Natural history of body mass index in Williams-Beuren syndrome.

Body mass index (BMI) is a useful tool for the investigation of obesity or underweight. It follows a typical pattern throughout childhood. During the first few years of life underweight due to feeding problems and gastrointestinal disturbances is considered a common sign in Williams-Beuren syndrome (WBS), whereas obesity is frequently reported in WBS adults. Systematic studies on weight gain and body mass index in WBS do not exist. Therefore, we studied weight gain relative to height expressed as BMI in 82 WBS girls (459 measurements of weight and height) and in 104 WBS boys (562 measurements). At birth BMI was significant lower in WBS than in normal infants in both sexes (P < 0.0001). During the first months of life, mean BMI showed a catch-up from the 3rd to the 10th-50th centiles in WBS infants relative to the normal standards. The further course of BMI was almost parallel to normal development. In addition, a gradual relative increase to the 50th centile of normal was seen in both sexes. In conclusion, weight gain during the first year of life was sufficient. Feeding and gastrointestinal problems seem not to have a severe impact on weight gain in infancy. Until adulthood weight relative to height continuously reached the 50th centile of normal. Thus, obesity is not a common finding in young adults with WBS. The results of this study may serve as a disease-specific reference of BMI development in WBS patients.