rs509035 — GHSR GHSR Metabolic Syndrome Variant

The Ghrelin Receptor Variant That Shapes Lean Body Mass and IGF-1

Ghrelin does far more than signal hunger. When it docks onto GHSR-1a (growth hormone secretagogue receptor)¹¹ GHSR-1a (growth hormone secretagogue receptor)
The canonical ghrelin receptor, expressed in the pituitary gland, hypothalamus, and across peripheral tissues. Named for its original discovery as the receptor mediating growth hormone secretion in response to synthetic GH secretagogues., it triggers a powerful pulse of growth hormone release from the pituitary. That GH pulse drives the liver to secrete IGF-1 (insulin-like growth factor 1)²² IGF-1 (insulin-like growth factor 1)
The primary mediator of GH's anabolic effects: stimulates muscle protein synthesis, promotes linear bone growth, and regulates fat metabolism. Circulating IGF-1 levels closely track GH secretion patterns over hours to days., and IGF-1 is the hormone that actually builds lean tissue — muscle, bone, connective tissue. rs509035 is an intronic variant within the GHSR gene itself, sitting at chromosome 3:172,445,659 (GRCh38). It does not change the receptor's amino acid sequence, but GWAS data from populations totalling hundreds of thousands of individuals shows that the A allele is associated with higher fat-free mass, greater adult stature, and elevated serum IGF-1 — the three expected downstream consequences of enhanced GHSR-mediated GH pulsatility.

The Mechanism

rs509035 sits within an intron of GHSR, likely in a regulatory element that influences how efficiently the gene is transcribed or the mRNA is processed. The exact molecular function has not been characterized by gel-shift or reporter assays (unlike the functionally annotated nearby promoter variant rs490683), so the mechanism is inferred from the downstream phenotype pattern rather than direct biochemical evidence. The convergence of three independent large GWAS signals — lean body mass, height, and IGF-1 — pointing to the same A allele strongly implies that A tracks with modestly elevated GHSR expression or activity, producing more frequent or larger GH pulses, more IGF-1, and consequently more lean tissue accretion over a lifetime.

Animal model support comes from studies of GHSR knockout mice³³ GHSR knockout mice
Labarthe et al. 2022 (PMID 33774644): GHS-R1a deletion reduced pulsatile GH secretion, decreased linear growth, and reduced hypothalamic GHRH mRNA expression in males — demonstrating that GHSR is causally required for normal GH pulsatility and growth., which show reduced GH pulsatility and impaired linear growth when the receptor is absent. If loss of GHSR reduces lean mass and growth, it follows that variants that enhance GHSR signaling would move these phenotypes in the opposite direction — and rs509035-A appears to do exactly that at the population level.

The Evidence

The strongest evidence comes from a sex-stratified GWAS in the UK Biobank by Hübel et al. 2019⁴⁴ Hübel et al. 2019
Genomics of body fat percentage may contribute to sex bias in anorexia nervosa. Am J Med Genet B Neuropsychiatr Genet. 2019;180(3):222-235. N=155,961 healthy UK Biobank participants., which identified rs509035 as a genome-wide significant hit for fat-free mass (overall beta = 0.188, p = 2×10⁻¹⁵; males beta = 0.214, p = 1×10⁻⁸; females beta = 0.151, p = 5×10⁻⁹). The effect is present in both sexes but is modestly larger in men, consistent with the testosterone–GH axis interaction in lean mass regulation.

Height GWAS results from Wood et al. 2014⁵⁵ Wood et al. 2014
Nature Genetics, N=253,288 adults; the A allele (frequency 0.316) shows beta = 0.031 SD per allele, p = 3×10⁻²³. confirm that the lean mass signal has a growth axis explanation — the same allele that promotes lean tissue accretion also produces slightly greater adult height.

The CHARGE Consortium IGF-1 meta-analysis by Teumer et al. 2016⁶⁶ Teumer et al. 2016
Aging Cell, N=30,884 European adults; rs509035 A allele associated with higher serum IGF-1, p = 2×10⁻⁸. provides the mechanistic link: the A allele is associated with higher circulating IGF-1, which is the molecular effector translating GH pulsatility into lean tissue construction. Together, these three GWAS signals (fat-free mass, height, IGF-1) form a coherent picture of enhanced GHSR-to-GH-to-IGF-1 anabolic signaling in A allele carriers.

Glucose and insulin metabolism may also be modified. In the Finnish Diabetes Prevention Study (Mager et al. 2008, N=507), rs509035 was associated with several glucose and insulin measures during 3-year follow-up⁷⁷ rs509035 was associated with several glucose and insulin measures during 3-year follow-up
Mager U et al. PLoS One. 2008;3(8):e2941. The paper studied 7 GHSR SNPs in overweight adults with impaired glucose tolerance; rs509035 and rs490683 were the two variants showing significant metabolic associations., though the specific direction and magnitude of the effect for rs509035 were not separately published in the abstract. IGF-1 itself has insulin-sensitizing effects at the receptor level, so the higher IGF-1 in A allele carriers may partially explain glucose metabolism differences.

Practical Actions

For GG individuals (the majority), the GHSR intronic variant confers typical lean mass accrual potential without the enhanced GH-axis signaling that A allele carriers appear to have. For those pursuing body composition goals, the GG genotype means that lean mass gains depend primarily on training stimulus and protein adequacy rather than a genetically elevated IGF-1 floor. Monitoring IGF-1 levels is more informative for AA individuals than GG individuals, as the GG baseline is uncharacterized relative to the A allele effect.

For A allele carriers (AG and AA), enhanced GHSR-mediated GH pulsatility confers a measurable lean mass and IGF-1 advantage. This is actionable in resistance training contexts: a higher IGF-1 floor generally means faster muscle protein synthesis recovery and potentially better hypertrophic response to resistance training. Adequate protein intake (1.6–2.2 g/kg body weight daily) is necessary to fully leverage the elevated anabolic signaling environment.

Interactions

rs509035 is an intronic variant in the same GHSR gene as the promoter variants rs490683 and rs9819506, which have independent associations with appetite drive and body weight change during dietary intervention. The functional NF-1 binding site variant rs490683 (promoter) affects ghrelin receptor expression level; rs509035 (intronic) appears to operate through a downstream mechanism influencing the GH/IGF-1 anabolic axis more than appetite per se. Individuals carrying rs490683-GG (elevated appetite drive) combined with rs509035-AA (elevated IGF-1) may have a phenotype characterized by both high appetite and efficient lean tissue accretion — the genetic profile of a mesomorphic body type that gains muscle readily but also experiences strong hunger during caloric restriction.