How is DMD caused in girls? Around 1 in 50 million girls have Duchenne. It may be rare, but it does happen. Girls and women with DMD, Duchenne UK is here to support you. More boys than girls are affected by DMD because of the way the genes are passed down from parents to children. For more information, about genes and chromosomes, click on the ‘What are the causes of DMD?’ section above. A girl only develops DMD if both of her X chromosomes have faults in their dystrophin genes. This can only happen if one of the following extremely rare events takes place: - The girl inherits a faulty dystrophin gene on one of her X chromosomes from her mother and also develops a spontaneous mutation in her other X chromosome - The girl’s healthy dystrophin gene on one X chromosome becomes ‘switched off’ by a process called X-linked inactivation because she has inherited a faulty dystrophin gene on her other X chromosome - The girl’s father is a man with DMD and her mother is a woman who carried a defective DMD gene (‘a carrier’) - The girl develops spontaneous mutations in the DMD gene on both of her X chromosomes We are here to help everyone affected by DMD – girls and women, as well as boys and men.