CYP21 mutations and congenital adrenal hyperplasia

Decoding the Role of CYP450 Enzymes in Metabolism and Disease: A Comprehensive Review

Cytochrome P450 (CYP450) is a group of enzymes that play an essential role in Phase I metabolism, with 57 functional genes classified into 18 families in the human genome, of which the CYP1, CYP2, and CYP3 families are prominent. Beyond drug metabolism, CYP enzymes metabolize endogenous compounds such as lipids, proteins, and hormones to maintain physiological homeostasis. Thus, dysregulation of CYP450 enzymes can lead to different endocrine disorders. Moreover, CYP450 enzymes significantly contribute to fatty acid metabolism, cholesterol synthesis, and bile acid biosynthesis, impacting cellular physiology and disease pathogenesis. Their diverse functions emphasize their therapeutic potential in managing hypercholesterolemia and neurodegenerative diseases. Additionally, CYP450 enzymes are implicated in the onset and development of illnesses such as cancer, influencing chemotherapy outcomes. Assessment of CYP450 enzyme expression and activity aids in evaluating liver health state and differentiating between liver diseases, guiding therapeutic decisions, and optimizing drug efficacy. Understanding the roles of CYP450 enzymes and the clinical effect of their genetic polymorphisms is crucial for developing personalized therapeutic strategies and enhancing drug responses in diverse patient populations.

Monozygotic twins with identical premature timing of acne onset: A Case report

Acne vulgaris, a common dermatological condition that affects most adolescents and young adults, can indicate an underlying pathology if present prematurely in mid-childhood. Premature acne can be caused by premature adrenarche secondary to non-classical congenital adrenal hyperplasia (NC-CAH), a condition arising from 21-hydroxylase deficiency. This report describes a pair of monozygotic twin brothers with identical premature onset of acne, who were found to have an identical homozygous mutation in the promoter region of the CYP21A2 gene. While it is widely known that NCCAH is associated with genetic changes, the drive behind onset of adrenarche are widely unknown. As such, this report provokes thoughts on whether adrenarche could be influenced by adrenal genetic polymorphisms.

Non-Classical 21-Hydroxylase Deficiency: Analysis of a Mutant Gene in a Uyghur Family and Literature Review

OBJECTIVE

The gene mutation and clinical characteristics of a patient with non-classical 21-hydroxylase deficiency and his family were analyzed.

METHODS

A patient was diagnosed with non-classical 21-hydroxylase deficiency in the Department of Endocrinology of People's Hospital of Xinjiang Uygur Autonomous Region in December 2016. The clinical data and related gene-sequencing results were analyzed. The detected mutations were verified in nine members of the family.

RESULTS

Gene-sequencing results revealed that the proband and the other three members of the family (proband, proband's mother's younger brother and the proband's mother's younger brother's younger daughter, and proband's second elder sister) shared the following mutations: Ile173Asn, Ile237Asn, Val238Glu, Met240Lys, Val282Leu, Leu308Phefs*6, Gln319Ter, Arg357Trp, and Arg484Profs. The Val282Leu mutation was heterozygous in the proband's mother's younger brother's younger daughter, but homozygous in the other three individuals. The father of the proband, the elder brother of the father of the proband, the third younger brother of the father of the proband, and the elder sister of the proband all carried only the Val282Leu mutation.

CONCLUSION

Val282Leu is the gene responsible for non-classical 21-hydroxylase deficiency. Screening for this gene in the offspring of patients with non-classical 21-hydroxylase deficiency may help to identify cases early.

A Case of Salt-Wasting Congenital Adrenal Hyperplasia with Triple Homozygous Mutation: Review of Literature

Congenital adrenal hyperplasia (CAH) due to steroid 21-hydroxylase deficiency represents a group of autosomal recessive disorders characterized by impaired cortisol production due to altered upstream steroid conversions, subclassified as classic and nonclassic forms. The genotype-phenotype correlation is possible in the most frequent case but not in all. Despite in literature many mutations are known, there is the possibility of finding a new genetic pattern in patients with CAH.

