LONG-CHAIN POLYNSATURATED ACIDS PROFILE IN PLASMA PHOSPHOLIPIDS OF HYPERPHENYLALANINEMIC CHILDREN ON UNRESTRICTED DIET

Introduction Hyperphenylalaninemia (HPA) is an autosomal recessive inborn error of metabolism, caused by a mutated gene of the hepatic enzyme phenylalanine hydroxylase (PAH; OMIM 261600), which converts the amino acid phenylalanine to other essential compounds in the body, such as tyrosine. The range of disease severity observed among patients with this form of HPA is mostly due to allelic heterogeneity at the PAH locus. Various combinations of mutations result in a spectrum of metabolic phenotypes ranging from phenylketonuria (PKU, blood Phe levels >360 micromol/L), which require dietary management, to mild hyperphenylalaninaemia (MHP, blood Phe levels ranging 120–360 micromol/L) in which dietary restriction may be not necessary. PKU diet is similar to a vegetarian diet in that all animal-based foods and further some foods with high protein contents (cereals, bread, pasta and protein rich vegetables) must be avoided and replaced in part by low protein dietetic products. Therefore, children with PKU may have non adequate food supply of docosahexaenoic acid (DHA, 22:6n-3), except during infancy, when they may receive breast milk or infant formula preparations supplemented with DHA. The phenylketonuric (PKU) diet determines a low intake of long chain polyunsaturated fatty acids (LCPUFA), such as arachidonic acid (AA) and docosahexaenoic-acid (DHA), which are contained only in food of animal source. This lack of LCPUFA may be firstly explained by the inhibitory effect of phenylalanine and its metabolites on the endogenous synthesis of DHA and AA; it has been speculated, infact, that high plasma Phe levels, above the upper limit of 120 μmol/L, could impair the metabolic steps of LCPUFA synthesis. Therefore, PKU patients must rely only on the endogenous synthesis of LCPUFA from their precursors, the content of which also is often suboptimal in dietary products for patients with PKU, particularly that of α-linolenic acid (ALA), the precursor of DHA. In other words, “successful” dietary treatment of PKU appears to result in an iatrogenic decrease of the circulating DHA pools. Aim of the study: The primary aim of the present study was to examine whether MHP children (on unrestricted dietary regimen) may exhibit a different plasma phospholipids LCPUFA profile from PKU children on a strict dietary control especially concerning DHA and AA, comparing them with an healthy reference population. Patients and Methods: 45 MHP children (age 9-14 years) were age and sex matched with 45 PKU and 45 healthy control children and then admitted to the Department of Paediatrics, San Paolo Hospital, Milan, from July 2009 to July 2011 for routine examinations. Plasma phospholipds fatty acids were determined and expressed as % of total fatty acids. Inclusion criteria were as follows: age at recruitment 9-14 years, weight at birth > 2500 g, gestational age 37–42 week inclusive, singleton birth, having white parents. Children exhibiting diabetes mellitus and/or endocrine diseases, chronic liver diseases, overweight/obesity according to the International Obesity Task Force, and/or hyperlipidemia according to Italian guidelines, were excluded to prevent possible bias effects on plasma fatty acid status. PKU children non compliant with the recommended diet were also excluded. Compliance was evaluated according to age adjusted reference threshold values of plasma Phe. In all participating children fasting blood samples were taken in the morning at 8 h ± 30 min, within 3 days of recruitment. Fatty acid (FA) plasma levels were measured. In both HPA groups the FA analyses demonstrated reductions of long-chain polyunsaturated fatty acids (LCPUFA). Results: MHP children showed phospholipds docosahexaenoic acid levels higher than PKU children (mean difference, 0.2%; 95% confidence interval, 0.02% to 0.38%), although difference was not significant after correction for multiple comparisons (P=0.117), and lower than healthy children (0.8%; -1.01% to -0.59%). Conclusions: the results suggest that MHP children may exhibit a plasma phospholipds LCPUFA profile not appreciably differing from PKU children whereas show lower DHA levels than healthy children. While disadvantaged DHA levels of PKU may be mainly explained on the basis of the restricted dietary regimen, extra-dietary factors possibly connected with features of deranged metabolic pathways may play a role in hyperphenylalaninemic children. To clarify the possible role of hyperphenylalaninemia per se in determining the inhibition of LCPUFA synthesis, it appears interesting to examine plasma DHA levels in HPA children on unrestricted dietary regimen. In this study, MHP children showed levels of docosahexaenoic acid in plasma phospholipids around 12% higher than PKU children although difference was no significant after correction for multiple comparisons. All these results together suggest that independently of the dietary regimen, MHP children may exhibit DHA levels in plasma phospholipids not appreciably different from PKU children, but worse than in healthy subjects.