Abstract
Background/Objective: Reduced bone mineral density is a feature of patients with reduced mobility. The
aim of this study was to assess bone mineral density in children with spinal muscular
atrophy (SMA) and to evaluate bone mineral density in relation to age and motor disability.
Patients and Methods: We analysed bone mineral density measurements on twelve patients (4 with SMA type
II, mean age 8.2 years [range 6.2 - 11.8]; 8 with SMA type III, mean age 11.8 years
[range 5.5 - 20]). Dual-energy X-ray absorptiometry (DXA) was used to determine total
body bone mineral density. The results were matched with published normative data
for age and sex for a white Caucasian population.
Results: The total body bone mineral density values were in the normal range in 10 out of
the 12 SMA patients studied, all below the age of 17 (mean age 8.8 years [range 5.5
- 16.33]). Four of them had SMA II and six had had SMA III and were still ambulant.
Total body bone mineral density was, however, below 2 SD in the remaining 2 patients
aged 19.7 and 20 years, respectively. Both had SMA III but had lost independent ambulation
for a period of 3.5 years.
Conclusion: Our results suggest that bone mineral density was surprisingly normal in most of
the young SMA children studied. This is in contrast to what is reported in other conditions
characterised by reduced mobility such as Duchenne muscular dystrophy. However, there
was a tendency to decreasing bone mineral density with increasing age, not always
related to the ability to walk, with the two eldest patients having the lowest values
in spite of a relatively good mobility. These findings suggest that factors other
than mobility are likely to have an effect on SMA bone mineral density.
Key words
Spinal muscular atrophy - mobility - bone mineral density - muscle weakness
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Professor Francesco Muntoni
Dubowitz Neuromuscular Centre
Department of Paediatrics
Imperial College
Hammersmith Hospital
Du Cane Road
London W12 OHN
U.K.
Email: f.muntoni@ic.ac.uk
