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. MAMLD1 is one of the recognized DSD genes. However, its role is controversial as some MAMLD1 variants are present in normal individuals, several MAMLD1 mutations have wild-type activity in functional studies, and the Mamld1 -knockout male mouse presents with normal genitalia and reproduction. We previously tested nine MAMLD1 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 CYP17A1 and HES3 . In addition, protein expression of MAMLD1 variants was similar to wild-type, except for the truncated L210X. We hypothesized that MAMLD1 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 MAMLD1 variants. WES data were filtered by an algorithm including disease-tailored lists of MAMLD1 -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 MAMLD1 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.

Oligogenic Origin of Differences of Sex Development in Humans

“…Interestingly, MAML3 (one variant in our 46,XX DSD patient) was found in a network related to female gonadal development [52]. Overall, three genes seemed prominent in the network analysis: NOTCH1/NOTCH2 and GLI3 (Figure 2) [6]. Interaction network of DSD-and MAMLD1-related genes identified in DSD individuals harboring genetic variants in MAMLD1.…”

“…More recently, we performed a WES study in eight DSD patients (seven 46,XY and one 46,XX) carrying sequence variation in MAMLD1 previously detected by Sanger sequencing [6]. Seven of eight MAMLD1 sequence variations did not show alterations in functional activity in vitro when compared to wild-type MAMLD1 and thus did not explain the DSD phenotype sufficiently [40].…”

“…Oligogenic DSD origin has been revealed either as a result of HTS directly or in a second approach, when the first candidate gene detected seemed not sufficient to explain the phenotype. Several recent studies demonstrate that many patients carry a gene variant likely responsible for the phenotype together with other variants in known or new candidate genes for DSD [4][5][6][7][8][9][10][11][12][13][14].…”

“…We, therefore, hypothesized that MAMLD1 variants may also not suffice to explain the 46,XY DSD phenotype. WES data from these patients were obtained and filtered by an algorithm including disease-tailored lists of MAMLD1-related and DSD-related genes [6]. This analysis showed that patients harbored 1-16 variants in 1-16 genes together with their MAMLD1 variation.…”

“…Oligogenic disease has been proposed. In fact, multiple genetic hits, which might not be deleterious by themselves, have been found in individuals with DSD [4][5][6][7][8][9][10][11][12][13][14].…”