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Open AccessArticle

Large Neutral Amino Acid Therapy Increases Tyrosine Levels in Adult Patients with Phenylketonuria: A Long-Term Study

1
Neurology Unit, San Bassiano Hospital, 36061 Bassano del Grappa, Italy
2
Division of Inherited Metabolic Diseases, Department of Woman’s and Child’s Health, University Hospital, 35128 Padova, Italy
*
Author to whom correspondence should be addressed.
Nutrients 2019, 11(10), 2541; https://doi.org/10.3390/nu11102541
Received: 10 September 2019 / Revised: 14 October 2019 / Accepted: 16 October 2019 / Published: 21 October 2019
The standard treatment for phenylketonuria (PKU) is a lifelong low-phenylalanine (Phe) diet, supplemented with Phe-free protein substitutes; however, adult patients often show poor adherence to therapy. Alternative treatment options include the use of large neutral amino acids (LNAA). The aim of this study was to determine the Phe, tyrosine (Tyr), and Phe/Tyr ratio in a cohort of sub-optimally controlled adult patients with classical PKU treated with a new LNAA formulation. Twelve patients received a Phe-restricted diet plus a slow-release LNAA product taken three times per day, at a dose of 1 g/kg body weight (mean 0.8 ± 0.24 g/kg/day), over a 12-month period. The product is in a microgranulated formulation, which incorporates all amino acids and uses sodium alginate as a hydrophilic carrier to prolong its release. This LNAA formulation provides up to 80% of the total protein requirement, with the rest of the protein supplied by natural food. Patients had fortnightly measurements of Phe and Tyr levels over a 12-month period after the introduction of LNAA. All patients completed the 12-month treatment period. Overall, adherence to the new LNAA tablets was very good compared with a previous amino acid mixture, for which taste was a major complaint by patients. Phe levels remained unchanged (p = 0.0522), and Tyr levels increased (p = 0.0195). Consequently, the Phe/Tyr ratio decreased significantly (p < 0.05) in the majority of patients treated. In conclusion, LNAA treatment increases Tyr levels in sub-optimally controlled adult PKU patients, while offering the potential to improve their adherence to treatment. View Full-Text
Keywords: phenylketonuria; large neutral amino acids; phenylalanine; tyrosine; treatment; blood–brain barrier phenylketonuria; large neutral amino acids; phenylalanine; tyrosine; treatment; blood–brain barrier
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Burlina, A.P.; Cazzorla, C.; Massa, P.; Polo, G.; Loro, C.; Gueraldi, D.; Burlina, A.B. Large Neutral Amino Acid Therapy Increases Tyrosine Levels in Adult Patients with Phenylketonuria: A Long-Term Study. Nutrients 2019, 11, 2541.

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