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Spring 2002 Table of Contents
Versión Español de este artículo (Spanish Version)

Mitochondrial Diseases

Excerpted and reprinted with permission from the United Mitochondrial Disease Foundation, Inc.
http://www.umdf.org/

SEE/HEAR Editor's note: A number of children in Texas who are visually impaired or deafblind have as the cause of their sensory loss, Mitochondrial diseases. In order to understand more about these diseases, I visited the United Mitochondrial Disease Foundation website. I learned that we have a great opportunity in Texas to learn more about these diseases because their 5th International Conference on Mitochondrial Diseases will be held this year in Dallas. I want to thank the UMDF for letting me excerpt portions of the wealth of information they provide on their website to share with our SEE/HEAR readers. I encourage you to visit this website if you have a child with a Mitochondrial disease or if you are a teacher working with one of these children.

Basis of the Disease

Mitochondrial diseases result from failures of the mitochondria, specialized compartments present in every cell of the body except red blood cells. Mitochondria are responsible for creating more than 90% of the energy needed by the body to sustain life and support growth. When they fail, less and less energy is generated within the cell. Cell injury and even cell death follow. If this process is repeated throughout the body, whole systems begin to fail, and the life of the person in whom this is happening is severely compromised. The disease primarily affects children, but adult onset is becoming more and more common.

Diseases of the mitochondria appear to cause the most damage to cells of the brain, heart, liver, skeletal muscles, kidney and the endocrine and respiratory systems.

Depending on which cells are affected, symptoms may include loss of motor control, muscle weakness and pain, gastro-intestinal disorders and swallowing difficulties, poor growth, cardiac disease, liver disease, diabetes, respiratory complications, seizures, visual/hearing problems, lactic acidosis, developmental delays and susceptibility to infection.

When to Suspect Mitochondrial Dysfunction

There is no one identifying feature of mitochondrial disease. Patients can have combinations of problems whose onset may occur from before birth to late adult life. Think mitochondria when:

• A "common disease" has atypical features that set it apart from the pack.
• Three or more organ systems are involved.
• Recurrent setbacks or flare ups in a chronic disease occur with infections.

Mitochondrial diseases, or cytopathies, should be considered in the differential diagnosis when there are these unexplained features, especially when these occur in combination:

Symptoms

• Encephalopathy
  • Seizures
  • Developmental Delay or Regression (including early and late-onset dementia)
  • Myoclonus
  • Movement Disorders (dystonia, dyskinesias, chorea, etc.)
  • Complicated Migraine
  • Stroke    
• Neuropathy
• Cardiac Conduction Defects or Cardiomyopathy
• Hearing Deficits
• Short Stature
• Disorders of Extraoccular Muscles
  • ptosis
  • acquired strabismus
  • ophthalmoplegia
• Diabetes
• Renal Tubular Disease
• Visual Loss
  • retinitis pigmentosa
  • optic atrophy
• Lactic Acidosis (may be mild)

Mitochondrial diseases with associated vision and hearing losses and descriptions

There are quite a large number of Mitochondrial diseases listed on the United Mitochondrial Disease Foundation website. Some of these have various visual conditions and hearing loss associated with them. Some of the ones listed include:

Alpers Disease

Long name: Progressive Infantile Poliodystrophy.

Symptoms: seizures, dementia, spasticity, blindness, liver dysfunction, and cerebral degeneration.

Complex I Deficiency

Long Name: NADH dehydrogenase (NADH-CoQ reductase) deficiency.

Symptoms: Three major forms:

1. Fatal infantile multisystem disorder, characterized by developmental delay, muscle weakness, heart disease, congenital lactic acidosis, and respiratory failure.
2. Myopathy beginning in childhood or in adult life, manifesting as exercise intolerance or weakness. Elevated lactic acid common.
3. Mitochondrial encephalomyopathy (including MELAS), which may begin in childhood or adult life and consists of variable combinations of symptoms and signs, including ophthalmoplegia, seizures, dementia, ataxia, hearing loss, pigmentary retinopathy, sensory neuropathy, and uncontrollable movements. May cause Leigh Syndrome.

Complex III Deficiency

Long Name: Ubiquinone-cytochrome c oxidoreductase deficiency.

