Chimeric CYP21A1P/CYP21A2 genes identified in Czech patients with congenital adrenal hyperplasia

Chimeric CYP21A1P/CYP21A2 Genes in 21-Hydroxylase Deficiency Detected by Long-Read Sequencing and Phenotypes Correlation

CONTEXT

21-Hydroxylase deficiency (21-OHD) is caused by pathogenic variants in CYP21A2. High homology between CYP21A2 and its pseudogene CYP21A1P causes mismatches, leading to deletions and CYP21A1P/CYP21A2 chimeras.

OBJECTIVE

To detect chimeric CYP21A1P/CYP21A2 in 21-OHD patients using long-read sequencing (LRS) and analyze genotype-phenotype correlations.

METHODS

From 2015 to 2023, 869 21-OHD patients were enrolled at Peking Union Medical College Hospital, with 113 identified harboring CYP21A2 large deletion. Long-range PCR and LRS were used to identify the types of CYP21A1P/CYP21A2 chimeric. Haplotype analysis explored founder effects, and in vitro assays assessed the functional impact of novel mutations. Clinical data were retrospectively collected and patients were classified into 4 groups based on genotypes and residual enzyme activity to study genotype-phenotype correlations.

RESULTS

Ten types of chimeric CYP21A1P/CYP21A2 genes were identified across 119 alleles, including a novel type, CH-10. The most common, CH-1, accounted for 50.4% of all types. Haplotype analysis of 24 SNPs within CYP21A1P/CYP21A2 CH-1 revealed 25 haplotypes, with haplotype 11 being the most prevalent. Variants p.L100P and p.L301V of CYP21A2 showed enzyme activities of 1.36 ± 0.44% or 1.63 ± 0.19% for 17-hydroxyprogesterone to 11-deoxycortisol, and 1.36 ± 0.58% or 3.99 ± 1.09% for progesterone to 11-deoxycorticosterone, respectively, linked to the simple virilizing type. Genotype-phenotype consistency rates were 78.6% to 84% across the 4 groups.

CONCLUSION

LRS is a comprehensive genetic testing method for 21-OHD patients, effectively detecting both CYP21A2 gene variants and CYP21A1P/CYP21A2 chimeric gene types. This study expands the CYP21A2 variant spectrum by identifying a novel chimera. Haplotype analysis revealed diverse haplotypes for each chimeric gene type, suggesting the absence of a common founder effect. The strong genotype-phenotype correlation aids genetic counseling and supports personalized treatment.

Long-Read Sequencing Identifying the Genetic Complexity of Congenital Adrenal Hyperplasia in the Pedigree

BACKGROUND

High sequence homology between CYP21A2 and CYP21A1P poses challenges to genetic diagnosis of congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency (21-OHD). Traditional genetic testing is unable to provide an accurate diagnosis due to the genetic complexity of CAH.

METHODS

Deletions, duplications, and recombination breakpoints were precisely identified by long-read sequencing (LRS).

RESULTS

This study presented a pregnant woman, a 21-OHD carrier detected by MLPA, and her husband, a normal subject also detected by MLPA. The fetus was suspected of having 21-OHD based on clinical presentations such as enlarged adrenal glands, atypical external genitalia and karyotyping of 46, XX. LRS further identified the fetus as having the most severe salt-wasting (SW) form of 21-OHD with a compound heterozygote genotype. One allele was TNXA/TNXB CH-2, while the other allele was CYP21A1P/CYP21A2 CH-8. LRS precisely determined the genotypes of the fetus's father and grandmother with duplications, which misdiagnosed by MLPA. The multidisciplinary team recommended immediate glucocorticoid and mineralocorticoid treatment for the child after birth to prevent life-threatening adrenal crisis.

CONCLUSIONS

LRS provides precise diagnosis for family members with CYP21A2 deletion or duplication, improving disease management and preventing potential adrenal crises. When used in pre-pregnancy genetic testing, LRS can indicate high genetic risk and guide the appropriate therapy during pregnancy and immediately after birth.