Analysis of phenotypes and genotypes in 84 patients with 21-Hydroxylase deficiency in southern China

OBJECTIVE

21-hydroxylase deficiency (21-OHD) caused by mutation in CYP21A2 gene is the most common form of Congenital adrenal hyperplasia (CAH). This study aimed to analyze the gene mutation frequency and the phenotype-genotype correlation of 21-OHD patients from southern China.

METHOD

The clinical features, laboratory tests and gene mutational analysis of 84 patients with 21-OHD were retrospectively investigated. Subsequently, the correlation between phenotypes and genotypes of these patients was analyzed.

RESULTS

59 of 84 cases of 21-OHD (70.2%) were classified as salt-wasting (SW) forms presenting adrenal crisis or other signs of salt loss at the age between neonatal period and 2 months, and other 25 cases were classified as simple virilizing (SV) forms. Mutations of CYP21A2 gene on both alleles were found in all 84 patients (168 alleles). The most common types of mutations included micro-conversions (129/168, 76.8%), large gene conversions and deletions (23/168, 13.7%), and bona fide point mutations (16/168, 9.5%). In increasing order of frequency, the most common micro-conversions were I2G (41.1%), p.I172N (13.1%), p.R356W (7.7%), p.Q318* (7.7%) and E6 Cluster (3.0%). Genotypes and phenotypes correlated in 86.1% of the patients analyzed.

CONCLUSION

Micro-conversions were the most common types of CYP21A2 gene mutations in our study, and the frequency of the identified mutations was not significantly different compared with most other Chinese areas and different ethnic regions. However, fewer large gene conversions and deletions were found compared to studies in other ethnic populations. Genotype-phenotype correlation was found in patients with the SW and SV forms of 21-OHD. This study expanded the number of mutations affecting CYP21A2 gene in Chinese patients with 21-OHD, providing additional information for a precise clinical diagnosis and genetic counseling.

Clinical presentation and mutational spectrum in a series of 166 patients with classical 21-hydroxylase deficiency from South China

Classical 21-hydroxylase deficiency (21-OHD) due to mutations in the cytochrome P450 family 21 subfamily A member 2 (CYP21A2) gene is the most common type of congenital adrenal hyperplasia (CAH). In this study, we analyzed clinical and molecular data of 166 patients with classical CAH in South China. Sanger sequencing and multiplex ligation-dependent probe amplification (MLPA) method were used to detect mutations in these 99 salt wasting (SW) patients and 67 simple virilizing (SV) patients. Micro-conversion mutation IVS2-13A/C > G (I2G) was the most frequent mutation in both SW form (42.9%) and SV form (41.8%) in our large cohort, and large gene deletion or large gene conversion also commonly resulted in classical CAH. Rare mutations only account for 8.4% of all alleles, among them four novel variants p.S126X, p.C429X, c.1209_1210insT and c.840delG were responsible for the clinical presentations. CYP21A2 gene duplications linked to the mutation Q319X were found in our cohort, though these cases were rather rare. In this study, we provided detailed clinical data and mutation spectrum to confirm the common mutations in Chinese populations, especially in South China,which will contribute to further genetic consultation and prenatal diagnosis. Sanger sequencing combined with MLPA method could detect most mutation types in the CYP21A2 gene effectively.

CYP21A2 intronic variants causing 21-hydroxylase deficiency

Congenital adrenal hyperplasia (CAH) is an autosomal recessive disorder mainly caused by defects in the steroid 21-hydroxylase gene (CYP21A2). Most of CYP21A2 mutations result from intergenic recombinations between CYP21A2 and closely linked CYP21A1P pseudogene. Rare mutations not generated by gene conversion account for 5-10% of 21-hydroxylase deficiency alleles. Intronic variants represent only a little part of these but their effect on the protein is generally deleterious. The aim of this paper is to provide a comprehensive literary review regarding all intronic CYP21A2 pathological variants reported to date. In addition, we describe three novel causing disease variants in our patients affected by the classic form of CAH: IVS4-1G>A, IVS5-8T>A, IVS8-2A>G. In silico analysis revealed that all these substitutions affect the splicing process leading to a non-functional protein. Based on these results, we are able to classify them as pathological variants according to the patient's phenotype.

