Background: Androgen insensitivity syndrome (AIS), ranging from complete (CAIS) to partial (PAIS) and to mild (MAIS) forms of androgen resistance, is caused by mutations in the X-linked AR gene that encodes the androgen receptor. Some cases, however, remain without a molecular genetic diagnosis that would confirm the diagnosis especially in cases that have phenotypic similarities with other 46,XY disorders of sex development.
Objective and hypotheses: The objective of this study was to identify the genetic cause of complete AIS in two siblings without identified mutations in the AR coding region or in the conserved splice sites.
Method: Whole-genome sequencing of the two siblings and their healthy father was performed at BGI, and the sequencing data was searched for candidate causal variants outside the AR coding region. RNA was extracted from the patients genital skin fibroblasts and the AR cDNA was analysed by PCR. The amount of AR protein was also studied by immunoprecipitation and western blot.
Results: Analysis of the cDNA revealed aberrant splicing of the AR mRNA caused by a deep intronic mutation (c.2450-118A>G) in intron 6. The mutation creates a de novo 5 splice site and a putative exonic splicing enhancer motif, leading to the preferential formation of two aberrantly spliced mRNAs (predicted to include a premature stop codon) and significant reduction of normal mRNA levels. Patient fibroblasts showed similar levels of AR mRNA when compared to controls but no detectable AR protein.
Conclusion: This is the first reported case of AR pseudoexon activation leading to androgen insensitivity syndrome. Similar deep intronic mutations that can lead to pseudoexon activation may underlie AIS in cases where routine genetic screens reveal no mutations in the coding region nor in the conserved splice sites.
10 Sep 2016 - 12 Sep 2016