What types of amyotrophic lateral sclerosis are there?
Two major types of amyotrophic lateral sclerosis are known: familial and sporadic. Familial amyotrophic lateral sclerosis accounts for about 10% of all ALS cases. As the name suggests, familial ALS is believed to be caused by the inheritance of one or more faulty genes. About 15% of families with this type of ALS have mutations in the gene for SOD-1. SOD-1 gene defects are dominant, meaning only one gene copy is needed to develop the disease. Therefore, a parent with the faulty
gene has a 50% chance of passing the gene along to a child.
Sporadic amyotrophic lateral sclerosis has no known cause. While many environmental toxins have been suggested as causes, to date no research has confirmed any of the candidates investigated, including aluminum and metal dental fillings. As research progresses, it is likely that many cases of sporadic ALS will be shown to have a genetic basis as well.
A third type, called Western Pacific amyotrophic lateral sclerosis, occurs in Guam and other Pacific islands. This form combines symptoms of both ALS and Parkinson's disease.