Gestational Hyperandrogenism in Developmental Programming

Androgen excess (hyperandrogenism) is a common endocrine disorder affecting women of reproductive age. The potential causes of androgen excess in women include polycystic ovary syndrome, congenital adrenal hyperplasia (CAH), adrenal tumors, and racial disparity among many others. During pregnancy, luteoma, placental aromatase deficiency, and fetal CAH are additional causes of gestational hyperandrogenism. The present report reviews the various phenotypes of hyperandrogenism during pregnancy and its origin, pathophysiology, and the effect of hyperandrogenism on the fetal developmental trajectory and offspring consequences.

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.

Genotype-phenotype correlation in 27 pediatric patients in congenital adrenal hyperplasia due to 21-hydroxylase deficiency in a single center

PURPOSE

The purpose of the study was to evaluate endocrine patterns of patients with congenital adrenal hyperplasia and each gene mutation and to analyze the correlation between each phenotype and genotype.

METHODS

This was a retrospective study of the patients with congenital adrenal hyperplasia in the pediatric outpatient clinic at the Samsung Medical Center from November 1994 to December 2012. We analyzed the medical records of 27 patients (male, 19; female, 8) with congenital adrenal hyperplasia who had been diagnosed by genetic testing to have 21-hydroxylase deficiency.

RESULTS

In genetic analysis of 54 alleles from 27 patients, 13 types of mutations were identified. The distribution of 21-hydroxylase deficiency gene mutations revealed that intron 2 splice site (c.293-13A/C>G) mutations and large deletions were the most common, at 31.5% and 22.2% respectively, followed by p.I173N, p.R356W, and p.I172N mutations at 11.1%, 9.3%, and 9.3%, respectively. Other mutations were observed at 1.9-3.7%. No novel mutations were detected.

CONCLUSION

The analysis of 54 alleles revealed 13 types of mutation. The salt wasting form showed a good correlation between genotype and phenotype, but the simple virilizing and nonclassic forms showed inconsistencies between genotype and phenotype. The distribution of CYP21A2 mutations was evaluated for 21-hydroxylase deficiency patients from a single center. This study provides limited data on mutation spectrum and genotype-phenotype correlation of 21-hydroxylase deficiency in Korea.

Glucocorticoid-induced osteoporosis in children with 21-hydroxylase deficiency

21-Hydroxylase deficiency (21-OHD) is the most common cause of congenital adrenal hyperplasia (CAH), resulting from deletions or mutations of the P450 21-hydroxylase gene (CYP21A2). Children with 21-OHD need chronic glucocorticoid (cGC) therapy, both to replace congenital deficit in cortisol synthesis and to reduce androgen secretion by adrenal cortex. GC-induced osteoporosis (GIO) is the most common form of secondary osteoporosis that results in an early, transient increase in bone resorption accompanied by a decrease in bone formation, maintained for the duration of GC therapy. Despite the conflicting results in the literature about the bone status on GC-treated patients with 21-OHD, many reports consider these subjects to be at risk for osteoporosis and fractures. In bone cells, at the molecular level, GCs regulate various functions including osteoblastogenesis, osteoclastogenesis, and the apoptosis of osteoblasts and osteocytes. In this paper, we focus on the physiology and biosynthesis of endogenous steroid hormones as well as on the effects of GCs on bone cells, highlighting the pathogenetic mechanism of GIO in children with 21-OHD.

A sequence variation in 3'UTR of CYP21A2 gene correlates with a mild form of congenital adrenal hyperplasia

BACKGROUND

Congenital adrenal hyperplasia (CAH) is mainly caused by the deficiency of the 21-hydroxylase enzyme coded by the CYP21A2 gene. However, some alleles in the non-classical form (NC-CAH) remain without identified mutations, suggesting the involvement of regulatory regions.

