A Novel Homozygous Missense Mutation in the FU-CRD2 Domain of the R-spondin1 Gene Associated with Familial 46,XX DSD

R-spondin proteins are secreted agonists of canonical WNT/β-catenin signaling. Homozygous RSPO1 mutations cause a syndrome of 46,XX disorder of sexual development (DSD), palmoplantar keratoderma (PPK), and predisposition to squamous cell carcinoma. We report exome sequencing data of two 46,XX siblings, one with testicular DSD and the other with suspected ovotesticular DSD. Both have PPK and hearing impairment and carried a novel homozygous mutation c.332G>A (p.Cys111Tyr) located in the highly conserved furin-like cysteine-rich domain-2 (FU-CRD2). Cysteines in the FU-CRDs are strictly conserved, indicating their functional importance in WNT signaling through interaction with the leucine-rich repeat-containing G-protein-coupled receptors. This is the first RSPO1 missense mutation reported in association with human disease.