Tibial muscular dystrophy (TMD) is a form of muscular dystrophy that affects the muscles in the ankle and tibia (the shinbone). TMD also is known as Udd distal myopathy,

The genetic cause of TMD

TMD is caused by a mutation in the TTN gene, which provides instructions to build the titin protein. Titin plays a vital role in the contraction and relaxation of muscles. As a result of mutations in the TTN gene, the function of the titin protein is altered, which causes muscle weakness and wasting over time.

The TTN gene is located on chromosome 2, which is an autosomal (non-sex)  chromosome. Chromosomes are structures within the cell that store genetic information. Everyone has 22 pairs of autosomal chromosomes, and mutations in an autosomal gene affect men and women equally.

How is TMD inherited?

Everyone has two copies of the TTN gene, one is inherited from the mother, the other one from the father. TMD is inherited in an autosomal dominant pattern, meaning that one mutated copy of the TTN gene is sufficient to cause the disease.

A person with TMD has a 50% chance of passing the disease to their children. If both parents have the disease, there is a 75% chance their children will inherit the disease.

In rare cases, TMD can be inherited in an autosomal recessive pattern, when the disease develops only if a person inherits two faulty copies of the TTN gene.

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