Predisposition for de novo gene aberrations in the offspring of mothers with a duplicated CYP21A2 gene
ABSTRACT Although CYP21A2 de novo mutations are assumed to account for 1 to 2% of congenital adrenal hyperplasia (CAH) alleles and CYP21 genotyping has been done worldwide, there are only a few well-documented cases of CYP21A2 de novo mutations. The majority of these are deletions resulting from unequal crossings over owing to misalignment of homologous chromosomes during meiosis. Whereas so far, only heterozygous deletions of the CYP21A1P pseudogene were seen as premutations for de novo aberrations, the present report addresses such a predisposing role for parental duplicated CYP21A2 genes.
As part of routine diagnostic procedures, CYP21 genotyping has been performed in two unrelated female CAH index patients and in their clinically asymptomatic parents and siblings.
Both patients have inherited the paternal Intron2splice mutation and have harbored a de novo gene aberration (large deletion and I271N/exon 4) on their maternal haplotype. Surprisingly, both mothers were carriers of rare duplicated CYP21A2 haplotypes carrying CAH alleles, which were not detected in the daughters. Among 133 CAH alleles that were detected in patients and that could be traced to the respective family members by genotyping, these two de novo aberrations (representing 1.5% of 133 traced CAH alleles) were the only ones identified.
Because both de novo CYP21A2 gene aberrations so far identified in our laboratory occurred in the gametes of mothers carrying rare duplicated CYP21A2 haplotypes, we hypothesize that duplicated CYP21A2 genes could predispose for de novo mutations in the offspring, which is of relevance for prenatal CYP21 genotyping and genetic counseling.
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ABSTRACT: The human RCCX is a common multiallelic copy number variation locus whose number of segments varies between one and four in a chromosome. The monomodular form normally comprises four functional genes, but in duplicated RCCX segments generally only the gene-encoding complement component C4 produces a protein. C4 genes can code either for a C4A or a C4B isotype protein and exhibit dichotomous size variation. Distinct RCCX variants show association with numerous diseases; however, identification of the basis of these associations is often challenging, not least because the RCCX is localized in the major histocompatibility complex (MHC) region, a genomic area characterized by exceedingly long-range linkage disequilibrium. Here we present a detailed analysis on RCCX variants and their relationship with so-called 'ancestral' or 'conserved extended' MHC haplotypes in healthy Caucasians. In addition to former investigations, precise order and size of all C4A and C4B genes were determined even in trimodular RCCX structures. Considering C4 copy numbers, length, isotype specificity and CYP21A2 copy numbers, we have identified 15 distinct RCCX variants and described the RCCX structures involved in 29 repeatedly occurring MHC haplotypes. The findings should become a useful tool for future RCCX- and MHC-related disease association studies.Genes and immunity 07/2012; 13(7):530-5. DOI:10.1038/gene.2012.29 · 3.79 Impact Factor
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ABSTRACT: Congenital adrenal hyperplasia (CAH) is characterized by impaired biosynthesis of cortisol. 21-hydroxylase deficiency is the most common cause of CAH affecting 1 in 10000-15000 live births over the world. The frequency of the disorder is very high in Iran due to frequent consanguineous marriages. Although biochemical tests are used to confirm the clinical diagnosis, molecular methods could help to define accurate diagnosis of the genetic defect. Recent molecular approaches such as polymerase chain reaction based methods could be used to detect carriers and identify different genotypes of the affected individuals in Iran which may cause variable degrees of clinical expression of the condition. Molecular tests are also applied for prenatal diagnosis, and genetic counseling of the affected families. Here, we are willing to delineate mechanisms underlying the disease, genetic causes of CAH, genetic approaches being used in the country and recommendations for health care improvement on the basis of the molecular and clinical genetics to control and diminish such a high prevalent disorder in Iran. Also, the previous studies on CAH in Iran are gathered and a diagnostic algorithm for the genetic causes is proposed.06/2011; 21(2):139-50.
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ABSTRACT: Genetic analysis is commonly performed in patients with congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency. The objective of the study was to describe comprehensive CYP21A2 mutation analysis in a large cohort of CAH patients. Targeted CYP21A2 mutation analysis was performed in 213 patients and 232 parents from 182 unrelated families. Complete exons of CYP21A2 were sequenced in patients in whom positive mutations were not identified by targeted mutation analysis. Copy number variation and deletions were determined using Southern blot analysis and PCR methods. Genotype was correlated with phenotype. In our heterogeneous U.S. cohort, targeted CYP21A2 mutation analysis did not identify mutations on one allele in 19 probands (10.4%). Sequencing identified six novel mutations (p.Gln262fs, IVS8+1G>A, IVS9-1G>A, p.R408H, p.Gly424fs, p.R426P) and nine previously reported rare mutations. The majority of patients (79%) were compound heterozygotes and 69% of nonclassic (NC) patients were compound heterozygous for a classic and a NC mutation. Duplicated CYP21A2 haplotypes, de novo mutations and uniparental disomy were present in 2.7% of probands and 1.9 and 0.9% of patients from informative families, respectively. Genotype accurately predicted phenotype in 90.5, 85.1, and 97.8% of patients with salt-wasting, simple virilizing, and NC mutations, respectively. Extensive genetic analysis beyond targeted CYP21A2 mutational detection is often required to accurately determine genotype in patients with CAH due to the high frequency of complex genetic variation.The Journal of Clinical Endocrinology and Metabolism 10/2010; 96(1):E161-72. DOI:10.1210/jc.2010-0319 · 6.31 Impact Factor