Our Experience with Long Neutral Amino Acid Supplementation in Paediatric PKU Patients in India

Introduction: The mainstay treatment in patients with classical PKU and pterin metabolism disorders presenting with hyperphenylalaninemia is a lifelong Phe-restricted diet, however, this is difficult to adhere to due to compliance issues, thus alternative therapies have been introduced including the use of Long Neutral Amino Acids (LNAA).

Aim: To study the effect of LNAA therapy in paediatric patients with PKU.

Methods: This is a retrospective study of three paediatric patients with classical PKU and one patient with PTPS deficiency prescribed LNAA due to their non-compliance with standard dietary restrictions. All patients were diagnosed symptomatically as there is no newborn screening programme in India. Information about LNAAs was gathered by the patients from the Internet and they requested a trial. The patients were given LNAAs to provide approximately 30% of the total protein intake (along with 40% from natural sources and 30% from PKU formula). Each 5 g sachet of LNAA contained the protein equivalent of 2.2 g and 2.6 g of amino acids of which 980 mg was tyrosine and 310 mg was tryptophan.

Results: LNAA was tolerated and accepted in all patients with no side effects noted so far. Compliance was good. All patients improved clinically with reduced aggressiveness and hyperactivity, increased attention span and improved behaviour, and a decreased frequency of seizures. Biochemically, phenylalanine levels were reduced in all patients after LNAA therapy [Phenylalanine (in µmol/L) reduced from 1340 to 802 in P1, 2088 to 1194 in P2, 1996 to 1424 in P3 and 1026 to 673 in P4]. The ratio of Phe/Tyr also improved in all patients.

Conclusion: LNAA therapy had good compliance and showed biochemical and clinical improvements in all paediatric patients receiving the therapy. There was a significant improvement in phenylalanine levels and the Phe/Tyr ratio, thus LNAA is a good adjuvant therapy in paediatric patients where compliance with PKU formula is poor.