Hsieh M C, Berry H K, Bofinger M K, Phillips P J, Guilfoile M B, Hunt M M
Clin Genet. 1983 Jun;23(6):415-21. doi: 10.1111/j.1399-0004.1983.tb01975.x.
Serum phenylalanine (phe) concentrations during and following phe challenges and liver phenylalanine hydroxylase (PH) activity were compared in 13 phenylketonuric (PKU) patients. These patients were separated into two groups: eight patients with no detectable PH activity (PH degrees) and five patients with residual PH activity (PH-) ranging from 9 to 24% of the activity obtained in 10 non-PKU subjects. The rise in serum phe concentration during 3 days of oral loading did not differentiate the two groups. However, the difference in serum phe concentration of the PH degrees and PH- groups reached statistical significance at 24 h postloading (p less than 0.01). We concluded that combined results from multiple measurements during the oral challenge, namely serum phe concentration after termination of loading, serum phe clearance rate, post-loading phe tolerance index and urinary metabolite excretion, make a better indicator for predicting residual PH activity for the majority of PKU subjects than peak phe concentrations during phe challenge.
