rs35318931 — SRPX Ser413Phe

Stretch Mark Shield — How a Missense Variant in an Extracellular Matrix Protein Protects Skin

When your skin stretches rapidly — during growth spurts, pregnancy, or weight change — the dermal connective tissue can tear, producing striae distensae¹¹ striae distensae
the medical term for stretch marks, caused by rupture of elastic fibers and reorganization of collagen in the dermis. Whether you develop visible stretch marks depends partly on your genes. The SRPX gene encodes a sushi-repeat-containing protein²² sushi-repeat-containing protein
a class of extracellular proteins with complement control protein (CCP) domains, also called sushi domains, that mediate protein-protein interactions in the extracellular matrix expressed in multiple tissues and localized to the collagen-containing extracellular matrix. rs35318931 changes a serine to phenylalanine at position 413, and carriers of this variant are significantly less likely to develop stretch marks.

The Mechanism

SRPX sits on the X chromosome at Xp21.1 and encodes a 464-amino-acid transmembrane protein with three sushi domains³³ sushi domains
compact ~60 amino acid modules that form protein interaction surfaces; found in complement factors, selectins, and extracellular matrix proteins in its N-terminal region. The protein is predicted to function as an extracellular matrix structural constituent⁴⁴ extracellular matrix structural constituent
proteins that contribute to the physical scaffolding of tissues, including collagen, elastin, and fibrillin and localizes to the collagen-containing extracellular matrix. It has also been characterized as a peroxiredoxin-like protein⁵⁵ peroxiredoxin-like protein
a class of antioxidant enzymes that reduce hydrogen peroxide and organic hydroperoxides with tumor-suppressor activity, capable of inducing apoptosis through caspase-12/9/3 activation.

The rs35318931 variant replaces serine (small, polar) with phenylalanine (large, aromatic)⁶⁶ serine (small, polar) with phenylalanine (large, aromatic)
BLOSUM62 score of -2 indicates an unfavorable substitution from a conservation standpoint, yet the variant is common in Europeans at ~8% allele frequency. This position is conserved across mammalian orthologs (mouse and rat maintain serine), suggesting functional importance. The exact mechanism by which this amino acid change protects against stretch marks remains unknown, but given SRPX's localization to collagen-containing extracellular matrix, the variant may alter how the protein interacts with dermal structural fibers — potentially strengthening elastic microfiber networks that resist tearing under mechanical stress.

Because SRPX is on the X chromosome, males are [hemizygous | having only one copy of a gene, as occurs with X-linked genes in males (XY)] — they carry either G or A, with no heterozygous state. Females can be GG, AG, or AA. This means the variant's protective effect may be more pronounced in males, where a single copy determines the phenotype without the buffering effect of a second allele.

The Evidence

Tung et al. (2013)⁷⁷ Tung et al. (2013)
Genome-wide association analysis implicates elastic microfibrils in the development of nonsyndromic striae distensae. J Invest Dermatol 133:2628-2631 conducted the first GWAS for stretch marks, surveying 33,930 unrelated 23andMe customers of European descent (13,068 cases, 20,862 controls). rs35318931 reached genome-wide significance with P = 1.1 x 10^-13 and an odds ratio of 0.82 (95% CI: 0.77-0.86), meaning A allele carriers had an 18% reduced risk of developing stretch marks. The association replicated in a validation cohort of 4,967 pregnant women for striae gravidarum (P = 0.026, beta = -0.067).

The study identified four genome-wide significant loci in total: rs7787362 near ELN⁸⁸ ELN
the elastin gene, encoding the primary component of elastic fibers in skin, rs35318931 in SRPX, rs10798036 in HMCN1⁹⁹ HMCN1
hemicentin-1, a large extracellular matrix protein related to fibulin, and rs7594220 near TMEM18. Three of the four loci implicate extracellular matrix and elastic microfiber biology, reinforcing the hypothesis that stretch marks arise from genetically determined variation in dermal connective tissue resilience.

UniProt classifies the Ser413Phe substitution as likely benign or benign (LB/B)¹⁰¹⁰ likely benign or benign (LB/B)
functional prediction tools (SIFT: tolerated; PolyPhen-2: possibly damaging) give mixed signals, but the variant's high frequency in Europeans argues against pathogenicity. This is consistent with its role as a common protective variant rather than a disease-causing mutation.

SRPX was originally identified through its deletion in patients with X-linked retinitis pigmentosa¹¹¹¹ deletion in patients with X-linked retinitis pigmentosa
Meindl et al. 1995 found SRPX deleted in RP patients, though subsequent screening of 34 XLRP families found no further mutations, and RPGR was later identified as the primary RP3 gene. While the retinitis pigmentosa link was not confirmed, the deletion studies established SRPX as a real, expressed gene with tissue-specific functions. More recently, SRPX has emerged as a tumor suppressor — SRPX knockout mice develop tumors at a 30% rate¹²¹² SRPX knockout mice develop tumors at a 30% rate
including lymphoma, lung cancer, hepatoma, and sarcoma — adding another dimension to this gene's functional significance.

Practical Actions

The A allele at rs35318931 is protective: carriers are less likely to develop stretch marks during periods of rapid skin stretching (puberty, pregnancy, weight fluctuations, muscle building). If you carry the G allele (reference, non-protective), you have the standard population risk for stretch marks. This is especially relevant during pregnancy, where striae gravidarum affect 50-90% of women.

While genetics loads the gun, environmental factors pull the trigger. Regardless of genotype, maintaining skin hydration and elasticity through appropriate skincare can modulate stretch mark risk. For those with the GG genotype (or hemizygous G in males), proactive measures during high-risk periods may help compensate for the absence of SRPX-mediated protection.

Interactions

rs35318931 sits within a network of extracellular matrix genes that collectively determine skin connective tissue resilience. The same GWAS identified rs7787362 near ELN (elastin) as the strongest stretch mark locus, and rs10798036 in HMCN1 (hemicentin-1) as a third hit. These genes encode different components of the dermal extracellular matrix: elastin provides elastic recoil, hemicentin stabilizes basement membranes, and SRPX contributes to the collagen-containing matrix scaffold. Individuals carrying protective alleles at multiple loci likely have the most resilient dermal connective tissue.

MMP1 (rs1799750), already in the GeneOps database, encodes matrix metalloproteinase 1 (collagenase-1), the primary enzyme that degrades fibrillar collagen in skin. MMP1 activity and SRPX matrix function represent opposing sides of the same biology: collagen remodeling versus collagen stability. An interaction between high-activity MMP1 variants and the non-protective SRPX G allele could compound stretch mark susceptibility, though this specific combination has not been tested in published studies.