Uniparental Isodisomy of Chromosome 1 Unmasking an Autosomal Recessive 3-Beta Hydroxysteroid Dehydrogenase Type II-Related Congenital Adrenal Hyperplasia

Abstract

Steroid 3-beta hydroxysteroid dehydrogenase type II (3β-HSD2) deficiency is a rare autosomal recessive form of congenital adrenal hyperplasia (CAH). We report the genetic basis of 3β-HSD2 deficiency arising from uniparental isodisomy (UPD) of chromosome 1. We describe a term undervirilized male whose newborn screen indicated borderline CAH. The patient presented on the 7^th day of life in salt-wasting adrenal crisis. Steroid hormone testing revealed a complex pattern suggestive of 3β-HSD deficiency. Chromosomal microarray and single nucleotide polymorphism analysis revealed complete UPD of chromosome 1. Sanger sequencing of HSD3B2 revealed a previously described missense mutation, c.424G>A (p.E142K) in homozygous state, thus confirming the diagnosis of 3β-HSD2 deficiency. We provide evidence of the existence of an uncommon mechanism for HSD3B2 gene-related CAH arising from UPD of chromosome 1.

Figure 1. Uniparental isodisomy of chromosome 1. The figure demonstrates a normal copy number of chromosome 1 represented by probes in the top panel (blue arrow) averaging log₂R=0 in the absence of AB alleles shown in the bottom panel