Duplications of the dosage sensitive sex locus Xp21.2 have been associated with 46,XY gonadal dysgenesis (GD) for nearly 25 years. In the past, duplications have always included the NR0B1 (nuclear receptor subfamily 0 group B, member 1, also known as DAX1) gene, a known antagonist of SF1 (Steroidogenic Factor 1) dependent SOX9 (SRY Box 9) activation and the GD was attributed to its "double gene dose". However, recent findings have questioned the necessity of NR0B1 to be included in the duplications and identified upstream copy number variations (CNVs) associated with 46,XY GD.
A real-time qPCR (quantitative PCR) routine for identifying CNVs at the Xp21.2 locus was established and validated using samples with known Xp21.2 duplications including and excluding NR0B1 identified by chromosomal microarray analysis (CMA).
The qPCR was then used to screen 93 patients with elusive genetic cause of 46,XY disorders/differences of sex development (DSD). This revealed two previously unidentified duplications and one unidentified triplication of NR0B1. The number of published cases of non-syndromic NR0B1 duplications associated with 46,XY GD is in the single digits and it remains a very rare diagnosis. Thus, Xp21.2 duplications are potentially underdiagnosed as cause of 46,XY DSD. The qPCR approach offers a short turnaround time at low consumable costs for identifying these patients. The CNVs could then be confirmed by other methods such as multiplex ligation mediated probe amplification, CMA and studied in more detail, including their point of insertion through whole genome sequencing.
19 - 21 Sep 2019
European Society for Paediatric Endocrinology