The frequency and the effects of 21-hydroxylase gene defects in congenital adrenal hyperplasia patients

Neonatal Screening for Congenital Adrenal Hyperplasia in Indian Newborns with Reflex Genetic Analysis of 21-Hydroxylase Deficiency

Congenital adrenal hyperplasia (CAH), screened for in neonates, is the second most common endocrinopathy after congenital hypothyroidism.Newborn screening for CAH due to CYP21A2 deficiency is performed by immunologic assay for 17-hydroxyprogesterone (17-OHP). The second-tier test for confirmation of diagnosis is carried out on recall venous blood sample from screen positives measuring 17-OHP, or other metabolites of steroid metabolism by liquid chromatography–tandem mass spectroscopy. However, as steroid metabolism is dynamic, it can affect these parameters even in the recall sample of a stressed neonate. Moreover, there is some time delay in recalling the neonate for repeat testing. Reflex genetic analysis of blood spot from the initial Guthrie cards of screen positive neonates, if used for confirmatory testing, can avoid this time delay as well as the effect of stress on steroid metabolism. In this study, we used Sanger sequencing and MLPA in a reflex manner for molecular genetic analysis to confirm CYP21A2-mediated CAH. Out of 220,000 newborns screened, 97 were positive on the initial biochemical screen, of which 54 were confirmed true positives with genetic reflex testing, giving incidence of CAH as 1:4074. Point mutations were more common than deletions, indicating that Sanger sequencing should be used ahead of MLPA for molecular diagnosis in India. Amongst the variants detected, the most common was I2G-Splice variant (44.5%), followed by c.955C>T (p.Gln319Ter) (21.2%); Del 8 bp and c.-113G>A were detected with frequencies of 20.3% and 20%, respectively. In conclusion, reflex genetic testing is an effective strategy for identifying true positives in CAH screening in neonates. This will obviate need for recall samples and also aid effective counselling and timely prenatal diagnosis in the future. In Indian newborns, as point mutations are more common than large deletions, Sanger sequencing should be the initial method of choice for genotyping, ahead of MLPA.

The spectrum of CYP21A2 gene mutations in patients with classic salt wasting form of 2l-hydroxylase deficiency in a Chinese cohort

Background

21‐Hydroxylase deficiency (21‐OHD) caused by the CYP21A2 gene mutations is the most common form of congenital adrenal hyperplasia. It is an autosomal recessive disorder that results in defective synthesis of cortisol and aldosterone. The incidences of various CYP21A2 gene mutations and the genotype–phenotype correlations vary among different populations.

Materials and Methods

The clinical and molecular data of 22 patients were analyzed in this study. All patients were recruited from the neonatal intensive care unit. Locus‐specific polymerase chain reaction and Sanger sequencing were applied to identify gene micro‐conversions, and multiplex ligation‐dependent probe amplification was used to detect large fragment deletions/conversions. Then, the genotypes were categorized in to Null, A, B, C, and D groups to analyze the relationships between genotypes and phenotypes.

Results

All 22 patients were classified into classic salt wasting form of 21‐OHD. Molecular defects were detected in 44 alleles (100%). Micro‐conversion mutation IVS2‐13A/C>G (70.5%) is most common in our cohort, followed by large gene deletions and conversions (22.7%). The other mutations present were p.R357 W (4.5%) and E6 Cluster (2.3%). Genotypes of 22 patients (100%) were consistent with the predictive phenotypes.

Conclusion

In this study, we identified the mutation spectrum of CYP21A2 gene in Chinese patients, especially the younger age cohort in pediatrics. Micro‐conversions were the most popular mutations. Moreover, the genotypes and phenotypes were well correlated in this cohort of salt wasting 21‐OHD recruited from neonatal intensive care unit.

We identified the mutation spectrum of CYP21A2 gene in Chinese patients, especially the younger age cohort admitted in NICU. The genotypes and phenotypes in 21‐OHD were well correlated.

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.

Translating genomics to the clinical diagnosis of disorders/differences of sex development

The medical and psychosocial challenges faced by patients living with Disorders/Differences of Sex Development (DSD) and their families can be alleviated by a rapid and accurate diagnostic process. Clinical diagnosis of DSD is limited by a lack of standardization of anatomical and endocrine phenotyping and genetic testing, as well as poor genotype/phenotype correlation. Historically, DSD genes have been identified through positional cloning of disease-associated variants segregating in families and validation of candidates in animal and in vitro modeling of variant pathogenicity. Owing to the complexity of conditions grouped under DSD, genome-wide scanning methods are better suited for identifying disease causing gene variant(s) and providing a clinical diagnosis. Here, we review a number of established genomic tools (karyotyping, chromosomal microarrays and exome sequencing) used in clinic for DSD diagnosis, as well as emerging genomic technologies such as whole-genome (short-read) sequencing, long-read sequencing, and optical mapping used for novel DSD gene discovery. These, together with gene expression and epigenetic studies can potentiate the clinical diagnosis of DSD diagnostic rates and enhance the outcomes for patients and families.

Development of CYP21A2 Genotyping Assay for the Diagnosis of Congenital Adrenal Hyperplasia

BACKGROUND

Steroid 21-hydroxylase deficiency due to CYP21A2 gene mutations represents more than 90% of all congenital adrenal hyperplasia cases. This deficiency is screened by measuring levels of 17-hydroxyprogesterone, which may vary, causing false positive or false negative results. In order to assist the diagnosis, molecular methodologies have been employed. This work aimed to perform genotyping assays to detect mutations in the CYP21A2 gene and compare the findings with other population studies.

