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What

Tarui Disease is a genetic disease that affects glycogen metabolism. Glycogen is the storage form of glucose and, in normal individuals, it is produced during periods of carbohydrate loading. It is metabolized as an energy source when glucose demand is high such as during periods of fasting or exercise. The majority of glycogen is stored in the liver and muscle, but muscle tissue is most affected by Tarui disease. In Tarui disease, the body is unable to break down glycogen and produce glucose for energy use. There are three subtypes of this disease - classic, infantile-onset and late-onset - which are each defined by the patient’s history of symptoms.

Who

The incidence of all the glycogen storage diseases together is estimated at 1 in 20,000 live births, with Tarui Disease only accounting for 0.2% of these cases. This disease is most common among Japanese and Ashkenazi Jews. More males than females have been reported to have this disease.

Signs and Symptoms

Classic Tarui disease typically presents before the age of 20 years with fatigue, muscle cramps, and exercise intolerance. These episodes are more likely to occur after high carbohydrate meals and exercise. Patients often experience rhabdomyolysis (muscle tissue breakdown) upon physical exertion because the muscle is not able to utilize the glycogen stores for energy and therefore “starves” when energy demands exceed that which can be provided for by the blood glucose alone. They may have myoglobulinuria, which is burgundy-red colored urine caused by a protein that is released from muscle tissue as it is damaged. The most serious potential complication is kidney failure caused by the kidneys having to filter large amounts of myoglobin,. Some patients will also experience destruction of red blood cells which can cause anemia and jaundice. Symptoms of the Infantile form may include myopathy, psychomotor retardation, cataracts, joint rigidity, and death during childhood. Patients with the late-onset form may present in adulthood with progressive muscle weakness.

Possible Causes

Tarui Disease is inherited in an autosomal recessive pattern. This means that a child must inherit a defective copy for the gene encoding phosphofructokinase (an enzyme found in the muscles needed to break down glycogen to produce glucose) from both parents in order to manifest the disease. It is important to point out that each parent is a carrier of the disease but because they still have one functioning copy of the gene for the enzyme, they do not have any symptoms of the disease. There are a number of inborn errors of glycogen metabolism that result from mutations in genes for virtually all of the enzymes involved in glycogen synthesis, degradation, or regulation. Those disorders that result in abnormal storage of glycogen are known as glycogen storage diseases. They have largely been categorized by number according to the chronology of recognition of the responsible enzyme defect. Therefore, Tarui Disease is also referred to as the Type VII glycogen storage disease

Diagnosis

There are a number of blood tests that are used to diagnose this condition. For example, the levels of creatine kinase and/or myoglobin, proteins normally found within muscle, will be elevated in the bloodstream due to damage to the muscle tissue. Also, if there is red blood cell destruction, patients may be anemic (lower than normal level of red blood cells) and may have higher than normal levels of bilirubin and/or uric acid in their blood. A muscle biopsy may be performed and will suggest a glycogen storage disease if there is an abnormally high amount of glycogen stored within the muscle. This demonstrates that the patient can produce glycogen but is unable to break it down. Once the physician is rather confident that a glycogen storage disease is the cause of the patient’s symptoms, further testing can identify which specific enzyme is deficient. If these tests demonstrate that the deficient enzyme is phosphofructokinase, the diagnosis of Tauri Disease is made.

Treatment

The hormone glucagon is used to treat this disease because it increases the blood sugar level to better sustain muscle tissue. There are also a number of preventative measures that can be taken to prevent the painful and dangerous rhabdomyolytic episodes. For example, patients are instructed to avoid high-carbohydrate meals and, unfortunately, most forms of physical activity. Hospitalization may be required after a rhabdomyolytic crisis to prevent/treat kidney failure.

Prognosis

Prognosis varies depending on the patient’s threshold of activity in causing a rhabdomyolytic crisis as well as their compliance to activity and dietary restrictions. High patient compliance can lead to a near-normal life expectancy. Once a patient is diagnosed with this disorder, the parents will be informed that they are carriers of the disease and future pregnancies between them have a 25% chance of having the same diagnosis. Prenatal testing of subsequent pregnancies is available for affected families if the specific gene mutation is identified in the patient.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

Association for Glycogen Storage Disease
This website offers information to parents and patients with the various types of Glycogen Storage Diseases, medical information on glucose metabolism, parent support and lots of links to other websites for further information.

Association for Glycogen Storage Disease (UK)
This UK website contains newsletters, conferences, forums to inform and support parents and patients with the various Glycogen Storage Diseases. There are several links to helpful sites.

Muscular Dystrophy Association
Because GSD affects muscles, this website is appropriate to search for supplemental help. The MDA site offers current research and studies.

Google Search for Tarui Disease

References and Sources

UpToDate Online www.utdol.com/enterprise.asp?bhcp=1 eMedicine www.emedicine.com/derm/topic723.htm www.emedicine.com/ped/topic2209.htm