Application of the DHPLC method for mutational detection of the CYP21A2 gene in congenital adrenal hyperplasia

The Complexities in Genotyping of Congenital Adrenal Hyperplasia: 21-Hydroxylase Deficiency

The deficiency of 21-hydroxylase due to CYP21A2 pathogenic variants is a rather frequent disease with serious consequences, going from a real mortality risk to infertility and to milder symptoms, nevertheless important for affecting the patients' self-esteem. In the most severe cases life-threatening adrenal salt wasting crises may occur. Significant morbidity including the possibility of mistaken gender determination, precocious puberty, infertility and growth arrest with consequent short stature may also affect these patients. In the less severe cases milder symptoms like hirsutism will likely affect the image of the self with strong psychological consequences. Its diagnosis is confirmed by 17OH-progesterone dosages exceeding the cut-off value of 10/15 ng/ml but genotyping is progressively assuming an essential role in the study of these patients particularly in confirming difficult cases, determining some aspects of the prognosis and allowing a correct genetic counseling. Genotyping is a difficult process due to the occurrence of both a gene and a highly homologous pseudo gene. However, new tools are opening new possibilities to this analysis and improving the chances of a correct diagnosis and better understanding of the underlying mechanisms of the disease. Beyond the 10 classic pathogenic variants usually searched for in most laboratories, a correct analysis of 21OH-deficiency cases implies completely sequencing of the entire gene and the determination of gene duplications. These are now recognized to occur frequently and can be responsible for some false positive cases. And finally, because gene conversions can include several pathogenic variants one cannot be certain of identifying that both alleles are affected without studying parental DNA samples. A complete genotype characterization should be considered essential in the preparation for pregnancy, even in the case of parents with milder forms of the disease, or even just carriers, since it has been reported that giving birth to progeny with the severe classic forms occurs with a much higher frequency than expected.

Novel method to characterize CYP21A2 in Florida patients with congenital adrenal hyperplasia and commercially available cell lines

Congenital adrenal hyperplasia (CAH) is an autosomal recessive disorder and affects approximately 1 in 15,000 births in the United States. CAH is one of the disorders included on the Newborn Screening (NBS) Recommended Uniform Screening Panel. The commonly used immunological NBS test is associated with a high false positive rate and there is interest in developing second-tier assays to increase screening specificity. Approximately 90% of the classic forms of CAH, salt-wasting and simple virilizing, are due to mutations in the CYP21A2 gene. These include single nucleotide changes, insertions, deletions, as well as chimeric genes involving CYP21A2 and its highly homologous pseudogene CYP21A1P. A novel loci-specific PCR approach was developed to individually amplify the CYP21A2 gene, the nearby CYP21A1P pseudogene, as well as any 30 kb deletion and gene conversion mutations, if present, as single separate amplicons. Using commercially available CAH positive specimens and 14 families with an affected CAH proband, the single long-range amplicon approach demonstrated higher specificity as compared to previously published methods.

Mutational analysis of CYP21A2 gene and CYP21A1P pseudogene: long-range PCR on genomic DNA

CYP21A2, the gene that codes for P450c21 (Steroid 21-hydroxylase), has a duplicated pseudogene called CYP21A1P. The gene and the pseudogene share 98 % and 96 % sequence homology in exons and in noncoding sequences, respectively, and are located 30 kb apart within the HLA class III human histocompatibility complex locus on chromosome 6p21.3. CYP21A1P is inactive due to the presence of 11 deteriorated mutations in its coding region. These mutations can be transferred to the functional CYP21A2 through intergenic recombination during meiosis or mitosis and lead to the congenital adrenal hyperplasia (CAH) resulting from 21-hydroxylase deficiency. Conversely, portions of CYP21A2 sequence can be transferred to CYP21A1P, modifying the haplotype. Here, we describe a well-established protocol that can be used to unambiguously study the mutational profile of CYP21A2 gene and CYP21A1P pseudogene. The protocol is based on long-range PCR amplification with allele-specific primers, followed by DNA sequencing of smaller fragments.

Comprehensive mutation analysis of the CYP21A2 gene: an efficient multistep approach to the molecular diagnosis of congenital adrenal hyperplasia

Congenital adrenal hyperplasia, due to 21-hydroxylase deficiency (21-OHD) is an autosomal recessive disorder of adrenal steroidogenesis caused by mutations in the CYP21A2 gene. Direct comparison of established and novel methodologies of CYP21A2 genetic analysis in a large cohort representing a wide range of genotypes has not been previously reported. We genotyped a cohort of 129 unrelated patients with 21-OHD, along with 145 available parents, using Southern blot (SB) analysis, multiplex ligation-dependent probe amplification (MLPA), PCR-based restriction fragment length polymorphism (RFLP) analysis, multiplex minisequencing and conversion-specific PCR, duplication-specific amplification, and DNA sequencing. CYP21A2 genotyping identified four duplicated CYP21A2 genes (1.53%) and 79 chimeric CYP21A1P/CYP21A2 genes (30.15%). Parental SB data were essential for determining the CYP21 haplotype in three cases, whereas PCR-based RFLP analysis was necessary for MLPA results to be accurately interpreted in the majority of cases. The comparison of different methods in detecting deletion and duplication showed that MLPA with PCR-based RFLP was comparable with SB analysis, with parental data of 100% sensitivity and specificity. DNA sequencing was required for the identification of 16 (6.1%) rare point mutations and determination of clinically significant chimera junction sites. MLPA with PCR-based RFLP analysis is an excellent substitute for SB analysis in detecting CYP21A2 deletion and duplication and a combination of MLPA, PCR-based RFLP, duplication-specific amplification, and DNA sequencing is a convenient and comprehensive strategy for mutation analysis of the CYP21A2 gene in patients with 21-OHD.