Osteoporosis and Ambulation in Girls with Rett Syndrome

Background:  

Rett syndrome (RTT) is a severe neurodevelopmental disorder associated with a broad spectrum of symptoms including diminished motor skills and locomotion, epileptic seizures, developmental regression, movement disorders and subsequent global developmental delay. For the majority of patients with RTT, the cause is a de novo mutation in the X-linked gene methyl-CpG-binding protein 2 (MECP2) located at Xq28. Growth failure can complicate the clinical course of RTT.  The growth trajectory of children with RTT deviates from the typical pattern of growth failure in children who have chronic illnesses or other central nervous system or chromosomal disorders which is characterized by early deceleration of head growth, followed by deceleration of height and weight gain. 

Prior studies have investigated some of the multiple factors responsible for the growth abnormalities seen in girls with RTT such as the rett/MECP2 mutation, nutrition, and medications. The frequent occurrence of osteoporosis and generalized growth failure in RTT raises the question of the influence maintaining ambulation has on bone health. Bone formation and remodeling are complex processes and dependent upon various conditions, ambulation and exercise being important factors. 

Objectives:  We hypothesized if girls with RTT maintain ambulation, they will have improved bone growth and thus a higher percentile (z-score) in height for age. This study was designed to broaden our understanding of the effects maintaining ambulatory status on children with RTT.

Methods:  All girls with Rett syndrome seen in the Rett Clinic at Children's Hospital Los Angeles were weighed and measured by a clinical dietician familiar with girls with Rett syndrome.  Growth was plotted on a standard growth chart and z-score for height was calculated. 

Results: Girls who were independent ambulators had a higher height Z-score for age compared to those who were nonambulators or partially dependent ambulators. Further, the height z-score for age was closer to the 50%th percentile regardless of age. 

Conclusions:  Girls with Rett syndrome who are able to ambulate have higher height z-score for age compared to those girls who were either nonambulators, or partially dependent ambulators.  Therefore, promotion of ambulation may benefit girls with Rett syndrome by promoting bone health and growth.