Genetics of familial amyotrophic lateral sclerosis

The completion of the Human Genome Project, together with a better understanding of some of the emerging genetic patterns of human disease, has enabled a thorough examination of the most appropriate genetic models for amyotrophic lateral sclerosis (ALS). The pathology and epidemiology of ALS have been intensively studied since Adar, Charcot, and Duchenne first described the disease in the 1860 s. Results of genetic studies that have emerged over the past two decades have led to the identification of SOD1 as a well-established causative gene for ALS. However, the identification of SOD1 has not been followed up by the identification of other genes responsible for classic ALS. This leads to the speculation that more complex genetic mechanisms are involved than initially assumed. While mutations in single genes are still likely to constitute a small proportion of ALS cases, the genes responsible for ALS in families with clusters of two or three affected individuals, and more particularly in sporadic cases, are far from being determined. Multigenic, somatic mutation, and gene-environment models may all contribute to the genetic etiology of ALS. The challenge now lies in determining which models are the most appropriate to dissect out the genetic components involved. This research will ultimately aid in identifying the cumulative risk of developing ALS.