X-linked recessive inheritance Inheritance and genetics

X-linked recessive inheritance includes but is not limited to: Duchenne muscular dystrophy, Becker muscular dystrophy, Emery-Dreifuss muscular dystrophy, X-linked myotubular myopathy (X-MTM)

These conditions are caused by a mutation in a gene on the X chromosome, which is one of the sex chromosomes. Males have one X chromosome and one Y chromosome; females have two X chromosomes.

If a male’s X chromosome has the mutated gene, then he will have the condition. He has only one copy of the gene and the mutation isn’t on the Y chromosome.

If a female has the mutated gene on one of her X chromosomes, she still has a healthy copy of the gene on her other X chromosome. This makes her a ‘carrier’ and she will not usually have symptoms of the condition.

If a carrier of an X-linked condition and a non-carrier have children, there is a 50 percent chance that each son will have the condition and a 50 percent chance that each daughter will be a carrier (see first diagram).

This diagram shows what would be a likely outcome if a carrier mother of an X-linked recessive condition had children with an unaffected father. They have 4 offspring, 1 unaffected daughter, 1 unaffected son. They also have a carrier daughter and an affected son.

Diagram 1

This probability is the same for each child born. So, for instance, if this couple have two sons, each son will have a 50 percent chance of inheriting the condition.

Unaffected males cannot pass on an X-linked condition. Affected males cannot pass an X-linked condition to their sons, but all of their daughters will be carriers (see second diagram)

This diagram shows the likely outcome if a non-carrier mother and an affected father had children. They have 4 children; two carrier daughters and two unaffected sons.

Diagram 2