Tibial muscular dystrophy is caused by mutations in the TTN gene, which encodes for a protein called titin. The disease is inherited in an autosomal dominant manner, meaning that a single copy of the mutated gene is sufficient to cause the disease.
The main symptoms of tibial muscular dystrophy are muscle weakness and cardiomyopathy, which is heart muscle disease.
For most patients with tibial muscular dystrophy, symptoms of muscle weakness start after age 35. Patients might find it difficult to walk or may feel their ankles are weak.
The first muscles affected are the leg muscles that lay over the tibia or shinbone. This is the muscle responsible for controlling the up-and-down motion of the feet. As the muscle atrophies (weakens, or shrinks), patients gradually find it more difficult to walk on their heels.
The most common form of the disease progresses very slowly. About one-third of patients begin having problems lifting their toes when they walk (foot drop) 10 or 20 years after the onset of the muscle weakness in the legs. The foot drop may make it difficult to walk without a brace or other support, but most patients never lose the ability to walk.
For patients with the more severe form of the disease, symptoms of muscle weakness begin in childhood and become more severe as they age. These patients are likely to lose the ability to walk by the time they are 30. For these patients, the muscle atrophy spreads from the lower leg muscles to the upper leg muscle (the quadriceps) and the arm muscles.
Some patients also may develop cardiomyopathy, which can make it difficult for the heart to beat. Cardiomyopathy is more likely to occur in patients with the early onset form of the disease.
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