Symptoms: Four major forms:

1. Fatal infantile encephalomyopathy, congenital lactic acidosis, hypotonia, dystrophic posturing, seizures, and coma. Ragged-red fibers common.
2. Encephalomyopathies of later onset (childhood to adult life): various combinations of weakness, short stature, ataxia, dementia, hearing loss, sensory neuropathy, pigmentary retinopathy, and pyramidal signs. Ragged-red fibers common. Possible lactic acidosis.
3. Myopathy, with exercise intolerance evolving into fixed weakness. Ragged-red fibers common. Possible lactic acidosis.
4. Infantile histiocytoid cardiomyopathy.

Complex IV Deficiency / COX Deficiency

Long Name: Cytochrome c oxidase deficiency is caused by a defect in Complex IV of the respiratory chain.

Symptoms: Two major forms:

1. Encephalomyopathy: Typically normal for the first 6 to 12 months of life and then show developmental regression, ataxia, lactic acidosis, optic atrophy, ophthalmoplegia, nystagmus, dystonia, pyramidal signs, and respiratory problems. Frequent seizures. May cause Leigh Syndrome.
2. Myopathy: Two main variants:
   1. Fatal infantile myopathy: may begin soon after birth and accompanied by hypotonia, weakness, lactic acidosis, ragged-red fibers, respiratory failure, and kidney problems.
   2. Benign infantile myopathy: may begin soon after birth and accompanied by hypotonia, weakness, lactic acidosis, ragged-red fibers, respiratory problems, but (if the child survives) followed by spontaneous improvement.

CPEO

Long Name: Chronic Progressive External Ophthalmoplegia Syndrome.

Symptoms: Similar to those of KSS plus: visual myopathy, retinitis pigmentosa, dysfunction of the central nervous system.

KSS

Long name: Kearns-Sayre Syndrome.

Symptoms: Progressive external ophthalmoplegia, pigmentary retinopathy, heart block, and high cerebrospinal protein.

LCHAD

Long name: Long-Chain Hydroxyacyl-CoA Dehydrogenase.

Symptoms: Encephalopathy, liver dysfunction, cardiomyopathy, and myopathy. Also pigmentary retinopathy and peripheral neuropathy.

LHON

Long Name: Leber Hereditary Optic Neuropathy.

Symptoms: Primarily blindness in young men. Less common symptoms: mild dementia, ataxia, spasticity, peripheral neuropathy, and heart conduction defects.

MERRF

Long Name: Myoclonic Epilepsy and Ragged-Red Fiber Disease.

Symptoms: Myoclonus, epilepsy, progressive ataxia, muscle weakness and degeneration, deafness, and dementia.

NARP

Long Name: Neuropathy, Ataxia, and Retinitis Pigmentosa.

Heading to Texas in June 2002

The mission statement for UMDF is "to promote research for cures and treatments of mitochondrial disorders and to provide support to affected families." One activity that supports this mission is their international symposium. The 5th International UMDF Symposium on Mitochondrial Disease for Mitochondrial Specialists, Clinicians, and Families will take place this summer at the Westin Galleria, in Dallas, Texas. Meetings are planned for everyone's needs and families will have the opportunity to attend the medical meeting for clinicians. Also new this year will be a special session for affected adults. A special tract will be offered for newcomers to learn the basics of mitochondrial disease before the detailed medical sessions. Other topics include insurance, legal issues, estate planning, and practical tools for couples and non-affected siblings. There are three different tracks offered at this event:

Scientific Meeting - "Mechanisms of Mitochondrial Function and Disease" - June 6-7, 2002

Meeting for Clinicians - "Troubleshooting Difficult Cases in the Clinical Setting" - June 8, 2002

Family Meetings - June 7-9, 2002

For registration information about the Family Meetings, please contact the UMDF office by phone (412) 793-8077 or e-mail info@umdf.org, or visit the UMDF website at www.umdf.org . For medical professionals seeking information about the Scientific Meetings or Meetings for Clinicians, contact the University of Texas Southwestern Medical Center at Dallas by phone (800) 688-8678 or e-mail Misti.fitzner@utsouthwestern.edu, or access their website at www.utsouthern.edu.

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Last Revision: July 30, 2002