Novel rapid molecular diagnosis methods for comprehensive genetic analysis of 21-hydroxylase deficiency

BACKGROUND

Molecular analysis of the CYP21A2 gene is highly important for understanding the aetiology of 21-hydroxylase deficiency (21-OHD). The aim of this study was to use a novel approach named CNVplex, together with the SNaPshot assay and direct sequencing, to identify CYP21A2 mutations efficiently and comprehensively. Targeted CYP21A2 mutation analysis was performed in 113 patients and 226 parents. Large rearrangements of CYP21A2 were characterized by CNVplex; twenty prevalent mutations, including nine common micro-conversions and eleven high-frequency mutations reported in the literature, were detected by SNaPshot; and rare mutations were investigated by direct sequencing.

RESULTS

Among the 113 21-OHD patients, 95.6% of the affected alleles were detected accurately by SNaPshot and CNVplex. Prevalent mutations were detected in 69.5% of the alleles; 62.4% of alleles contained pseudogene-derived micro-conversions, 1.8% contained nonpseudogene-derived mutations, and 5.3% contained complex variations resulting from multiple recombinations between CYP21A2 and CYP21A1P. Large rearrangements were identified in 27.0% of the alleles, including five types (CH-1, CH-3, CH-4, CH-5 and CH-8) of chimeric CYP21A1P/CYP21A2 genes. Two novel CYP21A2 haplotypes and four de novo CYP21A2 mutations were characterized. A rare haplotype with a c.955 C > T mutation in the duplicated CYP21A2 gene was found in 0.9% of the probands and 33.3% of the parents. In addition, four parents were also diagnosed with 21-OHD.

CONCLUSION

CNVplex and SNaPshot appear to be highly efficient and reliable techniques for use in a molecular diagnosis laboratory, and combined with direct sequencing based on locus-specific PCR, they might constitute a definitive way to detect almost all common and rare 21-OHD-related alleles.

Rare nonclassic type of Congenital adrenal hyperplasia due to 21-hydroxylase deficiency and genotype-phenotypic correlation

Objective

To explore the correlation between different CYP21A2 pathogenic gene mutations and clinical phenotypes in Congenital adrenal hyperplasia (CAH) patients. Moreover, combined with the specific phenotypes of patients in the clinic, diagnosis and treatment suggestions should be made for CAH patients.

Methods

In this study, a genetic status of a Chinese family in three generations of 21-hydroxylase deficiency was comprehensively presented, and the pathogenic genes in the family were found and traced in detail. We measured CYP21A2 gene in this family by Sanger sequencing and MLPA. The trophoblast cells of female proband's embryos were detected by PGT-M which used Copy-Number Variations of a Single Human Cell and high throughput sequencing. The CYP21A2 gene mutation site in each embryo were detected by Sanger sequencing, whole genome sequencing and single nucleotide polymorphism (SNP).

Results

There are many related pathogenic genes of CAH in this family. The female proband showed a compound heterozygous mutation in the CYP21A2 gene, including a CYP21A1P/A2 fusion gene (CH-8) (classical phenotype) and a new mutation c.1034T > C (p. L354S) (unknown clinical significance). In the proband's family, a heterozygous gene mutation of c.1034T > C and a CYP21A1P/A2 fusion gene (CH-8) was carried by her father and mother, respectively. Meanwhile, the husband of the proband also has a genetic family with related disease. Both the husband and his father carried the CYP21A2 gene c.844G > T heterozygous mutation, while his mother had no related mutation in the CYP21A2 gene. Furthermore, PGTM gene detection was carried out on the four blastocysts of the proband's offspring through IVF. The results showed that embryos T1, T2 and T4 all carried CYP21A1P/A2 fusion gene (CH-8), as well as embryo T3 carried c.1034T > C heterozygous mutation of maternal origin.

Conclusion

This case is a family report showing a complete genetic map of the proband and her family, describing the genetic process of different pathogenic genes in detail and clearly corresponding to the patient's different phenotypes. It is speculated that the pathogenesis of CAH is caused by different mutations in the CYP21A2 gene and their interactions, which may affect the different phenotypes of CAH patients.

