Molecular model of human CYP21 based on mammalian CYP2C5: structural features correlate with clinical severity of mutations causing congenital adrenal hyperplasia

cyp21a2 Knockout Tadpoles Survive Metamorphosis Despite Low Corticosterone

Corticosteroids are so vital for organ maturation that reduced corticosteroid signaling during postembryonic development causes death in terrestrial vertebrates. Indeed, death occurs at metamorphosis in frogs lacking proopiomelanocortin (pomc) or the glucocorticoid receptor (GR; nr3c1). Some residual corticosteroids exist in pomc mutants to activate the wild-type (WT) GR and mineralocorticoid receptor (MR), and the elevated corticosteroids in GR mutants may activate MR. Thus, we expected a more severe developmental phenotype in tadpoles with inactivation of 21-hydroxylase, which should eliminate all interrenal corticosteroid biosynthesis. Using CRISPR/Cas9 in Xenopus tropicalis, we produced an 11-base pair deletion in cyp21a2, the gene encoding 21-hydroxylase. Growth and development were delayed in cyp21a2 mutant tadpoles, but unlike the other frog models, they survived metamorphosis. Consistent with an absence of 21-hydroxylase, mutant tadpoles had a 95% reduction of aldosterone in tail tissue, but they retained some corticosterone (∼40% of WT siblings), an amount, however, too low for survival in pomc mutants. Decreased corticosteroid signaling was evidenced by reduced expression of corticosteroid-response gene, klf9, and by impaired negative feedback in the hypothalamus-pituitary-interrenal axis with higher messenger RNA expression levels of crh, pomc, star, and cyp11b2 and an approximately 30-fold increase in tail content of progesterone. In vitro tail-tip culture showed that progesterone can transactivate the frog GR. The inadequate activation of GR by corticosterone in cyp21a2 mutants was likely compensated for by sufficient corticosteroid signaling from other GR ligands to allow survival through the developmental transition from aquatic to terrestrial life.

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.

Genetic aetiology of primary adrenal insufficiency in Chinese children

BACKGROUND

Primary adrenal insufficiency (PAI) is life-threatening, and a definitive aetiological diagnosis is essential for management and prognostication. We conducted this study to investigate the genetic aetiologies of PAI in South China and explore their clinical features.

METHODS

Seventy children were enrolled in this cross-sectional study. Clinical information was collected, and combined genetic tests were performed according to the children's manifestations. Statistical analysis was performed among the different groups. In silico or in vitro experiments were applied to determine the pathogenicity of novel variants.

RESULTS

Among the 70 children, 84.3% (59/70) were diagnosed with congenital adrenal hyperplasia (CAH), and 21-hydroxylase deficiency (21-OHD) was genetically confirmed in 91.5% of these cases. Salt wasting (SW), simple virilization (SV), and non-classic (NC) CAH accounted for 66.1% (39/59), 30.5% (18/59), and 3.4% (2/59) of the cases, respectively. The 17-hydroxyprogesterone (17-OHP) and testosterone (TES) levels were significantly higher in children with SW than with SV. The 17-OHP and cortisol levels in female SW patients were significantly higher than those in males. The 17-OHP, cortisol, dehydroepiandrosterone (DHEAS) and TES levels in female SW patients were significantly higher than those in female SV patients. Additionally, 72.7% (8/11) of uncharacterized PAI patients had positive genetic findings. Among all the patients, two novel variants in the CYP21A2 gene (c.833dupT and c.651 + 2T > G) were found. A microdeletion (Xp21.2-21.3) and five novel variants, including 2 in the NR0B1 gene (c.323-324CG > GA and c.1231_1234delCTCA), 2 in the AAAS gene (c.399 + 1G > A and c.250delT) and 1 in the NNT gene (c.2274delT), were detected. The novel variant c.399 + 1G > A in the AAAS gene was further confirmed to lead to exon 4 skipping during mRNA transcription and produce a truncated ALADIN protein.

CONCLUSIONS

We found ethnicity-based differences in the CYP21A2 gene variant spectrum among different study populations. Female 21-OHD patients tended to have higher 17-OHP and TES levels, which warrants caution in relation to the effects of virilization. Novel gene variants detected in the CYP21A2, NR0B1, AAAS and NNT genes expanded the genetic spectrum of PAI, however, further improvement of genetic testing tools beyond our protocol are still needed to uncover the complete aetiology of PAI in children.

Clinical outcomes and characteristics of P30L mutations in congenital adrenal hyperplasia due to 21-hydroxylase deficiency

Despite numerous studies in the field of congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency, some clinical variability of the presentation and discrepancies in the genotype/phenotype correlation are still unexplained. Some, but not all, discordant phenotypes caused by mutations with known enzyme activity have been explained by in silico structural changes in the 21-hydroxylase protein. The incidence of P30L mutation varies in different populations and is most frequently found in several Central and Southeast European countries as well as Mexico. Patients carrying P30L mutation present predominantly as non-classical CAH; however, simple virilizing forms are found in up to 50% of patients. Taking into consideration the residual 21-hydroxulase activity present with P30L mutation this is unexpected. Different mechanisms for increased androgenization in patients carrying P30L mutation have been proposed including influence of different residues, accompanying promotor allele variability or mutations, and individual androgene sensitivity. Early diagnosis of patients who would present with SV is important in order to improve outcome. Outcome studies of CAH have confirmed the uniqueness of this mutation such as difficulties in phenotype classification, different fertility, growth, and psychologic issues in comparison with other genotypes. Additional studies of P30L mutation are warranted.

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

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

Novel non-classic CYP21A2 variants, including combined alleles, identified in patients with congenital adrenal hyperplasia

OBJECTIVE

Congenital adrenal hyperplasia (CAH) is an inborn error of metabolism and a common disorder of sex development where >90% of all cases are due to 21-hydroxylase deficiency. Novel and rare pathogenic variants account for 5% of all clinical cases. Here, we sought to investigate the functional and structural effects of four novel (p.Val358Ile, p.Arg369Gln, p.Asp377Tyr, and p.Leu461Pro) and three combinations of CYP21A2 variants (i.e. one allele containing two variants p.[Ile172Asn;Val358Ile], p.[Val281Leu;Arg369Gln], or p.[Asp377Tyr;Leu461Pro]) identified in patients with CAH.

METHODS

All variants were reconstructed by in vitro site-directed mutagenesis, the proteins were transiently expressed in COS-1 cells and enzyme activities directed toward the two natural substrates (17-hydroxyprogesterone and progesterone) were determined. In parallel, in silico prediction of the pathogenicity of the variants based on the human CYP21 X-ray structure was performed.

RESULTS

The novel variants, p.Val358Ile, p.Arg369Gln, p.Asp377Tyr, and p.Leu461Pro exhibited residual enzymatic activities within the range of non-classic (NC) CAH variants (40-82%). An additive effect on the reduction of enzymatic activity (1-17%) was observed when two variants were expressed together, as identified in several patients, resulting in either NC or more severe phenotypes. In silico predictions were in line with the in vitro data except for p.Leu461Pro.