AIM

Our objective was to study an allele carrying the variant *13 G>A in the 3'UTR of the CYP21A2 gene identified in some patients with a mild form of NC-CAH in order to verify the possible implication of this variation with the phenotype observed.

SUBJECTS AND METHODS

Among all the subjects in whom the CYP21A2 gene was analyzed, 14 patients and 7 relatives heterozygous or homozygous for the *13 G>A substitution in 3'UTR were selected. Sequencing of DNA, genotyping, multiplex ligation-dependent probe amplification (MLPA), in vitro studies and bioinformatic analysis were performed.

RESULTS

The haplotype of the *13 G>A allele was identical in all the subjects with a monomodular structure composed by one C4A gene and one CYP21A2 gene without a second module with the CYP21A1P pseudogene. No other concomitant mutations were found in the region extending from 3 kb in the promoter and encompassing the polyadenylation signal. Both bioinformatic analysis and in vitro studies predicted an alteration of the RNA folding and expression, but no miRNA target sequences were found in this region.

CONCLUSIONS

The identification of a substitution in the 3'UTR of the gene associated with a mild form of NC-CAH suggests the importance of analyzing the CYP21A2 untranslated regions to better characterize and treat this subgroup of patients.

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.

Comparing the Southern blot method and polymerase chain reaction product analysis for chimeric RCCX detection in CYP21A2 deficiency

The 3.2-kb TaqI-produced fragment of the CYP21A1P pseudogene and the 3.7-kb TaqI-produced fragment of the functional CYP21A2 gene exist on chromosome 6p21.3. We used the polymerase chain reaction (PCR) product and Southern blot method with TaqI endonuclease digestion to identify a chimeric RCCX module in two unrelated patients with congenital adrenal hyperplasia (CAH). After TaqI cleavage, the PCR product analysis revealed that patient 1 with the chimeric CYP21A1P/CYP21A2 gene in one allele and IVS2-12A/C>G in combination with the 707-714del mutation in the other allele produced a configuration of 3.2- and 2.4-kb fragments. Patient 2, who carried IVS2-12A/C>G in combination with the 707-714del mutation in one allele and the chimeric TNXA/TNXB gene in the other allele, presented with 3.2- and 2.3-kb fragments. However, Southern blot analysis showed that patients 1 and 2 produced 3.2-, 2.4-, and 2.5-kb fragments. We conclude that the chimeric CYP21A1P/CYP21A2 gene, IVS2-12A/C>G in combination with the 707-714del mutation, and the chimeric TNXA/TNXB gene cannot be distinguished by the Southern blot method. Conversely, the chimeric TNXA/TNXB gene was identified in the PCR product analysis due to the appearance of the 2.37-kb fragment, which indicates the occurrence of the chimeric TNXA/TNXB formation extending to the boundary of TNXA in the RCCX region.

Functional analysis of two rare CYP21A2 mutations detected in Italian patients with a mildest form of congenital adrenal hyperplasia

BACKGROUND

More than 90% of all cases of congenital adrenal hyperplasia (CAH) result from steroid 21-hydroxylase gene (CYP21A2) mutations. Most of these mutations result from intergenic recombinations between CYP21A2 and closely linked CYP21A1P pseudogene. Rare mutations not generated by gene conversion account for 5-10% of 21-hydroxylase deficiency alleles.

OBJECTIVE

Functional analysis of two novel CYP21A2 missense mutations (p.R224W and p.D407N) was performed.

DESIGN

Our study was composed of two Italian patients suffering from a very mild form of nonclassic CAH (NC-CAH). To assay the enzymatic activity of mutants, the in vitro analysis was performed in transiently transfected COS-1 cells.

RESULTS

The residual activities obtained for p.R224W and p.D407N mutants allow their classification as NC-CAH mutations. These results correlate with the rate of severity of the patients' disease.

CONCLUSIONS

In this paper, we report two novel CYP21A2 mutations in two Italian individuals affected by 21-hydroxylase deficiency. Based on the functional in vitro analysis we can classify these mutations as NC-CAH variants.

