotype was associated with 2.5-fold increased risk of hypogonadism, likely because the combination of high SHBG and obesity-related testosterone suppression leaves insufficient free hormone. For women, higher SHBG is generally beneficial in PCOS as it reduces free androgen excess, but the effect may be modest compared to the SHBG-suppressing effects of insulin resistance.