CONCLUSIONS

Altogether, the combination of clinical data, in silico prediction, and data from in vitro studies are important for establishing a correct genotype and phenotype correlation in patients with CAH.

Measuring the structural impact of mutations on cytochrome P450 21A2, the major steroid 21-hydroxylase related to congenital adrenal hyperplasia

Congenital adrenal hyperplasia is an inherited autosomal recessive disorder related to deficient cortisol synthesis. The deficiency of steroid 21-hydroxylase (cytochrome P450 21A2), an enzyme involved in cortisol synthesis, is responsible for ∼95% of cases of congenital adrenal hyperplasia. This metabolic disease exhibits three clinical forms: salt-wasting, simple virilizing, and non-classical form, which are divided according to the degree of severity. In the present study, structural and mutational analyses were performed in order to identify the structural impact of mutations on cytochrome P450 21A2 and correlate them with patient clinical severity. The following mutations were selected: arginine-356 to tryptophan (R356W), proline-30 to leucine (P30L), isoleucine-172 to asparagine (I172N), valine-281 to leucine (V281L), and the null mutation glutamine-318 (Q318X). Our computational approach mapped the location of residues on P450 and identified their implications on enzyme electrostatic potential mapping to progesterone and heme binding pockets. Using molecular dynamics simulations, we analyzed the structural stability of ligand binding and protein structure, as well as possible conformational changes at the catalytic pocket that leads to impairment of enzymatic activity. Our study sheds light on the impact structural mutations have over steroid 21-hydroxylase structure-function in the cell.Communicated by Ramaswamy H. Sarma.

Genotype-phenotype correlation study and mutational and hormonal analysis in a Chinese cohort with 21-hydroxylase deficiency

Background

Steroid 21‐hydroxylase deficiency (21OHD) is the most common enzymatic defect, but the genotype–phenotype associations have not been well established in Chinese patients. Here, a Chinese 21OHD cohort was enrolled to investigate the clinical, biochemical, and genetic characteristics of this disorder.

Methods

Mutation analysis of CYP21A2 gene, 21‐hydroxylase activity assays and in silico predictions of protein structure were performed. Genotype–phenotype associations were analyzed in both the cohort and 487 Chinese CAH patients ever reported.

Results

Among the total cohort (72 patients), 47 patients (65.3%) were diagnosed as salt‐wasting (SW) phenotype, 11 (15.3%) were simple virilizing (SV) type, and 14 (19.4%) were nonclassic (NC) type. The value of FSH and LH for prediction of the SW phenotype was up to 0.862 and 0.669, respectively. Overall, the detection rate of CYP21A2 mutation was 97.9%, which revealed 25 mutations and 36 genotypes. Four novel mutations (p.L199X, p.E321del, p.H393Q, and p.L459‐P464del) were detected and induced a significantly reduced 21‐hydroxylase activity. Generally, disease severity can be predicted with the genotypes. The most common genotypes in Chinese population were I2G/I2G (12.5%), I2G/Large lesion (12.1%), I173N/I2G (10.3%), and I173N/Large lesion (9.2%). The SW form of CAH is prominent in deletion or intronic splice mutations, namely I2G/I2G (18.6%), I2G/Large lesion (17.2%) and Large lesion/Large lesion (8.6%).

Conclusion

Four novel mutations were identified and a high consistency of genotype–phenotype association was found in SW CAH. Moreover, FSH and LH levels were proved to be a promising marker for predicting the severity of the disease.

Data on the functional consequences of the mutations identified in 21-Hydroxylase deficient CAH patients

This article presents the data set regarding the functional characterization of mutations in CYP21A2 gene in CAH patients as described in “Functional characterization and molecular modeling of the mutations in CYP21A2 gene from patients with Congenital Adrenal Hyperplasia (Khajuria et al., 2018) [1]. This data set features about the identification of mutations and their functional characterization by bioinformatic tools (mutation severity prediction softwares). Molecular modeling enabled us to locate the site of the amino-acid residues in 3-Dimensional model of 21-Hydroxylase protein which were mutated in patients.

Functional characterization and molecular modeling of the mutations in CYP21A2 gene from patients with Congenital Adrenal Hyperplasia

Steroid 21-Hydroxylase deficiency is an inherited autosomal recessive metabolic disorder of the adrenal steroidogenesis caused due to mutations in the CYP21A2 gene in 95% of CAH cases. Notably, the de novo mutations arise at the rate of 3-5%, therefore the functional characterization is of utmost importance for categorization of the novel mutations. Herein, we have functionally characterized the CYP21A2 missense mutations viz., p. F306V and p. H365N. Notably, both the mutations were harbored by the patients exhibiting the non classical phenotype. We followed the approach of in vitro characterization of the mutant proteins expressed in COS7 cells. Of note, all the mutant constructs exhibited reduced residual enzyme activity fraternized with altered kinetic constants accompanied by higher requirement for the activation energy. Further, there was reduced protein expression in the mutant constructs to that of the wild-type. Molecular modeling suggested alteration in the structure-function relationship of the protein due to mutations. The evidence suggested by the in vitro and the in silico characterization of mutations directed us to conclude that both, p. F306V and p. H365N should be considered as non classical CAH causing mutations. Conceivably, the knowledge about the functional consequences of the mutations is the basis for improved genetic counseling with respect to prognosis and therapeutic implications.

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.

Alternative Splicing in the Cytochrome P450 Superfamily Expands Protein Diversity to Augment Gene Function and Redirect Human Drug Metabolism

The human genome encodes 57 cytochrome P450 genes, whose enzyme products metabolize hundreds of drugs, thousands of xenobiotics, and unknown numbers of endogenous compounds, including steroids, retinoids, and eicosanoids. Indeed, P450 genes are the first line of defense against daily environmental chemical challenges in a manner that parallels the immune system. Several National Institutes of Health databases, including PubMed, AceView, and Ensembl, were queried to establish a comprehensive analysis of the full human P450 transcriptome. This review describes a remarkable diversification of the 57 human P450 genes, which may be alternatively processed into nearly 1000 distinct mRNA transcripts to shape an individual's P450 proteome. Important P450 splice variants from families 1A, 1B, 2C, 2D, 3A, 4F, 19A, and 24A have now been documented, with some displaying alternative subcellular distribution or catalytic function directly linked to a disease pathology. The expansion of P450 transcript diversity involves tissue-specific splicing factors, transformation-sensitive alternate splicing, trans-splicing between gene transcripts, single-nucleotide polymorphisms, and epigenetic regulation of alternate splicing. Homeostatic regulation of variant P450 expression is influenced also by nuclear receptor signaling, suppression of nonsense-mediated decay or premature termination codons, mitochondrial dysfunction, or host infection. This review focuses on emergent aspects of the adaptive gene-splicing process, which when viewed through the lens of P450-nuclear receptor gene interactions, resembles a primitive immune-like system that can rapidly monitor, respond, and diversify to acclimate to fluctuations in endo-xenobiotic exposure. Insights gained from this review should aid future drug discovery and improve therapeutic management of personalized drug regimens.

