Five novel mutations and two large deletions in a population analysis of the phenylalanine hydroxylase gene

Mutational spectrum of the phenylalanine hydroxylase (PAH) deficiency was investigated in 107 families (90% of the Slovene PKU population). The entire coding region of the PAH gene was analyzed with dHPLC to select the samples where subsequently the automated sequencing analysis was performed. MLPA analysis was performed to identify large deletions, which were later confirmed with long-range PCR. Correlations with patients' phenotypes and genotype-based predictions of BH4-responsiveness were assessed. Altogether, disease-causing mutations were identified on 209 alleles (detection rate 97.7%). A spectrum of 36 different disease-causing mutations was identified: 20 missense mutations (80% of the alleles), eight splicing mutations (13% of the alleles), one nonsense mutation (0.5% of the alleles), four small deletions with frame shift (6% of the alleles), one small insertion with frame shift (0.5% of the alleles), and two large deletions (2% of the alleles). The most frequent mutation was p.R408W in exon 12, representing 29% of the alleles, which is in concordance with other neighboring and/or Slavic PKU populations. Other common mutations were: p.R158Q, p.A403V, p.P281L and p.E390G, accounting for 9%, 7%, 7% and 7% of the alleles respectively. Five novel mutations were detected: c.43_44insAG, c.56_59+1delACAGG, p.V45A, p.L62P and p.R157S. Large deletion of exon 5 (EX5del955) was found in three patients and a deletion of exon 3 (EX3del4765) in one patient. A spectrum of 64 different genotypes was found, seven of them accounting for over than a third of all families. Among thirteen families with homozygous mutation (13% of the PKU population), 10 had p.R408W, two had p.R158Q and one had p.E390G. Among 107 families, 58 were classified as classic PKU (54.2%), 28 as mild PKU (25.9%) and 21 as MHP (19.6%). Twenty-six different genotypes (40.6%) were predicted to be BH4-responsive, represented by 38 different families (35.5%).

► A spectrum of 36 mutations was identified, five of them were novel.
► Two large deletions were identified in 2% of the alleles.
► A spectrum of 64 different genotypes was identified.
► Over 35% of the families were predicted to be BH4-responsive.