Etude cytogénétique et moléculaire des désordres du développement sexuel.

Abstract

Disorders of sex determination/differentiation (DSD) comprise a heterogeneous group of congenital conditions in which chromosomal, gonadal or anatomical sex is discordant. In recent years, a number of new candidate genes have been identified to be associated with DSD and the diagnostic yield using the whole exome sequencing (WES) approach has been remarkable. The objective of our study performed on patients with DSD (46,XY and 46,XX), is focusing on the identification of known gene variants causing DSD in the Algerian population, largely unexplored, on the one hand, and on the other hand to identify new genes involved in DSD and atypical clinical features. Patients and methods: approximately 350 DNAs (patients, parents and/or siblings) were extracted by NaCl method, to perform WES and in silico functional study for the 125 individuals recruited, as well as the parents of 34 patients. Determination of the presence of the SRY gene by conventional PCR was systematic. Depending on the availability of parental DNA, the transmission of certain gene variants was demonstrated by Sanger sequencing. Results and discussion: the mean age at diagnosis ranged between 1 day to 22 years and a history of consanguinity was noted in 36% of cases. Genetic etiology was established in 49.6% (62/125) of individuals, including 42.2% of patients with 46,XY non-syndromic DSD and 69.2% of patients with 46,XY syndromic DSD. Variants in the AR, HSD17B3, NR5A1 and SRD5A2 genes were the most common in our cohort. Other variants involving genes associated with HHC have been reported, including CHD7 and PROKR2. All 30 previously unreported pathogenic/probably pathogenic variants, involving a total of 25 different genes causing DSD, were found in 24% of the cohort. 11.5% of the 46,XY DSD group carried variants classified as pathogenic/likely pathogenic in more than one gene. In addition, 3 pathogenic/probably pathogenic variants in the CACNA1F, COL1A1 and NGLY1 genes explaining only somatic phenotypes were recorded in 3 cases. Similarly, 2 new variants of uncertain significance in the SCLY and VEGFB genes were identified by a WES comparative analysis of discordant twins for the DSD phenotype. In addition, another variant in the NR2F2 gene was noted in a patient with 46,XY DSD. Furthermore, parental recruitment allowed to establish a more accurate genetic diagnosis by classifying the variants as benign, likely benign or of uncertain significance rather than pathogenic or likely pathogenic. The phenotypic variability observed in familial cases with identical genetic variants may be due to incomplete penetrance. Conclusion: Molecular analysis using WES and functional study in silico revealed a genetic diagnosis in about half of the study population. This technology is useful for the detection of mononucleotide and dinucleotide variants. Variants of uncertain significance require further work to elucidate their roles, thus allowing for the broadening of the phenotypic spectrum associated with genes known to cause DSD. Other technologies are also needed to detect genetic causes in patients who do not carry any variants.