Hyperphenylalaninemia in the Czech Republic: genotype-phenotype correlations and in silico analysis of novel missense mutations.

BACKGROUND: Hyperphenylalaninemia (HPA) is one of the most common inherited metabolic disorders caused by deficiency of the enzyme phenylalanine hydroxylase (PAH). HPA is associated with mutations in the PAH gene, which leads to reduced protein stability and/or impaired catalytic function. Currently, almost 700 different disease-causing mutations have been described. The impact of mutations on enzyme activity varies ranging from classical PKU, mild PKU, to non-PKU HPA phenotype. METHODS: We provide results of molecular genetic diagnostics of 665 Czech unrelated HPA patients, structural analysis of missense mutations associated with classical PKU and non-PKU HPA phenotype, and prediction of effects of 6 newly discovered HPA missense mutations using bioinformatic approaches and Molecular Dynamics simulations. RESULTS: Ninety-eight different types of mutations were indentified. Thirteen of these were novel (6 missense, 2 nonsense, 1 splicing, and 4 small gene rearrangements). Structural analysis revealed that classical PKU mutations are more non-conservative compared to non-PKU HPA mutations and that specific sequence and structural characteristics of a mutation might be critical when distinguishing between non-PKU HPA and classical PKU mutations. The greatest impact was predicted for the p.(Phe263Ser) mutation while other novel mutations p.(Asn167Tyr), p.(Thr200Asn), p.(Asp229Gly), p.(Leu358Phe), and p.(Ile406Met) were found to be less deleterious.

Identification of CYP21A2 mutant alleles in Czech patients with 21-hydroxylase deficiency.

Congenital adrenal hyperplasia (CAH) is comprised of a group of autosomal recessive disorders caused by an enzymatic deficiency which impairs the biosynthesis of cortisol and, in most of the severe cases, also the biosynthesis of aldosterone. Approximately 90-95% of all the CAH cases are due to mutations in the steroid 21-hydroxylase gene (CYP21A2). In this study, the molecular genetic analysis of CYP21A2 was performed in 267 Czech probands suspected of 21-hydroxylase deficiency (21OHD). 21OHD was confirmed in 241 probands (2 mutations were detected). In 26 probands, a mutation was found only in 1 CYP21A2 allele. A set of 30 different mutant alleles was determined. We describe i) mutated CYP21A2 alleles carrying novel point mutations (p.Thr168Asn, p.Ser169X and p.Pro386Arg), ii) mutated CYP21A2 alleles carrying the novel chimeric gene designated as CH-7, which was detected in 21.4% of the mutant alleles, iii) an unusual genotype with a combination of the CYP21A2 duplication, 2 point mutations and the CYP21A2 large-scale gene conversion on the second allele, and (iv) a detailed analysis of the chimeric CYP21A1P/CYP21A2 genes. In conclusion, our genotyping approach allowed for the accurate identification of the CYP21A2 gene mutations in 21OHD patients and their families and provided some useful information on diagnosis and genetic counselling.

Wilson disease as a cause of liver injury in cystic fibrosis.

Cystic fibrosis-related liver disease affects approximately one third of all patients with cystic fibrosis. Initial signs of other liver diseases including the genetically determined disorders of the liver co-inherited with cystic fibrosis may be obscured by or ascribed to cystic fibrosis-related liver disease. We report a patient shown to suffer simultaneously from cystic fibrosis and hepatic Wilson disease. Our case documents that in patients with cystic fibrosis presenting with liver disease, when unusual clinical and/or laboratory abnormalities appear and fail to respond to standard therapy, a second disease, including rare inherited metabolic disorders such as the hepatic form of Wilson disease or alpha(1)-antitrypsin deficiency, should be suspected.