In today’s #apaperaday, Prof. Aartsma-Rus reads and comments on the paper titled: Trabecular Bone Volume Is Reduced, With Deteriorated Microstructure, With Aging in a Rat Model of Duchenne Muscular Dystrophy
Today’s pick is from the journal of university of occupational environment and health Japan (JUOEH) by Obara et al on the analysis of bone volume in rats with and without dystrophin. DOI: 10.7888/juoeh.44.323
Duchenne is caused by lack of dystrophin. This causes loss of muscle tissue and function and also osteoporosis and fractures. Increased fracture risk is due to a combination of factors: patients fall more often due to muscle weakness, and have osteoporosis.
Osteoporosis is due to reduced bone loading (from reduced function) but also (not mentioned by the author) from chronic use of corticosteroids (care standards. Authors here study the bone mineral density (with the confusing abbreviation BMD – not Becker md in this case).
The do this analysis in a rat model for Duchenne and they study 15 and 30 week old rat (adolescent and adult rats). The body weight of rats without dystrophin is lower and the bone length at 15 weeks was reduced (but not at 30 weeks).
The bone mineral density of the rats without dystrophin is reduced to wild type. Further analysis showed this is due to reduced trabecular density and volume (i.e. the inside of the bone), while the cortical bone (hard outside shell) was the same. Authors discuss that the same is seen in mdx mice and that also in patients bone density is reduced, especially after loss of ambulation when patients no longer load the bones.
They outline limitations as well: the bodyweight was higher for wild types: this means they apply more load on the bones, which also will result in higher bone density. Furthermore, they did not study function (more active = generally better bone density) or bone dynamics (absorption and bone building).
This work does show bone density is reduced even without steroids when dystrophin is missing. However, authors should have mentioned that in Duchenne patients things are even worse for the bone density due to chronic steroid use. NOTE that steroids slow down disease progression.
While this side effect is not desirable, the benefit from chronic steroids (longer walking, better heart and respiratory function, less scoliosis) outweighs the risk of osteoporosis for most patients.