Predicting Severity of Disease-Causing Variants

Most diseases, including those of genetic origin, express a continuum of severity. Clinical interventions for numerous diseases are based on the severity of the phenotype. Predicting severity due to genetic variants could facilitate diagnosis and choice of therapy. Although computational predictions have been used as evidence for classifying the disease relevance of genetic variants, special tools for predicting disease severity in large scale are missing. Here, we manually curated a dataset containing variants leading to severe and less severe phenotypes and studied the abilities of variation impact predictors to distinguish between them. We found that these tools cannot separate the two groups of variants. Then, we developed a novel machine-learning-based method, PON-PS (http://structure.bmc.lu.se/PON-PS), for the classification of amino acid substitutions associated with benign, severe, and less severe phenotypes. We tested the method using an independent test dataset and variants in four additional proteins. For distinguishing severe and nonsevere variants, PON-PS showed an accuracy of 61% in the test dataset, which is higher than for existing tolerance prediction methods. PON-PS is the first generic tool developed for this task. The tool can be used together with other evidence for improving diagnosis and prognosis and for prioritization of preventive interventions, clinical monitoring, and molecular tests.

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.

21-hydroxylase deficiency-induced congenital adrenal hyperplasia in 230 Chinese patients: Genotype-phenotype correlation and identification of nine novel mutations

Steroid 21-hydroxylase deficiency (21-OHD) caused by the CYP21A2 gene mutations accounts for more than 90% of congenital adrenal hyperplasia (CAH) cases. In this study, molecular defects of 230 patients with 21-OHD were investigated. Point mutations of CYP21A2 gene were analyzed by Sanger sequencing, and large gene deletions were detected by multiplex ligation-dependent probe amplification (MLPA). Nine micro-conversions and 18 spontaneous mutations accounted for 74.6% of alleles, while large gene deletions and large gene conversions accounted for 25.4% of alleles. The most frequent micro-conversion was c.292-13A/C>G (I2G) (35%), followed by p.I173N (14.3%), p.R357W (5.9%) and p.Q319* (4.6%). Nine novel mutations were identified in these patients, which were predicted to hamper the 21-hydroxylase protein function in varying degrees. Genotype and phenotype correlated well in 89.6% of our patients, but disparity in phenotypic appearance also appeared in a small portion of the patients. 16.1% of the patients carried homozygous genotypes while 83.9% of patients carried compound heterozygous mutations. We concluded that the frequency of CYP21A2 mutations in our study was slightly different from those reported for other ethnic groups. Micro-conversions were the main category of the mutation spectrum, while large deletions and large gene conversions could also cause 21-OHD. A large portion of different types of the compound heterozygous genotypes may partially contribute to the discordance in genotype-phenotype comparison. This study expanded the CYP21A2 mutation spectrum of Chinese patients and could be helpful in prenatal diagnosis and genetic counseling for 21-OHD patients.

Functional and Structural Consequences of Nine CYP21A2 Mutations Ranging from Very Mild to Severe Effects

We present the functional and structural effects of seven novel (p.Leu12Met, p.Arg16Cys, p.Ser101Asn, p.Ser202Gly, p.Pro267Leu, p.Gln389_Ala391del, and p.Thr450Met) and two previously reported but not studied (p.Ser113Phe and p.Thr450Pro) CYP21A2 mutations. Functional analyses were complemented with in silico prediction of mutation pathogenicity based on the recently crystallized human CYP21A2 structure. Mutated proteins were transiently expressed in COS-1 cells and enzyme activities towards 17-hydroxyprogesterone and progesterone were determined. Residual enzyme activities between 43% and 97% were obtained for p.Arg16Cys, p.Ser101Asn, p.Ser202Gly, p.Pro267Leu, and p.Thr450Met, similar to the activities of the well-known nonclassic mutations p.Pro453Ser and p.Pro482Ser, whereas the p.Leu12Met variant showed an activity of 100%. Conversely, the novel p.Ser113Phe, p.Gln389_Ala391del, and p.Thr450Pro mutations drastically reduced the enzyme function below 4%. The K_m values for all novel variants were in the same order of magnitude as for the wild-type protein except for p.The450Met. The maximum velocity was decreased for all mutants except for p.Leu12Met. We conclude that p.Leu12Met is a normal variant; the mutations p.Arg16Cys, p.Ser101Asn, p.Ser202Gly, p.Pro267Leu, and p.Thr450Met could be associated with very mild nonclassic CAH, and the mutations p.Ser113Phe, p.Gln389_Ala391del, and p.Thr450Pro are associated with classic CAH. The obtained residual activities indicated a good genotype-phenotype correlation.

Molecular genetic study of congenital adrenal hyperplasia in Serbia: novel p.Leu129Pro and p.Ser165Pro CYP21A2 gene mutations

PURPOSE

Congenital adrenal hyperplasia (CAH) is an autosomal recessive disease characterized by impaired adrenal steroidogenesis and most often caused by CYP21A2 gene mutations. For the first time, we reported complete spectrum and frequency of CYP21A2 gene mutations in 61 unrelated patients with classical and non-classical CAH from Serbia.

METHODS

Direct DNA sequencing of whole CYP21A2 gene and polymerase chain reaction with sequence-specific primers for detection of CYP21A1P/CYP21A2 chimeras were combined.

RESULTS

We identified 18 different pathogenic alleles-two of them novel. Mutation detection rate was highest in patients with salt-wasting form of CAH (94.7%). The most prevalent mutation was intron 2 splice site mutation, c.290-13A/C>G (18.5%). Other mutation frequencies were: CYP21A1P/CYP21A2 chimeras (13%), p.P30L (13%), p.R356W (11.1%), p.G110fs (7.4%), p.Q318X (4.6%), p.V281L (4.6%), p.I172N (2.8%), p.L307fs (2.8%), p.P453S (1.9%), etc. Mainly, frequencies were similar to those in Slavic populations and bordering countries. However, we found 6.5% of alleles with multiple mutations, frequently including p.P453S. Effects of novel mutations, c.386T>C (p.Leu129Pro) and c.493T>C (p.Ser165Pro), were characterized in silico as deleterious. The effect of well-known mutations on Serbian patients' phenotype was as expected.

CONCLUSIONS

The first comprehensive molecular genetic study of Serbian CAH patients revealed two novel CYP21A2 mutations. This study will enable genetic counseling in our population and contribute to better understanding of molecular landscape of CAH in Europe.

