Silvia Parajes

Functional Consequences of Seven Novel Mutations in the CYP11B1 Gene: Four Mutations Associated with Nonclassic and Three Mutations Causing Classic 11β-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.

High Frequency of Copy Number Variations and Sequence Variants at CYP21A2 Locus: Implication for the Genetic Diagnosis of 21-Hydroxylase Deficiency

Background The systematic study of the human genome indicates that the inter-individual variability is greater than expected and it is not only related to sequence polymorphisms but also to gene copy number variants (CNVs). Congenital Adrenal Hyperplasia due to 21-hydroxylase deficiency (21OHD) is the most common autosomal recessive disorder with a carrier frequency of 1∶25 to 1∶10. The gene that encodes 21-hydroxylase enzyme, CYP21A2, is considered to be one of the most polymorphic human genes. Copy number variations, such as deletions, which are severe mutations common in 21OHD patients, or gene duplications, which have been reported as rare events, have also been described. The correct characterization of 21OHD alleles is important for disease carrier detection and genetic counselling Methodology and Findings CYP21A2 genotyping by sequencing has been performed in a random sample of the Spanish population, where 144 individuals recruited from university students and employees of the hospital were studied. The frequency of CYP21A2 mutated alleles in our sample was 15.3% (77.3% were mild mutations, 9% were severe mutations and 13.6% were novel variants). Gene dosage assessment was also performed when CYP21A2 gene duplication was suspected. This analysis showed that 7% of individuals bore a chromosome with a duplicated CYP21A2 gene, where one of the copies was mutated. Conclusions As far as we know, the present study has shown the highest frequency of 21OHD carriers reported by a genotyping analysis. In addition, a high frequency of alleles with CYP21A2 duplications, which could be misinterpreted as 21OHD alleles, was found. Moreover, a high frequency of novel genetic variations with an unknown effect on 21-hydroxylase activity was also found. The high frequency of gene duplications, as well as novel variations, should be considered since they have an important involvement in carrier testing and genetic counseling.

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.

High variability in CYP21A2 mutated alleles in Spanish 21‐hydroxylase deficiency patients, six novel mutations and a founder effect

Objective To detect common as well as rare and novel CYP21A mutations in 21‐hydroxylase deficiency patients. To estimate the distribution of mutations and compare them with other European studies. To construct haplotypes linked to a recurrent novel mutation.

A novel entity of clinically isolated adrenal insufficiency caused by a partially inactivating mutation of the gene encoding for P450 side chain cleavage enzyme (CYP11A1).

CONTEXT Cytochrome P450 side-chain cleavage enzyme (CYP11A1) facilitates the first and rate-limiting step of steroidogenesis. Only nine patients with CYP11A1 deficiency have been described. All patients presented with adrenal insufficiency (AI) and disorder of sex development in 46,XY individuals. OBJECTIVE Our objective was to define the pathogenic consequences of a novel CYP11A1 mutation (p.R451W) found in two brothers with isolated adrenal insufficiency. PATIENTS The two brothers (46,XY) presented with AI and normal male genital development. The older boy first presented with signs and symptoms suggestive of AI at the age of 2.8 yr but was only diagnosed at the age of 4.1 yr during an adrenal crisis. The younger brother was diagnosed with AI at the age of 2.5 yr while being clinically asymptomatic. Both boys had entirely normal appearance of their external genitalia. RESULTS The novel p.R451W mutation and five published missense CYP11A1 mutations were characterized employing two in vitro approaches using the natural substrate cholesterol and the intermediate 22R-hydroxycholesterol, respectively. Pregnenolone generation was measured by highly specific liquid chromatography tandem mass spectrometry. p.R451W had 30% of wild-type activity consistent with the clinical phenotype in our patients. Two previously published mutations (p.L222P and p.A359V) had 2- to 3-fold higher in vitro activities than originally reported, correlating better with the associated phenotypes. CONCLUSIONS We provide the first evidence that partial CYP11A1 deficiency has to be considered as a differential diagnosis in clinically isolated adrenal insufficiency. Our assays demonstrate a tighter genotype-phenotype correlation in CYP11A1 deficiency than previous in vitro studies.