A new CYP21A1P/CYP21A2 chimeric gene identified in an Italian woman suffering from classical congenital adrenal hyperplasia form

Background

More than 90% of Congenital Adrenal Hyperplasia (CAH) cases are associated with mutations in the 21-hydroxylase gene (CYP21A2) in the HLA class III area on the short arm of chromosome 6p21.3. In this region, a 30 kb deletion produces a non functional chimeric gene with its 5' and 3' ends corresponding to CYP21A1P pseudogene and CYP21A2, respectively. To date, five different CYP21A1P/CYP21A2 chimeric genes have been found and characterized in recent studies. In this paper, we describe a new CYP21A1P/CYP21A2 chimera (CH-6) found in an Italian CAH patient.

Methods

Southern blot analysis and CYP21A2 sequencing were performed on the patient. In addition, in order to isolate the new CH-6 chimeric gene, two different strategies were used.

Results

The CYP21A2 sequencing analysis showed that the patient was homozygote for the g.655C/A>G mutation and heterozygote for the p.P30L missense mutation. In addition, the promoter sequence revealed the presence, in heterozygosis, of 13 SNPs generally produced by microconversion events between gene and pseudogene. Southern blot analysis showed that the woman was heterozygote for the classic 30-kb deletion producing a new CYP21A1P/CYP21A2 chimeric gene (CH-6). The hybrid junction site was located between the end of intron 2 pseudogene, after the g.656C/A>G mutation, and the beginning of exon 3, before the 8 bp deletion. Consequently, CH-6 carries three mutations: the weak pseudogene promoter region, the p.P30L and the g.655C/A>G splice mutation.

Conclusion

We describe a new CYP21A1P/CYP21A2 chimera (CH-6), associated with the HLA-B15, DR13 haplotype, in a young Italian CAH patient.

Linkage analysis of the C4A/C4B copy number variation and polymorphisms of the adjacent steroid 21-hydroxylase gene in a healthy population

Genes encoding the steroid 21-hydroxylase (CYP21A2) and the complement component C4 proteins (C4A and C4B) are located in the MHC region in a strongly linked structure named RCCX module. Previous studies found that carriers of C4B gene deficiency (C4B*Q0) have higher risk for cardiovascular diseases. A potential explanation is that lacking the C4B gene may result in altered function of the neighboring CYP21A2 gene. Therefore we sequenced the CYP21A2 gene in 96 healthy individuals to identify polymorphisms and to characterize their linkage pattern. Fifty-three variations were detected including a new one which alters the TATA-box of the gene. Only three known mutations (V281L, Q318X and R479L) associated with congenital adrenal hyperplasia, were found in 7, 2 and 1 subjects, respectively. Linkage analysis revealed that some variations exhibit strong correlation with the C4 copy number polymorphism and constituents of the MHC III region. Rare alleles of three polymorphisms were identified as components of the 8.1 ancestral haplotype. Haplotyping and family study confirmed that the variant alleles of two intronic SNPs were constituents of haplotype blocks lacking the C4B gene. These results suggest that variations of CYP21A2 gene can be involved in disease associations of the 8.1 haplotype and the C4B*Q0 genotype.

Multiplex ligation-dependent probe amplification (MLPA) assay for the detection of CYP21A2 gene deletions/duplications in congenital adrenal hyperplasia: first technical report

BACKGROUND

More than 90% of the cases of Congenital Adrenal Hyperplasia (CAH) are associated with mutations in 21-hydroxylase gene (CYP21A2). Up to now, large CYP21A2 rearrangements have been mainly detected by Southern blot analysis, although more rapid methods have been alternatively proposed. In this paper, we report the use of a multiplex ligation-dependent probe amplification (MLPA) method for easy and rapid detection of deletions/duplications in the CYP21A2 gene.

METHODS

We collected 18 CAH Italian patients previously analyzed by gene sequencing and Southern blot technique. In addition, a prenatal diagnosis study was performed.

RESULTS

Of the 7 known subjects with CYP21A2 deletions and 2 with gene duplications previously characterized in our laboratory, all were successfully identified by the MLPA analysis. In the prenatal diagnosis study, the MLPA assay was able to identify the presence of a CYP21A2 gene duplication in the fetus, as well in other two family members.

