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Diseases

Genetic and Rare Diseases Information Center (GARD)

Spinal muscular atrophy


Inheritance

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How is spinal muscular atrophy inherited?

Most forms of spinal muscular atrophy (types I, II, III, and IV, specifically) are inherited in an autosomal recessive pattern.[1] This means that to be affected, a person must have a mutation in both copies of the responsible gene in each cell. The parents of an affected person usually each carry one mutated copy of the gene and are referred to as carriers. Carriers typically do not show signs or symptoms of the condition. When two carriers of an autosomal recessive condition have 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 of the parents, and a 25% chance to not have the condition and not be a carrier.

Finkel type spinal muscular atrophy is inherited in an autosomal dominant pattern, which means an affected person only needs a mutation in one copy of the responsible gene in each cell.[1]

X-linked infantile spinal muscular atrophy is inherited in an X-linked pattern. The gene associated with this condition is located on the X chromosome, which is one of the two sex chromosomes. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), a mutation would have to occur in both copies of the gene to cause the disorder. Because it is unlikely that females will have two altered copies of this gene, males are affected by X-linked disorders much more frequently than females. A striking characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.[1]
Last updated: 1/7/2016

References
  1. Spinal muscular atrophy. Genetics Home Reference (GHR). January 2013; http://ghr.nlm.nih.gov/condition/spinal-muscular-atrophy.


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