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Immune function in children with classical phenylketonuria and tetrahydrobiopterin deficiencies
Tevfik Karagoz1, Turgay Coskun, Imran Ozalp
1Nutrition and Metabolism Unit, Department of Pediatrics, Hacettepe University Faculty of Medicine, Sihhiye, Ankara 06100, Turkey. ktevfik@ hotmail.com
Insights
Phenylketonuria (PKU) patients with high phenylalanine (PA) levels show impaired immune responses, potentially linked to zinc deficiency. Tetrahydrobiopterin (BH4) deficiencies do not appear to affect these immune parameters.
Area of Science:
- Immunology
- Metabolic Disorders
- Nutritional Science
Background:
- Increased infection susceptibility is noted in phenylketonuria (PKU) patients.
- The exact causes, whether amino acid alterations or other factors, remain unclear.
Purpose of the Study:
- To assess B cell and T cell functions in children with PKU and BH4 deficiencies.
- To investigate the impact of high plasma phenylalanine (PA) concentrations on immune parameters.
Main Methods:
- Studied B and T cell functions in 33 children with PKU (two groups based on PA levels) and 11 with BH4 deficiencies.
- Compared results with healthy controls and analyzed plasma PA, IgG, IgM, serum zinc, and iron levels.
Main Results:
- Impaired delayed type skin hypersensitivity responses were observed in PKU patients with high PA (Group I) and BH4 deficiency (Group III).
- Lower plasma IgG and IgM concentrations were found in Group I. Zinc and iron deficiencies were more pronounced in Groups I and III.
- BH4 deficiency did not appear to significantly impact the studied immune parameters.
Conclusions:
- High PA levels in PKU may contribute to low IgG, with zinc deficiency also playing a potential role.
- Impaired skin hypersensitivity responses are likely linked to severe zinc deficiency in PKU and BH4 deficiency.
- Further research is needed to clarify the PKU-immune function relationship after correcting micronutrient status.
Background:
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.
Objective:
This study is designed to establish B cell and T cell functions in 44 children with classical PKU and tetrahydrobiopterin (BH4) deficiencies and the effects of too high plasma phenylalanine (PA) concentrations (16.53 to 30.54 mg/dL) on the same parameters.
Design:
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 BH4 deficiencies (Group III) were studied. The results were compared between the groups and referenced with previously reported values from healthy controls.
Result:
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.
Conclusion:
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. BH4 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.