CONCLUSION

MLPA analysis represents a simple, rapid and sensitive tool for the detection of CYP21A2/CYP21A1P deletions/duplications in CAH molecular diagnosis. Compared to Southern blot, MLPA may be considered a high throughput analysis, allowing the simultaneous study of several samples in the same experiment and the investigation of both gene (CYP21A2) and pseudogene (CYP21A1P) in each patient.

Diversity of the CYP21A2 gene: a 6.2-kb TaqI fragment and a 3.2-kb TaqI fragment mistaken as CYP21A1P

The 3.7- and 3.2-kb fragments produced by TaqI digestion are respective crucial markers of the CYP21A2 and CYP21A1P genes for the analysis of the RCCX module in chromosome 6p21.3. Herein, we report two distinct CYP21A2 haplotypes. One occurred in a CAH patient with a 6.2-kb TaqI fragment caused by a mutation at the TaqI site (TCGA) located downstream of the CYP21A2 gene, and the other was a parent in a suspected CAH family with a 3.2-kb TaqI fragment resulting from a 156-bp fragment conversion of the CYP21P promoter sequence which led to the production of a TaqI site at nt -209 and two additional CYP21A1P nucleotides at nt -198 (C>T) and -188/-189 (T insertion). From further sequencing analysis, the promoter region of the 3.2-kb allele showed four normal transcriptional sequences positioned at nt -126C, -113G, -110T, and -103A. However, other nucleotides such as at nt -294T, -293A, and -282A were unchanged. We concluded that the 6.2-kb TaqI fragments of the CYP21A2 haplotype may lead to an incorrect result in the analysis between CYP21A2 and CYP21A1P. The formation of the 3.2-kb TaqI fragment allele which can be mistaken for the CYP21A1P gene may be caused by small-scale conversions of the CYP21A1P gene located between nt -126C and -282A. Therefore, the CYP21A2 haplotype not only presents a 3.7-kb TaqI fragment but also may possibly exist in multiple forms including both 6.2- and 3.2-kb fragments.

CYP21A2 mutations in Portuguese patients with congenital adrenal hyperplasia: identification of two novel mutations and characterization of four different partial gene conversions

More than 90% of congenital adrenal hyperplasia (CAH) cases are caused by 21-hydroxylase deficiency. In this study, the CYP21 gene was genotyped in 56 Portuguese unrelated patients with clinical symptoms of 21-hydroxylase deficiency, in a total of 112 independent alleles. CYP21A2 mutations were identified in 99.1% of the alleles. The most common point mutation was 1688G>T (25.9%). A previously unreported partial gene conversion, extending from exon 1 to 7, was found in 16.1% of the alleles, in most cases associated to the mutation 1688G>T in the other chromosome, and in patients with nonclassical CAH. Other three distinct partial gene conversions were also identified, with lower frequencies: one extends from exon 1 to 3 and the others from exons 3 to 7 and 3 to 8. Two novel mutations were identified in two salt-wasting patients: a putative splicing mutation, IVS2+5G>A, and the transition 2557C>T, that gives rise to the nonsense mutation R445X. Seven point mutations and a partial gene conversion were responsible for 88 of the studied disease causing alleles, and the overall concordance between genotype and phenotype was 92.9%. With this study the molecular basis of CAH was characterized, for the first time, in Portuguese patients, providing useful results for clinicians in terms of prediction of disease severity, genetic and prenatal counseling.

