Bone Abstracts

Objective: In girls with Rett syndrome

Describe bone mineral density (BMD) and contributing factors in a cross-section of subjects.

Examine serial DXA measures.

Examine effect of pamidronate on BMD over time.

Methods: We reviewed the clinical course, medications, level of ambulation, 25-OH-Vit D levels, fracture history and DXA results in 13 girls with Rett syndrome. Eight subjects had more than one DXA study, including two treated with Pamidronate. Body sites scanned included whole body when possible (WB), lumbar spine (LS), and lateral distal femur (LDF). Age and gender-matched Z-scores were calculated using manufacturer-provided normative values for LS and WB, and published norms for the LDF.

Results: 13 girls with a mean age of 9.6 years (range 6.6–18.2) at the time of initial DXA were included in this study. Eight were partially or fully ambulatory.

We were able to obtain LDF and LS DXAs on all subjects. Mean (and range) LS BMD Z-scores were −1.9 (−0.1 to −4.4); for the LDF: R1: −4.5 (−1.9 to −8.5); R2: −3.4 (−1.3 to −7.8); and R3: −3.5 (0.1 to −11.2).

Only six WB scans could be acquired, with a mean Z-score of −2.6 (−1.3 to −4.4). The inability to lie still and positioning limitations precluded WB DXA measurement.

25-OH-Vit D levels ranged from 6.0 to 50.8 ng/dl at the time of initial DXA, with a median level of 26.0.

Serial DXA studies: Length of observation in the six untreated subjects ranged from 3.1 to 6.1 years after the initial study, and 2.8 to 8.2 years in the two treated girls. The two girls treated with Pamidronate, of whom one was ambulatory, had a history of multiple fractures prior to treatment, and the lowest baseline LS and LDF DXA Z-scores. As expected, their Z-scores increased dramatically with Pamidronate. In contrast, there was no clear pattern in BMD Z-scores in the six untreated girls; slight increases and decreases were observed over time, seemingly unrelated to ambulatory status and vitamin D levels.

Conclusions: Girls with Rett syndrome have below normal BMD, particularly of the lower extremities. The two who suffered multiple fractures and then received bisphosphonate, have had no fractures since treatment began. As demonstrated in other disabled populations, the LDF proved to be an easily-obtained, useful alternative DXA site in Rett syndrome.