Complete androgen insensitivity syndrome caused by a deep intronic pseudoexon-activating mutation in the androgen receptor gene

Mutations in the X-linked androgen receptor (AR) gene underlie complete androgen insensitivity syndrome (CAIS), the most common cause of 46,XY sex reversal. Molecular genetic diagnosis of CAIS, however, remains uncertain in patients who show normal coding region of AR. Here, we describe a novel mechanism of AR disruption leading to CAIS in two 46,XY sisters. We analyzed whole-genome sequencing data of the patients for pathogenic variants outside the AR coding region. Patient fibroblasts from the genital area were used for AR cDNA analysis and protein quantification. Analysis of the cDNA revealed aberrant splicing of the mRNA caused by a deep intronic mutation (c.2450-118A>G) in the intron 6 of AR. The mutation creates a de novo 5′ splice site and a putative exonic splicing enhancer motif, which leads to the preferential formation of two aberrantly spliced mRNAs (predicted to include a premature stop codon). Patient fibroblasts contained no detectable AR protein. Our results show that patients with CAIS and normal AR coding region need to be examined for deep intronic mutations that can lead to pseudoexon activation.