Wednesday, August 28, 2013

Genetics may be to blame for exercise intolerance

This article explains how exercise intolerance may have a genetic component, although does not seem to be a hereditary condition.

Some cases of exercise intolerance have been linked to mutations in a gene found in the mitochondria, the “powerhouses” of the cell, according to a study.
Exercise intolerance is a condition in which a person experiences extreme fatigue, muscle pain or cramps after minimal exercise. Mitochondria provide energy that muscles require to function, so a defect in these could severely limit the ability to exercise.
Mitochondrial DNA — which is separate from DNA found in the nucleus, or control center of the cell — is inherited directly from the mother, so if a child has a disorder linked to the mitochondria, the mother usually also has it.
However, the research team from the Columbia College of Physicians and Surgeons in New York, found that in the patients studied, there was no maternal link to the mutation, and no evidence of the mutation in tissues other than muscles. This suggests that mutation is not inherited but occurs in the embryo, the team suggests. Five patients with exercise intolerance and no family history of the disease enrolled in the study.
Analyses of the patients’ cells revealed that all had defects in respiratory chain enzymes, which are used by mitochondria to make substances that store energy for muscles. Sophisticated techniques narrowed the deficiencies down to mutations in the mitochondrial cytochrome b gene.
The investigators conclude that such mitochondrial gene mutations may be common, and recommend that physicians consider this as a possible diagnosis in patients with “the often elusive symptoms of aches, pain, and cramps.”
No treatments have been developed for this condition, but as a therapeutic course for the patients, researchers suggest “genetic counseling” to explain to the patients that they will not pass their disease onto their children. Also, patients can engage in “appropriate exercise programs,” which might have some benefit, they add.
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