A novel 9-bp insertion detected in steroid 21-hydroxylase gene (CYP21A2): prediction of its structural and functional implications by computational methods

EMQN best practice guidelines for molecular genetic testing and reporting of 21-hydroxylase deficiency

Molecular genetic testing for congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency (21-OHD) is offered worldwide and is of importance for differential diagnosis, carrier detection and adequate genetic counseling, particularly for family planning. In 2008 the European Molecular Genetics Quality Network (EMQN) for the first time offered a European-wide external quality assessment scheme for CAH (due to 21-OH deficiency). The interest was great and over the last years at about 60 laboratories from Europe, USA and Australia regularly participated in that scheme. These best practice guidelines were drafted on the basis of the extensive knowledge and experience got from those annually organized CAH-schemes. In order to obtain the widest possible consultation with practicing laboratories the draft was therefore circulated twice by EMQN to all laboratories participating in the EQA-scheme for CAH genotyping and was updated by that input. The present guidelines address quality requirements for diagnostic molecular genetic laboratories, as well as criteria for CYP21A2 genotyping (including carrier-testing and prenatal diagnosis). A key aspect of that article is the use of appropriate methodologies (e.g., sequencing methods, MLPA (multiplex ligation dependent probe amplification), mutation specific assays) and respective limitations and analytical accuracy. Moreover, these guidelines focus on classification of variants, and the interpretation and standardization of the reporting of CYP21A2 genotyping results. In addition, the article provides a comprehensive list of common as well as so far unreported CYP21A2-variants.

How do mutations affect the structural characteristics and substrate binding of CYP21A2? An investigation by molecular dynamics simulations

CYP21A2 mutations affect the activity of the protein leading to CAH disease.

Novel variants of CYP21A2 in Vietnamese patients with congenital adrenal hyperplasia

BACKGROUND

Congenital adrenal hyperplasia (CAH) (OMIM #201910) is a complex disease most often caused by pathogenic variant of the CYP21A2 gene. We have designed an efficient multistep approach to diagnose and classify CAH cases due to CYP21A2 variant and to study the genotype-phenotype relationship.

METHODS

A large cohort of 212 Vietnamese patients from 204 families was recruited. We utilized Multiplex Ligation-dependent Probe Amplification to identify large deletion or rearrangement followed by complete gene sequencing of CYP21A2 to map single-nucleotide changes and possible novel variants.

RESULTS

Pathogenic variants were identified in 398 out of 408 alleles (97.5%). The variants indexed span across most of the CYP21A2 gene regions. The most common genotypes were: I2g/I2g (15.35%); Del/Del (14.4%); Del/I2g (10.89%); p.R356W/p.R356W (6.44%); and exon 1-3 del/exon 1-3 del (5.44%). In addition to the previously characterized and documented variants, we also discovered six novel variants which were not previously reported, in silico tools were used to support the pathogenicity of these variants.

CONCLUSION

The result will contribute in further understanding the genotype-phenotype relationship of CAH patients and to guide better treatment and management of the affected.

Prenatal diagnosis of steroid 21-hydroxylase-deficient congenital adrenal hyperplasia: Experience from a tertiary care centre in India

Background & objectives:

Congenital adrenal hyperplasia (CAH) is an autosomal recessive disorder with a wide range of clinical manifestations. The disease is attributed to mutations in CYP21A2 gene encoding 21-hydroxylase enzyme. In view of severe phenotype in salt-losing cases, issues related to genital ambiguity in girls and precocity in boys, most families opt for prenatal testing and termination of affected foetus. CAH can be diagnosed in utero through direct molecular analysis of CYP21A2 gene, using DNA extracted from foetal tissues or cells obtained from chorionic villus sampling or amniocentesis. The objective of this study was to evaluate the feasibility and accuracy of prenatal diagnosis (PND) using sequencing and multiplex ligation probe amplification (MLPA) methods in families at risk for CAH.

Methods:

Fifteen pregnant women at risk of having an affected offspring with CAH were included in this study. Ten families had previous affected children with salt-wasting/simple virilising form of CAH and five families did not have live children but had a high index of suspicion for CAH in previous children based on history or records. Mutation analysis was carried out by Sanger sequencing and MLPA method.