Chimeric CYP11B2/CYP11B1 causing 11β-hydroxylase deficiency in Chinese patients with congenital adrenal hyperplasia

CYP11B1 and CYP11B2 are highly homologous genes that can form chimera following unequal crossing-over during meiosis. A chimeric CYP11B1/CYP11B2 gene causes glucocorticoid-remediable aldosteronism (GRA), while the rare CYP11B2/CYP11B1 chimeric gene leads to 11β-hydroxylase deficiency (11-OHD). The aim of the study was to find the underlying genetic causes of three distinct Chinese pedigrees with 11-OHD. The family history, clinical data, laboratory findings and alterations in the CYP11B1 gene sequence were analyzed in all patients. We found that patient 1 and patient 2 harbored novel homozygotic chimeric CYP11B2/CYP11B1 genes consisting of the promoter, exons 1-6 of CYP11B2, and exons 7-9 of CYP11B1. Patient 3 had compound heterozygotic mutation with one allele containing the promoter and exons 1-6 of CYP11B2 and exons 7-9 of CYP11B1, and the other allele comprising novel, previously undescribed p.W56X (c.168G>A) mutation in exon 1 of CYP11B1. The breakpoints to form Chimeric CYP11B2/CYP11B1 were not the same for the three patients. Rare chimeric CYP11B2/CYP11B1 gene mutations are the underlying cause of disease in three patients with 11-OHD. We hypothesize that the lack expression of CYP11B1 under the control of the CYP11B2 promoter in zona fasciculata may contribute to a cortisol defect as well as the resultant 11-OHD.

Genetic defects of the CYP21A2 gene in girls with premature adrenarche

OBJECTIVES

To seek evidence on the prevalence of CYP21A2 genetic defects and consequences in girls with premature adrenarche (PA).

METHODS

The study included 59 girls diagnosed with PA. Direct DNA sequencing and MLPA analysis were performed to identify mutations in CYP21A2 gene.

RESULTS

Twelve girls were diagnosed with non-classic congenital adrenal hyperplasia (NC-CAH) based on stimulated 17-hydroxyprogesterone (17-OHP) levels and the presence of two mutations in CYP21A2, 19 were heterozygotes. The most frequent mutations detected were the mild p.Val281Leu and p.Pro453Ser. Higher levels of mean stimulated 17-OHP were found in the carriers of the p.Val281Leu mutation. The detection rate for two CYP21A2 mutations was higher in girls with PA than in adult females with hyperandrogenemia in our studied population. A notable increased allelic frequency for the known p.Asn493Ser polymorphism was observed in the pool of the 28 girls with PA in whom no mutation was identified.

CONCLUSIONS

In girls with PA, the frequency of the underlying CYP21A2 genetic defects is similar to that observed in other populations. The carrier status is likely a contributing factor in the genotype-phenotype correlation in NC-CAH. However, polymorphisms and other genes may be implicated in the clinical manifestation of the disease.

Mechanistic basis of electron transfer to cytochromes p450 by natural redox partners and artificial donor constructs

Cytochromes P450 (P450s) are hemoproteins catalyzing oxidative biotransformation of a vast array of natural and xenobiotic compounds. Reducing equivalents required for dioxygen cleavage and substrate hydroxylation originate from different redox partners including diflavin reductases, flavodoxins, ferredoxins and phthalate dioxygenase reductase (PDR)-type proteins. Accordingly, circumstantial analysis of structural and physicochemical features governing donor-acceptor recognition and electron transfer poses an intriguing challenge. Thus, conformational flexibility reflected by togging between closed and open states of solvent exposed patches on the redox components was shown to be instrumental to steered electron transmission. Here, the membrane-interactive tails of the P450 enzymes and donor proteins were recognized to be crucial to proper orientation toward each other of surface sites on the redox modules steering functional coupling. Also, mobile electron shuttling may come into play. While charge-pairing mechanisms are of primary importance in attraction and complexation of the redox partners, hydrophobic and van der Waals cohesion forces play a minor role in docking events. Due to catalytic plasticity of P450 enzymes, there is considerable promise in biotechnological applications. Here, deeper insight into the mechanistic basis of the redox machinery will permit optimization of redox processes via directed evolution and DNA shuffling. Thus, creation of hybrid systems by fusion of the modified heme domain of P450s with proteinaceous electron carriers helps obviate the tedious reconstitution procedure and induces novel activities. Also, P450-based amperometric biosensors may open new vistas in pharmaceutical and clinical implementation and environmental monitoring.

In vitro functional studies of rare CYP21A2 mutations and establishment of an activity gradient for nonclassic mutations improve phenotype predictions in congenital adrenal hyperplasia

BACKGROUND

A detailed genotype-phenotype evaluation is presented by studying the enzyme activities of five rare amino acid substitutions (Arg233Gly, Ala265Ser, Arg341Trp, Arg366Cys and Met473Ile) identified in the CYP21A2 gene in patients investigated for Congenital adrenal hyperplasia (CAH).

OBJECTIVE

To investigate whether the mutations identified in the CYP21A2 gene are disease causing and to establish a gradient for the degree of enzyme impairment to improve prediction of patient phenotype.

DESIGN AND PATIENTS

The CYP21A2 genes of seven patients investigated for CAH were sequenced and five mutations were identified. The mutant proteins were expressed in vitro in COS-1 cells, and the enzyme activities towards the two natural substrates were determined to verify the disease-causing state of the mutations. The in vitro activities of these rare mutations were also compared with the activities of four mutations known to cause nonclassic CAH (Pro30Leu, Val281Leu, Pro453Ser and Pro482Ser) in addition to an in silico structural evaluation of the novel mutants.

MAIN OUTCOME MEASURE

To verify the disease-causing state of novel mutations.

RESULTS

Five CYP21A2 mutations were identified (Arg233Gly, Ala265Ser, Arg341Trp, Arg366Cys and Met473Ile). All mutant proteins exhibited enzyme activities above 5%, and four mutations were classified as nonclassic and one as a normal variant. By comparing the investigated protein changes with four common mutations causing nonclassic CAH, a gradient for the degree of enzyme impairment could be established. Studying rare mutations in CAH increases our knowledge regarding the molecular mechanisms that render a mutation pathogenic. It also improves phenotype predictions and genetic counselling for future generations.

Phenotypic variability of hyperandrogenemia in females heterozygous for CYP21A2 mutations

OBJECTIVES

The objective was to seek evidence on the prevalence and consequences of heterozygous CYP21A2 mutations in girls, adolescent, and adult females with clinical manifestation of androgen excess.

PATIENTS AND METHODS

The study included 64 girls diagnosed with premature adrenarche (PA) in childhood and 141 females with clinical hyperandrogenemia manifested in adolescence or adulthood. Direct DNA sequencing and multiplex ligation-dependent probe amplification analysis were used to identify mutations in the CYP21A2 gene.

RESULTS

(1) Thirty-four patients were diagnosed with nonclassical-congenital adrenal hyperplasia (NC-CAH) based on the 17-hydroxyprogesterone (17-OHP) levels and the presence of two mutations in CYP21A2 and therefore were excluded from the study, 66 were found to be heterozygotes and finally 105 had no identifiable mutations. The most frequent mutations among the carriers were the mild p.Val281 Leu and p.Qln318stop. Higher levels of mean stimulated 17-OHP were found in the carriers of the p.Val281 Leu. (2) A notable increased allelic frequency for the known p.Asn493 Ser polymorphism was observed in the pool of females with hyperandrogenemia in whom no mutation was identified. (3) In girls, who presented early with PA, 26.6% were diagnosed with NC-CAH and carried two mutations, 28.7% were identified as heterozygotes 43.7% had no identifiable genetic defect in the translated region of the CYP21A2 gene. On the contrary, in the group of 141 females with late onset hyperandrogenemia, the presence of 2 mutations was detected in 12%, 1 mutation in 33.4% and no mutation in 54.6%.

