Additional costs of a low-protein diet in children and adolescents with phenylketonuria

Introduction

Phenylketonuria (PKU) is one of the most common disorders of the metabolism of aromatic amino acids [1]. People with PKU are unable, or have a limited ability, to break down the essential amino acid phenylalanine (Phe). The disease is congenital and inherited in an autosomal recessive manner [3]. PKU is one of the target diseases in advanced screenings of newborns and is identified by means of a blood test [4]. In Germany, the prevalence was 1:7,914 in 2016 [5].

In healthy humans, Phe, which is not required for endogenous functions, is converted into tyrosine with the help of the enzyme phenylalanine hydroxylase (PAH). This reaction requires tetrahydrobiopterin (BH4) as a cofactor [6]. In patients with PKU, various mutations of the coding gene result in changes in the PAH enzyme so that there is no – or very little – conversion of Phe into tyrosine [3]. For that reason, partially through alternative conversion methods of transamination and decarboxylation, Phe is converted into phenylpyruvic acid, phenyllactic acid and phenylacetic acid, among others, and excreted in urine [7]. Since not all Phe can be converted using these alternative methods, it accumulates in the blood and tissues (e.g. brain) [2]. In the absence of treatment, the Phe concentration in the blood increases and interferes with the transport of other essential amino acids to the brain [8]. This pathological situation results e.g. in a decreased share of neurotransmitters (e.g. serotonin and dopamine) and a reduction in the protein synthesis [2]. Typical clinical symptoms include retardation, epilepsy, behavioral problems, a “musty” body odor, eczema and reduced skin and hair pigmentation [9].

Abstract

Phenylketonuria (PKU) is a congenital disorder of the metabolism of aromatic amino acids. The impaired breakdown of phenylalanine (Phe) into tyrosine leads to an accumulation of Phe and the production of unwanted metabolites. At the same time, the lack of tyrosine results in the reduced formation of melanine and catecholamines. The therapy for avoiding the various clinical symptoms is based on a low-protein – or low-Phe – diet. In addition to comprehensive instructions by nutritional experts, this special diet requires the consumption of specific foods. As a result of the present study, it has been found that depending on the age group, the dietary treatment of PKU costs between 67 € and 164 € more per month than the diet of a healthy adolescent. Aside from the increased financial demand, the extra time spent on implementing the diet should also be considered.

Keywords: Phenylketonuria, low-protein diet, Phe reduction, nutritional therapy, costs

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