Metabolic Control in Patients With Phenylketonuria Pre- and Post-Sapropterin Loading Test

• Main Authors: Catarina Sousa Barbosa BSc, Manuela F. Almeida BSc, Cátia Sousa BSc, Sara Rocha MD, Arlindo Guimas MD, Rosa Ribeiro MD, Esmeralda Martins MD, PhD, Anabela Bandeira MD, Bruno M. P. M. Oliveira PhD, Nuno Borges PhD, Anita MacDonald PhD, Júlio C. Rocha PhD
• Format: Article
• Language: English
• Published: SciELO 2018-08-01
• Series: Journal of Inborn Errors of Metabolism and Screening
• Online Access: https://doi.org/10.1177/2326409818788898

In Portugal, tetrahydrobiopterin (BH4)-responsive patients with phenylketonuria (PKU) are identified using a loading test (LT). Phenylalanine/natural protein (Phe/NP) intake is increased to elevate blood Phe prior to the LT. In a longitudinal retrospective study, the impact of Phe/NP titration post-LT in 58 patients (19.6 ± 8.2 years) with PKU during 4 study periods (SPs) was examined. In SP1 (2010-2013), patients were diet treated only; in SP2 (2014), the Phe/NP titration was followed by the LT in SP3 (2015). In SP4 (2016), patients received diet treatment only (n = 49) or BH4 + diet (n = 9). The median percentage blood Phe within the target range was higher in SP1 versus SP4 (64 [28-85] vs 45 [0-66]; P < .001). Our results suggest that transient Phe/NP titration, associated with a deliberate increase in NP, may adversely affect metabolic control. Controlled studies are necessary to examine the longer term impact of temporary increased NP with BH4 LT in non-BH4-responsive patients.