CONCLUSIONS

The carrier status for 21-OHD, may be an important factor in the variable phenotype of hyperandrogenism and may be a contributing factor for the early manifestation of the disease.

MutaCYP: Classification of missense mutations in human cytochromes P450

BACKGROUND

Cytochrome P450 monooxygenases (CYPs) represent a large and diverse family of enzymes involved in various biological processes in humans. Individual genome sequencing has revealed multiple mutations in human CYPs, and many missense mutations have been associated with variety of diseases. Since 3D structures are not resolved for most human CYPs, there is a need for a reliable sequence-based prediction that discriminates benign and disease causing mutations.

METHODS

A new prediction method (MutaCYP) has been developed for scoring de novo missense mutations to have a deleterious effect. The method utilizes only five features, all of which are sequence-based: predicted relative solvent accessibility (RSA), variance of predicted RSA among the residues in close sequence proximity, Z-score of Shannon entropy for a given position, difference in similarity scores and weighted difference in size between wild type and new amino acids. The method is based on a single neural network.

RESULTS

MutaCYP achieves MCC = 0.70, Q2 = 88.52%, Recall = 93.40% with Precision = 91.09%, and AUC = 0.909. Comparative evaluation with other existing methods indicates that MutaCYP outperforms SIFT and PolyPhen-2. Predictions by MutaCYP appear to be orthogonal to predictions by the evaluated methods. Potential issues on reliability of annotations of mutations in the existing databases are discussed.

CONCLUSIONS

A new accurate method, MutaCYP, for classification of missense mutations in human CYPs is presented. The prediction model consists of only five sequence-based features, including a real-valued predicted relative solvent accessibility. The method is publicly available at http://research.cchmc.org/MutaSense/.

Characterisation of three novel CYP11B1 mutations in classic and non-classic 11β-hydroxylase deficiency

BACKGROUND

Congenital adrenal hyperplasia (CAH) is one of the most common autosomal recessive inherited endocrine diseases. Steroid 11β-hydroxylase (P450c11) deficiency (11OHD) is the second most common form of CAH.

AIM

The aim of the study was to study the functional consequences of three novel CYP11B1 gene mutations (p.His125Thrfs*8, p.Leu463_Leu464dup and p.Ser150Leu) detected in patients suffering from 11OHD and to correlate this data with the clinical phenotype.

METHODS

Functional analyses were done by using a HEK293 cell in vitro expression system comparing WT with mutant P450c11 activity. Mutant proteins were examined in silico to study their effect on the three-dimensional structure of the protein.

RESULTS

Two mutations (p.His125Thrfs*8 and p.Leu463_Leu464dup) detected in patients with classic 11OHD showed a complete loss of P450c11 activity. The mutation (p.Ser150Leu) detected in a patient with non-classic 11OHD showed partial functional impairment with 19% of WT activity.

CONCLUSION

Functional mutation analysis enables the correlation of novel CYP11B1 mutations to the classic and non-classic 11OHD phenotype respectively. Mutations causing a non-classic phenotype show typically partial impairment due to reduced maximum reaction velocity comparable with non-classic mutations in 21-hydroxylase deficiency. The increasing number of mutations associated with non-classic 11OHD illustrate that this disease should be considered as diagnosis in patients with otherwise unexplained hyperandrogenism.

17-Hydroxyprogesterone in children, adolescents and adults

17-Hydroxyprogesterone (17-OHP) is an intermediate steroid in the adrenal biosynthetic pathway from cholesterol to cortisol and is the substrate for steroid 21-hydroxylase. An inherited deficiency of 21-hydroxylase leads to greatly increased serum concentrations of 17-OHP, while the absence of cortisol synthesis causes an increase in adrenocorticotrophic hormone. The classical congenital adrenal hyperplasia (CAH) presents usually with virilisation of a girl at birth. Affected boys and girls can have renal salt loss within a few days if aldosterone production is also compromised. Diagnosis can be delayed in boys. A non-classical form of congenital adrenal hyperplasia (NC-CAH) presents later in life usually with androgen excess. Moderately raised or normal 17-OHP concentrations can be seen basally but, if normal and clinical suspicion is high, an ACTH stimulation test will show 17-OHP concentrations (typically >30 nmol/L) above the normal response. NC-CAH is more likely to be detected clinically in females and may be asymptomatic particularly in males until families are investigated. The prevalence of NC-CAH in women with androgen excess can be up to 9% according to ethnic background and genotype. Mutations in the 21-hydroxylase genes in NC-CAH can be found that have less deleterious effects on enzyme activity. Other less-common defects in enzymes of cortisol synthesis can be associated with moderately elevated 17-OHP. Precocious puberty, acne, hirsutism and subfertility are the commonest features of hyperandrogenism. 17-OHP is a diagnostic marker for CAH but opinions differ on the role of 17OHP or androstenedione in monitoring treatment with renin in the salt losing form. This review considers the utility of 17-OHP measurements in children, adolescents and adults.

Functional studies of p.R132C, p.R149C, p.M283V, p.E431K, and a novel c.652-2A>G mutations of the CYP21A2 gene

Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is the most frequent inborn error of metabolism and accounts for 90–95% of CAH cases. In the present work, we analyzed the functional consequence of four novel previously reported point CYP21A2 mutations -p.R132C, p.R149C, p.M283V, p.E431K- found in Argentinean 21-hydroxylase deficient patients. In addition, we report an acceptor splice site novel point mutation, c.652-2A>G, found in a classical patient in compound heterozygosity with the rare p.R483Q mutation. We performed bioinformatic and functional assays to evaluate the biological implication of the novel mutation. Our analyses revealed that the residual enzymatic activity of the isolated mutants coding for CYP21A2 aminoacidic substitutions was reduced to a lesser than 50% of the wild type with both progesterone and 17-OH progesterone as substrates. Accordingly, all the variants would predict mild non-classical alleles. In one non-classical patient, the p.E431K mutation was found in cis with the p.D322G one. The highest decrease in enzyme activity was obtained when both mutations were assayed in the same construction, with a residual activity most likely related to the simple virilizing form of the disease. For the c.652-2A>G mutation, bioinformatic tools predicted the putative use of two different cryptic splicing sites. Nevertheless, functional analyses revealed the use of only one cryptic splice acceptor site located within exon 6, leading to the appearance of an mRNA with a 16 nt deletion. A severe allele is strongly suggested due to the presence of a premature stop codon in the protein only 12 nt downstream.

Genotype-phenotype correlation in 153 adult patients with congenital adrenal hyperplasia due to 21-hydroxylase deficiency: analysis of the United Kingdom Congenital adrenal Hyperplasia Adult Study Executive (CaHASE) cohort

CONTEXT

In congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency, a strong genotype-phenotype correlation exists in childhood. However, similar data in adults are lacking.

