Receive
e-mail news, tips and updates from MDA or ask us
a quick question.
Juvenile Spinal Muscular Atrophy
(SMA, SMA3 or KW) (Also known as SMA Type 3, Kugelberg-Welander)
Definition - a genetic disease in which loss of
nerve cells in the spinal cord called motor neurons affects the part of the
nervous system that controls voluntary muscle movement.
Cause - A deficiency of a motor neuron protein called SMN, for survival
of motor neurons, resulting from a faulty gene on chromosome 5.
Onset - after 18 months
Symptoms - Weakness is most severe in muscles closest to the center of
the body, such as those of the shoulders, hips, thighs and upper back.
Respiratory muscle weakness and spinal curvature sometimes develop.
Progression - Disease progresses slowly, with walking ability usually
maintained until at least adolescence. Wheelchair often required later in life.
Life span usually not affected.
Most doctors now consider SMN-related SMA to be a continuum of severity and
prefer not to make rigid predictions about life expectancy or weakness.
Inheritance - autosomal recessive; a faulty gene must be inherited from
each parent.
