Continuous use of glycomacropeptide in the nutritional management of patients with phenylketonuria: a clinical perspective

Abstract

Background: In phenylketonuria (PKU), modified casein glycomacropeptide supplements (CGMP-AA) are used as an alternative to the traditional phenylalanine (Phe)-free L-amino acid supplements (L-AA). However, studies focusing on the long-term nutritional status of CGMP-AA are lacking. This retrospective study evaluated the long-term impact of CGMP-AA over a mean of 29 months in 11 patients with a mean age at CGMP-AA onset of 28 years (range 15 to 43) [8 females; 2 hyperphenylalaninaemia (HPA), 3 mild PKU, 3 classical PKU and 3 late-diagnosed]. Outcome measures included metabolic control, anthropometry, body composition and biochemical parameters. Results: CGMP-AA, providing 66% of protein substitute intake, was associated with no significant change in blood Phe with CGMP-AA compared with baseline (562 ± 289 µmol/L vs 628 ± 317 µmol/L; p=0.065). In contrast, blood tyrosine significantly increased on CGMP-AA (52.0 ± 19.2 μmol/L vs 61.4 ± 23.8 μmol/L; p=0.027). Conclusions: Biochemical nutritional markers remained unchanged which is an encouraging finding in adults with PKU, many of whom are unable to maintain full adherence with nutritionally fortified protein substitutes. Longitudinal, prospective studies with larger sample sizes are necessary to fully understand the metabolic impact of using CGMP-AA in PKU.

Effect of nutritional intervention on nutritional status among children with disorders of amino acid and nitrogen metabolism (AANMDs): A scoping review

“…Based on the included studies, children and adolescents who were given CGMP-AA, a mixture of CGMP and essential and conditional amino acids, had significantly higher levels of plasma phenylalanine in comparison to those given a phenylalanine-free formula. However, these findings differ from a meta-analysis (61) and few clinical trials which only found a negligible difference in phenylalanine concentrations between the two groups (58,62,63). Participant age could explain the disparity of the findings as the only participants included in this scoping review were children and adolescents while the other studies included adults.…”

Protein status in phenylketonuria: A scoping review

“…Whilst not significant, Daly et al (2021) demonstrated improved LBM in people with PKU taking a cGMP-based protein substitute. No differences in body composition parameters were reported in adolescents and adults taking L-AA compared to cGMP [45,46].…”

“…Thirty-seven studies, including 24 full text papers and 13 conference abstracts, reported anthropometric assessments of protein status. Seven were interventional studies but only three reported the study design; two had a retrospective design [45,46] and one was…”

“…Randomised control trials were conducted by Prince et al (1997), Giovannini et al (2014) and Ney et al (2016). Two studies were prospective [74,75], and two were retrospective longitudinal studies [45,46]. The remaining 11 studies did not identify the study design; however, based on the reported methods, had an interventional design [7,36,39e41,69,72,76e79].…”

“…A range of biochemical measurements were used to assess protein status, and most studies included multiple measurement (Table 3). Serum albumin [36,41,42,56,62,63,69,72,74,78,85,86,95], prealbumin [26,34,37,57,80,81,84,87,89] or both [33,38,40,45,46,76,77,82,83,88,90,91,93,94] were the most common biochemical measurements reported. Total protein [36,40e42,56,63,72,76,78,80,81,85,86,91,93,94] and blood urine nitrogen (BUN) [33,40,45,74,75,78,85,86,93] were also frequently used.…”