rs62623713 — SYPL2 E99G

SYPL2 E99G — A Rare Obesity Susceptibility Variant Shaping Fat Distribution

SYPL2 (synaptophysin-like 2, also known as MG29) encodes a membrane protein related to synaptophysin, a major constituent of synaptic vesicles. In the context of metabolism, SYPL2 is expressed in adipose tissue and skeletal muscle and appears to influence fat cell biology and the response to physical activity. The rs62623713 variant introduces a missense substitution — glutamic acid to glycine at position 99 (E99G) — in a protein already implicated in adipose function by animal studies showing that mice lacking Sypl2 display reduced body weight¹¹ mice lacking Sypl2 display reduced body weight
Jiao et al., European Journal of Human Genetics, 2015.

The G allele is rare globally (approximately 4–6% in Europeans, under 0.1% in East Asians), placing this variant in the category of low-frequency coding variants rather than common GWAS polymorphisms. Its rarity made it invisible to early GWAS arrays, requiring exome sequencing to discover — a study design that is increasingly revealing low-frequency variants with larger per-allele effect sizes than common SNPs.

The Mechanism

The E99G substitution replaces a charged glutamic acid with the smallest amino acid, glycine, at position 99 of the SYPL2 protein. This change occurs in the cytoplasmic domain of the protein, potentially altering its interaction with intracellular partners involved in vesicular trafficking and membrane dynamics. Although computational predictions (SIFT score 0.58, PolyPhen score 0.0) classify the substitution as "tolerated" and "benign," these scores reflect evolutionary conservation rather than quantitative metabolic effects, and the observed human phenotype suggests functionally relevant consequences in adipose tissue not captured by these algorithms.

SYPL2 expression is notably down-regulated in less physically active children²² down-regulated in less physically active children
Galmés et al., Scientific Reports, 2023, alongside other genes associated with cardiometabolic benefit. This positions SYPL2 at the intersection of physical activity response and metabolic phenotype, though the precise molecular pathway linking E99G to increased adiposity remains to be fully characterized.

The Evidence

The primary discovery came from a 2015 exome sequencing study³³ 2015 exome sequencing study
Jiao H et al., European Journal of Human Genetics by researchers at Karolinska Institutet. Using pooled exome sequencing in 100 morbidly obese and 100 normal-weight Swedish subjects, followed by validation in 3,197 genotyped individuals, they identified rs62623713 as a low-frequency (minor allele frequency 2.9%) non-synonymous variant with striking effect size: each G allele increased BMI by 2.13 kg/m² (95% CI: 1.09–3.18, p = 6.28 × 10⁻⁵) and conferred an odds ratio of 1.32 for morbid obesity. This effect size is notably larger than common obesity variants⁴⁴ notably larger than common obesity variants
Common GWAS hits like FTO rs9939609 increase BMI by only ~0.4 kg/m² per allele, consistent with the general observation that rare coding variants carry larger per-allele effects.

A 2016 follow-up study⁵⁵ 2016 follow-up study
de Toro-Martín J et al., Obesity Science & Practice from Laval University extended the analysis to 3,693 participants from two Canadian cohorts, genotyping rs62623713 alongside two additional SYPL2 tagging SNPs (rs9661614 and rs485660). This study revealed a notable sex-specific dimension: tagging SNPs in the SYPL2 region associated with hip circumference specifically in women (FDR-corrected p = 1.7 × 10⁻²), suggesting that SYPL2 may preferentially influence a gynoid (hip-and-thigh) pattern of fat deposition in females. Male participants showed no significant associations with hip circumference, pointing to sex-hormone modulation of SYPL2's role in regional adipose distribution.

Critically, the evidence requires context: both studies used relatively modest sample sizes by modern GWAS standards, and the Jiao 2015 discovery cohort was a Swedish population, raising questions about generalizability. The variant has not yet been independently replicated in large-scale exome sequencing studies, and it does not appear in the NHGRI-EBI GWAS Catalog of genome-wide significant findings. The evidence level is therefore classified as emerging — a biologically plausible association with suggestive statistics, but requiring replication in larger, diverse cohorts before clinical utility can be established.

Practical Actions

For carriers of the G allele, the actionable message centers on lifestyle factors that are particularly relevant given the metabolic phenotype associated with SYPL2. Physical activity data specifically show SYPL2 expression is coupled to active status, suggesting that movement may partially compensate for the functional effects of the E99G variant. Women carrying G alleles who are concerned about gynoid fat distribution have additional context from the de Toro-Martín follow-up.

Given the emerging evidence status, specific dietary or supplementation protocols targeting SYPL2 biology are not yet established. The primary practical value of this variant lies in its contribution to personalized obesity risk assessment and motivating attention to body composition monitoring and physical activity behaviors that evidence links to SYPL2 expression.

Interactions

SYPL2's role in fat distribution shows sex-specific patterns, with the strongest associations in women for hip circumference. This suggests potential interaction with sex hormone signaling pathways in adipose tissue. The de Toro-Martín study found that tagging SNPs rs9661614 and rs485660 recapitulate much of the regional distribution phenotype, indicating these variants likely tag the same functional haplotype as rs62623713.

No documented compound interactions with other obesity-related variants (such as FTO rs9939609 or MC4R variants) have been studied for rs62623713, though pathway-level interactions in adipose biology are biologically plausible. Given the similar biological domain — adipose tissue and body composition — future studies may find additive effects with more common obesity variants.