The reported prevalence of scoliosis in children with Prader-Willi syndrome varies from 15% to 86%. Objective: To study the prevalence of scoliosis and the effects of age, gender, body mass index (BMI), total lean body mass (LBM), LBM of the trunk (trunkLBM) and genotype. Design: Radiographs were taken, length and weight were measured (BMI standard deviation scores (BMI SDS) and body surface area (BSA)), and dual energy x-ray absorptiometry was performed, measuring LBM and trunkLBM. Patients:

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... children, median (interquartile range) age 4.8 years (2.1 to 7.5), were included in a multicentre study. None received growth hormone treatment. Main outcome measures: Two types of scoliosis were identified: (1) long C-curve type scoliosis (LCS) and (2) idiopathic scoliosis (IS). Children were divided into age categories (infants, 0-3 years; juveniles, 3-10 years; adolescents, 10-16 years). Results: The prevalence of scoliosis was 37.5% and increased with age (infants and juveniles, ,30%; adolescents, 80%); 44% of children with scoliosis had a Cobb angle above 20u. Children with scoliosis were significantly older than those without. Children with LCS were younger and more hypotonic than those with IS: median (interquartile range) age 4.4 years (1.7-5.9) vs 11.1 years (6.5-12.1) (p = 0.002) and trunkLBM/BSA ratio 7080 (6745-7571) vs 7830 (6932-8157) (p = 0.043). Conclusions: The prevalence of scoliosis in children with Prader-Willi syndrome is high (37.5%). Many children with scoliosis (13%) had undergone brace treatment or surgery. The type of scoliosis is affected by age and trunkLBM/BSA ratio.