Background: Most congenital adrenal hyperplasia (CAH) patients carry mutations derived from conversion events involving the pseudogene, and the remaining carry new mutations varying according to ethnicity. A good genotype-phenotype correlation is observed, allowing the use of molecular analysis in clinical practice.
Objective and hypotheses: To review the molecular diagnosis in a large cohort of CAH patients in order to create a diagnostic panel in our population.
Method: DNA was extracted from 480 patients (158 SW, 116 SV, 206 NC); Point mutations were screened by allele- specific PCR and large gene rearrangements by Southern blotting/MLPA; CYP21A2 sequencing was performed in those with incomplete genotype. Gene founder effect was analyzed through microsatellite studies. Patients were divided into 4 genotypes, according to in vitro enzymatic activity (Null, A:<2%, B:37%, C: >20%).
Results: Targeted methodologies identified mutations in both alleles in 89% of SW, 86% of SV and 80% of NC patients. CYP21A2 sequencing allowed genotype definition in 100% of classical and 87% of NC patients. Seven rare mutations (p.G424S, p.R408C, IVS2-2A>G, p.Ser170fs, p.R426H, p.H365Y, p.W19X) and a novel variant (p.E351V) were identified in 11% of alleles. Gene founder effect was observed in all but the p.W19X. Genotypes Null, A (I2 splice), B and C comprised mainly patients with SW (88%), SW (70%), SV (98%) and NC form (100%), respectively. The median basal 17OHP level was significantly higher in genotype A/C (median 17.5 ng/ml) than in C/C (median 7.6 ng/ml) as was ACTHstimulated 17OHP level (P=0.005). The lowest stimulated-17OHP level in group C was 11 ng/ml.
Conclusion: We identified a good genotypephenotype correlation providing useful results regarding prediction of disease severity and genetic counseling. Sequencing is essential to optimize molecular diagnosis in our population, considering the high frequency of gene founder effect mutations.
10 Sep 2016 - 12 Sep 2016