OR15-07 Novel Genes Involved in Sex Differentiation Identified by Whole-Exome Sequencing in a Cohort of Children with Disorders of Sex Development

Background: Disorders of sex development (DSD) are classified as a congenital discrepancy between external genitalia, gonadal and chromosomal sex. Despite extensive laboratory and imaging investigations, the etiology of DSD is unknown in more than 50% of patients and the diagnosis is often delayed to the second decade of life. Our objective was to evaluate the etiology of DSD by whole-exome sequencing (WES) in children in whom hormonal and candidate gene approaches had not identified the etiology. Methods: Nine patients diagnosed with DSD (eight 46,XY and one 46,XX) were enrolled. Patients underwent hormonal evaluation, including ACTH, GnRH and hCG tests. Candidate genes were sequenced in accordance with the hormonal results. WES was performed for the probands and their parents. Results: The eight 46,XY patients presented with micropenis, cryptorchidism and hypospadias at birth and the 46,XX patient with fusion of the labia majora. In six of the nine patients (66%), a pathogenic mutation was identified by WES that explained the phenotype: four known DSD-causing genes—POR, CHD7, HSD17B3 and WT1—and two novel genes—BMP4 and RFXP2. In three patients, variants of unknown significance were found. An 11-y-old boy had a novel de-novo mutation in BMP4. In humans, mutations in this gene, encoding bone morphogenetic protein 4, are associated with autosomal dominant microphthalmia. BMP4 is expressed in the urethral epithelium and has a role in the development of external genitalia and the pituitary. This is the first report of a BMP4 mutation in a child with DSD. A 12-y-old boy had a mutation in RFXP2, encoding insulin-like 3 hormone receptor, which has been previously reported in adult males with cryptorchidism. This is the first case of an RFXP2 mutation in a child with DSD. Conclusions: WES has a crucial role in early diagnosis of the etiology of DSD, making extensive endocrine testing unnecessary, and has important implications for sex of rearing decisions.