Glycomacropeptide: long-term use and impact on blood phenylalanine, growth and nutritional status in children with PKU.

In phenylketonuria, casein glycomacropeptide (CGMP) requires modification with the addition of some essential and semi essential amino acids to ensure suitability as a protein substitute. The optimal amount and ratio of additional amino acids is undefined. AIM: A longitudinal, parallel, controlled study over 12 months evaluating a CGMP (CGMP-AA2) formulation compared with phenylalanine-free L-amino acid supplements (L-AA) on blood Phe, Tyr, Phe:Tyr ratio, biochemical nutritional status and growth in children with PKU. The CGMP-AA2 contained 36 mg Phe per 20 g protein equivalent. METHODS: Children with PKU, with a median age of 9.2 y (5-16y) were divided into 2 groups: 29 were given CGMP-AA2, 19 remained on Phe-free L-AA. The CGMP-AA2 formula gradually replaced L-AA, providing blood Phe concentrations were maintained within target range. Median blood Phe, Tyr, Phe:Tyr ratio and anthropometry, were compared within and between the two groups at baseline, 26 and 52 weeks. Nutritional biochemistry was studied at baseline and 26 weeks only. RESULTS: At the end of 52 weeks only 48% of subjects were able to completely use CGMP-AA2 as their single source of protein substitute. At 52 weeks CGMP-AA2 provided a median of 75% (30-100) of the total protein substitute with the remainder being given as L-AA. Within the CGMP-AA2 group, blood Phe increased significantly between baseline and 52 weeks: [baseline to 26 weeks; baseline Phe 270 µmol/L (170-430); 26 weeks, Phe 300 µmol/L (125-485) p = 0.06; baseline to 52 weeks: baseline, Phe 270 µmol/L (170-430), 52 weeks Phe 300 µmol/L (200-490), p < 0.001)]. However, there were no differences between the CGMP-AA2 and L-AA group for Phe, Tyr, Phe:Tyr ratio or anthropometry at any of the three measured time points. Within the CGMP-AA2 group only weight (p = 0.0001) and BMI z scores (p = 0.0001) increased significantly between baseline to 52 weeks. Whole blood and plasma selenium were significantly higher (whole blood selenium [p = 0.0002]; plasma selenium [p = 0.0007]) at 26 weeks in the CGMP-AA2 group compared L-AA. No differences were observed within the L-AA group for any of the nutritional markers. CONCLUSIONS: CGMP-AA increases blood Phe concentrations and so it can only be used partly to contribute to protein substitute in some children with PKU. CGMP-AA should be carefully introduced in children with PKU and close monitoring of blood Phe control is essential.

Refining low protein modular feeds for children on low protein tube feeds with organic acidaemias.

Children with inherited metabolic disorders (IMD) who are dependent on tube feeding and require a protein restriction are commonly fed by 'modular tube feeds' consisting of several ingredients. A longitudinal, prospective two-phase study, conducted over 18 months assessed the long-term efficacy of a pre-measured protein-free composite feed. This was specifically designed to meet the non-protein nutritional requirements of children (aged over 1 year) with organic acidaemias on low protein enteral feeds and to be used as a supplement with an enteral feeding protein source. METHODOLOGY: All non-protein individual feed ingredients were replaced with one protein-free composite feed supplying fat, carbohydrate, and micronutrients. Thirteen subjects, median age 7.4y (3-15.5y), all nutritionally tube dependent (supplying nutritional intake: ≥ 90%, n = 12; 75%, n = 1), and diagnosed with organic acidaemias (Propionic acidaemia, n = 6; Vitamin B12 non-responsive methyl malonic acidaemia, n = 4; Isovaleric acidaemia, n = 2; Glutaric aciduria type1, n = 1); were studied. Nutritional intake, biochemistry and anthropometry were monitored at week - 8, 0, 12, 26 and 79. RESULTS: Energy intake remained unchanged, providing 76% of estimated energy requirements. Dietary intakes of vitamins, minerals and essential fatty acids significantly increased from week 0 to week 79, but sodium, potassium, magnesium, decosahexanoic acid and fibre did not meet suggested requirements. Plasma zinc, selenium, haemoglobin and MCV significantly improved, and growth remained satisfactory. Natural protein intake met WHO/FAO/UNU 2007 recommendations. CONCLUSIONS: A protein-free composite feed formulated to meet the non-protein nutritional requirements of children aged over 1 year improved nutritional intake, biochemical nutritional status, and simplified enteral tube feeding regimens in children with organic acidaemias.

The challenges of vitamin and mineral supplementation in children with inherited metabolic disorders: a prospective trial.

BACKGROUND: In order to achieve metabolic stability, dietary treatment of inborn errors of metabolism may require restriction of protein, fat or carbohydrate. Manipulation of dietary intake potentially reduces micronutrient status, and provision of a comprehensive vitamin and mineral supplement becomes an essential adjunct to dietary treatment. AIM: To review the efficacy of a new complete vitamin and mineral supplement [Fruitivits, Vitaflo Ltd] in 14 subjects in an open prospective 26-week study. METHOD: All subjects had dietary restrictions: low protein diets (57%, n = 8), regular daytime cornstarch and overnight glucose polymer tube feeds (29%, n = 4), low fat diet (7%, n = 1) and modified Atkins diet (7%, n = 1). Plasma nutritional biochemistry, anthropometry and food frequency questionnaires were collected at week 0, 12 and 26 weeks respectively. RESULTS: Five nutritional parameters showed a significant improvement from baseline (week 0) to study end (week 26): folate (P = 0.01), vitamin E (P = 0.04), plasma selenium (P = 0.002), whole blood selenium (P = 0.04) and total vitamin D (P = 0.008). All the other nutritional markers did not significantly change. Even with regular monitoring, 37% of the product remained unused. CONCLUSIONS: Despite improvements in some nutritional markers, overall use of the vitamin and mineral supplement was less than prescribed. New methods are needed to guarantee delivery of micronutrients in children at risk of deficiencies as a result of an essential manipulation of diet in inborn disorders of metabolism.