Molecular Diagnosis of Steroid 21-Hydroxylase Deficiency: A Practical Approach

Adrenal insufficiency in paediatric patients is mostly due to congenital adrenal hyperplasia (CAH), a severe monogenic disease caused by steroid 21-hydroxylase deficiency (21-OHD, encoded by the CYP21A2 gene) in 95% of cases. CYP21A2 genotyping requires careful analyses that guaranty gene-specific PCR, accurate definition of pseudogene-gene chimeras, gene duplications and allele dropout avoidance. A small panel of well-established disease-causing alterations enables a high diagnostic yield in confirming/discarding the disorder not only in symptomatic patients but also in those asymptomatic with borderline/positive results of 17-hydroxyprogesterone. Unfortunately, the complexity of this locus makes it today reluctant to high throughput techniques of massive sequencing. The strong relationship existing between the molecular alterations and the degree of enzymatic deficiency has allowed genetic studies to demonstrate its usefulness in predicting/classifying the clinical form of the disease. Other aspects of interest regarding molecular studies include its independence of physiological variations and analytical interferences, its usefulness in the diagnosis of simple virilizing forms in males and its inherent contribution to the genetic counseling, an aspect of great importance taking into account the high carrier frequency of CAH in the general population. Genetic testing of CYP21A2 constitutes an irreplaceable tool to detect severe alleles not just in family members of classical forms but also in mild late-onset forms of the disease and couples. It is also helpful in areas such as assisted reproduction and preimplantation diagnosis. Molecular diagnosis of 21-OHD under expert knowledge definitely contributes to a better management of the disease in every step of the clinical course.

Copy Number Variations in Genetic Diagnosis of Congenital Adrenal Hyperplasia Children

Background: Congenital adrenal hyperplasia (CAH) is a monogenic disorder caused by genetic diversity in the CYP21A2 gene, with 21-hydroxylase deficiency (21-OHD) as the most common type. Early sex assignment and early diagnosis of different genetic variations with a proper technique are important to reduce mortality and morbidity. Proper early sex identification reduces emotional, social, and psychological stress.

Aim: Detection of a spectrum of aberrations in the CYP21A2 gene, including copy number variations, gene conversion, chimeric genes, and point variations.

Methods: The CYP21A2 gene was screened using MLPA assay in 112 unrelated Egyptian children with 21-OHD CAH (33 males and 79 females).

Results: In the studied group, 79.5% were diagnosed within the first month of life. 46.8% of the genetic females were misdiagnosed as males. Among the copy number variation results, large deletions in 15.4% and three types of chimeric genes in 9% (CH-1, CH-7, and CAH-X CH-1) were detected. Regarding gene dosage, one copy of CYP21A2 was found in 5 cases (4.5%), three copies were detected in 7 cases (6.3%), and one case (0.9%) showed four copies. Eight common genetic variants were identified, I2G, large deletions, large gene conversion (LGC), I172N, F306 + T, -113 SNP, 8bp Del, and exon 6 cluster (V237E and M239K) with an allelic frequency of 32.62%, 15.45%, 7.30%, 3.00%, 2.58%, 2.15%, 0.86%, and 0.86%, respectively.

Conclusion: High prevalence of copy number variations highlights the added value of using MLPA in routine laboratory diagnosis of CAH patients.

PB-Motif-A Method for Identifying Gene/Pseudogene Rearrangements With Long Reads: An Application to CYP21A2 Genotyping

Long read sequencing technologies have the potential to accurately detect and phase variation in genomic regions that are difficult to fully characterize with conventional short read methods. These difficult to sequence regions include several clinically relevant genes with highly homologous pseudogenes, many of which are prone to gene conversions or other types of complex structural rearrangements. We present PB-Motif, a new method for identifying rearrangements between two highly homologous genomic regions using PacBio long reads. PB-Motif leverages clustering and filtering techniques to efficiently report rearrangements in the presence of sequencing errors and other systematic artifacts. Supporting reads for each high-confidence rearrangement can then be used for copy number estimation and phased variant calling. First, we demonstrate PB-Motif's accuracy with simulated sequence rearrangements of PMS2 and its pseudogene PMS2CL using simulated reads sweeping over a range of sequencing error rates. We then apply PB-Motif to 26 clinical samples, characterizing CYP21A2 and its pseudogene CYP21A1P as part of a diagnostic assay for congenital adrenal hyperplasia. We successfully identify damaging variation and patient carrier status concordant with clinical diagnosis obtained from multiplex ligation-dependent amplification (MLPA) and Sanger sequencing. The source code is available at: github.com/zstephens/pb-motif.

