Bone Abstracts

Objectives: To evaluate bone status and body composition in patients with phenylketonuria and hyperphenylalaninemia.

Methods: Eighty patients (48 with phenylketonuria and 32 with hyperphenylalaninemia), aged 5–18 years, early-diagnosed, underwent dual energy X-ray absorptiometry. Bone mineral density (lumbar spine and total body), bone strength (bone mineral content:lean tissue mass ratio), lean tissue mass, body fat percentage, and fat mass index were measured. The above parameters were compared to reference population values.

Results: Compared to controls, all patients had bone strength and bone mineral density within normal range at both sites (Z-score between −2 and 2), with low-normal Z-scores at the spine (between −1 and −2) in 16% of patients with phenylketonuria and 31% of hyperphenylalaninemics. Nearly 20% of patients in both groups appeared sarcopenic (lean tissue mass Z-score <−2) and 33% had low-normal muscle mass. Regarding fatness, 33% of the subjects in both groups were either overweight or obese. Phenylketonuric, female teenagers with poor dietary compliance were most at risk of being fat. In the hyperphenylalaninemia group, no sex-related difference was detected; however, adolescents also tended to be heavier. A positive correlation was found between bone mineral density and muscle mass; also, between bone and fat mass. Moreover, Phenylalanine levels and fat indices were positively correlated. Between the two groups, a higher body fat percentage was recorded in the hyperphenylalaninemic subjects. There was no difference in muscle and fat mass.

Conclusion: Despite the muscle-fat imbalance in patients with phenylketonuria and hyperphenylalaninemia, bone status is relatively preserved. Adolescent patients with poor dietary compliance or low-normal bone mineral density should be targeted towards participation in more active exercise programs and more frequent follow-up.