Abstract
The gold standard treatment for phenylketonuria (PKU) is a lifelong low-phenylalanine (Phe) diet supplemented with Phe-free protein substitutes. Adherence to therapy becomes difficult after childhood. Supplementing with large neutral amino acids (LNAAs) has been proposed as an alternative medication to Phe-free protein substitutes (i.e., amino acid mixtures). The aim of this study was to evaluate adherence to therapy and quality of life (QoL) in a cohort of sub-optimally controlled adult PKU patients treated with a new LNAA formulation. Twelve patients were enrolled in a 12-month-trial of slow-release LNAAs (1g/kg/day) plus a Phe-restricted diet. Medication adherence was measured with the Morisky Green Levine Medication Adherence Scale; the QoL was measured using the phenylketonuria-quality of life (PKU-QoL) questionnaire. Phe, tyrosine (Tyr) levels, and Phe/Tyr ratios were measured fortnightly. Before treatment, 3/12 patients self-reported a ‘medium’ adherence to medication and 9/12 reported a low adherence; 60% of patients reported a full adherence over the past four weeks. After 12 months of LNAA treatment, all patients self-reported a high adherence to medication, with 96% reporting a full adherence. Phe levels remained unchanged, while Tyr levels increased in most patients. The Phy/Tyr ratio decreased. All patients had a significant improvement in the QoL. LNAAs may give patients a further opportunity to improve medication adherence and, consequently, their QoL.
Highlights
Phenylketonuria (PKU; OMIM 261600) is a rare genetic disease caused by mutations of the gene encoding for phenylalanine hydroxylase enzyme (PAH; EC1.14.16.1) [1,2].PKU patients are detected by neonatal screening and start a low-phenylalanine (Phe) diet soon after birth [3]
The Phe-restricted diet is based on three components: (1) natural protein and Phe restriction according to Phe tolerance, (2) supplementation with protein substitutes, (3) the prescription of special low-protein foods (SLPF) in order to achieve energy requirements for growth and maintenance
In the 12-month period prior to the introduction of large neutral amino acids (LNAAs), the mean ± standard deviation (SD) Phe and Tyr values ranged from 628 ± 148 to 1033 ± 198 μmol/L and from 32 ± 7 to 87 ± 35 μmol/L, respectively, while the mean ± SD Phe/Tyr ratio ranged from 9.7 ± 2.2 to 19.9 ± 2.8 μmol/L
Summary
PKU patients are detected by neonatal screening and start a low-phenylalanine (Phe) diet soon after birth [3]. The gold standard therapy for patients with classical PKU is a Phe-restricted diet with the supplementation of Phe-free protein substitutes [4]. The Phe-restricted diet is based on three components: (1) natural protein and Phe restriction according to Phe tolerance, (2) supplementation with protein substitutes (some protein substitutes are not 100% Phe-free, since glycomacropeptide-based protein substitutes are available in several countries), (3) the prescription of special low-protein foods (SLPF) in order to achieve energy requirements for growth and maintenance. Nutrients 2020, 12, 2078 efficacy in preventing intellectual disability, but adherence to this therapy is difficult, especially for adolescent and adult patients, and these difficulties could influence many aspects of the patients’ social and emotional lives [5,6]. Difficulty in maintaining blood Phe values within the recommended range (
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