Genes and Pseudogenes: Complexity of the RCCX Locus and Disease

Copy Number Variations (CNVs) account for a large proportion of human genome and are a primary contributor to human phenotypic variation, in addition to being the molecular basis of a wide spectrum of disease. Multiallelic CNVs represent a considerable fraction of large CNVs and are strictly related to segmental duplications according to their prevalent duplicate alleles. RCCX CNV is a complex, multiallelic and tandem CNV located in the major histocompatibility complex (MHC) class III region. RCCX structure is typically defined by the copy number of a DNA segment containing a series of genes - the serine/threonine kinase 19 (STK19), the complement 4 (C4), the steroid 21-hydroxylase (CYP21), and the tenascin-X (TNX) - lie close to each other. In the Caucasian population, the most common RCCX haplotype (69%) consists of two segments containing the genes STK19-C4A-CYP21A1P-TNXA-STK19B-C4B-CYP21A2-TNXB, with a telomere-to-centromere orientation. Nonallelic homologous recombination (NAHR) plays a key role into the RCCX genetic diversity: unequal crossover facilitates large structural rearrangements and copy number changes, whereas gene conversion mediates relatively short sequence transfers. The results of these events increased the RCCX genetic diversity and are responsible of specific human diseases. This review provides an overview on RCCX complexity pointing out the molecular bases of Congenital Adrenal Hyperplasia (CAH) due to CYP21A2 deficiency, CAH-X Syndrome and disorders related to CNV of complement component C4.

Detection of a novel severe mutation affecting the CYP21A2 gene in a Chilean male with salt wasting congenital adrenal hyperplasia

PURPOSE

21-hydroxylase deficiency (21-OHD) is a congenital adrenal disease with more than 200 mutations published to date. The aim of this report is to describe a severe novel mutation of the CYP21A2 gene.

METHOD

We describe a case of a 39-year-old male diagnosed with a salt wasting congenital adrenal hyperplasia (SWCAH) due to 21-OHD. The genetic testing was done using a combination of three methods (PCR XL, SALSA-MLPA, and bidirectional sequencing) and finally an in silico analysis.

RESULTS

The genetic testing demonstrated three severe mutations of the CYP21A2 gene (p.Gln318*; c.290-13C>G; and p.Trp86*), being the last one a novel mutation not previously reported. The in silico modeling of the p.Trp86* (c.258G>A) showed a truncated CYP21A2 protein that loses all the main structural features required for activity, such as the HEM binding domain and the hormone binding site.

CONCLUSION

We present an adult man with an SWCAH due to 21-OHD who carried three severe mutations of the CYP21A2 gene, one of them, p.Trp86* (c.258G>A) has not been previously described.

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.

Revisiting the association of HLA alleles and haplotypes with CYP21A2 mutations in a large cohort of patients with congenital adrenal hyperplasia

The CYP21A2 gene encoding 21‑hydroxylase is on chromosome 6p21.3 within the human leukocyte antigen (HLA) class III major histocompatibility complex and an association between congenital adrenal hyperplasia (CAH) due to 21‑hydroxylase deficiency and HLA class I and II alleles has been shown in genetically isolated populations. One-third of CAH causing alleles are 30-kb deletions due to homologous recombination events between active and pseudogenes resulting in chimeric genes. The aim of this study was to re-visit the association between the CYP21A2 variants and HLA polymorphisms in a large ethnically diverse cohort of patients with CAH who underwent comprehensive CYP21A2 genotyping, including specification of chimeric gene subtypes (CAH CH-1 through CH-9 of CYP21A1P/CYP21A2 chimeras; CAH-X CH-1 through CH-3 of TNXA/TNXB chimeras) in alleles with 30-kb deletions. The study population included 201 patients (86 males, 115 females, age 3-75 years) with CAH due to 21‑hydroxylase deficiency (159 classic, 42 nonclassic) and 194 parents. Based on the availability of parental genotype, we determined the haplotypes of CYP21A2 mutations and HLA types in 95 probands (190 alleles). Five prevalent haplotype associations were found: p.V281L and B*14-C*08 (P < 0.0001); p.I172N and DQB1*03 (P = 0.035); and of the chimeric genes caused by 30-kb deletions: CH-1 and A*03 (P = 0.033); CH-5 and C*06-DRB1*07 (P < 0.0001); and CAH-X CH-1 and DQB1*03 (P = 0.004). Our findings show that a number of associations between HLA alleles and haplotypes and CYP21A2 mutations, including large 30-kb deletions, exist commonly across ethnicities. These HLA associations may have clinical implications for patients with CAH and may provide insight into the genetics of this highly complex region of the human genome.

