A novel variant in the MAP3K1 genomic locus reveals abnormal cell apoptosis as a potential pathogenic mechanism in 46, XY disorders of sex development.

Disorders of sex development (DSDs) are characterized by discrepancies among karyotype, the gonadal phenotype and gonadal anatomy following birth. Among these, 46, XY DSD is the most complex sub‑type and a major cause of birth defects associated with sexual development. However, due to the considerable heterogeneity in pathogenic genes, numerous cases remain genetically undiagnosed. In the present study, a novel gain‑of‑function variant was identified in the mitogen‑activated protein 3 kinase 1 (MAP3K1) gene, contributing to 46, XY DSD through the induction of abnormal cell apoptosis. Genetic analysis of a pediatric male patient and his family revealed a heterozygous MAP3K1 c.4445 G>A variant, resulting in an arginine‑to‑glutamine substitution. The variant site is highly conserved across species and the amino acid transition induced structural changes in the MAP3K1 protein. In vitro experiments demonstrated that the MAP3K1 c.4445 G>A variant markedly increased apoptotic signaling, leading to abnormal cell apoptosis, disruption of the cell cycle and reduced cell viability. Moreover, the variant exhibited increased levels of ERK1/2 and p38 phosphorylation, indicative of a gain‑of‑function effect. Subsequent analysis revealed increased expression of the testis‑determining gene, SOX9 and reduced expression of the ovary‑determining gene, FOXL2. Notably, alterations in gene expression were associated with the MAP3K1 c.4445 G>A variant, providing a mechanistic basis for the pathogenesis of 46, XY DSD. Collectively, these findings offer novel insights into the anti‑apoptotic role of MAP3K1, advancing genetic diagnosis and pre‑natal screening for individuals with DSDs.