Broad Phenotypes of Disorders/Differences of Sex Development in MAMLD1 Patients Through Oligogenic Disease

Abstract

Disorders/differences of sex development (DSD) are the result of a discordance between chromosomal, gonadal, and genital sex. DSD may be due to mutations in any of the genes involved in sex determination and development in general, as well as gonadal and/or genital development specifically. <i>MAMLD1</i> is one of the recognized DSD genes. However, its role is controversial as some <i>MAMLD1</i> variants are present in normal individuals, several <i>MAMLD1</i> mutations have wild-type activity in functional studies, and the <i>Mamld1</i>-knockout male mouse presents with normal genitalia and reproduction. We previously tested nine <i>MAMLD1</i> variants detected in nine 46,XY DSD patients with broad phenotypes for their functional activity, but none of the mutants, except truncated L210X, had diminished transcriptional activity on known target promoters <i>CYP17A1</i> and <i>HES3</i>. In addition, protein expression of <i>MAMLD1</i> variants was similar to wild-type, except for the truncated L210X. We hypothesized that <i>MAMLD1</i> variants may not be sufficient to explain the phenotype in 46,XY DSD individuals, and that further genetic studies should be performed to search for additional hits explaining the broad phenotypes. We therefore performed whole exome sequencing (WES) in seven of these 46,XY patients with DSD and in one 46,XX patient with ovarian insufficiency, who all carried <i>MAMLD1</i> variants. WES data were filtered by an algorithm including disease-tailored lists of <i>MAMLD1</i>-related and DSD-related genes. Fifty-five potentially deleterious variants in 41 genes were identified; 16/55 variants were reported in genes in association with hypospadias, 8/55 with cryptorchidism, 5/55 with micropenis, and 13/55 were described in relation with female sex development. Patients carried 1-16 variants in 1-16 genes together with their <i>MAMLD1</i> variation. Network analysis of the identified genes revealed that 23 genes presented gene/protein interactions with MAMLD1. Thus, our study shows that the broad phenotypes of individual DSD might involve multiple genetic variations contributing towards the complex network of sexual development.