The Effect of Large Neutral Amino Acids on Blood Phenylalanine Levels in Patients with Classical Phenylketonuria

Abstract

Purpose: Phenylketonuria PKU is an inherited metabolic disease caused by low levels of the enzyme phenylalanine hydroxylase. Treatment includes dietary restriction of phenylalanine Phe and supplementation with tetrahydrobiopterin and large neutral amino acids LNAAs . The purpose of this study is to evaluate the effect of LNAA therapy on blood Phe levels in patients undergoing treatment for at least 6 months.Methods: Blood Phe levels in 34 patients with classical PKU receiving LNAA supplementation for longer than 6 months were compared before the treatment and during the first 3 years of treatment.Results: The mean age of patients was 20.7±6.6 years, and the mean age at the beginning of LNAA therapy was 16.0±6.1 years. The median duration of LNAA use was 32 months minimum-maximum: 8-171 months . The mean blood Phe level before the use of LNAA supplementation was 23.1±5.9 mg/dL, whereas the first blood Phe level 1 month after the start of LNAA therapy was 18.9±5.5 mg/dL p=0.000 . The mean blood Phe levels in the first n=34 , second n=33 , and third year n=28 after the beginning of LNAA supplementation were 21.1±5.0 mg/dL, 21.2±6.4 mg/dL, and 21.3±5.8 mg/dL, respectively. There was no significant variation between these and pre-treatment values p>0.05 .Conclusion: There were no significant decreases in the blood Phe levels of patients receiving LNAA supplementation observed in this study. This may be due to poor dietary compliance. Nevertheless, since LNAA supplementation reduces the passage of Phe through the blood-brain barrier, it is still recommended in all adolescent and adult patients with PKU not complying with diet therapy, even if blood values do not change

Keywords

• Phenylalanine,classical phenylketonuria,LNAA supplementation

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