Diversity of theCYP21P-Like Gene inCYP21Deficiency

More than 90% of cases of congenital adrenal hyperplasia (CAH) are caused by mutations of the CYP21 gene. The occurrence of defective CYP21 genes, including 15 mutations, has been attributed to intergenic recombination of DNA sequences from CYP21P, and shows no influence on the RP1-C4A-CYP21P-XA-RP2-C4BCYP21- TNXB gene locus on chromosome 6p21.3. However, multiple gene deletions in this region produce at least three categories of gene arrangements: (a) C4A-CYP21P/CYP21-TNXB, in which there is a CYP21P/CYP21 fusion gene; (b) C4A-XCYP21-TNXB, where XCYP21 indicates that the CYP21 gene contains mutations of IVS2 (-12A/C>G and 707-714delGAGACTAC); and (c) C4A-CYP21P-TNXA/TNXB, in which the TNX A and B genes are fused. Among them, seven different structures of the CYP21 haplotype were found at these three loci. Formation of the C4A-CYP21P/CYP21-TNXB locus produced four distinct CYP21P/CYP21 chimeras. The C4A-XCYP21-TNXB locus contained the IVS2 mutation -12A/C>G and 707-714delGAGACTAC from the XCYP21 gene; and two kinds of TNXA/TNXB hybrids were found in the C4A-CYP21P-TNXA/TNXB locus. The seven different CYP21 alleles produced 3.2 kb Taq I fragments caused by deletion of the RP2-XA-C4B locus. Therefore, production of a 3.2-kb CYP21 allele shows diversity, but is not a unique feature of the CYP21P gene. Most of these gene arrangements probably exist in the C4A-XCYP21-TNXB and C4A-CYP21P/CYP21-TNXB gene loci. The existence of the C4A-CYP21P-TNXA/TNXB locus might not be common in CAH patients with 21-hydroxylase deficiency.

Estudo multicêntrico de pacientes brasileiros com deficiência da 21-hidroxilase: correlação do genótipo com o fenótipo

Analisamos as características clínicas e moleculares de 205 pacientes portadores das diferentes formas clínicas da deficiência da 21-hidroxilase, com diagnóstico hormonal e molecular definidos. As mutações mais freqüentes foram a I2 splice na forma perdedora de sal, a I172N na forma virilizante simples e a V281L na forma não clássica, com freqüências semelhantes às de outros estudos. Obtivemos baixa freqüência de deleção do gene da 21-hidroxilase, de forma semelhante ao identificado nas populações argentina e mexicana. Cinco mutações novas foram descritas em nossa população: G424S, H28+C, Ins 1003^1004 A, R408C e IVS2-2A>G. A severidade do genótipo também se correlacionou diretamente com níveis mais elevados de 17OH-progesterona e de testosterona. As mutações foram classificadas em três grupos, de acordo com o comprometimento da atividade enzimática observado in vitro: Grupo A: atividade de 0-2%; Grupo B: atividade de 3-7% e Grupo C: atividade >20%. Houve forte correlação do grupo A com a forma perdedora de sal, do grupo B com a forma virilizante simples e do grupo C com a forma não clássica. A mutação I2 splice (Grupo A) em homo ou hemizigose conferiu o fenótipo de forma clássica, embora tanto a forma perdedora de sal quanto a forma virilizante simples tenham sido identificadas. A boa correlação do genótipo com o fenótipo na HAC-21OH permite sua aplicação na prática clínica, para o aconselhamento genético, diagnóstico e tratamento pré-natal das gestações de risco para a forma clássica da HAC-21OH e para confirmação diagnóstica após screening neonatal da HAC-21OH, exceto na presença da mutação I2splice.

The chimeric CYP21P/CYP21 gene and 21-hydroxylase deficiency

The chimeric CYP21P/CYP21 gene is a consequence of a 26- or 32-kb deletion in the C4-CYP21 repeat module of CYP21P, tenascin A ( XA), serine/threonine nuclear protein kinase ( RP2), and the C4B and CYP21 genes in congenital adrenal hyperplasia (CAH) with steroid 21-hydroxylase deficiency. To date, there have been three distinct chimeras found in CAH patients in ethnic Chinese. Initiation for production of these molecules is proposed to be chi-like sequences and a minisatellite consensus existing in several noncoding regions in CYP21 genes. These molecules have the 5' end of the CYP21P-specific sequence in common but differ in the 3' end of CYP21-specific genes. In addition, there appears to be a 3.2-kb fragment generated by Taq I digestion, which leads to allele dropout in PCR amplification for detecting the aberrant splicing site of the IVS2 -12A/C>G mutation at nucleotide (nt) 655 in the CYP21 gene. Therefore, the chimeric CYP21P/CYP21 cannot be detected by conventional methods. It has been demonstrated that a PCR product amplified with allele-specific primers covering tenascin B ( TNXB) to the 5' end of the CYP21 gene combined with Southern analysis by Ase I and Nde I digestion may be used for identifying the chimera in the CYP21 gene.

