NcoI and HinfI RFLPs detected with a dihydropteridine reductase cDNA probe

Tetrahydrobiopterin-deficient hyperphenylalaninemia in the Chinese

BACKGROUND

Hyperphenylalaninemia (HPA) may be caused by either a deficiency in phenylalanine-4-hydroxylase or in tetrahydrobiopterin (BH4), the essential cofactor required for the hydroxylation of aromatic amino acids. The most common forms of BH4 deficiency are 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency (MIM 261640) and dihydropteridine reductase (DHPR) deficiency (MIM 261630), which require a different treatment from classical HPA.

RESULTS

Approximately 86% of BH4-deficient HPA in the Chinese population was found to be caused by PTPS deficiency. Eleven missense (73C-->G, 120T-->G, 155A-->G, 166G-->A, 200C-->T, 209T-->A, 226C-->T, 259C-->T, 286G-->A, 317C-->T, 430G-->C), one splicing (IVS3+1G-->A) and two deletion mutations (116-119delTGTT, 169-171delGTG) were identified in 37 unrelated PTPS-deficient Chinese families. Among these, 155A-->G, 259C-->T and 286G-->A mutation accounted for about 80% of the mutant alleles. The 155A-->G and 286G-->A mutations were found to be the common mutation in southern and northern Chinese, respectively. Only two Chinese DHPR-deficient families were detected among about 300 Chinese hyperphenylalaninemia cases. A single base transition 508G-->A on the DHPR cDNA was identified in two consanguineous DHPR-deficient siblings. A reduced level of DHPR mRNA expression was found in the other DHPR-deficient patient, which suggested that the mutation might lie in the regulatory region of the DHPR gene.

CONCLUSIONS

The BH4-deficient HPA was estimated to make up around 30% of the Chinese population in Taiwan suffering from HPA, which is much higher than in Caucasian populations (1.5-2% of HPA).

Restriction fragment length polymorphisms among Japanese detected with a dihydropteridine reductase cDNA gene probe

Using a human dihydropteridine reductase (DHPR) cDNA, the frequency of restriction fragment length polymorphisms (RFLPs) with restriction endonucleases AvaII, MspI, NcoI and HinfI was estimated in unrelated, unaffected Japanese. The allele frequencies are different from those found in Caucasians, especially with MspI and HinfI. However, approximately 60% of Japanese are heterozygous for at least one of the RFLPs and analysis of one family with DHPR deficiency was shown to be informative. RFLP linkage analysis will be useful in the Japanese population as previously reported for Caucasians.