ESPE Abstracts

Background: Prader–Willi syndrome (PWS) results from loss of paternally imprinted genes from the 15q11–13 region and causes hypotonia with weight faltering in infancy, followed later by obesity which is classically attributed to hyperphagia.

Objective and hypotheses: To determine, where possible, the age at onset of unwanted weight gain (as opposed to actual obesity) in children with PWS attending a specialist clinic.

Methods: BMI was calculated for each clinic visit in patients with PWS (M=24; F=16) from a single centre over a 20-year period. Two researchers independently scrutinised the BMI chart for each patient to identify the age at which an inappropriate rise in BMI began.

Results: Seventy-six patients were identified of which 36 had insufficient data for analysis, leaving 40 for study. No inappropriate increase in BMI trend occurred in ten patients at the last data point of 5.3 (1.5–15.2) years. Age at BMI increase was not ascertainable in nine patients, all of whom became obese (BMI SDS >2) by 3.2 (2–5) years. Of 21 subjects in whom age at BMI increase could be either estimated (eight patients) or precisely identified (13 patients) the median age at the time of increase was 2 (0.5–3.8) years, with 18/21 patients showing onset of increase between 1 and 2 years.

Conclusion: The critical age of inappropriate BMI increase in PWS is frequently between 1 and 2 years. This is attributable to physical inactivity related to the hypotonia rather than to hyperphagia, the onset of which is >2 years of age. Efforts to increase physical activity in young children with PWS, including encouraging regular swimming, should be promoted in parallel with healthy eating habits and appropriate portion sizes.