Familial Amyotrophic Lateral Sclerosis
If a person has amyotrophic lateral sclerosis (ALS) and one or more immediate family members also has the disease (for example, a parent, sibling, or grandparent), then the condition is considered familial amyotrophic lateral sclerosis. This inherited form of the disease is not as common as sporadic ALS, but symptoms and treatment are similar.
Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a rapidly progressive, invariably fatal, neurological disease. ALS attacks the nerve cells (neurons) responsible for controlling voluntary muscles. This disease belongs to a group of disorders known as motor neuron diseases, which are characterized by the gradual degeneration and death of motor neurons.
About 5 out of every 100 people who get ALS have an inherited, or familial, form. This means that one or more of their immediate family members -- parents, brothers, sisters, or grandparents -- also has the disease. Children of parents with familial amyotrophic lateral sclerosis have a 50-50 chance of developing the disease themselves.
In 1993, scientists identified a gene (SOD1 -- superoxidase dismutase 1) that, when defective, is associated with some cases of familial amyotrophic lateral sclerosis. This gene carries the "operating instructions" for a protein whose function is to neutralize cell-damaging substances called free radicals. Some scientists believe that when the gene is defective, an excessive buildup of free radicals may kill motor neurons.
However, this genetic mutation is found in only about one-fifth of people with familial ALS, and it has not been detected in anyone with the sporadic (noninherited) form of the disease, which is far more common.
Because not all cases of familial ALS are due to the SOD1 mutation, other unidentified genetic causes clearly exist.