ESPE Abstracts

Disorders or Differences of sex development (DSD) are a heterogeneous group of congenital conditions, involving variations of chromosomal, gonadal, or anatomical development. Diagnosis is based on clinical, biochemical, imaging and genetic evaluation. In recent years knowledge about genetic causes has increased, mainly due to improved genetic techniques. In this study we investigated the yield of exome sequencing in our patients with DSD. Patients and methods: Genetic investigations are performed by karyotyping as a first step, followed by additional DNA analysis in case of 46,XX or 46,XY. Based on biochemical and imaging results and family history either a DSD genepanel (containing 53 genes) is used, or targeted gene-sequencing (by direct Sanger sequencing) is performed. Exome sequencing is performed using Illumina HiSeq by BGI-Europe.

Results: Since the introduction of exome sequencing in our DSD expertise center (2014), exome sequencing with the DSD genepanel was performed in 64 patients; of which 19 external referrals. Of the 45 internal referrals, 9 children were 46,XX, 35 46,XY and 1 child with 45,X/46,XY karyotype. In children with 46,XY, homozygous or compound heterozygous SRD5A2 mutations were found in 3 patients. NR5A1 variants were found in 2 patients (1 de novo, 1 maternally inherited; both considered likely pathogenic). A pathogenic AR mutation was found in 1 patient, and a DMRT1 variant was found in 1 patient (possibly pathogenic). (Likely) pathogenic variants were thus found in 13% of patients (6/45). In 46,XX DSD cases, 2 patients had a heterozygous CYP17A1 mutation. In the 19 external samples 1 NR5A1 variant of unknown inheritance was found, 1 patient with homozygous CYP17A1 mutations, 1 patient with homozygous HSD17B3 mutations, 1 patient with homozygous DHCR7 mutations, and 1 patient with a WT1 mutation; all considered pathogenic. In total, exome sequencing revealed a likely pathogenic cause in 17% (11/64). In the same period pathogenic mutations were found with direct sequencing in: SRY gene (46,XY DSD), SRD5A2 (46,XY, compound heterozygous mutations), DHCR7 (46,XY, homozygous mutations). In an additional 11 patients with 46,XX DSD and a strong suspicion of CAH, bi-allelic CYP21A2 mutations were found.

Conclusion: In DSD exome sequencing is a valuable tool as a first-step diagnostic tool, but in selected cases when phenotype and biochemical tests suggest a specific genetic defect direct DNA sequencing can be appropriate. Early identification of a genetic cause is important for optimal management of the patient.