Compared with conventional low-phenylalanine protein substitutes, a prolonged-release protein substitute caused fewer gastrointestinal problems in children and adolescents with phenylketonuria (PKU), a study has found.

The study, “An Observational Study Evaluating the Introduction of a Prolonged-Release Protein Substitute to the Dietary Management of Children with Phenylketonuria,” was published in the journal Nutrients.

PKU is a metabolic disorder caused by the lack of activity of an enzyme called phenylalanine hydroxylase (PAH), which is needed to break down the amino acid phenylalanine. Amino acids are the building blocks of proteins.

In the absence of PAH, phenylalanine builds up to toxic levels in the brain and other organs, ultimately leading to irreversible intellectual impairments in children with the condition who remain untreated.

Although there is no cure for the disease, studies suggest that it is possible to prevent such intellectual impairments by having children with PKU follow a lifelong phenylalanine-restricted diet. These PKU diets usually eliminate all protein-rich foods that contain high levels of phenylalanine, such as meat, fish, and dairy. Meanwhile, people with the disease are encouraged to consume phenylalanine-free protein substitutes.

“However, current dietary treatments are associated with some major issues, such as low adherence attributed to unpalatable and burdensome dietary supplements and subtle but chronic neuropsychological impairments despite early intervention, particularly in adulthood, including mood and psychiatric issues,” the investigators wrote.

Now, researchers at Birmingham Women’s and Children’s Hospital, in the U.K., reported the findings of an observational study that sought to determine if a new, prolonged-release protein substitute could overcome some of the limitations of conventional substitutes in children with PKU. This new prolonged-release substitute contains substances in its formulation to mask its smell and bitter taste.

Called PKU GOLIKE PLUS 3–16 — for children ranging in age from 3 to 16 — and sold by Applied Pharma Research, the prolonged-release protein substitute was used in the study for a period of seven days. It was mixed with the children’s food or fruit juice, and used to replace at least one daily dose of their usual protein substitute.

“The study product provided 20–27.3% of the [child’s] usual protein equivalent intake per day; the remaining protein equivalent intake was from each [child’s] usual protein substitute,” the investigators wrote.

A total of 13 children and adolescents with PKU, ages 7-16, were enrolled in the study. All of the participants were diagnosed with the condition following newborn screening, and were started on a phenylalanine-restricted diet immediately after that.

Only seven of the 13 children and adolescents initially enrolled in the study were able to take the entire prescribed dose of the prolonged-release protein substitute, the researchers noted. All analyses were based on this subset of patients.

The researchers said the primary reason why the remaining six children failed to take the entire prescribed dose of the new protein substitute was due to its texture. The protein substitute was described as being “bitty and gritty” when added to food. “One child described the amount of powder as ‘a little overpowering’ when added to food,” the team also noted.

Nevertheless, over a period of seven days, five of the seven children and adolscents who took their entire prescribed dose of the new substitute saw their phenylalanine levels drop.

Four of these children also reported having fewer gastrointestinal problems, including flatulence, burping, and regurgitation, while taking the prolonged-release protein substitute.

None of the patients experienced diarrhea, constipation, bloating, nausea, or vomiting during the study. There was one case of abdominal discomfort and pain, which was attributed to menstruation.

The children “maintained satisfactory blood phenylalanine control and were able to take their protein substitute in a different way to their usual practice,” the researchers wrote.

“The prolonged-release protein substitute was well tolerated, with [children and adolescents] experiencing fewer gastrointestinal symptoms than with their previous treatment regimen,” they wrote.

“Although the results of this pilot study provide reassuring data, longer-term studies evaluating adherence and blood phenylalanine control are necessary,” the team concluded.