Genetic, Genomic and Biophysical Case Study: Familial 46, XY Sex Reversal due to a Novel Inherited Mutation in Human Testis-Determining Factor SRY

ObjectiveTo describe the clinical, histopathological and molecular features of a novel inherited SRY allele (p.Met64Val; consensus box position 9) observed within an extensive pedigree: two 46, XY sisters with primary amenorrhea (16 and 14 years of age; probands P1 and P2), their normal father and brother, and an affected paternal XY grandaunt. Design, Setting, Participants and Outcome MeasurementsFollowing DNA sequencing to identify the SRY mutation, hormonal studies of the probands and histopathological examination of their gonads were performed. Functional consequences of p.Met64Val (and other mutations at this site) were also investigated. ResultsBreast development in P1 and P2 was Tanner II and IV, respectively. Mullerian structures and gonads resembling ovaries were found in each sister. Histopathology revealed gonadal dysgenesis, gonadablastoma and dysgerminoma. AMH/MIS, P450 SCC, and P450 aromatase were expressed in gonadoblastoma tissues. Genomic sequencing revealed no candidate mutations in other genes related to sexual differentiation. Variant p.Met64Val impaired Sox9 transcriptional activation associated with attenuated occupancy of the testis-specific enhancers Enh13 and TESCO. Biophysical studies indicated that the mutant HMG box retains specific DNA binding and DNA bending but with accelerated rate of protein-DNA dissociation. ConclusionThe partial biological activity of p.Met64Val SRY, maintained at the threshold of SRY function, rationalizes opposing paternal and proband phenotypes (the "the father-daughter paradox"). Steroidal biosynthesis by gonadoblastoma may delay genetic diagnosis and recognition of gonadal tumors. Quantitative assessment of inherited SRY alleles highlights the tenuous transcriptional threshold of developmental decision-making in the bipotential gonadal ridge.