A Diagnosis Not to Be Missed: Nonclassic Steroid 11β-Hydroxylase Deficiency Presenting With Premature Adrenarche and Hirsutism

CONTEXT Steroid 11β-hydroxylase (CYP11B1) deficiency (11OHD) is the second most common form of congenital adrenal hyperplasia. Milder nonclassic forms are rare and at risk to be missed. OBJECTIVE The objective of the study was to demonstrate the challenges in diagnosing nonclassic 11OHD. PATIENTS AND METHODS Patient 1, a 10-year-old boy, presented with high-normal blood pressure and previously unexplained exaggerated adrenarche from age 4 years. Previous tests at the age of 8 years showed normal 17-hydroxyprogesterone concentrations with increased androgens. Patient 2, a 14-year-old female, presented with facial hirsutism, primary amenorrhea, and high-normal blood pressure. Novel CYP11B1 mutations were functionally analyzed in transiently transfected COS7 cells measuring the conversion of 11-deoxycortisol to cortisol by liquid chromatography-tandem mass spectrometry. RESULTS Biochemical findings including urinary steroid metabolite analysis by gas chromatography-mass spectrometry were suggestive of 11OHD in all patients. CYP11B1 mutation analysis revealed compound heterozygosity in patient 1 (g.235T>A, p.F79I/g.2608C>T, p.R138C) and a homozygous mutation in patient 2 and two siblings (g.2623C>T, p.R143W). Functional in vitro analysis demonstrated partially impaired CYP11B1 activity compared with wild-type (p.F79I: 8.8% ± 0.8% (SEM); p.R138C: 9.8% ± 0.8%; p.R143W: 10.6% ± 1.2%). CONCLUSION In addition to nonclassic 21-hydroxylase deficiency and steroid-secreting tumors, nonclassic 11OHD should be considered as an important differential diagnosis in patients with unexplained hyperandrogenism without 46,XX disorder of sex development. Nonclassic 11OHD is likely to be missed when relying on measuring standard steroid hormone panels. This diagnosis needs to be established early in life to avoid long-term health problems such as short stature, hyperandrogenism-related metabolic complications, potentially severe arterial hypertension, and cardiovascular consequences.

Hypochondroplasia and acanthosis nigricans: a new syndrome due to the p.Lys650Thr mutation in the fibroblast growth factor receptor 3 gene?

BACKGROUND Hypochondroplasia (HCH) is a skeletal dysplasia inherited in an autosomal dominant manner due, in most cases, to mutations in the fibroblast growth factor receptor 3 (FGFR3). Acanthosis nigricans (AN) is a velvety and papillomatous pigmented hyperkeratosis of the skin, which has been recognized in some genetic disorders more severe than HCH involving the FGFR3 gene. OBJECTIVE AND DESIGN After initial study of the proband, who had been consulted for short stature and who also presented AN, the study was extended to the patients mother and to 12 additional family members. METHODS Clinical, biochemical and radiological studies were performed on the family. In addition, exons 11 and 13 of FGFR3 were analyzed. RESULTS The proband and ten relatives presented HCH plus AN and the analysis of FGFR3 showed the p.Lys650Thr mutation. The members with normal phenotypes were non-carriers of the mutation. CONCLUSION This is the first report of a large pedigree with the clinical phenotype of HCH plus AN due to a FGFR3 mutation, p.Lys650Thr. This finding demonstrates the coexistence of both conditions due to the same mutation and it might represent a true complex, which should be further established by searching for AN in mild HCH patients or for HCH in patients with AN.

Redefining the initiation and maintenance of zebrafish interrenal steroidogenesis by characterizing the key enzyme cyp11a2.