Duplication of 111 bases in exon 1 of the CYP21 gene is combined with deletion of CYP21P-C4B genes in steroid 21-hydroxylase deficiency

Congenital adrenal hyperplasia (CAH) is a common autosomal recessive disorder mainly caused by defects in the steroid 21-hydroxylase (CYP21) gene. A 9.3-kb fragment generated by NdeI and AseI digestion by Southern blot analysis indicated that a consequence of deletion of the C4-CYP21 repeat module was the production of a distinct chimeric CYP21P/CYP21 molecule. In the present study, we report a novel CYP21 genotype in two CAH families in which the gene appeared as 9.4- and 3.3-kb fragments by TaqI digestion, rather than as a chimeric gene. From the analysis of PCR amplification patterns and DNA sequencing, we found that there was a duplication of 111 bases from codons 21 to 57 inserted at codon 58 in exon 1 of the CYP21 gene. In addition, codon 21 in the repeated sequence changed from TGG to AGG. Furthermore, this novel CYP21 gene present in both CAH families showed no mutations at IVS2-12A/C>G, 707-714delGAGACTAC, and P30L. Interestingly, the 5' end region of these two CYP21 genes showed the sequence of the CYP21P gene at nucleotides (nt) -103, -110, -123, and thereafter. Our data suggest that these two CYP21 genes are caused by deletion of the CYP21P, XA, RP2, and C4B genes. Possibly, the additional 111-base duplicated coding sequence may be generated by multiple intergenic recombinations, while there seems to be no relationship with deletion of the CYP21P-C4B regions.

Mutation of IVS2 -12A/C>G in combination with 707-714delGAGACTAC in the CYP21 gene is caused by deletion of the C4-CYP21 repeat module with steroid 21-hydroxylase deficiency

More than 90% of the cases of congenital adrenal hyperplasia are caused by mutations of the CYP21 gene. Approximately 75% of the defective CYP21 genes are generated through intergenic recombination, termed apparent gene conversion, from the neighboring CYP21P pseudogene. Among them, mutation of the aberrant splicing donor site of IVS2 -12A/C>G at nucleotide (nt) 655 is believed to be a result derived from this mechanism and is the most prevalent case among all ethnic groups. However, mutation of 707-714delGAGACTAC rarely exists alone, although this locus is a distance of 53 nt away from IVS2 -12A/C>G. From the molecular characterization of the mutation of IVS2 -12A/C>G combined with 707-714delGAGACTAC in patients with congenital adrenal hyperplasia, we found that it appeared to be in a 3.2-rather than a 3.7-kb fragment generated by Taq I digestion in a PCR product of the CYP21 gene. Interestingly, the 5' end region of such a CYP21 haplotype had CYP21P-specific sequences. Our results indicate that the coexistence of these two mutations is caused by deletion of the CYP21P, XA, RP2, and C4B genes and intergenic recombination in the C4-CYP21 repeat module. Surprisingly, this kind of the haplotype of the mutated CYP21 gene has not been reported as a gene deletion.

Genetic Polymorphism of Human Cytochrome P450 Involved in Drug Metabolism

Recent advances in human gene analysis promoted by the human genome project have brought us a massive amount of information. These data can be seen and analyzed by personal computer through individual Web sites. As a result, the best use of bioinformatic is essential for recent molecular biology research. Genetic polymorphism of drug-metabolizing enzymes influences individual drug efficacy and safety through the alteration of pharmacokinetics and disposition of drugs. Considerable amounts of data have now accumulated as allelic differences of various drug metabolizing enzymes. Current understanding of genotype information on cytochrome P450 is hereby summarized, based on the Web site for their use in individual optimization of drug therapy.