METHODS

The SNaPshot assay was developed to simultaneously detect 12 frequent point mutations in the CYP21A2 gene (p.Arg409Cys, p.Gln319Ter, p.Arg357Trp, p.Leu308PhefsTer6, p.Val237Glu, IVS2-13A/C > G, p.Ile173Asn, p.Pro31Leu, p.Pro454Ser, p.Val282Leu, p.Gly111ValfsTer21 and p.His63Leu). The direct sequencing and multiplex ligation-dependent probe amplification assays were used to confirm point mutations present in the developed method. The latter was also used to search large deletions and gene conversion, complementing the investigation. A total of 166 cases were studied.

RESULTS

The SNaPshot assay was successfully developed to detect the 12 mutations. The results of mutation analysis indicated 84 pathogenic alleles in 48 cases, with p.Val282Leu (27.1%) and IVS2-13A/C > G (20.8%) being the most frequently found mutations. Between the findings of this study and those of other South American studies, there were significant differences in frequency for p.Pro31Leu and p.Val282Leu (p < 0.001). A new variant T in IVS2-13A/C > G was identified in two patients via the SNaPshot assay.

CONCLUSION

The molecular strategy developed for CYP21A2 gene mutation screening allowed us to detect the principle mutations described around the world. Furthermore, the first Southern Brazilian mutation frequencies concerning the CYP21A2 gene were obtained.

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.

Structure-based activity prediction of CYP21A2 stability variants: A survey of available gene variations

Congenital adrenal hyperplasia due to 21-hydroxylase deficiency accounts for 90-95% of CAH cases. In this work we performed an extensive survey of mutations and SNPs modifying the coding sequence of the CYP21A2 gene. Using bioinformatic tools and two plausible CYP21A2 structures as templates, we initially classified all known mutants (n = 343) according to their putative functional impacts, which were either reported in the literature or inferred from structural models. We then performed a detailed analysis on the subset of mutations believed to exclusively impact protein stability. For those mutants, the predicted stability was calculated and correlated with the variant's expected activity. A high concordance was obtained when comparing our predictions with available in vitro residual activities and/or the patient's phenotype. The predicted stability and derived activity of all reported mutations and SNPs lacking functional assays (n = 108) were assessed. As expected, most of the SNPs (52/76) showed no biological implications. Moreover, this approach was applied to evaluate the putative synergy that could emerge when two mutations occurred in cis. In addition, we propose a putative pathogenic effect of five novel mutations, p.L107Q, p.L122R, p.R132H, p.P335L and p.H466fs, found in 21-hydroxylase deficient patients of our cohort.

The spectrum of CYP21A2 mutations in Congenital Adrenal Hyperplasia in an Indian cohort

Congenital Adrenal Hyperplasia (CAH) is a common autosomal recessive disorder of the adrenal steroidogenic pathway. The most common form of CAH is due to mutations in CYP21A2 gene. The incidence of mutations in the CYP21A2 gene and the genotype-phenotype correlations vary among different populations. Therefore, the aim of the study was to establish the spectrum of mutations and to evaluate genotype-phenotype correlation in Indian CAH population. Molecular defects were investigated in 110 alleles (55 patients) in the present study. Notably, we identified disease causing mutations in 106 of 110 (96.4%) alleles whereas the frequency of undetectable mutations was 3.6%. The i2g mutation (20%) was found to be the most common in CAH patients. The second most common mutation was p.R356W (14.5%). p.I172N and 8-bp deletion in exon 3 accounted for 12.7% of the mutated alleles. In descending order, the other mutations present were p.Q318X (9%), E6 Cluster (5.4%), p.V281L (3.6%) and large gene deletion (3.6%). Additionally, p.P267L and frameshift mutation (L307fs/F306+T) were also detected in the Indian cohort with frequency of 1.8% and 5.4% respectively.rare mutation/rare mutations in the CYP21A2 gene were detected viz., p.D234D (NCBI accession number - KF812549), p.F306V (NCBI accession number - KF534754), p.P357P (NCBI accession number - KF692099) and p.H365N (NCBI accession number - KF447378). The genotypes of the patients were categorized into four groups null, A, B and C. Of note, correlation between genotype and phenotype is sufficiently strong, to be of clinical significance in the genetic counseling.

Preventing female virilisation in congenital adrenal hyperplasia: The controversial role of antenatal dexamethasone

Congenital adrenal hyperplasia (CAH) refers to a group of recessively inherited disorders of cortisol production, which in the classical form results in virilisation of female fetuses. Since the 1980s, antenatal treatment with dexamethasone has been recommended in high-risk pregnancies to minimise the risk of virilising the female genitalia of affected fetuses. To be effective, this treatment requires implementation in early pregnancy, prior to the commencement of autonomous fetal adrenal androgen synthesis. Using this approach, seven of eight high-risk pregnancies are treated unnecessarily, prior to establishing the fetal gender or the confirmed diagnosis of a genetically affected pregnancy. In the face of ongoing concerns regarding potential adverse maternal-fetal effects of antenatal dexamethasone exposure, a review of this practice has been advocated by expert advisory groups. In this review, we summarise current controversies, potential improvements and future directions in the management of pregnancies at risk of CAH. In high-risk families, recent genomic advances include early prenatal diagnosis utilising noninvasive genetic techniques to minimise unnecessary dexamethasone exposure to unaffected fetuses. In affected pregnancies when families elect for antenatal treatment, optimal antenatal dosing regimens need to be defined and a standardised treatment and follow-up protocol are recommended. Establishment of a national registry with standardised follow-up will allow future families to be better informed of the risks and benefits of both treated and untreated fetal CAH.