These conditions are inherited, and the different muscular dystrophies follow various inheritance patterns. The best-known type, Duchenne muscular dystrophy (DMD), is inherited in an X-linked recessive pattern, meaning that the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes, and is thus considered sex-linked. 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 must generally be present in both copies of the gene to cause the disorder (relatively rare exceptions, manifesting carriers, do occur due to dosage compensation/X-inactivation). Males are therefore affected by X-linked recessive disorders much more often than females. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.
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Last Updated: Feb 1, 2011