Amyotrophic lateral sclerosis
- Amyotrophic lateral sclerosis type 1
- Lou Gehrig disease
Your QuestionDoes a father who develops ALS in his late forties have an increased risk for his son or future generations to have ALS?
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Most familial cases are inherited in an autosomal dominant manner. This means that only one altered (mutated) copy of the disease-causing gene in each cell is sufficient to cause the condition. In most of these cases, an affected individual has one parent with the condition. When an individual with an autosomal dominant form of ALS has children, each child has a 50% (1 in 2) risk to inherited the mutated copy of the gene and be affected.
Less frequently, ALS is inherited in an autosomal recessive manner. In autosomal recessive inheritance, both copies of the disease-causing gene (typically one copy inherited from each parent) must have a mutation for the individual to be affected. The parents of an individual with an autosomal recessive condition, who presumably each carry one mutated copy of the gene, are referred to as carriers. Carriers typically do not have any signs or symptoms of the condition. When two carriers for the same condition are having children, each child has a 25% (1 in 4) risk to have the condition, a 50% (1 in 2) risk to be a carrier like each parent, and a 25% risk to not have the condition and not be a carrier. Autosomal recessive forms of ALS may be mistaken for non-inherited (sporadic) forms due to having a negative family history of the condition.
In rare cases, ALS is inherited in an X-linked dominant manner. This occurs when the disease-causing gene is located on the X chromosome (a sex chromosome). Although females have 2 X chromosomes, having a mutation in one X chromosome is still sufficient to cause the condition. Males who have a mutation (and only one X chromosome) will have the condition. Usually, males with an X-linked dominant form of ALS experience more severe symptoms than females with the same form.
Some individuals who do inherit a mutation known to cause ALS never develop signs and symptoms of ALS, although the reason for this is unclear. This phenomenon is referred to as reduced penetrance.
Onset of ALS may occur any time from the teenage years up to the late 80s. The average age of onset for sporadic (non-inherited) ALS has been estimated to be around 56 to 65 years (estimates vary among sources). The average age of onset for familial ALS is approximately 46 years. However, onset of either form may occur years before or after these average ages.
You can find laboratories offering clinical and research genetic testing for ALS on a Web site called GeneTests. To see GeneTests' list of the types of ALS for which genetic testing is available, click here. Click on "Testing" next to each type of ALS of interest to see a list of the laboratories that offer clinical testing. Click on "Research" next to each type of ALS of interest to see a list of the laboratories that offer research testing.
Please note that most of the laboratories listed through GeneTests do not accept direct contact from patients and their families. Therefore, if you are interested in learning more, you will need to work with a health care provider or a genetics professional.
The following online resources can help you find a genetics professional in your community:
- The National Society of Genetic Counselors provides a searchable directory of US and international genetic counseling services.
- The American College of Medical Genetics has a searchable database of US genetics clinics.
- The University of Kansas Medical Center provides a list of US and international genetic centers, clinics, and departments.
- The American Society of Human Genetics maintains a database of its members, which includes individuals who live outside of the United States. Visit the link to obtain a list of the geneticists in your country, some of whom may be researchers that do not provide medical care.
- Amyotrophic lateral sclerosis. Genetics Home Reference. August 2012; http://ghr.nlm.nih.gov/condition/amyotrophic-lateral-sclerosis. Accessed 1/7/2013.
- Lisa Kinsley and Teepu Siddique. Amyotrophic Lateral Sclerosis Overview. GeneReviews. May 31, 2012; http://www.ncbi.nlm.nih.gov/books/NBK1450/. Accessed 1/11/2013.
- Carmel Armon. Amyotrophic Lateral Sclerosis (ALS). Medscape Reference. August 26, 2011; http://emedicine.medscape.com/article/1170097-overview#a0156. Accessed 1/11/2013.
- Nigel Leigh and Lokesh Wijesekera. Amyotrophic lateral sclerosis. Orphanet. May 2011; http://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN&Expert=803. Accessed 1/11/2013.
- Donkervoort S, Siddique T. Amyotrophic Lateral Sclerosis. GeneReviews . 2009; http://www.ncbi.nlm.nih.gov/books/NBK1450/. Accessed 4/12/2011.