OBJECTIVE

The objective of the study was to test whether the severity of disease-causing CYP21A2 mutations influences the treatment and health status in adults with CAH.

RESEARCH DESIGN AND METHODS

We analyzed the genotype in correlation with treatment and health status in 153 adults with CAH from the United Kingdom Congenital adrenal Hyperplasia Adult Study Executive cohort.

RESULTS

CYP21A2 mutations were distributed similarly to previously reported case series. In 7 patients a mutation was identified on only 1 allele. Novel mutations were detected on 1.7% of alleles (5 of 306). Rare mutations were found on 2.3% of alleles (7 of 306). For further analysis, patients were categorized into CYP21A2 mutation groups according to predicted residual enzyme function: null (n = 34), A (n = 42), B (n = 36), C (n = 34), and D (n = 7). Daily glucocorticoid dose was highest in group null and lowest in group C. Fludrocortisone was used more frequently in patients with more severe genotypes. Except for lower female height in group B, no statistically significant associations between genotype and clinical parameters were found. Androgens, blood pressure, lipids, blood glucose, and homeostasis model assessment of insulin resistance were not different between groups. Subjective health status was similarly impaired across groups.

CONCLUSIONS

In adults with classic CAH and women with nonclassic CAH, there was a weak association between genotype and treatment, but health outcomes were not associated with genotype. The underrepresentation of males with nonclassic CAH may reflect that milder genotypes result in a milder condition that is neither diagnosed nor followed up in adulthood. Overall, our results suggest that the impaired health status of adults with CAH coming to medical attention is acquired rather than genetically determined and therefore could potentially be improved through modification of treatment.

Structure-phenotype correlations of human CYP21A2 mutations in congenital adrenal hyperplasia

Mutations in the cytochrome p450 (CYP)21A2 gene, which encodes the enzyme steroid 21-hydroxylase, cause the majority of cases in congenital adrenal hyperplasia, an autosomal recessive disorder. To date, more than 100 CYP21A2 mutations have been reported. These mutations can be associated either with severe salt-wasting or simple virilizing phenotypes or with milder nonclassical phenotypes. Not all CYP21A2 mutations have, however, been characterized biochemically, and the clinical consequences of these mutations remain unknown. Using the crystal structure of its bovine homolog as a template, we have constructed a humanized model of CYP21A2 to provide comprehensive structural explanations for the clinical manifestations caused by each of the known disease-causing missense mutations in CYP21A2. Mutations that affect membrane anchoring, disrupt heme and/or substrate binding, or impair stability of CYP21A2 cause complete loss of function and salt-wasting disease. In contrast, mutations altering the transmembrane region or conserved hydrophobic patches cause up to a 98% reduction in enzyme activity and simple virilizing disease. Mild nonclassical disease can result from interference in oxidoreductase interactions, salt-bridge and hydrogen-bonding networks, and nonconserved hydrophobic clusters. A simple in silico evaluation of previously uncharacterized gene mutations could, thus, potentially help predict the often diverse phenotypes of a monogenic disorder.

Nonclassic congenital adrenal hyperplasia

PURPOSE OF REVIEW

Late-onset or nonclassic congenital adrenal hyperplasia (NCAH) due to 21-hydroxylase deficiency is one of the most common autosomal recessive disorders. Reported prevalence ranges from 1 in 30 to 1 in 1000. Affected individuals typically present due to signs and symptoms of androgen excess. The purpose of this review is to provide current information regarding the pathophysiology, molecular genetics, and management of this common disorder.

RECENT FINDINGS

Subfertility and the consequences of elevated progesterone concentrations have been increasingly documented for women with NCAH. Although testicular adrenal rest tumors (TARTs) are more common in men with classical congenital adrenal hyperplasia, oligospermia and TARTs have been described in men with NCAH. The phenotypic spectrum of defects in other components of the steroidogenic pathway such as P450 oxidoreductase and steroidogenic acute regulatory protein has been expanded to include milder forms.

SUMMARY

Treatment needs to be directed toward the symptoms. Goals of treatment include normal linear growth velocity, normal rate of skeletal maturation, 'on-time' puberty, regular menstrual cycles, prevention of or limited progression of hirsutism and acne, and fertility. Treatment needs to be individualized and should not be initiated merely to decrease abnormally elevated hormone concentrations.

Investigating protein variants using structural calculation techniques

Structure calculation techniques can be very useful to bridge the gap between available sequence information and structural knowledge. In order to understand the molecular mechanisms behind diseases caused by residue exchanges, knowledge about the modified structure is needed. In this chapter, we describe how energy minimizations and molecular dynamics can be useful tools in order to study the structural effects of sequence variation. With these techniques, together with investigation of other properties, it is often possible to obtain a complete picture of the effect and mechanism behind disease-causing mutations. To take this information one step further, we also describe prediction methods that can be used to judge the effects of mutations and how to evaluate these and the interplay between the protein properties.

Identification and functional characterization of a novel mutation P459H and a rare mutation R483W in the CYP21A2 gene in two Chinese patients with simple virilizing form of congenital adrenal hyperplasia

BACKGROUND

Steroid 21-hydroxylase deficiency (21-OHD) is the most common cause of congenital adrenal hyperplasia (CAH). Clinically, 21-OHD is categorized into saltwasting, simple-virilizing (SV), and non-classical (NC) forms. It is well recognized that a good correlation exists between genotype and clinical phenotype of CAH.

AIM

The aim of this study was to identify CYP21A2 gene mutations in 2 Chinese patients with SV CAH along with their parents and other family members.

STUDY DESIGN AND RESULTS

By direct sequencing the CYP21A2 gene, a novel mutation, P459H, was detected in 1 patient; and a previously described uncharacterized mutation, R483W, was found in another patient. The 21-hydroxylase activities were determined by measuring the converting rate of progesterone to 11-deoxycorticosterone in COS-7 cells overexpressed with these mutated proteins. Our results revealed significantly reduced enzyme activity in both mutants: residual activity of P459H and R483W towards progesterone was 6.8%±2.1 and 2.9%±1.5, respectively compared to that of the wild type. We also demonstrated the loss of 21-hydroxylase activities using a three-dimensional model of CYP21A2.

CONCLUSION

Both R483W and P459H mutations are confirmed to be related to NC CAH by in vitro functional study, with phenotype variance of R483W in Tunisian and Chinese patients. This study will aid in predicting disease severity and in facilitating family genetic counseling.

