Risk factors that may be associated with ALS include: 1) genetic mutations, including the intermediate CAG repeat expansion in ATXN2; 2) previous exposure to heavy metals such as lead and mercury; 3) previous exposure to organic chemicals, such as pesticides and solvents; 4) history of electric shock; 5) history of physical trauma/injury (including head trauma/injury); 6) smoking (a weak risk factor for ALS in women); and 6) other risk factors, such as participating in professional sports, lower body mass index, lower educational attainment, or occupations requiring repetitive/strenuous work, military service, exposure to Beta-N-methylamino-l-alanin and viral infections.