Immune function in children with classical phenylketonuria and tetrahydrobiopterin deficiencies.

[classical phenylketonuria]

An increased susceptibility to infections has been observed in some patients with phenylketonuria (PKU ), which is not well known whether it is due to alterations of plasma essential amino acid concentrations or to some other factors .This study is designed to establish B cell and T cell functions in 44 children with classical PKU and tetrahydrobiopterin (BH 4 ) deficiencies and the effects of too high plasma phenylalanine (PA ) concentrations (16 .53 to 30 .54 mg /dL ) on the same parameters .B and T cell functions of 33 children with classical PKU (divided into two groups based on fasting mean plasma PA concentrations : Group -I = 20 .9 +/- 3 .7 mg /dL , Group -II = 3 .8 +/- 1 .02 mg /dL ), and 11 children with BH 4 deficiencies (Group III ) were studied . The results were compared between the groups and referenced with previously reported values from healthy controls .Delayed type skin hypersensitivity responses to purified protein derivative (PPD ) in Group I and phytohaemagglutinin (PHA ) in Group I , III were lower than the other groups and healthy controls . Plasma IgG and IgM concentrations of Group I was lower than the reference values . Although mean serum zinc and iron levels of all patients were lower than published values of healthy children , zinc and iron deficiencies in Group I , III were much more prominent as compared to Group II .The somewhat low plasma IgG concentrations in Group I may be related to the very high plasma PA levels , however the role of zinc deficiency as a causal factor can not be ruled out . BH 4 metabolism defects do not appear to affect the same parameters . Impaired delayed skin hypersensitivity responses in Group I and III can be explained by severe serum zinc deficiency . In the light of this study , we conclude that in order to establish a causal relationship between PKU and immune functions , further studies need to be conducted after the correction of micro-nutrient status of such children .