Age-appropriate body mass index in children with achondroplasia: interpretation in relation to indexes of height.

BACKGROUND Achondroplasia is the most common short stature skeletal dysplasia, with an estimated worldwide prevalence of 250 000. Body mass index (BMI)-for-age references are required for weight management guidance for children with achondroplasia, whose body proportions are unlike those of the average stature population. OBJECTIVE This study used weight and height data in a clinical setting to derive smoothed BMI-for-age percentile curves for children with achondroplasia and explored the relation of BMI with its components, weight and height. DESIGN This was a longitudinal observational study of anthropometric measures of children with achondroplasia from birth through 16 y of age. RESULTS The analysis included 1807 BMI data points from 280 children (155 boys, 125 girls) with achondroplasia. As compared with the BMI of peers of average stature, the BMI in children with achondroplasia is higher at birth, lacks a steep increase in infancy and a later nadir between 1 and 2 y of age, and remains substantially higher through 16 y of age in both sexes. Patterns of change in height and weight in children with achondroplasia are unique in that there is no overlap in the height distribution after 6 mo of age and no spike in height velocity during infancy or puberty-the 2 periods of greatest linear growth in individuals of average stature. CONCLUSIONS Sex- and age-specific BMI curves are available for children with achondroplasia (birth to 16 y of age) for health surveillance and future research to determine associations with health outcomes (eg, cardiovascular disease, diabetes, and indication for and outcome of surgery).