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.

Head circumference is considered an important parameter of brain growth and development. Syndrome-specific standards for head circumference in Williams-Beuren syndrome (WBS) are not available to date, although mental retardation is a leading manifestation in the syndrome. Therefore, we investigated head growth in 63 girls (251 measurements) and 88 boys (298 measurements) with WBS between birth and adulthood. Most measurements in both sexes were from the first 4 years of life (n = 162 in girls and n = 189 in boys). Mean (+/- SD) head circumference at birth was 33.39 +/- 1.38 cm and 34.02 +/- 1.44 cm for term girls and boys, respectively. Although head growth in WBS girls and boys was at a slower velocity, the pattern of head circumference was similar to that in the normal population. After the age of 3 months, head circumference started to fall below the normal mean in girls (0.5-2 cm). In boys, mean head circumference was below the normal mean already at 1 month of age (2 cm). The deficit increased to 3 cm from 6 months to 4 years. Adult OFC was 52.85 +/- 1.75 cm (n = 16) compared to 55.70 +/- 1.83 cm (n = 46; P < 0.00001) in WBS women and 55.51 +/- 1.68 cm (n = 30) compared to 57.87 +/- 1.29 cm (n = 31; P < 0.00001) in WBS men. During development, microcephaly is only seen in about one third of WBS patients.