Association between Foot Growth and Musculoskeletal Loading in Children with Prader-Willi Syndrome before and during Growth Hormone Treatment

Objective To explore how foot growth relates to musculoskeletal loading in children with Prader-Willi syndrome (PWS). Study design In 37 children with PWS, foot length (FL) before and after 6 years of growth hormone therapy (GHT) was retrospectively evaluated with parental and sibling's FL, height, and factors reflecting musculoskeletal loading, such as weight for height (WfH), lean body mass (LBM: dual energy X-ray absorptiometry, deuterium labeled water), physical activity (accellerometry). and walk age. Because of the typically biphasic evolution of body mass and the late walk age in PWS, 2 age groups were separated (group 1, >2.5 years. group 2, <= 2.5 years). Results Children with PWS normalized height, but not FL after 6 years of GHT. Parental FL correlation with PWS's FL was lower than with sibling's FL. In group 1, FL positively correlated with WfH, LBM, and physical activity. In group 2, FL negatively correlated with age at onset of independent ambulation. Foot catch-up growth with GHT was slower in group 2 compared with group 1. Conclusion In PWS, FL is positively associated with musculoskeletal loading. Small feet in children with PAN'S before and during long-term GHT maybe more than just mother dysmorphic feature, but may possibly reflect decreased musculoskeletal loading influencing foot growth and genetic and endocrine factors. (J Pediatr 2009,154:225-9)