Emery-Dreifuss muscular dystrophy (EDMD) is a type of muscular dystrophy characterized by muscle weakness and wasting in the upper arms and shoulders, as well as the calf muscles in the legs. Many patients with EDMD also develop heart problems.
EDMD is a genetic disorder caused by mutations in three genes: EMD, FHL1, and LMNA. These mutations can be inherited in several distinct patterns.
X-linked recessive inheritance
When EDMD is caused by mutations in EMD or FHL1, it is inherited in an X-linked recessive pattern. X-linked means that the mutation is carried on the X-chromosome (one of two sex chromosomes, which determine biological gender). Males have only one X-chromosome, so inheriting a copy of a disease-causing mutation means they will develop the disease. That is why males are more likely than females to develop EDMD caused by mutations in EMD or FHL1.
For females, the situation is more complex because they have two X-chromosomes. In most cases, females develop the disease only if they inherit the disease-causing mutation from both parents. However, females with only one copy of a disease-causing mutation sometimes do show symptoms of the disease, including heart problems and muscle weakness (though usually milder than males).
Autosomal dominant inheritance
In most cases of EDMD caused by mutations in the LMNA gene, the disease is inherited in an autosomal dominant pattern. “Autosomal” means that the genetic mutation is carried on a chromosome that is not a sex chromosome. Therefore, it affects men and women equally. Dominant inheritance means that a single copy of a disease-causing mutation (inherited from either parent) is enough to cause disease.
About 65 percent of autosomal dominant EDMD cases are caused by novel mutations (occurring in an individual with no history of the disease). The remaining cases are caused by the inheritance of the mutation from one parent.
Autosomal recessive inheritance
Rarely, EDMD caused by LMNA gene mutations can be inherited in an autosomal recessive pattern. Autosomal recessive means that patients develop the disease only if they inherit two copies of the faulty gene, one from each parent. Most often, the parents of a child with this type of EDMD each will have a single copy of the disease-causing mutation (making them carriers of the disease). In such cases, (that is, both parents being carriers of a disease-causing mutation) the children have a one-in-four chance of inheriting two copies of the mutation and developing the disease. Children also have a one-in-four chance of inheriting two healthy copies of the gene and not developing the disease, and a 50-50 chance of inheriting only one copy of the faulty gene and being a carrier like their parents.
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