Diagnosis of phenylalanine hydroxylase deficiency (phenylketonuria)
H. K. Berry, M. H. Hsieh, M. K. Bofinger and W. K. Schubert
Needle liver biopsies were carried out on patients with phenylketonuria
(PKU) to establish a diagnosis either of partial or complete phenylalanine
hydroxylase (PH) deficiency. Ten phenylketonuric patients and two parents
were studied. Nine of the ten patients had completed a three-day oral
phenylalanine challenge. Each met the accepted criteria as having classic
PKU, based on a sustained rise in the serum phenylalanine level greater
than 20 mg/dL. A diagnosis of classic PKU was confirmed in six patients by
the absence of hepatic PH activity. Four of the PKU patients had PH
activity ranging from 9% to 24% of that found in liver from non-PKU control
subjects. The two parents had 27% and 42% of the PH activity found in the
control subjects; their child had no activity. Current methods for
distinguishing partial from complete PH deficiency are not always reliable,
and the degree of the deficiency can best be established by direct
measurement of the enzyme in liver.
