Genetic testing can help determine the cause of FALS in a family. Testing is most useful in a person who has been diagnosed with ALS. About 50% of individuals with FALS will have a mutation identified. Those families with FALS where a mutation is not identified probably have FALS caused by a gene or genes that have not yet been discovered. Not having an identified genetic mutation does not eliminate a FALS diagnosis and other family members may still be at risk for developing ALS. If a person in the family with ALS has a negative genetic test result (no identified genetic mutation), testing family members without a diagnosis of ALS will not provide more information. If no one in the family with ALS is available for genetic testing, a negative test result in an unaffected person cannot be interpreted. Because FALS usually doesn’t usually appear until later in life, genetic testing of children under age 18 is not usually recommended.