Spinal muscular atrophy affects individuals of all ethnic groups, unlike other well-known autosomal recessive disorders, such as sickle cell disease and cystic fibrosis, which have significant differences in occurrence rate among ethnic groups. SMA linked to chromosome 5 (SMN-related), types 0-4 In spinal muscular atrophy (SMA ) types 0 through 4, symptoms vary on a continuum from severe to mild based on how much functional SMN protein there is in the nerve cells called motor neurons. (“SMN” stands for survival of motor neuron.) The more SMN protein there is, the later in life symptoms begin and the milder the course of the disease . The number of copies of SMN2 genes, which can offset malfunctioning SMN1 genes, determines SMA ... Spinal muscular atrophy ( SMA ) causes muscle weakness and progressive loss of movement. It is caused by deterioration in the nerve cells (motor neurons) connecting the brain and spinal cord to the body’s muscles. SMA involves the loss of nerve cells called motor neurons in the spinal cord and is classified as a motor neuron disease . In the most common form of SMA (chromosome 5-related SMA, or SMN-related SMA), there is wide variability in age of onset, symptoms, and rate of progression.
