Height loss with age in adults with Prader-Willi syndrome may result in artifactual increases in BMI

Modest decreases in height occur during normal aging, but usually have only a minimal effect on BMI (body mass index). Height loss may result from vertebral fractures, disc collapse, kyphosis, and/or scoliosis. Accurate determinations of BMI values are essential for prescribing diet and exercise regimens especially for adults with Prader-Willi syndrome (PWS). We measured standing heights in 28 PWS adults over a duration 11.3 ± 3.4 (range 5.1 to 16.2) years in our national multidisciplinary PWS clinic. Most had no or only minimal height loss, but in four individuals measured heights decreased by 6.2, 6.6, 7.0, and 6.3 cm, respectively. Height loss for these four patients resulted in artifactually high BMI values compared to values based on heights measured 7.9 to 16.1 years earlier. The apparent increase in BMI due to height loss rather than weight gain may lead to inappropriate recommendations for reduction in caloric intake. Even minor changes in diet restrictions can affect mood and behavior in individuals with PWS. Recognition of height loss as a contributing factor to BMI calculations is important for clinical studies evaluating effects of life-style changes and medical interventions for obesity.