Genotype-predicted tetrahydrobiopterin (BH4)-responsiveness and molecular genetics in Croatian patients with phenylalanine hydroxylase (PAH) deficiency.
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.
Karacić
Iva
I
School of Medicine, Zagreb, Croatia.
Meili
David
D
Sarnavka
Vladimir
V
Heintz
Caroline
C
Thöny
Beat
B
Ramadza
Danijela Petković
DP
Fumić
Ksenija
K
Mardesić
Dusko
D
Barić
Ivo
I
Blau
Nenad
N
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*
D001708:Biopterins; D010651:Phenylalanine Hydroxylase; C003402:sapropterin