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.

An overview of inborn errors of metabolism manifesting with primary adrenal insufficiency

Primary adrenal insufficiency (PAI) results from an inability to produce adequate amounts of steroid hormones from the adrenal cortex. The most common causes of PAI are autoimmune adrenalitis (Addison's disease), infectious diseases, adrenalectomy, neoplasia, medications, and various rare genetic syndromes and inborn errors of metabolism that typically present in childhood although late-onset presentations are becoming increasingly recognized. The prevalence of PAI in Western countries is approximately 140 cases per million, with an incidence of 4 per 1,000,000 per year. Several pitfalls in the genetic diagnosis of patients with PAI exist. In this review, we provide an in-depth discussion and overview on the inborn errors of metabolism manifesting with PAI, including genetic diagnosis, genotype-phenotype relationships and counseling of patients and their families with a focus on various enzymatic deficiencies of steroidogenesis.

Tenascin-X, Congenital Adrenal Hyperplasia, and the CAH-X Syndrome

Mutations of the CYP21A2 gene encoding adrenal 21-hydroxylase cause congenital adrenal hyperplasia (CAH). The CYP21A2 gene is partially overlapped by the TNXB gene, which encodes an extracellular matrix protein called Tenascin-X (TNX). Mutations affecting both alleles of TNXB cause a severe, autosomal recessive form of Ehlers-Danlos syndrome (EDS). Rarely, patients with severe, salt-wasting CAH have deletions of CYP21A2 that extend into TNXB, resulting in a "contiguous gene syndrome" consisting of CAH and EDS. Heterozygosity for TNXB mutations causing haploinsufficiency of TNX may be associated with the mild "hypermobility form" of EDS, which principally affects small and large joints. Studies of patients with salt-wasting CAH found that up to 10% had clinical features of EDS, associated joint hypermobility, haploinsufficiency of TNX and heterozygosity for TNXB mutations, now called "CAH-X." These patients have joint hypermobility and a spectrum of other comorbidities associated with their connective tissue disorder, including chronic arthralgia, joint subluxations, hernias, and cardiac defects. Other disorders are beginning to be associated with TNX deficiency, including familial vesicoureteral reflux and neurologic disorders. Further work is needed to delineate the full spectrum of TNX-deficient disorders, with and without associated CAH.

Genetics of Congenital Adrenal Hyperplasia

Congenital adrenal hyperplasia (CAH) refers to a group of autosomal recessive disorders due to single-gene defects in the various enzymes required for cortisol biosynthesis. CAH represents a continuous phenotypic spectrum with more than 95% of all cases caused by 21-hydroxylase deficiency. Genotyping is an important tool in confirming the diagnosis or carrier state, provides prognostic information on disease severity, and is essential for genetic counseling. In this article, the authors provide an in-depth discussion on the genetics of CAH, including genetic diagnosis, molecular analysis, genotype-phenotype relationships, and counseling of patients and their families.

