Myofibrillar myopathy (MFM) primarily affects skeletal muscles, which are muscles that the body uses for movement. In some cases, the heart (cardiac) muscle is also affected. The signs and symptoms of MFM vary widely among affected individuals, typically depending on the condition's genetic cause. Most people with this disorder begin to develop muscle weakness (myopathy) in mid-adulthood. However, features of this condition can appear anytime between infancy and late adulthood. Muscle weakness most often begins in the hands and feet (distal muscles), but some people first experience weakness in the muscles near the center of the body (proximal muscles). Other affected individuals develop muscle weakness throughout their body. Facial muscle weakness can cause swallowing and speech difficulties. Muscle weakness worsens over time. Other signs and symptoms of MFM can include a weakened heart muscle (cardiomyopathy), muscle pain (myalgia), loss of sensation and weakness in the limbs (peripheral neuropathy), and respiratory failure. Individuals with this condition may have skeletal problems including joint stiffness (contractures) and abnormal side-to-side curvature of the spine (scoliosis). Rarely, people with this condition develop clouding of the front surface of the eyes (cataracts).
Last updated: 3/18/2011
The signs, symptoms and rate of progression of myofibrillar myopathy (MFM) vary among affected individuals and may depend on the genetic cause of the condition, or the type of MFM that an individual has. Typically, the condition causes slowly progressive proximal, distal or both proximal and distal limb muscle weakness.
However, in some individuals, the condition is rapidly progressive.
The life expectancy for MFM would depend on the specific type that an affected individual has, as well as the age at which signs and symptoms first develop.
In a Mayo Clinic study including 80 individuals with MFM, the age of onset varied from two to 77 years, and the age at diagnosis ranged from 11 to 82 years. BAG3
-related myofibrillar myopathy usually presents in the first or second decade of life and is highly fatal. Desminopathies
may also present in the first decade of life, usually with cardiomyopathy
. However, the majority of MFM presents after 40 years of age.
The predominant first symptom is slowly progressive weakness; a minority of individuals experience sensory symptoms, muscle stiffness, aching, or cramps. The weakness can involve both proximal and distal muscles; however, distal muscle weakness is 25% more common than proximal weakness. Peripheral neuropathy
is present in approximately 20% of affected individuals, but muscle biopsy studies suggest an even higher frequency of peripheral nerve involvement. Overt cardiomyopathy can be a first sign or can appear later on in 15%-30% of affected individuals. Variable expressivity
(the range of signs and symptoms that are present among different people with the same condition) has been seen within families with mutations
in the DES
gene, with some family members showing signs of cardiomyopathy only, some showing signs of both myopathy and cardiomyopathy, and some with reduced penetrance
who do not show signs of either.
Last updated: 3/18/2011
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