Evolution of bone mineral density, bone metabolism and fragility fractures in Spinal Muscular Atrophy (SMA) types 2 and 3.


Spinal muscular atrophy (SMA) is caused by homozygous deletion and/or mutation of the survival motor neuron 1 (SMN1) gene on chromosome 5q13, leading to degeneration of lower motor neurons [1]. An increasing body of preclinical and anecdotal clinical studies suggest that SMA can be considered as a multi-system disorder, due to the ubiquity of the SMN protein [2–4]. Four types of SMA are currently recognized, with types 1 to 3 having a childhood onset. Infants with SMA type 1 are most severely affected, showing generalized muscle weakness, hypotonia, and inability to sit unsupported since early infancy, with death occurring within the first 2 years of life in the absence of proactive nutritional and respiratory support.


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