Molecular genetic analysis in 93 patients and 193 family members with classical congenital adrenal hyperplasia due to 21-hydroxylase deficiency in Croatia

Congenital adrenal hyperplasia owing to 21-hydroxylase deficiency is caused by mutation in the CYP21A2 gene. The frequency and spectrum of CYP21A2 mutations and genotype-phenotype correlations among different populations are variable. Aim of this study was to define mutation frequency and spectrum of CYP21A2 gene mutations in patients with classical 21-hydroxylase deficiency (21OHD) and their family members in Croatia and study genotype-phenotype correlation. Clinical features and mutations of CYP21A2 gene in 93 unrelated 21OHD patients and 193 family members were examined. In this cohort, 66 patients were affected with salt wasting (SW) form, and 27 were affected with simple virilizing (SV) form of the disease. Mutations were identified in both alleles (67% compound heterozygous and 33% homozygous) in 91 of 93 patients. Deletions and conversions were found in 18.8% and point mutations in 79.6% alleles. Mutations in 3 alleles (1.6%) remained unidentified (in one patient we found only one, while in other no mutations were found at all). The most common point mutations were Intron 2 splice mutation IVS2-13 A/C>G (35.5%) and p.R357W (16.7%). Genotypes were categorized into Groups 0, A, B and C according to the extent of enzyme impairment. Genotype-phenotype concordance was 100%, 85% and 75% for Groups 0, A and B, respectively. Since only classical 21OHD patients were studied, Group C comprised solely p.P31L mutation and had 73% patients with SV and 27% with SW phenotype. Intrafamilial phenotypic variability was found in two families. CYP21A2 genetic analysis in 193 family members showed that 126 parents were heterozygous carriers, 3 were newly discovered patients, 2 fathers were not biological parents, and mutations were not detected in 3. Among 59 siblings, 32 were heterozygous carriers, 15 carried normal alleles, and 12 were patients (4 newly diagnosed). Genotype-phenotype divergence observed in this study suggests caution in preconceptional counseling and prenatal diagnosis of CAH. High frequency of p.R357W mutation was found in Croatian patients with classical 21-OHD. Genotyping of family members discovered new patients and thus avoided pitfalls in genetic counseling when the parents were found to be affected.

Broadening the Spectrum of Ehlers Danlos Syndrome in Patients With Congenital Adrenal Hyperplasia

CONTEXT

The contiguous gene deletion syndrome (CAH-X) was described in a subset (7%) of congenital adrenal hyperplasia (CAH) patients with a TNXA/TNXB chimera, resulting in deletions of CYP21A2, encoding 21-hydroxylase necessary for cortisol biosynthesis, and TNXB, encoding the extracellular matrix glycoprotein tenascin-X (TNX). This TNXA/TNXB chimera is characterized by a 120-bp deletion in exon 35 and results in TNXB haploinsufficiency, disrupted TGF-β signaling, and an Ehlers Danlos syndrome phenotype.

OBJECTIVE

The objective of the study was to determine the genetic status of TNXB and resulting protein defects in CAH patients with a CAH-X phenotype but not the previously described TNXA/TNXB chimera. Design, Settings, Participants, and Intervention: A total of 246 unrelated CAH patients were screened for TNXB defects. Genetic defects were investigated by Southern blotting, multiplex ligation-dependent probe amplification, Sanger, and next-generation sequencing. Dermal fibroblasts and tissue were used for immunoblotting, immunohistochemical, and coimmunoprecipitation experiments.

MAIN OUTCOME MEASURES

The genetic and protein status of tenascin-X in phenotypic CAH-X patients was measured.

RESULTS

Seven families harbor a novel TNXB missense variant c.12174C>G (p.C4058W) and a clinical phenotype consistent with hypermobility-type Ehlers Danlos syndrome. Fourteen CAH probands carry previously described TNXA/TNXB chimeras, and seven unrelated patients carry the novel TNXB variant, resulting in a CAH-X prevalence of 8.5%. This highly conserved pseudogene-derived variant in the TNX fibrinogen-like domain is predicted to be deleterious and disulfide bonded, results in reduced dermal elastin and fibrillin-1 staining and altered TGF-β1 binding, and represents a novel TNXA/TNXB chimera. Tenascin-X protein expression was normal in dermal fibroblasts, suggesting a dominant-negative effect.

CONCLUSIONS

CAH-X syndrome is commonly found in CAH due to 21-hydroxylase deficiency and may result from various etiological mechanisms.

