6R-tetrahydrobiopterin treated PKU patients below 4 years of age: Physical outcomes, nutrition and genotype.

Abstract

BACKGROUND AND AIMS:

Phenylalanine-restricted diets have proven effective in treating phenylketonuria. However, such diets have occasionally been reported to hinder normal development. Our study aimed to assess whether treating 0-4-year-old phenylketonuric patients with 6R-tetrahydrobiopterin might prevent growth retardation later in life.

METHODS:

We conducted a longitudinal retrospective study which examined anthropometric characteristics of phenylketonuric patients on 6R-tetrahydrobiopterin therapy (22 subjects), and compared them with a group of phenylketonuric patients on protein-restricted diets (44 subjects). Nutritional issues were also considered. We further explored possible relationships between mutations in the PAH gene, BH4 responsiveness and growth outcome.

RESULTS:

No significant growth improvements were observed in either the group on 6R-tetrahydrobiopterin treatment (height Z-score: initial= -0.57 ± 1.54; final=-0.52 ± 1.29; BMI Z-score: initial=0.17 ± 1.05; final=0.18 ± 1.00) or the diet-only group (height Z-score: initial=-0.92 ± 0.96; final= -0.78 ± 1.08; BMI Z-score: initial=0.17 ± 0.97; final=-0.07 ± 1.03) over the 1-year observation period. Furthermore, we found no significant differences (p>0.05) between the two groups at any of the time points considered (0, 6 and 12 months). Patients on 6R-tetrahydrobiopterin increased their phenylalanine intake (from 49.1 [25.6-60.3] to 56.5 [39.8-68.3] mgkg(-1)day(-1)) and natural protein intake (from 1.0 [0.8-1.7] to 1.5 [1.0-1.8] g kg(-1)day(-1)), and some patients managed to adopt normal diets. Higher phenylalanine and natural protein intakes were positively correlated with better physical outcomes in the diet-only group (p<0.05). No correlation was found between patient genotype and physical outcomes, results being similar regardless of the nutritional approach used. We did not detect any side effects due to 6R-tetrahydrobiopterin administration.

CONCLUSIONS:

Our study indicates that treating 0-4-year-old phenylketonuric patients with 6R-tetrahydrobiopterin is safe. However, poor developmental outcomes were observed, despite increasing the intake of natural proteins. Genotype could be a valid predictor of tetrahydrobiopterin-responsiveness, since patients who carried the same genotype responded similarly to the 6R-tetrahydrobiopterin loading test. On the other hand, harbouring 6R-tetrahydrobiopterin responsive genotypes did not predispose patients to better physical outcomes.

• Authors: Luis Aldámiz-Echevarría, María A Bueno, María L Couce, Sergio Lage, Jaime Dalmau, Isidro Vitoria, Marta Llarena, Fernando Andrade, Javier Blasco, Carlos Alcalde, David Gil, María C García, Domingo González-Lamuño, Mónica Ruiz, María A Ruiz, Luis Peña-Quintana, David González, Felix Sánchez-Valverde
• Journal: Molecular genetics and metabolism (Mol Genet Metab) Vol. 115 Issue 1 Pg. 10-6 (May 2015) ISSN: 1096-7206 [Electronic] United States
• PMID: 25882749 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2015 Elsevier Inc. All rights reserved.

Chemical References

• Biopterin
• Phenylalanine
• sapropterin

Topics

• Biopterin (administration & dosage, analogs & derivatives, therapeutic use)
• Body Height
• Body Weight
• Child, Preschool
• Diet, Protein-Restricted
• Female
• Genotype
• Humans
• Infant
• Infant, Newborn
• Longitudinal Studies
• Male
• Mutation
• Nutritional Status
• Phenylalanine (administration & dosage, blood)
• Phenylketonurias (diet therapy, drug therapy, genetics, physiopathology)
• Retrospective Studies
• Spain