Splicing analysis of CYP11B1 mutation in a family affected with 11β-hydroxylase deficiency: case report

Identification and functional characterization of compound heterozygous CYP11B1 gene mutations

PURPOSE

11β-Hydroxylase deficiency (11β-OHD) is the second leading cause of congenital adrenal hyperplasia (CAH), a rare autosomal recessive disease caused by mutations in the CYP11B1 gene. We previously reported the case of a male Chinese patient with typical 11β-OHD symptoms. Sanger sequencing revealed that the patient carried a splice-site mutation, c.595+1G>A in the CYP11B1 gene. His mother and sister harbored the heterozygous mutation, c.595+1G>A. Paradoxically, Sanger sequencing did not detect any abnormality in the CYP11B1 gene of his father and brother. Therefore, in this study, we aimed to further explore the exact genetic etiology of 11β-OHD in this pedigree and analyze the functional consequence of the c.595+1G>A mutation.

METHODS

Gemomic DNA was extracted from the peripheral blood leukocytes of the family members and normal control individuals, followed by quantitative real-time polymerase chain reaction (qPCR) to detect the copy number of the target CYP11B1 gene fragment. Mutation analysis was also performed via whole-exome sequencing (WES) followed by Sanger sequencing validation. In vitro minigene assay was also performed to investigate the impact of the c.595+1G>A mutation on pre-mRNA splicing.

RESULTS

qPCR results suggested a heterozygous deletion encompassing position c.595+1 along with flanking exonic and intronic sequences in the CYP11B1 gene of the patient and his father. WES followed by Sanger sequencing verified that the patient carried compound heterozygous mutations in the CYP11B1 gene, including a novel 2840-bp deletion (c.395+661_c.1121+180del) and c.595+1G>A, while his father carried the heterozygous c.395+661_c.1121+180del mutation. No other novel CYP11B1 mutations were found in the rest of the family members. Furthermore, minigene assay revealed that the c.595+1G>A mutation resulted in a 70-bp deletion of exon 3 in the mRNA, and this altered the reading frame at amino acid 176 and created a premature stop codon at amino acid 197.

CONCLUSION

We identified a novel 2840-bp-sized large deletion and confirmed that the c.595+1G>A mutation disrupts normal pre-mRNA splicing. Either mutation could significantly alter the reading frame and abolish CYP11B1 enzyme activity. Therefore, our findings widen the mutation spectrum of CYP11B1 and provide an accurate diagnosis of 11β-OHD at a molecular genetic level.

Compound heterozygosity of a novel Q73X mutation and a known R141X mutation in CYP11B1 resulting in 11β-hydroxylase deficiency in a Chinese boy with congenital adrenal hyperplasia

Steroid 11β-hydroxylase deficiency (11β-OHD), which is caused by mutations of the CYP11B1 gene, is the second leading cause of congenital adrenal hyperplasia (CAH), an autosomal recessive inherited disorder. Here, we report a case of classic 11β-OHD in a Chinese boy characterized by hypertension, penile enlargement, skin pigmentation, and acne. Molecular analysis of CYP11B1 revealed that the patient was compound heterozygous for a c.217C > T (p.Q73X) mutation in exon 1 and a c.421C > T (p.R141X) mutation in exon 3. His parents carried the novel c.217C > T (p.Q73X) mutation and the prevalent c.421C > T (p.R141X) mutation. Furthermore, we identified a novel 217-bp substitution mutation (Q73X) in CYP11B1 that generates a truncated protein without biological activity, which is likely to be pathogenic. Pursuant to the phenotype of the proband and his family, the Q73X mutation is inferred to exacerbate the disease burden of the R141X mutation, a known pathogenic variant. To further explore this possibility, selecting the x-ray structure of human CYP11B2 as a template, we built three-dimensional homologous models of the normal and mutant proteins. In the mutant model, a change from a helix to terminal structure in amino acids 73 and 141 occurred that affected the binding capacity of CYP11B1 with heme and impaired 11β-hydroxylase activity. Taken together, our findings expand the spectrum of known mutations leading to 11β-OHD and provide evidence to study genotype-phenotype concordance, confirm early diagnosis and treatment of 11β-OHD, and prevent most complications.

46,XX DSD due to Androgen Excess in Monogenic Disorders of Steroidogenesis: Genetic, Biochemical, and Clinical Features

The term 'differences of sex development' (DSD) refers to a group of congenital conditions that are associated with atypical development of chromosomal, gonadal, or anatomical sex. Disorders of steroidogenesis comprise autosomal recessive conditions that affect adrenal and gonadal enzymes and are responsible for some conditions of 46,XX DSD where hyperandrogenism interferes with chromosomal and gonadal sex development. Congenital adrenal hyperplasias (CAHs) are disorders of steroidogenesis that mainly involve the adrenals (21-hydroxylase and 11-hydroxylase deficiencies) and sometimes the gonads (3-beta-hydroxysteroidodehydrogenase and P450-oxidoreductase); in contrast, aromatase deficiency mainly involves the steroidogenetic activity of the gonads. This review describes the main genetic, biochemical, and clinical features that apply to the abovementioned conditions. The activities of the steroidogenetic enzymes are modulated by post-translational modifications and cofactors, particularly electron-donating redox partners. The incidences of the rare forms of CAH vary with ethnicity and geography. The elucidation of the precise roles of these enzymes and cofactors has been significantly facilitated by the identification of the genetic bases of rare disorders of steroidogenesis. Understanding steroidogenesis is important to our comprehension of differences in sexual development and other processes that are related to human reproduction and fertility, particularly those that involve androgen excess as consequence of their impairment.

