Mutation detection of CYP21A2 gene in nonclassical congenital adrenal hyperplasia patients with premature pubarche

CYP21A2 Gene Analysis in Southern Iranian CAH Patients and a Brief Review of the Mutation Spectrum

Background

CYP21A2 gene mutations are responsible for more than 95% of Congenital Adrenal Hyperplasia (CAH) disorders with autosomal recessive inheritance. Most of these pathogenic mutations originate from the CYP21A1P, a neighboring pseudogene with 98% homology, due to unequal crossing over or gene conversion events. Mutation identification of the gene could be beneficial for accurate diagnosis and outcome prediction.

Methods

Twelve unrelated patients with CAH diagnosis were recruited for genetic counseling. To ensure distinct amplification of the CYP21A2 gene rather than its pseudogene, the complete sequence of the gene was amplified through two overlapping fragments by specific primers. The entire sequences were screened by direct Sanger sequencing using new sequencing primers.

Results

Only two pathogenic point mutations were identified. The c.293-13C>G, also known as In2G, and the c.955C>T mutations were found in 37.5 and 33.3% of alleles, respectively. One patient showed homozygous gene deletion. We also reviewed recent reports on CYP21A2 gene mutations in Iran.

Conclusion

Evaluating the ethnicity-specific gene mutation data is significant for populations with diverse ethnic groups including the Iranian population. Although several common mutations have been reported as causative mutations among CAH patients, identifying only two common point mutations in Fars province would help prioritize exon sequencing and reduce the cost and time of genotyping.

p.Gln318X and p.Val281Leu as the Major Variants of CYP21A2 Gene in Children with Idiopathic Premature Pubarche

Premature pubarche (PP) is the appearance of sexual hair in children before puberty. The PP phenotype may attribute to nonclassic congenital adrenal hyperplasia (NC-CAH). In this study, we investigated the role of CYP21A2 gene variants in patients with PP in the Iranian population. Forty patients (13 males and 27 females), clinically diagnosed with PP, were analyzed for molecular testing of CYP21A2 gene variants. Direct sequencing was performed for the samples. Also, gene dosage analysis was performed for the cases. Fourteen patients (35%) had a mutation of p.Gln318X and p.Val281Leu, out of which 10% had regulatory variants. Approximately 10% of the patients were homozygous (NC-CAH). 78.5% (11/14) of patients had trimodular RCCX of which 5 patients had two copies of CYP21A1P pseudogene. The prevalence of p.Val281Leu was higher than p.Gln318X in PP patients. In conclusion, CYP21A2 variant detection has implications in the genetic diagnosis of PP phenotype. The genetic characterization of the CYP21A2 gene is important for characterizing the variable phenotype of carriers and genetic counseling of PP and NC-CAH patients.

Identification of novel and rare CYP21A2 variants in Chinese patients with congenital adrenal hyperplasia due to 21-hydroxylase deficiency

OBJECTIVE

21-hydroxylase deficiency (21-OHD) is the most common cause of congenital adrenal hyperplasia due to CYP21A2 gene mutation. The aim of study is to expand CYP21A2 mutational spectrum in the Chinese population and to provide novel genetic information in terms of ethnic diversity.

DESIGN AND METHODS

95 Chinese suspected 21-OHD patients with phenotypes varying from salt-wasting (SW) to nonclassic symptoms were recruited. The clinical characteristics were retrospectively analyzed. Sanger sequencing and multiplex ligation-dependent probe amplification were used to detect point mutations and large gene deletions, respectively.

RESULTS

20 different mutant alleles were detected in 35 patients with 21-OHD. The most common variant was c.293-13A/C>G (30.0%), followed by p.I173N (20.0%), large gene conversions (14.3%), large gene deletions (11.4%), and p.R484Pfs*58 (4.3%). Remarkably, we identified a novel F450L variant, in silico predicted to be associated with the salt-wasting form. Two variants including p.R409C and p.R427H, previously considered as conserved in specific ethnicities due to a founder effect, were detected in our cohort. Further, a rare p.H63L + p.V70L variant, hitherto only observed in the Chinese population, in trans with different variants corresponding to the salt-wasting form resulted in diverse phenotypes.

CONCLUSIONS

One novel and four rare variants of CYP21A2 gene corresponding to severe phenotypes were identified in our cohort. Two variants including p.R409C and p.R427H have wider ethnic distributions. Therefore, the sequence of CYP21A2 gene must be analyzed carefully in case rare or novel deleterious variants exist. Our findings improve the understanding of CYP21A2 mutational spectrum in 21-OHD patients and contribute to the precise diagnosis and prenatal counseling.