Non‐phenylketonuria hyperphenylalaninaemia in Northern Ireland: Frequent mutation allows screening and early diagnosis

Up to 10% of newborn children with a positive Guthrie test have non‐phenylketonuria hyperphenylalaninaemia, i.e., mild elevation of serum phenylalanine that does not require dietary treatment. Depending on the relative frequencies of different phenylalanine hydroxylase mutations in a particular population, non‐PKU HPA is usually caused by the combined effect of a mild HPA mutation and a severe PKU mutation. Presented here is a comprehensive analysis of non‐PKU HPA in Northern Ireland. Of particular interest is one prevalent HPA mutation (T380M), which is present in over 70% of non‐PKU HPA patients in Northern Ireland. Screening for this mutation is easy and inexpensive and can help confirm the diagnosis of non‐PKU hyperphenylalaninaemia in the majority of cases at a very early stage. This may be clinically useful and reassuring for the parents. Other mutations described are V245A, L194P, and E390G. © 1994 Wiley‐Liss, Inc.