Spinal muscular atrophy

Spinal muscular atrophy (SMA) is a group of autosomal recessive, proximal disorders of the 2nd motor neuron (spinal α motoneuron), characterized by progressive loss of motor neurons in the anterior horn of the spinal cord. The retardation of motor neurons causes impulses not to be transmitted to the muscles. Events with the characteristics muscle atrophy and reduced muscle tension are the result. Cranial nerves may also be affected, resulting in additional impairments of swallowing, chewing and speech functions.

The different SMA types are distinguished and described in the table below.

The classification is mainly based on what the person concerned achieved at a maximum at motor ability. The distances between the types are fluid and by no means clearly defined. Even a prognosis is not possible in individual cases solely from the type classification. Early-onset forms are generally associated with unfavorable prognosis, while life expectancy in the late onset forms is nearly normal. Causes of death are respiratory insufficiency and infections.

Much depends on whether all currently available measures are taken in time to stabilize the respiratory situation, usually with a facial mask ventilation.

Clinical image
SMA type onset motor ability survival time
I 0 - 6 months Ø sitting 90%, < 2 years
II 6 - 18 months sitting, Ø free walking 70% > 20 years
III > 18 months free walking, wheelchair barely reduced
IV > 30 years minor restrictions not reduced