Molecular analysis of the CYP21A2 gene in Chinese patients with steroid 21-hydroxylase deficiency

OBJECTIVE

21-Hydroxylase deficiency (21-OHD) is the most common cause of congenital adrenal hyperplasia (CAH), a family of autosomal recessive disorders involving impaired cortisol synthesis. This study aimed to design a reliable and rational approach for identifying mutations in the CYP21A2 gene and to characterize the molecular basis of 21-OHD in 30 Chinese patients.

DESIGN AND METHODS

Copy number variations were investigated by multiplex ligation-dependent probe amplification (MLPA). Locus-specific polymerase chain reaction (PCR)/restriction endonuclease analysis was then used to verify CYP21A2 rearrangement products and prevent allele dropout. Direct sequencing of rearrangement products was performed to further refine recombination breakpoint locations. Direct sequencing of the entire CYP21A2 gene was used to detect microconversions.

RESULTS

We successfully characterized 60 CYP21A2 alleles from 30 patients with genetic defects. The most common one was intron 2 splice mutation (38.3%). Eighteen alleles with large gene deletions/conversions were identified, which accounted for nearly one-third (30.0%) of the genetic defects. Among these, three types of CYP21A1P/CYP21A2 chimeric genes (CH-1, CH-2, and CH-4) were characterized. Two novel CYP21A2 rearrangement genes were revealed and further demonstrated to be located downstream of the TNXB gene.

CONCLUSIONS

Our results indicate that the stepwise diagnostic procedure involving MLPA analysis, locus-specific PCR/restriction endonuclease analysis, and direct DNA sequencing can provide detailed genetic information about Chinese 21-OHD patients, which is helpful for characterizing structural rearrangements of CYP21A2.

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.

Steroid 21-hydroxylase gene mutational spectrum in 50 Tunisian patients: characterization of three novel polymorphisms

Congenital adrenal hyperplasia (CAH) is an autosomal recessive disease of steroid biosynthesis in humans. More than 90% of all CAH cases are caused by mutations of the 21-hydroxylase gene (CYP21A2), and approximately 75% of the defective CYP21A2 genes are generated through an intergenic recombination with the neighboring CYP21A1P pseudogene. In this study, the CYP21A2 gene was genotyped in 50 patients in Tunisia with the clinical diagnosis of 21-hydroxylase deficiency. CYP21A2 mutations were identified in 87% of the alleles. The most common point mutation in our population was the pseudogene specific variant p.Q318X (26%). Three novel single nucleotide polymorphism (SNP) loci were identified in the CYP21A2 gene which seems to be specific for the Tunisian population. The overall concordance between genotype and phenotype was 98%. With this study the molecular basis of CAH has been characterized, providing useful results for clinicians in terms of prediction of disease severity, genetic and prenatal counseling.

Lessons learned from 5 years of newborn screening for congenital adrenal hyperplasia in the Czech Republic: 17-hydroxyprogesterone, genotypes, and screening performance

The aims were to summarize the experience and to determine the performance metrics of newborn screening (NBS) for congenital adrenal hyperplasia (CAH) in the Czech Republic. 17-Hydroxyprogesterone (17OHP) was measured in NBS samples prospectively in 545,026 newborns and retrospectively in 31 CAH patients born outside the study period. A total of 2,811 screened newborns had abnormal 17OHP; CAH was confirmed in 46 probands. One patient with a severe-moderate genotype of CAH had 17OHP below the cut-off and was diagnosed clinically. This corresponds to a screening sensitivity of 98% and a false positive rate (FPR) of 0.51%. The median of 17OHP in the most severe genotypes was 484 nmol/L (n = 21); in severe/moderate, 321 nmol/L (n = 30); in moderate, 61 nmol/L (n = 20); and in mild genotypes, 31 nmol/L (n = 7). NBS is efficient to detect severe CAH but may fail to detect milder variants. However, the FPR is too high but could be improved by application of a second tier test.

Genetics of adrenocortical disease: an update

PURPOSE OF REVIEW

Disease states characterized by abnormal cellular function or proliferation frequently reflect aberrant genetic information. By revealing disease-specific DNA mutations, we gain insight into normal physiology, pathophysiology, potential therapeutic targets and are better equipped to evaluate an individual's disease risks. This review examines recent advances in our understanding of the genetic basis of adrenal cortical disease.