Three-dimensional structure of steroid 21-hydroxylase (cytochrome P450 21A2) with two substrates reveals locations of disease-associated variants

Steroid 21-hydroxylase (cytochrome P450 21A2, CYP21A2) deficiency accounts for ∼95% of individuals with congenital adrenal hyperplasia, a common autosomal recessive metabolic disorder of adrenal steroidogenesis. The effects of amino acid mutations on CYP21A2 activity lead to impairment of the synthesis of cortisol and aldosterone and the excessive production of androgens. In order to understand the structural and molecular basis of this group of diseases, the bovine CYP21A2 crystal structure complexed with the substrate 17-hydroxyprogesterone (17OHP) was determined to 3.0 Å resolution. An intriguing result from this structure is that there are two molecules of 17OHP bound to the enzyme, the distal one being located at the entrance of the substrate access channel and the proximal one bound in the active site. The substrate binding features locate the key substrate recognition residues not only around the heme but also along the substrate access channel. In addition, orientation of the skeleton of the proximal molecule is toward the interior of the enzyme away from the substrate access channel. The 17OHP complex of CYP21A2 provides a good relationship between the crystal structure, clinical data, and genetic mutants documented in the literature, thereby enhancing our understanding of congenital adrenal hyperplasia. In addition, the location of certain CYP21A2 mutations provides general understanding of structure/function relationships in P450s.

Molecular testing in congenital adrenal hyperplasia due to 21α-hydroxylase deficiency in the era of newborn screening

Newborn screening (NBS) identifies the majority of classical [salt-wasting (SW) and simple-virilizing (SV)] cases of congenital adrenal hyperplasia (CAH) due to 21α-hydroxylase (21α-OHase) during the first days of life. Diagnosis of classical CAH is confirmed by follow-up serum 17-hydroxyprogesterone and/or the adrenocorticotropin stimulation test; however, neither test definitively distinguishes between the classical subtypes. After confirmation, all newborns are started on hydrocortisone (glucocorticoid) and fludrocortisone (mineralocorticoid) treatment. While initiating fludrocortisone treatment in classical CAH patients, independent of subtype and before SW signs or symptoms occur, prevents a life-threatening SW crisis, it may later complicate distinguishing between the classical subtypes. Genotype-phenotype correlations in 21α-OHase deficiency are excellent; however, molecular testing is not a regular part of the diagnostic workup. Molecular testing on 39 patients (25 identified by NBS) with an already established diagnosis of CAH identified 11 SW patients (8 identified by NBS) whose mutations suggested further biochemical and clinical reassessment of their subtype. Overall, SW accounted for 57.6% of our classical CAH patients, below the generally accepted figure that >75% of classical CAH are comprised of the SW form. In the era of NBS, molecular testing is a valuable supplemental tool identifying patients who may benefit from reassessment of their salt-retaining ability.

Why human cytochrome P450c21 is a progesterone 21-hydroxylase

Human cytochrome P450c21 (steroid 21-hydroxylase, CYP21A2) catalyzes the 21-hydroxylation of progesterone (P4) and its preferred substrate 17α-hydroxyprogestrone (17OHP4). CYP21A2 activities, which are required for cortisol and aldosterone biosynthesis, involve the formation of energetically disfavored primary carbon radicals. Therefore, we hypothesized that the binding of P4 and 17OHP4 to CYP21A2 restricts access of the reactive heme-oxygen complex to the C-21 hydrogen atoms, suppressing oxygenation at kinetically more favorable sites such as C-17 and C-16, which are both hydroxylated by cytochrome P450c17 (CYP17A1). We reasoned that expansion of the CYP21A2 substrate-binding pocket would increase substrate mobility and might yield additional hydroxylation activities. We built a computer model of CYP21A2 based principally on the crystal structure of CYP2C5, which also 21-hydroxylates P4. Molecular dynamics simulations indicate that binding of the steroid nucleus perpendicular to the plane of the CYP21A2 heme ring limits access of the heme oxygen to the C-21 hydrogen atoms. Residues L107, L109, V470, I471, and V359 were found to contribute to the CYP21A2 substate-binding pocket. Mutation of V470 and I471 to alanine or glycine preserved P4 21-hydroxylase activity, and mutations of L107 or L109 were inactive. Mutations V359A and V359G, in contrast, acquired 16α-hydroxylase activity, accounting for 40% and 90% of the P4 metabolites, respectively. We conclude that P4 binds to CYP21A2 in a fundamentally different orientation than to CYP17A1 and that expansion of the CYP21A2 substrate-binding pocket allows additional substrate trajectories and metabolic switching.

Functional characterisation of the H365Y mutation of the 21-hydroxylase gene in congenital adrenal hyperplasia

The study subject was a 13 day-old boy admitted to hospital, with weight loss since birth. He presented with the vomiting and hypotension that are classical features of congenital adrenal hyperplasia (CAH). The most common type of CAH is an autosomal recessive disorder caused by mutations in the 21-hydroxylase (CYP21A2) gene. To examine the CYP21A2 gene, gene-specific PCR was carried out, followed by sequencing. The baby was shown to be a compound heterozygote H365Y/R356W for two CYP21A2 gene mutations each inherited from a different parent. One of the mutations has not previously been functionally characterised. The mutations were reconstructed in an expression plasmid and characterised in vitro after transient transfection into human embryonic kidney (HEK293T) and hepatoblastoma (C3A) cell lines followed by measurement of enzyme activity. The CYP21A2 H365Y mutant exhibited minimal 21-hydroxylase activity to convert 17-hydroxyprogesterone to 11-deoxycortisol or progesterone to 11-deoxycorticosterone. Western immunoblotting indicated that the H365Y enzyme was produced in more variable amounts than wild type; in particular, the H365Y mutant protein may be unstable and/or subject to a more rapid degradation by the human proteosome as well as catalytically inefficient. The double mutant genotype with a severe mutation on each allele is compatible with the clinical presentation.

Structure-based analysis of five novel disease-causing mutations in 21-hydroxylase-deficient patients

Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is the most frequent inborn error of metabolism, and accounts for 90–95% of CAH cases. The affected enzyme, P450C21, is encoded by the CYP21A2 gene, located together with a 98% nucleotide sequence identity CYP21A1P pseudogene, on chromosome 6p21.3. Even though most patients carry CYP21A1P-derived mutations, an increasing number of novel and rare mutations in disease causing alleles were found in the last years. In the present work, we describe five CYP21A2 novel mutations, p.R132C, p.149C, p.M283V, p.E431K and a frameshift g.2511_2512delGG, in four non-classical and one salt wasting patients from Argentina. All novel point mutations are located in CYP21 protein residues that are conserved throughout mammalian species, and none of them were found in control individuals. The putative pathogenic mechanisms of the novel variants were analyzed in silico. A three-dimensional CYP21 structure was generated by homology modeling and the protein design algorithm FoldX was used to calculate changes in stability of CYP21A2 protein. Our analysis revealed changes in protein stability or in the surface charge of the mutant enzymes, which could be related to the clinical manifestation found in patients.

