Mutations in the ALS2, SETX, SOD1, and VAPB genes cause amyotrophic lateral sclerosis. Humans normally have 46 chromosomes in each cell. These chromosomes are divided into 23 pairs. Each person has two copies of chromosome 9, one was inherited from each parent. Chromosome 9 is made up of about 140 million DNA building blocks and represents approximately four and a half percent of a persons total DNA. Many genetic conditions are related to changes or mutations in chromosome 9. One of these diseases is thought to be ALS. Research is focusing in on this chromosome for answers.