Prevalence, clinical characteristics and long-term outcomes of classical 11 β-hydroxylase deficiency (11BOHD) in Turkish population and novel mutations in CYP11B1 gene

Congenital adrenal hyperplasia (CAH) due to 11β-hydroxylase deficiency (11BOHD) is a rare autosomal recessive disorder and the second most common form of CAH.

AIM

To investigate genotype-phenotype correlation and to evaluate clinical characteristics and long-term outcomes of patients with 11BOHD.

METHODS

A total of 28 patients (n = 14, 46,XX; n = 14, 46,XY) with classical 11BOHD from 25 unrelated families were included in this study. Screening of CYP11B1 is performed by Sanger sequencing. Pathogenic features of novel variants are investigated by the use of multiple in silico prediction tools and with family based co-segregation studies. Protein simulations were investigated for two novel coding region alterations.

RESULTS

The age at diagnosis ranged from 6 days to 12.5 years. Male patients received diagnose at older ages than female patients. The rate of consanguinity was high (71.4%). Five out of nine 46,XX patients were diagnosed late (age 2-8.7 years) and were assigned as male due to severe masculinization. Twenty one patients have reached adult height and sixteen were ultimately short due to delayed diagnosis. Two male patients had testicular microlithiasis and 5 (35.7%) patients had testicular adrenal rest tumor during follow up. Four patients (28.6%) had gynecomastia. Mutation analyses in 25 index patients revealed thirteen different mutations in CYP11B1 gene, 4 of which were novel (c.393 + 3A > G, c.428G > C, c.1398 + 2T > A, c.1449_1451delGGT). The most frequent mutations were c.896T > C with 32%, c.954G > A with 16% and c.1179_1180dupGA with 12% in frequency. There was not a good correlation between genotype and phenotype; phenotypic variability was observed among the patients with same mutation.

CONCLUSION

This study presents the high allelic heterogeneity of CYP11B1 mutations in CAH patients from Turkey. Three dimensional protein simulations may provide additional support for the pathogenicity of the genetic alterations. Our results provide reliable information for genetic counseling, preventive and therapeutic strategies for the families.

Congenital adrenal hyperplasia due to 11-hydroxylase deficiency-Compound heterozygous mutations of a prevalent and two novel CYP11B1 mutations

11β-hydroxylase deficiency (11β-OHD) occurs in about 5-8% of congenital adrenal hyperplasia (CAH). In this study, we identified three CYP11B1 (encoding Cytochrome P450 11B1) heterozygous mutations: c.1358G>C (p.R453Q), c.1229T>G (p.L410R) and c.1231G>T (p.G411C) in a Chinese CAH patient due to classic 11β-OHD. His parents were healthy and respectively carried the prevalent mutation c.1358G>C (p.R453Q), and the two novel mutations c.1229T>G (p.L410R) and c.1231G>T (p.G411C). In vitro expression studies, immunofluorescence demonstrated that wild type and mutant (L410R and G411C) proteins of CYP11B1 were correctly expressed on the mitochondria, and enzyme activity assay revealed the mutant reduced the 11-hydroxylase activity to 10% (P<0.001) for the conversion of 11β-deoxycortisol to cortisol. Subsequently, three dimensional homology models for the normal and mutant proteins were built by using the x-ray structure of the human CYP11B2 as a template. Interestingly, in the heme binding site I helix, a change from helix to loop in four amino acide took place in the mutant model. In conclusion, this study expands the spectrum of mutations in CYP11B1 causing to 11β-OHD and provides evidence for prenatal diagnosis and genetic counseling. In addition, our results confirm the two novel CYP11B1 mutations led to impaired 11-hydroxylase activity in vitro.

CDHR1 mutations in retinal dystrophies

We report ophthalmic and genetic findings in patients with autosomal recessive retinitis pigmentosa (RP), cone-rod dystrophy (CRD) or cone dystrophy (CD) harboring potential pathogenic variants in the CDHR1 gene. Detailed ophthalmic examination was performed in seven sporadic and six familial subjects. Mutation screening was done using a customized next generation sequencing panel targeting 105 genes implicated in inherited retinal disorders. In one family, homozygosity mapping with subsequent candidate gene analysis was performed. Stringent filtering for rare and potentially disease causing variants following a model of autosomal recessive inheritance led to the identification of eleven different CDHR1 variants in nine index cases. All variants were novel at the time of their identification. In silico analyses confirmed their pathogenic potential. Minigene assays were performed for two non-canonical splice site variants and revealed missplicing for the mutant alleles. Mutations in CDHR1 are a rare cause of retinal dystrophy. Our study further expands the mutational spectrum of this gene and the associated clinical presentation.