Molecular characterization of 25 Chinese pedigrees with 21-hydroxylase deficiency

Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders mainly caused by a defect in the steroid 21-hydroxylase gene (CYP21A2). In this study, we investigated the molecular defects of 25 Chinese pedigrees with 21-hydroxylase deficiency (21-OHD). Diagnosis of the probands in the families was based on their typical clinical presentations, such as inborn ambiguous genitalia, or early onset of salt wasting and biochemical metabolite abnormalities. All 10 exons and exon-intron boundaries of the CYP21A2 gene were amplified from the genomic DNA of the probands and then analyzed by direct sequencing. The phenotypes of the 26 patients from 25 pedigrees were classified as the classical form of 21-OHD. One novel mutation (c.1223 G>T) and 13 recurrent mutations of CYP21A2 were identified in the 25 pedigrees by genetic analysis. The novel c.1223 G>T mutation results in the substitution of arginine by leucine at amino acid position 408 (p.Arg408Leu). The most frequent mutation alleles were IVS2-13A/C>G (14/52) and I172N (11/52), followed by chimeric mutations (10/52). Forty six of 52 mutated alleles resulted from pseudogene conversion and 6 of 52 from random mutations. The spectrum of CYP21A2 mutation in our study was slightly different from those previously reported in Chinese and in other ethnic groups of the world. Although microconversion events were the main cause of mutations in the CYP21 gene, random mutations with a common origin can also be the reason for 21-OHD.

Premature Moustache As Presenting Symptom of Nonclassic Congenital Adrenal Hyperplasia due to 2 Uncommon Mutations of theCYP21A2Gene

A Turkish boy was referred at the age of 3 6/12 years for the evaluation of a premature moustache. No other signs of virilisation were present. The endocrine evaluation led to the diagnosis of nonclassic congenital adrenal hyperplasia. Genetic analysis revealed 2 rare mutations of the CYP21A2 gene, the gene encoding for the 21-hydroxylase enzyme: a recently reported R132C mutation in exon 3 and a R339H mutation in exon 8, both reported in the nonclassic CAH. An early moustache, for which the term premature moustache can be coined, can be the presenting symptom of nonclassic CAH. In all children presenting with a sex or age inappropriate development of a moustache, an endocrine evaluation is indicated.

Comprehensive genetic analysis of 182 unrelated families with congenital adrenal hyperplasia due to 21-hydroxylase deficiency

BACKGROUND

Genetic analysis is commonly performed in patients with congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency.

STUDY OBJECTIVE

The objective of the study was to describe comprehensive CYP21A2 mutation analysis in a large cohort of CAH patients.

METHODS

Targeted CYP21A2 mutation analysis was performed in 213 patients and 232 parents from 182 unrelated families. Complete exons of CYP21A2 were sequenced in patients in whom positive mutations were not identified by targeted mutation analysis. Copy number variation and deletions were determined using Southern blot analysis and PCR methods. Genotype was correlated with phenotype.

RESULTS

In our heterogeneous U.S. cohort, targeted CYP21A2 mutation analysis did not identify mutations on one allele in 19 probands (10.4%). Sequencing identified six novel mutations (p.Gln262fs, IVS8+1G>A, IVS9-1G>A, p.R408H, p.Gly424fs, p.R426P) and nine previously reported rare mutations. The majority of patients (79%) were compound heterozygotes and 69% of nonclassic (NC) patients were compound heterozygous for a classic and a NC mutation. Duplicated CYP21A2 haplotypes, de novo mutations and uniparental disomy were present in 2.7% of probands and 1.9 and 0.9% of patients from informative families, respectively. Genotype accurately predicted phenotype in 90.5, 85.1, and 97.8% of patients with salt-wasting, simple virilizing, and NC mutations, respectively.

CONCLUSIONS

Extensive genetic analysis beyond targeted CYP21A2 mutational detection is often required to accurately determine genotype in patients with CAH due to the high frequency of complex genetic variation.

Phenotype-genotype correlations of 13 rare CYP21A2 mutations detected in 46 patients affected with 21-hydroxylase deficiency and in one carrier

CONTEXT

Steroid 21-hydroxylase deficiency is the most common enzymatic defect causing congenital adrenal hyperplasia with genotype/phenotype relationships for common mutations. Novel mutations of the CYP21A2 gene must be well studied to propose right genetic counseling for patients.

OBJECTIVE

Thirteen CYP21 mutations have been studied. A detailed description of phenotype was performed for all mutations (p.I77T, p.L167P, p.I230T, p.R233K, p.G291S, p.G292D, p.E320K, p.R341P, p.R354H, p.R369W, p.R408C, p.G424S, and p.R426H). In vitro and in silico studies were performed only for those not previously described (p.L167P, p.I230T, p.R233K, p.G292D, p.E320K, and p.R369W).

RESULTS

Regarding phenotype, patients with 10 of these mutations had a classical form. A patient with isolated p.I230T presented with nonclassical form and a patient with the association p.I230T + p.V281L in cis presented with a more severe phenotype. The p.R233K mutation was detected in a carrier partner. A patient with p.R369W presented with an intermediate form. Functional studies showed that all mutations except p.I230T and p.R369W decreased enzyme activity more than p.P30L: severity of p.R369W was intermediate between p.P30L and p.V281L, and finally p.I230T was less severe than p.V281L. Mutation analysis in a three-dimensional model structure of the CYP21 protein explained the observed in vitro effects, severe mutations being implicated in important functional domains of the protein.

CONCLUSION

According to phenotype and functional studies, 11 of the mutations described, except the isolated p.R369W and p.I230T, may be responsible for a severe phenotype underlying the necessity to manage children having them. The p.I230T is a nonclassical mutation, and for the p.R369W, we need more cases to precise its severity.

Functional consequences of seven novel mutations in the CYP11B1 gene: four mutations associated with nonclassic and three mutations causing classic 11{beta}-hydroxylase deficiency

CONTEXT

Steroid 11beta-hydroxylase (CYP11B1) deficiency (11OHD) is the second most common form of congenital adrenal hyperplasia (CAH). Cases of nonclassic 11OHD are rare compared with the incidence of nonclassic 21-hydroxylase deficiency.

OBJECTIVE

The aim of the study was to analyze the functional consequences of seven novel CYP11B1 mutations (p.M88I, p.W116G, p.P159L, p.A165D, p.K254_A259del, p.R366C, p.T401A) found in three patients with classic 11OHD, two patients with nonclassic 11OHD, and three heterozygous carriers for CYP11B1 mutations.

METHODS

We conducted functional studies employing a COS7 cell in vitro expression system comparing wild-type (WT) and mutant CYP11B1 activity. Mutants were examined in a computational three-dimensional model of the CYP11B1 protein.

RESULTS

All mutations (p.W116G, p.A165D, p.K254_A259del) found in patients with classic 11OHD have absent or very little 11beta-hydroxylase activity relative to WT. The mutations detected in patients with nonclassic 11OHD showed partial functional impairment, with one patient being homozygous (p.P159L; 25% of WT) and the other patient compound heterozygous for a novel mild p.M88I (40% of WT) and the known severe p.R383Q mutation. The two mutations detected in heterozygous carriers (p.R366C, p.T401A) also reduced CYP11B1 activity by 23 to 37%, respectively.

CONCLUSION

Functional analysis results allow for the classification of novel CYP11B1 mutations as causative for classic and nonclassic 11OHD, respectively. Four partially inactivating mutations are predicted to result in nonclassic 11OHD. These findings double the number of mild CYP11B1 mutations previously described as associated with mild 11OHD. Our data are important to predict phenotypic expression and provide important information for clinical and genetic counseling in 11OHD.

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.