RECENT FINDINGS

Important advances made in the past year have included identification of KCNJ5 potassium channel mutations in the pathogenesis of both aldosterone-producing adenomas and familial hyperaldosteronism type III; characterization of phosphodiesterase 11A as a modifier of phenotype in Carney complex caused by protein kinase, cAMP-dependent, regulatory subunit, type-I mutations; the finding of 11β-hydroxysteroid dehydrogenase type I mutations as a novel mechanism for cortisone reductase deficiency; and demonstration of potential mortality benefit in pursuing comprehensive presymptomatic screening for patients with Li-Fraumeni syndrome, including possible reduction in risks associated with adrenocortical carcinoma.

SUMMARY

This research review provides a framework for the endocrinologist to maintain an up-to-date understanding of adrenal cortical disease genetics.

Junction site analysis of chimeric CYP21A1P/CYP21A2 genes in 21-hydroxylase deficiency

BACKGROUND

Chimeric CYP21A1P/CYP21A2 genes, caused by homologous recombination between CYP21A2 (cytochrome P450, family 21, subfamily A, polypeptide 2) and its highly homologous pseudogene CYP21A1P (cytochrome P450, family 21, subfamily A, polypeptide 1 pseudogene), are common in patients with congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency (21-OHD). A comprehensive junction site analysis of chimeric CYP21A1P/CYP21A2 genes is needed for optimizing genetic analysis strategy and determining clinical relevance.

METHODS

We conducted a comprehensive genetic analysis of chimeric CYP21A1P/CYP21A2 genes in a cohort of 202 unrelated 21-OHD patients. Targeted CYP21A2 mutation analysis was performed, and genotyping of chimeric CYP21A1P/CYP21A2 genes was cross-confirmed with Southern blot, RFLP, and multiplex ligation-dependent probe amplification analyses. Junction sites of chimera genes were determined by sequencing the long-PCR products amplified with primers CYP779f and Tena32F. An updated bioinformatics survey of Chi-like sequences was also performed.

RESULTS

Of 100 probands with a chimeric allele, 96 had a chimera associated with the severe classic salt-wasting form of CAH, and the remaining 4 carried an uncommon attenuated chimera with junction sites upstream of In2G (c.293-13A/C>G), which is associated with a milder phenotype. In addition to 6 of 7 reported chimeras, we identified a novel classic chimera (CH-8) and a novel attenuated chimera (CH-9). Attenuated chimeras explained prior genotype-phenotype discrepancies in 3 of the patients. Sequencing the CYP779f/Tena32F amplicons accurately differentiated between classic and attenuated chimeras. The bioinformatics survey revealed enrichment of Chi-like sequences within or in the vicinity of intron 2.

CONCLUSIONS

Junction site analysis can explain some genotype-phenotype discrepancies. Sequencing the well-established CYP779f/Tena32F amplicons is an unequivocal strategy for detecting attenuated chimeric CYP21A1P/CYP21A2 genes, which are clinically relevant.

Genetics of congenital adrenal hyperplasia

Congenital adrenal hyperplasia (CAH) is one of the most common inherited metabolic disorders. It comprises a group of autosomal recessive disorders caused by the deficiency of one of four steroidogenic enzymes involved in cortisol biosynthesis or in the electron donor enzyme P450 oxidoreductase (POR) that serves as electron donor to steroidogenic cytochrome P450 (CYP) type II enzymes. The biochemical and clinical phenotype depends on the specific enzymatic defect and the impairment of specific enzyme activity. Defects of steroid 21-hydroxylase (CYP21A2) and 11beta-hydroxylase (CYP11B1) only affect adrenal steroidogenesis, whereas 17alpha-hydroxylase (CYP17A1) and 3beta-hydroxysteroid dehydrogenase type 2 (HSD3B2) deficiency also impact on gonadal steroid biosynthesis. Inactivating POR gene mutations are the cause of CAH manifesting with apparent combined CYP17A1-CYP21A2 deficiency. P450 oxidoreductase deficiency (ORD) has a complex phenotype including two unique features not observed in any other CAH variant: skeletal malformations and severe genital ambiguity in both sexes.