Growth and Body Composition in PKU Children—A 3 Year Prospective Study Comparing the Effects of L-Amino Acid to Glycomacropeptide Protein Substitutes

Abstract Background: Protein quality and quantity are important factors in determining lean body (muscle) mass (LBM). In phenylketonuria (PKU), protein substitutes provide most of the nitrogen either as amino acids (AA) or glycomacropeptide (CGMP-AA). Body composition and growth are important indicators of long-term health. In a 3-year prospective study comparing the impact of AA and CGMP AA on body composition and growth in PKU, 48 children were recruited. N=19, (median age 11.1y, range 5-15y) took AA only, n=16 (median age 7.3y, range 5-15y) took a combination of CGMP-AA and AA (CGMP50), and 13 children (median age 9.2y, range 5-16y) took CGMP-AA only (CGMP100). A dual energy X ray absorptiometry (DXA) scan at enrolment and 36 months measured LBM, % body fat (%BF) and fat mass (FM). Height was measured at enrolment, 12, 24 and 36 months. Results: No correlation or statistically significant differences were found between the three groups for LBM, FM and height compared with age, gender, puberty or phenylalanine blood concentrations. The change in height z scores: AA 0, CGMP50 +0.4 and CGMP100 +0.7 showed a trend that children in the CGMP100 group were taller, had improved LBM with decreased FM and % BF but this was not statistically significant. Conclusion: There appeared to be no advantage of AA compared to CGMP-AA protein substitutes on body composition after 3 years follow up of usage. Although statistical differences were not reached, a trend towards improved body composition was observed with CGMP when it provided the entire protein substitute requirement.Trial registry: IRAS 129497 (13/WM/10435) registered 10th November 2013 (hppt// www.hra.nhs)