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ABSTRACT: Lipoid congenital adrenal hyperplasia (Lipoid CAH) is the most severe form of the autosomal recessive disorder CAH. A general loss of the steroid biosynthetic activity caused by defects in the StAR gene manifests as life-threatening primary adrenal insufficiency. We report a case of Lipoid CAH caused by a so far not described homozygous deletion of the complete StAR gene and provide diagnostic results based on a GC-MS steroid metabolomics and molecular genetic analysis. The patient presented with postnatal hypoglycemia, vomiting, adynamia, increasing pigmentation and hyponatremia. The constellation of urinary steroid metabolites suggested Lipoid CAH and ruled out all other forms of CAH or defects of aldosterone biosynthesis. After treatment with sodium supplementation, hydrocortisone and fludrocortisone the child fully recovered. Molecular genetic analysis demonstrated a homozygous 12.1 kb deletion in the StAR gene locus. The breakpoints of the deletion are embedded into two typical genomic repetitive Alu Sx elements upstream and downstream of the gene leading to the loss of all exons and regulatory elements. We established deletion-specific and intact allele-specific PCR methods and determined the StAR gene status of all available family members over three generations. This analysis revealed that one of the siblings, who died a few weeks after birth, carried the same genetic defect. Since several Alu repeats at the StAR gene locus increase the probability of deletions, patients with typical symptoms of lipoid CAH lacking evidence for the presence of both StAR alleles should be analyzed carefully for this kind of disorder.
The Journal of steroid biochemistry and molecular biology 01/2012; 130(1-2):1-6. · 2.66 Impact Factor
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ABSTRACT: Aldosterone synthase deficiency (ASD) is an important differential diagnosis of diseases associated with salt wasting in early infancy.
The objective of this study was to investigate the molecular basis for the disorder by (1) molecular genetic analysis in the CYP11B2 from patients suffering from ASD type I. (2) Functional characterization of the missense mutant gene products. (3) Structural simulation of the missense mutations.
Patient 1 was a homozygous carrier of a novel mutation located in exon 4 causing a premature stop codon (p.W260X). Patient 2 was analyzed to be compound heterozygous for two novel mutations: The first was an insertion mutation (p.G206WfsX51), and the second was a deletion mutation (p.L496SfsX169). Two siblings (patients 3 and 4) were compound heterozygous carriers of two novel missense mutations (p.S315R, p.R374W). The expression studies of the mutant proteins in COS-1 cells showed a complete absence of CYP11B2 activity of p.S315R and p.R374W mutants for the conversion of 11-deoxycorticosterone to aldosterone. A 3-D model of CYP11B2 p.S315R and p.R374W indicated a change of the hydrogen bond network which might explain the cause of the dysfunction.
We have identified the first CYP11B2 gene defects in two Polish families associated with phenotypes of ASD type I. Analysis of the enzymatic function as a complementary procedure to genotyping revealed data for understanding the clinical phenotype of ASD. Molecular modeling of the mutated enzyme provided a rational basis for understanding the changed activities of the mutant proteins.
Molecular Genetics and Metabolism 08/2010; 100(4):357-64. · 3.19 Impact Factor
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ABSTRACT: Three siblings of Pakistani origin presented neonatally with isolated hyperreninemic hypoaldosteronism and were well controlled on fludrocortisone therapy during childhood and adolescence.
These individuals were reevaluated as adults after fludrocortisone withdrawal to investigate the biochemical and molecular basis of their disorder.
When reassessed off fludrocortisone treatment, hyperreninemic hypoaldosteronism was confirmed in all subjects but with significant hyperkalemia in only one case. Profiling of urinary steroid metabolites showed a biochemical pattern (elevated tetrahydrocorticosterone to 18-hydroxytetrahydro-11-dehydrocorticosterone ratio but normal 18-hydroxytetrahydro-11-dehydrocorticosterone to tetrahydroaldosterone ratio) consistent with partial type 1 aldosterone synthase deficiency. Sequencing of the CYP11B2 gene showed that affected subjects were homozygous for a single nucleotide substitution (T925C) in exon 5, corresponding to a serine to proline mutation (S308P) in the predicted protein, with unaffected family members being heterozygous. Consistent with structural modeling showing that the mutated residue is located within the alpha-helix I, close to the hemebinding, active site of the enzyme, functional characterization of the S308P mutant protein in vitro showed complete loss of enzyme activity. However, administration of dexamethasone further reduced levels of circulating aldosterone and its urinary metabolites in affected subjects, suggesting that some mineralocorticoid biosynthesis occurs in vivo.
We have identified the first CYP11B2 gene defect in a family of Asian origin, associated with a type 1 aldosterone synthase deficiency phenotype. Preservation of some aldosterone production suggests either residual mutant CYP11B2 enzyme activity in vivo or mineralocorticoid biosynthesis via an alternative pathway.
The Journal of clinical endocrinology and metabolism 01/2009; 94(3):914-9. · 6.50 Impact Factor
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ABSTRACT: Isolated hypoaldosteronism is a rare cause of salt wasting in infancy and may be life-threatening, especially in the newborn infant. In a 3wk-old-boy with hyponatremia and hyperkalemia a GC-MS steroid profile on a spot urinary sample showed no 18-oxygenated steroid metabolites indicative for aldosterone synthase deficiency type I. Sequence analysis of the CYP11B2 gene revealed that the patient was homozygous for a novel missense mutation (L451F) caused by a T to C transition at position c.1351 in exon 8, whereas each non-symptomatic parent possessed only one mutated allele. The mutant cDNA was transiently expressed in a human cell line, HCT116 p53(-/-), and activity of the expressed protein optimized by co-expression of different adrenodoxin species, showing complete aldosterone deficiency with 11-deoxycorticosterone or corticosterone as substrates. The L451F mutation is the first mutation found located immediately adjacent to the highly conserved heme-binding C450 of the cytochrome P450. Computer modeling shows that replacement of leucine by phenylalanine leads to a steric effect in the immediate vicinity of the heme thereby preventing the activity of CYP11B2. Thus, by combining highly sensitive hormone detection in a spot urine sample with expression of the mutated cDNA in cell culture the phenotype of the patient can be correlated with a particular molecular defect.
Molecular Genetics and Metabolism 05/2008; 93(4):458-67. · 3.19 Impact Factor
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ABSTRACT: 11-beta-hydroxylase deficiency (11betaOHD) is caused by CYP11B1 gene defects and leads to congenital adrenal hyperplasia associated with hypertension. Recently, a novel L299P mutation has been described in a compound heterozygous male individual. We observed two 46,XX siblings with a homozygous L299P mutation and investigated the functional properties of this CYP11B1 variant.
The index patient from a consanguineous Turkish family showed complete external virilization and was diagnosed incidentally at the age of 19 months during hospital admission for severe combined bacterial (urosepsis) and viral (CMV and EBV) infection. The younger sibling was diagnosed at the age of 5 months. Their genital phenotype was identical and both demonstrated borderline elevated blood pressure.
Biochemical findings revealed 11betaOHD. A homozygous L299P mutation of the CYP11B1 gene was detected. In vitro expression studies performed in HCT116 cells showed a markedly decreased CYP11B1 activity in the L299P mutant (1.6 +/- 0.8%) for the conversion of 11-deoxycortisol to cortisol.
Our study provides clear data on the functional properties and clinical phenotype in 46,XX individuals homozygous for this point mutation. Adrenal insufficiency might have contributed to the severe infectious disease that was present in the index patient at diagnosis.
Hormone Research 02/2008; 70(3):145-9. · 2.48 Impact Factor
