ESPE Abstracts

Background: Spinal Muscular Atrophy (SMA) is characterised by progressive muscle weakness, resulting from loss of anterior horn cells in the spinal cord and the brain stem nuclei. Survival motor neuron levels (SMN) are reduced due to mutations in the SMN1 gene. SMN function has been implicated in poor bone health. SMA is classified according to age of onset and clinical course accordingly: type 0 (prenatal), type 1 (onset <6 months, severe, never sit unsupported), type 2 (onset 6–12 months, intermediate, sit unsupported but never walk) and type 3 (onset >12 months and mild, walk). Congenital bone fractures have been described in type 1 SMA. Patients with SMA are at increased risk of osteoporosis, but there are very few studies quantifying this risk.

Objective and hypotheses: We sought to determine the prevalence of low bone mineral density (BMD) and to assess bone remodelling indices.

Method: BMD was measured at spine and whole body. Early morning fasting blood samples were obtained: 25-hydroxyvitamin D (25OHD), calcium, parathyroid hormone (PTH), procollagen type 1 N-terminal propeptide (P1NP), and timed-urine for N-terminal telopeptides of type 1 collagen (NTX).

Results: We studied ten patients (mean age 7 years (2–18 years)); eight had SMA type 2 and two were type 3. Median (range) for tests was as follows: 25OHD was 55.9 (34.2–74.5) nmol/l; P1NP was 353.5 (61.8–711) μg/l; NTX was 1058.7 (512–3081) nMBCE/mMCr; and spine Z-score −3.8 (−4.3 to −1.1). WB Z score could not be evaluated due to spinal surgery prosthesis.

Conclusion: Our patients frequently had low 25OHD, low bone formation and high bone resorption. Spine BMD was also suboptimal and lower than spinal BMD that we observed in boys with Duchenne muscular dystrophy. We suggest that bone health should be closely monitored in SMA.