"Typical spinal muscular atrophies begin in infancy or early childhood and are fatal, involving all motor neurons, but spinal muscular atrophy with lower extremity predominance, (SMA-LED) predominantly affects nerve cells controlling muscles of the legs.
"It is not fatal and the prognosis is good, although patients usually are moderately disabled and require assistive devices such as bracing and wheelchairs throughout their lives," said Robert H Baloh, who led the study at Cedars-Sinai Medical Center.
It is a molecule inside cells that acts as a motor to transport cellular components. Using cells cultured from patients, Baloh's group showed that the mutation disrupts this motor's function.
The scientists found that some subjects with mutations had global developmental delay in addition to weakness, indicating the brain also is involved.
"Our observations suggest that a range of DYNC1H1 -related disease exists in humans -- from a widespread neurodevelopmental abnormality of the central nervous system to more selective involvement of certain motor neurons, which manifests as spinal muscular atrophy," Baloh said.
He saidpointed out while this molecule is responsible for some inheritable cases of spinal muscular atrophy with lower extremity predominance, genetic mutation is absent in others.
"Although this is a rare form of motor neuron disease, it tells us that dynein function -- the molecular motor -- is crucial for the development and maintenance of motor neurons, which we hope will provide insight into the common form of spinal muscular atrophy and also amyotrophic lateral sclerosis," Baloh said in a release.