Causes Becker muscular dystrophy

Becker muscular dystrophy is a genetic condition – it is caused by a mutation or mistake in the genetic code (DNA). In Becker muscular dystrophy, the mutation occurs in a gene called dystrophin, which is located on the X-chromosome (girls have two X-chromosomes and boys have only one).

In Becker muscular dystrophy, the genetic mutation causes a faulty (smaller or less abundant than normal) protein called dystrophin to be produced in the muscles. This protein is important to maintain the integrity of the muscles, so when it is smaller or less abundant than normal, the muscle fibres gradually break down and the muscles slowly become weaker.

Some mutations result in the complete absence of the dystrophin protein in muscles and this causes the more severe form of muscular dystrophy, called Duchenne muscular dystrophy.

In some cases, Becker muscular dystrophy is inherited from the mother who is a carrier, but it can also be caused by a new mutation in the child’s genes. Each son of a carrier mother has a 50:50 chance of being affected and each daughter has a 50:50 chance of being a carrier.

If a woman carries the gene mutation, then she is known as a ‘carrier’. Usually female carriers are not affected because they have a second X-chromosome, which produces the dystrophin protein. A small number of female carriers have a degree of muscle weakness themselves and they are known as ‘manifesting carriers' (please see our factsheet called Manifesting carriers).

Genetic advice (counselling) and testing for other family members at risk of being carriers should be provided as soon as possible following a diagnosis of Becker muscular dystrophy. Your clinician or GP can arrange this for you.