Disorder Zone Archives

 

Mitochondrial Myopathy

Avi Wolfson

Introduction

The term "mitochondrial myopathy" refers to a group of neuromuscular disorders that all result in a decrease in energy production in the body’s tissues. Mitochondria, which are found in all cells in the body, use food and oxygen to produce energy. When the mitochondria are not working properly (as in the case of mitochondrial myopathy), there is an energy shortage within the body and those organs that consume large amounts of energy (such as muscle, brain and the heart), are then affected. The result is often muscle weakness, fatigue, and problems with the heart, eyes, and various other systems.

Mitochondrial myopathies are typically caused by defects in a part of the mitochondria called the respiratory chain. The respiratory chain consists of four protein complexes known as type I, II, III, and IV. If there is a deficiency in any of these complexes, the individual will have mitochondrial myopathy.

Mitochondrial myopathies are typically inherited disorders. That is, they are passed on from parent to child. Mitochondrial myopathies can be inherited following two different types of inheritance patterns: Mendelian and Maternal. Below is a comparison of these two patterns:

• Mendelian: The defect is in the chromosomal genes (nuclear genes). The defect can be passed on by either parent (autosomal dominant), by the mother (X-linked), or by both parents (autosomal recessive). Symptoms and severity are consistent within family members.

• Maternal: The defect is in the mitochondria’s own genes, known as mtDNA (which are separate from the nuclear genes). The mtDNA defect can only be passed on by the mother. Symptoms and severity are not consistent within family members because the ratio of mutated cells to normal cells can vary greatly from one pregnancy to another.

In some cases, mitochondrial myopathy is not passed on by a parent, but occurs as a result of a spontaneous mutation in the individual’s mtDNA. This mutation is said to occur in the early development of the embryo.

 

Features and Characteristics

Mitochondrial myopathies affect individuals in different ways due to the various types of inheritance patterns, as well as the number of mutated mtDNA genes in relation to normal genes. Below are features of the more common mitochondrial myopathies that are inherited from each of the three categories described earlier.

Mendelian Inheritance
Leigh’s Syndrome

• Seizures
• Hypotonia
• Fatigue
• Nystagmus
• Poor reflexes
• Eating and swallowing difficulties
• Breathing problems
• Poor motor function
• Ataxia

Maternal Inheritance
Mitochondrial Encephalomyopathy Lactic Acidosis and Stroke-like episodes (MELAS)

• Short statue
• Seizures
• Stroke-like episodes with focused neurological deficits
• Recurrent headaches
• Cognitive regression
• Disease progression
• Ragged-red fibers

Sporadic Occurrence
Kearns-Sayre Syndrome (KSS)

• Progressive external ophthalmoplegia
• Pigmentary retinopathy
• Heart block
• High cerebrospinal protein

Maternal Inheritance or Sporadic Occurrence
Myoclonus Epilepsy with Ragged-Red Fibers (MERRF)

• Myoclonus
• Epilepsy
• Progressive ataxia
• Muscle weakness and degeneration
• Deafness
• Dementia

Other symptoms found in mitochondrial myopathies are drooping eyelids, gastrointestinal disorders, liver disease, diabetes, developmental delays and susceptibility to infection.

 

Diagnosis

The diagnosis of mitochondrial myopathy is typically made by taking a muscle biopsy and examining it under a microscope. The mitochondria in muscle from individuals with a mitochondrial myopathy look abnormal, and they often accumulate around the edges of the muscle fibers. The United Mitochondrial Disease Foundation suggests that mitochondrial disease should be considered when an individual exhibits the following unexplained features, especially when they occur in combination with one another:

• Encephalopathy
• Neuropathy
• Cardiac conduction defects or cardiomyopathy
• Hearing deficits
• Short stature
• Disorders of extraoccular muscles
• Diabetes
• Renal tubular disease
• Visual loss
• Lactic acidosis (may be mild)

 

Treatment

There is no cure for mitochondrial myopathy, so treatment is based on managing symptoms. Excessive exertion, which may cause nausea, headache, and weakness, should be avoided. The use of vitamins in those who have severe muscle weakness can sometimes be quite helpful. Vitamin therapies include riboflavin, coenzyme Q, vitamins C and K, and carnitine. Physical therapy may be beneficial in that it may help extend the range of movement of muscles to improve dexterity.

 

What to Expect

Since mitochondrial myopathies affect people in many ways, as mentioned earlier, it is often times difficult to predict an individual’s prognosis (especially in those with maternal inheritance patterns). The prognosis also depends largely on the type of mitochondrial myopathy that the individual has and the degree of involvement of various organs. Generally speaking, mitochondrial myopathy can range in severity from mild weakness (almost unnoticeable) to, in some cases, a shortened life span.

 

Personal Stories

Avi's medical problems began, we think, when he was about a year old, although he was not diagnosed with a mitochondrial myopathy until 1993 when he was four. Avi is now 12 years old and actually we never thought we would come to realize this age. His journey through life so far has been splattered with hospitalizations and setbacks, some major and some minor. As with any journey, eventually you may find some status quo, some normalcy that you come to savor and miss when things get churned up as they often do. Avi has developmental delays and a mental age of about two, having lost many skills and his speech quite awhile ago. His numerous medical problems have moderated but behavioral issues are always there, especially since he has great difficulty communicating with others. If there is one paramount thing we have learned from all this, it is that TOMORROW IS ANOTHER DAY! If today was lousy, if we are mad at him or ourselves for whatever, when the next day comes the slate is clean and we start over. Avi has taught us much and taught others about the differences that exist in people, and that we all need to be tolerant and more understanding. - Sara and Doug Wolfson

 

Resources

If you are interested in meeting other parents who have a child with a mitochondrial disease, please visit http://www.umdf.org and click on "Support" then "Online Support" to subscribe to an e-mail discussion list.

For more information on mitochondrial myopathy, please see the following references:

• United Mitochondrial Disease Foundation http://www.umdf.org
• The Muscular Dystrophy Campaign http://www.muscular-dystrophy.org
• National Institute of Neurological Disorders and Stroke http://www.ninds.nih.gov/health_and_medical/disorders/mitochon_doc.htm
• Muscular Dystrophy Association http://www.mdausa.org

 

The Disorder Zone has been created for educational purposes only and is not intended to serve as medical advice. The information provided in The Zone should not be used for diagnosing or treating a health problem or disease. It is not a substitute for professional care. If your child has any health concerns, please consult your health care provider.

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