Growth Parameters and Prevalence of Obesity in PKU Patients and Peers: Is This the Right Comparison?

Background: One of the main objectives of Phenylketonuria (PKU) management is represented by optimising the growth trend under restricted protein diet regimen. The data on long-term growth in PKU children are limited and mostly based on earlier studies.

Methods: The data for this twelve-year longitudinal study were collected from 34 PKU children and 37 healthy peers, whose auxological parameters were taken at 7 time-points over the follow-up. The weight-for-length ratio (WLR) z-score and body mass index (BMI) z-score were considered according to age. Prevalence of overweight/obesity was evaluated at last assessment.

Results: The median BMI z-score of PKU children was normal and not statistically different from that of controls on all the seven time-point assessments. Their distributions tended to be wider than those of peers, with the upper limit exceeding the normal range since 12 months old, with a peak specifically at 3 years of age. In controls, there was a tendency to approach the BMI z-score values of overweight in later childhood. The prevalence of overweight was comparable (29% vs. 25%, : 0.78) between the two groups at last assessment, and obese subjects (3/37) were only detected in the control group.

Conclusions: In this study, we report data from a long-term follow-up on growth, highlighting that the median BMI z-score of PKU children was normal and not statistically different from that of controls. Also, the prevalence of obesity at 12 years of age was overlapping. However, the high prevalence of overweight children in the general population may explain the lack of difference and does not reassure about patients' nutritional risk.