What are the other Names for this Condition? (Also known as/Synonyms)

• MFM (Myofibrillar Myopathy)

What is Myofibrillar Myopathy? (Definition/Background Information)

• Myofibrillar Myopathy (MFM) is an extremely rare type of muscular dystrophy
• Myopathy, which literally means muscle disease in Greek, causes wasting and consequential weakness of the affected muscles. In MFM, protein fibers (myofibrils), which help the muscles contract, become degenerated
• Myofibrillar Myopathy typically affects individuals in their mid-adulthood; however, symptoms could potentially appear anytime between infancy to late adulthood
• Having a family member with MFM is considered a major risk factor for an individual in developing the condition. Mutations in certain genes are reported to cause Myofibrillar Myopathy. However, it could also occur in individuals with no family history of the condition
• The symptoms of MFM are typically a weakening of the muscles; either the proximal (such as hips and shoulders) or distal muscles (those farther away from the trunk) could be weakened. There could also be associated pain and cramping of the muscles
• Treatment for Myofibrillar Myopathy is usually geared towards tackling the symptoms and making the individual feel comfortable
• Myofibrillar Myopathy is not a preventable condition; however, early diagnosis and prompt treatment could help an individual lead a relatively normal quality of life

Who gets Myofibrillar Myopathy? (Age and Sex Distribution)

• Myofibrillar Myopathy is an extremely rare disorder. The prevalence of this condition is not exactly known
• Typically, MFM is observed during middle-age. But, the condition could potentially manifest between infancy and late adulthood
• Both male and female genders are affected
• There are no particular racial and ethnic group preference observed

What are the Risk Factors for Myofibrillar Myopathy? (Predisposing Factors)

• A family history of Myofibrillar Myopathy is the predisposing factor for the development of this disorder

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Myofibrillar Myopathy? (Etiology)

Myofibrillar Myopathy could occur as a result of inherited gene mutations, or spontaneously in individuals with no known family members affected by the disorder.

• When the cause is genetic, mutations in the following genes are responsible for half of all cases of MFM:
  • BAG3 gene
  • DES gene
  • MYOT gene
  • CRYAB gene
  • FLNC gene
  • LDB3 gene
• Of the 6 genes, mutations in DES, LDB3, and MYOT account for the majority of cases of MFM
• Myofibrillar Myopathy is an autosomal dominant condition, meaning that it is not carried on sex chromosomes X or Y (autosomal) and one copy of the defective gene is enough to cause MFM

Autosomal dominant: Autosomal dominant conditions are traits or disorders that are present when only one copy of the mutation is inherited on a non-sex chromosome. In these types of conditions, the individual has one normal copy and one mutant copy of the gene. The abnormal gene dominates, masking the effects of the correctly functioning gene. If an individual has an autosomal dominant condition, the chance of passing the abnormal gene on to their offspring is 50%. Children, who do not inherit the abnormal gene, will not develop the condition or pass it on to their offspring.

What are the Signs and Symptoms of Myofibrillar Myopathy?

Since Myofibrillar Myopathy affects various muscles, the symptoms could involve the entire body, and these may include:

• Muscle stiffness and weakness
• Stiffening of joints
• Muscle pain (myalgia)
• Cramps
• Frequent falls
• Facial weakness causing difficulty swallowing and impeded speech
• Numbness in the arms and legs (peripheral neuropathy)
• Weakening of heart muscles (cardiomyopathy), which could cause palpitations, fainting spells, etc.
• Skeletal defects such as scoliosis
• In rare cases, cataract

How is Myofibrillar Myopathy Diagnosed?

A physician or specialist may employ one or more of the following to arrive at an accurate diagnosis of Myofibrillar Myopathy:

• An assessment of the signs and symptoms
• Genetic testing, if MFM is suspected, to check for the kind of mutation involved
• Muscle biopsy to check for abnormalities in the muscle structure
• Electromyography to evaluate electrical activity in skeletal muscles

What are the possible Complications of Myofibrillar Myopathy?

• Since Myofibrillar Myopathy results in decreased muscle strength, strenuous physical activity may be limited or even impossible in some individuals with the condition
• The possible damage to the heart may result in palpitations, fainting, or even sudden death

How is Myofibrillar Myopathy Treated?

Currently, there is no specific cure for Myofibrillar Myopathy. The goal of treatment is to control the symptoms and build muscle strength, to allow the affected individual to live comfortably. The treatment may include:

• Bracing and stretching techniques to improve muscle abnormalities
• Specific orthopedic surgery to correct any abnormality of the joint or bone 
• Relieve pain, and reinstate independence to the affected individual
• A pacemaker may be used if the heart muscles are severely affected

How can Myofibrillar Myopathy be Prevented?

• Currently, there are no specific methods or guidelines to prevent Myofibrillar Myopathy, since it is a genetic condition
• Genetic testing of the expecting parents (and related family members) and prenatal diagnosis (molecular testing of the fetus during pregnancy) may help in understanding the risks better during pregnancy
• If there is a family history of the condition, then genetic counseling will help assess risks, before planning for a child
• Active research is currently being performed to explore the possibilities for treatment and prevention of inherited and acquired genetic disorders

What is the Prognosis of Myofibrillar Myopathy? (Outcomes/Resolutions)

• In general, most individuals affected by Myofibrillar Myopathy, who maintain a healthy lifestyle and receive supportive care, could live well into adulthood
• However, full life expectancy may not be achieved in the affected individuals

Additional and Relevant Useful Information for Myofibrillar Myopathy:

The Office of Rare Diseases of the National Institutes of Health (USA) has Myofibrillar Myopathy (MFM) listed as rare, due to the fact that it affects less than 200,000 of the US population.