title: Genotype-predicted tetrahydrobiopterin (BH4)-responsiveness and molecular genetics in Croatian patients with phenylalanine hydroxylase (PAH) deficiency.
abstract: Specific mutations in the gene encoding phenylalanine hydroxylase (PAH), located on chromosome 12q22-24.1, are linked to tetrahydrobiopterin (BH4; sapropterin)-responsive phenylketonuria (PKU). Diagnosis is usually done through the newborn screening for PKU, followed by a BH4 loading test. So far, more than 60 mutant alleles, presenting with a substantial residual PAH activity (average approximately 47%), were identified in more than 500 patients worldwide. We investigated the predictive value of BH4-responsive PAH mutations in Croatian population. From a group of 127 PKU patients, 62 were selected (based on the genotype) as potentially BH4-responsive and 39 loaded with BH4 (20 mg/kg). The overall frequency of BH4-responsiveness (>30% blood phenylalanine reduction within 24 h) was 36% (14 out of 39 patients with 23 different genotypes), significantly less than expected. The best responders were patients with mild hyperphenylalaninemia (4/4; 100%), followed by mild PKU (8/9; 89%), and classical PKU (2/26; 8%). The most common BH(4)-responsive genotypes were p.E390G/p.R408W and p.P281L/p.E390G. These genotypes correspond for approximately >30% residual PAH activity. The p.E390G mutation was 100% associated with BH4-responsiveness, regardless of the second allele (p.R408W, p.P281L, p.F55Lfs, p.L249P). With regard to the predicted relative PAH activity of recombinantly expressed mutant alleles, there was a significant (p<0.002) difference between BH4-responders and non-responders. In a general Croatian PKU population, disease-causing mutations were identified on 226 alleles (99%). There were 35 different mutations: 21 missense, 8 splice site, 3 nonsense, 2 single nucleotide deletions, and 1 in-frame deletion. Four mutations are reported for the first time: p.E76D, p.L333P, p.G346E, and IVS8-2A>G. Five mutations accounted for over two-thirds of investigated alleles: p.L48S, p.R261Q, p.P281L, p.E390G, and p.R408W. Thus, the Croatian PKU population seems to be more homogenous than some other Mediterranean or Central European populations. This study reveals the importance of a full genotype for the prediction of BH4-responsiveness. In contrast to previous assumption and with exception of the p.E390G mutation, single allele mutations are not reliable for the selection of potential PKU candidates for pharmacological therapy with BH4.
authors.affiliation: School of Medicine, Zagreb, Croatia.
authors.forename: Iva
authors.initials: I
authors.lastname: Karacić
authors.forename: David
authors.initials: D
authors.lastname: Meili
authors.forename: Vladimir
authors.initials: V
authors.lastname: Sarnavka
authors.forename: Caroline
authors.initials: C
authors.lastname: Heintz
authors.forename: Beat
authors.initials: B
authors.lastname: Thöny
authors.forename: Danijela Petković
authors.initials: DP
authors.lastname: Ramadza
authors.forename: Ksenija
authors.initials: K
authors.lastname: Fumić
authors.forename: Dusko
authors.initials: D
authors.lastname: Mardesić
authors.forename: Ivo
authors.initials: I
authors.lastname: Barić
authors.forename: Nenad
authors.initials: N
authors.lastname: Blau
mesh_terms: D000293:Adolescent; D000328:Adult; D000483:Alleles; D001708:Biopterins / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D002648:Child; D002675:Child, Preschool; D017523:Croatia; D005260:Female; D005838:Genotype; D006801:Humans; D007223:Infant; D008297:Male; D009154:Mutation / Q000235:genetics; D010651:Phenylalanine Hydroxylase / Q000172:deficiency* / Q000235:genetics*; D044465:White People / Q000235:genetics*
chemical_list: D001708:Biopterins; D010651:Phenylalanine Hydroxylase; C003402:sapropterin