Background: The MAMLD1 gene (Xp28) is thought to cause disorder of sex development (DSD) in 46, XY patients, mostly presenting with hypospadias, and, recently, also gonadal dysgenesis. However, there is some controversy about the role of MAMLD1 in sex development because i) some MAMLD1 variants are also detected in normal individuals, ii) others are not present in all affected DSD individuals of the same family; iii) several MAMLD1 mutations have wild-type (WT) activity in functional studies; iv) the male Mamld1 knockout mouse has normal genitalia and reproduction; and v) other species with or without DSD harbor also MAMLD1 variants in the genome.
Objective and hypotheses: We searched for MAMLD1 sequence variations in 108 46, XY DSD individuals presenting with a wide spectrum of DSD phenotypes. Identified variations were functionally tested in vitro, and findings were compared with reported cases and the literature of MAMLD1 focusing on sex development.
Method: Sanger sequencing was performed to detect MAMDL1 gene variations/mutations. Functional experiments were completed in non-steroidogenic HEK293, adrenal NCI-H295R and Leydig MA-10 cells. MAMLD1 transcriptional activity was tested on the Hes3 and CYP17A1 promoters. Effect of MAMLD1 on androgen production was assessed by testing the CYP17A1 activity. WT and mutant MAMLD1 expression was also assessed.
Results: We found nine MAMLD1 mutations (seven novel) in 9/108 46,XY DSD patients. In vitro assays revealed that most MAMLD1 variants acted similarly to the WT. Only the L210X mutation showed loss of function in all tests, while variants L724V and S730S showed a decrease in CYP17A1 promoter activation. We found no effect of either WT or any MAMLD1 variant on CYP17A1 enzyme activity. Also, no difference for MAMLD1 protein expression was found, except for a shorter L210X.
Conclusion: Our data support the notion that MAMLD1 sequence variations may not suffice to explain the DSD phenotype in carriers.
Funding: This work was supported by the Swiss National Science Foundation (320030146127), the Instituto de Salud Carlos III, Madrid, Spain CIBERER U-712, the AGAUR (University and Research Management and Evaluation Agency), Barcelona, Spain (2009SGR31), and by the private Foundation Bangerter-Rhyner, Basel, Switzerland.
01 Oct 2015 - 03 Oct 2015