Results:

Seven different mutations were identified in 15 families. Deletions and I2g mutation were the most common. Of the 15 foetuses analyzed, nine were unaffected while six were affected. Unaffected foetuses were delivered, they were clinically normal and their genotype was found to be concordant to the prenatal report. All except two families reported in the second trimester. None of the couples opted for prenatal treatment.

Interpretation & conclusions:

Our preliminary findings show that PND by direct mutation analysis along with MLPA is a feasible strategy that can be offered to families at risk.

CYP21A2 mutation update: Comprehensive analysis of databases and published genetic variants

Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders of adrenal steroidogenesis. Disorders in steroid 21-hydroxylation account for over 95% of patients with CAH. Clinically, the 21-hydroxylase deficiency has been classified in a broad spectrum of clinical forms, ranging from severe or classical, to mild late onset or non-classical. Known allelic variants in the disease causing CYP21A2 gene are spread among different sources. Until recently, most variants reported have been identified in the clinical setting, which presumably bias described variants to pathogenic ones, as those found in the CYPAlleles database. Nevertheless, a large number of variants are being described in massive genome projects, many of which are found in dbSNP, but lack functional implications and/or their phenotypic effect. In this work, we gathered a total of 1,340 GVs in the CYP21A2 gene, from which 899 variants were unique and 230 have an effect on human health, and compiled all this information in an integrated database. We also connected CYP21A2 sequence information to phenotypic effects for all available mutations, including double mutants in cis. Data compiled in the present work could help physicians in the genetic counseling of families affected with 21-hydroxylase deficiency.

Steered molecular dynamics simulation of the binding of the bovine auxilin J domain to the Hsc70 nucleotide-binding domain

The Hsp70 and Hsp40 chaperone machine plays critical roles in protein folding, membrane translocation, and protein degradation by binding and releasing protein substrates in a process that utilizes ATP. The activities of the Hsp70 family of chaperones are recruited and stimulated by the J domains of Hsp40 chaperones. However, structural information on the Hsp40-Hsp70 complex is lacking, and the molecular details of this interaction are yet to be elucidated. Here we used steered molecular dynamics (SMD) simulations to investigate the molecular interactions that occur during the dissociation of the auxilin J domain from the Hsc70 nucleotide-binding domain (NBD). The changes in energy observed during the SMD simulation suggest that electrostatic interactions are the dominant type of interaction. Additionally, we found that Hsp70 mainly interacts with auxilin through the surface residues Tyr866, Arg867, and Lys868 of helix II, His874, Asp876, Lys877, Thr879, and Gln881 of the HPD loop, and Phe891, Asn895, Asp896, and Asn903 of helix III. The conservative residues Tyr866, Arg867, Lys868, His874, Asp876, Lys877, and Phe891 were also found in a previous study to be indispensable to the catalytic activity of the DnaJ J domain and the binding of it with the NBD of DnaK. The in silico identification of the importance of auxilin residues Asn895, Asp896, and Asn903 agrees with previous mutagenesis and NMR data suggesting that helix III of the J domain of the T antigen interacts with Hsp70. Furthermore, our data indicate that Thr879 and Gln881 from the HPD loop are also important as they mediate the interaction between the bovine auxilin J domain and Hsc70.

A unique case of female pseudohermaphroditism with 21-hydroxylase deficiency and small supernumerary marker chromosome 7

Small supernumerary marker chromosomes (sSMCs) are present in ~2.6x10⁶ individuals worldwide. Concerning their clinical consequences as well as their chromosomal origin and shape, sSMCs are a heterogeneous group of derivative chromosomes; 70% of sSMC carriers are clinically normal. In the present study, we report on a female with mosaicism (45%) of a de novo sSMC derived from chromosome 7, in which the observed clinical signs do not correspond to comparable cases in the literature. She is clinically normal apart from problems in gender determination, a uterus without ovaries and an external penis, pointing overall towards an adrenogenital syndrome (AGS). 21-Hydroxylase deficiency (21-OHD) is the most common cause of AGS. A corresponding analysis for underlying mutations in the CYP21A2 gene revealed a homozygous mutation c.518T>A (p.Ile173Asn) inherited from both non-related parents. Overall, in this study, we report a unique case of female pseudohermaphroditism, classified as a simple virilization form of 21-OHD having an additional minute-shaped chromosome 7 [min(7)(:p11.1->q11.23:)]. Notably, AGS was due to a mutation in the CYP21A2 gene located on chromosome 6. This is a further example that detection of an sSMC does not always resolve the clinical case.