Effect of BH4 on blood phenylalanine and tyrosine variations in patients with phenylketonuria.

BACKGROUND: In patients with phenylketonuria, stability of blood phenylalanine and tyrosine concentrations might influence brain chemistry and therefore patient outcome. This study prospectively investigated the effects of tetrahydrobiopterin (BH4), as a chaperone of phenylalanine hydroxylase on diurnal and day-to-day variations of blood phenylalanine and tyrosine concentrations. METHODS: Blood phenylalanine and tyrosine were measured in dried blood spots (DBS) four times daily for 2 days (fasting, before lunch, before dinner, evening) and once daily (fasting) for 6 days in a randomized cross-over design with a period with BH4 and a period without BH4. The sequence was randomized. Eleven proven BH4 responsive PKU patients participated, 5 of them used protein substitutes during BH4 treatment. Natural protein intake and protein substitute dosing was adjusted during the period without BH4 in order to keep DBS phenylalanine levels within target range. Patients filled out a 3-day food diary during both study periods. Variations of DBS phenylalanine and Tyr were expressed in standard deviations (SD) and coefficient of variation (CV). RESULTS: BH4 treatment did not significantly influence day-to-day phenylalanine and tyrosine variations nor diurnal phenylalanine variations, but decreased diurnal tyrosine variations (median SD 17.6 µmol/l, median CV 21.3%, p = 0.01) compared to diet only (median SD 34.2 µmol/l, median CV 43.2%). Consequently, during BH4 treatment diurnal phenylalanine/tyrosine ratio variation was smaller, while fasting tyrosine levels tended to be higher. CONCLUSION: BH4 did not impact phenylalanine variation but decreased diurnal tyrosine and phenylalanine/tyrosine ratio variations, possibly explained by less use of protein substitute and increased tyrosine synthesis.

Screening of a healthy newborn identifies three adult family members with symptomatic glutaric aciduria type I.

We report three adult sibs (one female, two males) with symptomatic glutaric acidura type I, who were diagnosed after a low carnitine level was found by newborn screening in a healthy newborn of the women. All three adults had low plasma carnitine, elevated glutaric acid levels and pronounced 3-hydroxyglutaric aciduria. The diagnosis was confirmed by undetectable glutaryl-CoA dehydrogenase activity in lymphocytes and two pathogenic heterozygous mutations in the GCDH gene (c.1060A > G, c.1154C > T). These results reinforce the notion that abnormal metabolite levels in newborns may lead to the diagnosis of adult metabolic disease in the mother and potentially other family members.