Nutritional status in patients with phenylketonuria using glycomacropeptide as their major protein source

Low phenylalanine (PHE), glycomacropeptide-based protein substitute (GMP) is an alternative to traditional L-amino acid supplements (AA) used in the dietary management of phenylketonuria (PKU). In a retrospective, longitudinal study, we report the nutritional status of PKU patients taking AA and GMP.

Eleven PKU patients aged 27±10 years (1 HPA, 4 mild and 6 classical PKU) on dietary treatment were evaluated (anthropometry, body composition, blood pressure measurements, biochemical markers including vitamin, mineral, lipids, carbohydrates and protein status/metabolism, and nutritional intake assessment) at two different annual reviews. The mean time taking AA was 13±5 months and GMP 13±7 months. Blood phenylalanine (PHE) and tyrosine (TYR) were analysed before and after GMP introduction.

Both GMP and AA protein substitutes provided similar protein equivalent intake (0.85 vs 0.75 g/kg/day, P=0.182). In the GMP group, it contributed 57% (27-100%) of the protein substitute intake (with AA delivering the rest of protein substitute intake), providing an additional 34±12 mg/day PHE. Nutritional intake, anthropometry and body composition measurements were similar in both the groups. Median blood PHE did not change (P=0.594), although values within target range improved (36 vs 46%), but this was not statistically significant. Mean blood TYR increased (52.0±19.2 vs 63.2±25.6 μmol/l, P=0.033), and all biochemical markers remained stable, except for a lower A1C haemoglobin (P=0.011).

Partial GMP contribution to total protein substitute intake did not affect nutritional status in patients with PKU. Blood PHE control was not adversely affected. The increased blood TYR after GMP introduction necessitates further study.