Background Phenylketonuria (PKU) treatment requires a diet restricted from natural proteins and supplemented with phenylalanine (Phe)-free L-amino acid mixtures. Growth impairment and compromised bone mass have been described.

This study aims to evaluate anthropometric characteristics and bone mineral density (BMD) in a cohort of PKU patients.

Methods We conducted a retrospective longitudinal study collecting anthropometric characteristics (weight, height, body mass index (BMI) and BMD every 6 months from birth to 12 years of age in 34patients with diet restrictions.

We compared the data results, expressed as z-scores, with the general population, as well as between patients with Phe <360 mmol/ml (optimal) and patients with >360 mmol/ml.

Results Our PKU patients are shorter than the reference population; the sample mean was below z–score=0. Weight was comparable to that of the reference population and BMI had a tendency to be over the population mean.

Growth impairment in PHA-deficiency is not related to plasma Phe concentration at birth but might be related to its levels throughout the follow up; patients with <360 mmol/ml were shorter.

BMD was below the population mean in all cases (52% osteopenia).

Conclusions PKU children in our study have a below than average height. Weight is consistent with the population average and BMI tends to be above it.

Height seems more affected among those patients with better metabolic control.

BMD is below the population mean. These data do not vary depending on the levels of Phe at diagnosis, but by the phenylalaninemia during growth.

Further studies are needed to investigate the effect of diet restriction in PKU.