Absent phenylalanine hydroxylase activity without phenylketonuria

Abstract

A male infant is described who never manifested phenylketonuria even though phenylalanine hydroxylase activity was undetectable in liver tissue. Plasma phenylalanine were elevated in the range typical of PKU patients when the baby was at breast and declined with institution of a low phenylalanine diet. Physical and psychomotor development were normal with the baby on the latter treatment. The results indicate that the absence of phenylketonuria does not rule out phenylalanine hydroxylase activity.

Comparative diagnostic value of phenyla‐lanine challenge and phenylalanine hydroxylase activity in phenylketonuria

“…Her diagnostic serum phe concentration at 2 weeks of age was 3.6 mM (59 mg/dL), yet her serum phe has been relatively easy to control. These data are similar to those reported by Yudkoff & Segal (1980) who found no detectable hepatic PH activity in a male child who excreted no phenylalanine metabolites when plasma phe levels exceeded 1.2 mM (20 mg/dL). Bartholome et al (1975) likewise noted one patient with no detectable activity on two separate biopsies whose peak serum phe following standard challenge was 0.79 mM (13 mg/dL).…”