Zebrafish are emerging as a model to study steroid hormone action and associated disease. However, steroidogenesis in zebrafish is not well characterized. Mammalian P450 side-chain cleavage enzyme (CYP11A1) catalyzes the first step of steroidogenesis, the conversion of cholesterol to pregnenolone. Previous studies describe an essential role for zebrafish Cyp11a1 during early development. Cyp11a1 has been suggested to be the functional equivalent of mammalian CYP11A1 in the zebrafish interrenal gland (equivalent to the mammalian adrenal), gonad, and brain. However, reported cyp11a1 expression is inconsistent in zebrafish larvae, after active cortisol synthesis commences. Recently a duplicated cyp11a gene, cyp11a2, has been described, which shares an 85% identity with cyp11a1. We aimed to elucidate the specific role of the two cyp11a paralogs. cyp11a1 was expressed from 0 to 48 hours post-fertilization (hpf), whereas cyp11a2 expression started after the development of the interrenal primordium (32 hpf) and was the only paralog in larvae. cyp11a2 is expressed in adult steroidogenic tissues, such as the interrenal, gonads, and brain. In contrast, cyp11a1 was mainly restricted to the gonads. Antisense morpholino knockdown studies confirmed abnormal gastrulation in cyp11a1 morphants. cyp11a2 morphants showed impaired steroidogenesis and a phenotype indicative of metabolic abnormalities. The phenotype was rescued by pregnenolone replacement in cyp11a2 morphants. Thus, we conclude that cyp11a1 is required for early development, whereas cyp11a2 is essential for the initiation and maintenance of zebrafish interrenal steroidogenesis. Importantly, this study highlights the need for a comprehensive characterization of steroidogenesis in zebrafish prior to its implementation as a model organism in translational research of adrenal disease.

Genetic study of the hepcidin gene ( HAMP ) promoter and functional analysis of the c.-582A > G variant

BackgroundHepcidin acts as the main regulator of iron homeostasis through regulation of intestinal absorption and macrophage release. Hepcidin deficiency causes iron overload whereas its overproduction is associated with anaemia of chronic diseases. The aims of the study were: to identify genetic variants in the hepcidin gene (HAMP) promoter, to asses the associations between the variants found and iron status parameters, and to functionally study the role on HAMP expression of the most frequent variant.ResultsThe sequencing of HAMP promoter from 103 healthy individuals revealed two genetic variants: The c.-153C > T with a frequency of 0.014 for allele T, which is known to reduce hepcidin expression and the c.-582A > G with a 0.218 frequency for allele G. In an additional group of 224 individuals, the c.-582A > G variant genotype showed no association with serum iron, transferrin or ferritin levels.The c.-582G HAMP promoter variant decreased the transcriptional activity by 20% compared to c.-582A variant in cells from the human hepatoma cell line HepG2 when cotransfected with luciferase reporter constructs and plasmid expressing upstream stimulatory factor 1 (USF1) and by 12-14% when cotransfected with plasmid expressing upstream stimulatory factor 2 (USF2).ConclusionsThe c.-582A > G HAMP promoter variant is not associated with serum iron, transferrin or ferritin levels in the healthy population. The in vitro effect of the c.-582A > G variant resulted in a small reduction of the gene transactivation by allele G compared to allele A. Therefore the effect of the variant on the hepcidin levels in vivo would be likely negligible. Finally, the c.-153C > T variant showed a frequency high enough to be considered when a genetic analysis is done in iron overload patients.

Functional characterization of three CYP21A2 sequence variants (p.A265V, p.W302S, p.D322G) employing a yeast co-expression system.

Congenital adrenal hyperplasia (CAH) due to steroid 21‐hydroxylase (CYP21A2) deficiency is the commonest inborn error in steroid hormone biosynthesis. Functional in vitro assessment of mutant activity generally correlates well with clinical phenotype and therefore has contributed greatly to phenotype prediction in this CAH variant. Three CYP21A2 sequence variants (g.1641C>T, p.A265V; g.1752G>C, p.W302S; and g.2012A>G, p.D322G) identified in patients with non‐classic and simple virilizing CAH were characterized using a yeast co‐expression system and a computational three‐dimensional CYP21A2 model. Computational analysis of the mutants in the three‐dimensional structural model predicted no relevant effect of p.A265V, while p.W302S and p.D322G were predicted to impact significantly on enzyme function. Consistent with these findings, in vitro mutant analysis revealed enzyme activity similar to wild‐type for p.A265V, whereas p.W302S and p.D322G exerted activities compatible with simple virilizing and non‐classical CAH, respectively. The results indicate that p.A265V is an allelic variant rather than a disease‐causing amino acid change, whilst p.W302S and p.D322G could be confirmed as functionally relevant mutations. These findings emphasize the value of in vitro functional analysis of sequence variations in predicting genotype‐phenotype correlations and disease severity.