Molecular Genetics and Genotype-Based Estimation of BH4-Responsiveness in Serbian PKU Patients: Spotlight on Phenotypic Implications of p.L48S
Phenylketonuria (PKU) is caused by mutations in the gene encoding phenylalanine hydroxylase (PAH) enzyme. Here, we report the updated spectrum of PAH mutations in 61 Serbian PKU patients. By using both DGGE/DNA sequencing and PCR-RFLP, we identified 26 disease-causing mutations (detection rate 99%). The most frequent ones were p.L48S (31%), p.R408W (16.4%), p.P281L (6%), p.E390G (5.2%), and p.I306V (5.2%). Homozygosity value indicated high heterogeneity of Serbian population.
To overcome possible pitfalls of patients’ phenotypic classification, we used two parameters: pretreatment/maximal phenylalanine blood concentration and Phe tolerance. The two phenotypes did not match only for patients with p.L48S. Therefore, we used Mann-Whitney statistical test to compare pretreatment/maximal blood Phe concentration and Phe tolerance detected in patients with p.[L48S];[null] and p.[missense];[null] genotypes. For patients with p.L48S, our results implied that Phe tolerance is a better parameter for phenotypic classification. Also, Fisher’s exact test was used to compare p.L48S effect on phenotype of homozygous and functionally hemizygous patients. Our findings showed that effect of p.L48S was altered in functional hemizygotes. Moreover, phenotypic inconsistency found in homozygotes suggested that interallelic complementation and/or additional factors play a role in genotype-phenotype correlation.
Since BH4-supplementation therapy is not available in Serbia, we made the first estimation of its potential benefit based on patients’ genotypes. In the analyzed cohort, the total frequency of BH4-responsive mutations was 52.6%. Furthermore, we found a significant number of genotypes (26.2% BH4-responsive and 51% probably BH4-responsive) that may respond to BH4 therapy. This led us to a conclusion that BH4-supplementation therapy could bring benefit to Serbian PKU patients.
This work has been funded by the Ministry of Education and Science, Republic of Serbia, grant No. III 41004.
- Eiken HG, Knappskog PM, Apold J (1993) Restriction enzyme-based assays for complete genotyping of phenylketonuria patients. Dev Brain Dysfunct 6:53–59Google Scholar
- Scriver CR, Levy H, Donlon J (2008) Hyperphenylalaninemia: phenylalanine hydroxylase deficiency. In: Valle D, Beaudet AL, Vogelstein B, Kinzler KW, Antonarakis S, Ballabio A (eds) Scriver CR, Childs B, Sly WS (eds emeritus) The online metabolic and molecular basis of inherited disease. McGraw-Hill, New York. Online Chapter 77 (www.ommbid.com)
- Trefz FK, Schmidt H, Bartholome K, Mahle M, Mathis P, Pecht G (1985) Differential diagnosis and significance of various hyperphenylalaninemias. In: Bickel H, Wachtel U (eds) Inherited diseases of amino acid metabolism. Thieme, Stuttgart, pp 86–100Google Scholar