Central Core Disease (CCD) was one of the first congenital myopathies specifically documented. It was so named because of the metabolically inactive "cores" present in muscle fibers. Mitochrondria, the energy-producing parts of muscle cells, are missing in these cores. CCD tends to cause proximal muscle weakness, although there is sometimes distal and facial weakness as well. Although we cannot know for certain without a muscle biopsy, my son appears to have CCD.
As with all the myopathies, the degree of weakness can vary greatly. The disorder generally presents as a benign, non-progressive (or sometimes very slowly progressive) weakness, but there is variation in the amount of involvement. Approximately 40% of people showing central cores on muscle biopsy are asymptomatic, while the rest show a wide range of weakness. There seems to be no correlation between the number of muscle fibers showing cores and the severity of weakness. Some children with CCD show mildly delayed motor milestones, then seem to catch up and appear only a bit uncoordinated. Others have more severe delays, but also catch up somewhat and are fully ambulatory, although with more limitations. Some use braces for walking, and a very few use wheelchairs. Many people with CCD cannot run or jump, and have difficulty climbing stairs, but some have no difficulty with those skills. As you can see, there is a wide range of severity associated with the disorder.
CCD, like the other myopathies, is a hereditary disorder, and the inheritance is usually dominant. Even asymptomatic persons with central cores can pass the disorder on to their offspring. Dominant inheritance means that an individual with CCD has a 50% chance of passing it on to each child. There are also instances of sporadic inheritance, where a gene mutates spontaneously to cause the disorder in a person with no family history of the disorder.
One of the most serious effects of CCD is the danger of Malignant Hyperthermia, a potentially fatal reaction to anesthesia. Many people with a suseptibility to MH do not have CCD, but suseptibility to MH does tend to go along with CCD. Researchers are not sure exactly what causes this correlation, but they hypothesize that the two genes are closely linked, and the mutations may be related. Doctors recommend that anyone with CCD be aware of the possible danger of MH.
New research indicates that the calcium release mechanism in the muscle cell may be faulty in individuals with CCD. When a muscle contracts, the nervous system sends a signal which causes a burst of calcium to be released. The calcium remains in the cell just long enough to start the contraction, then drains out. Researchers have found that with CCD, the calcium leaks into the main part of the muscle cell even when the muscle isn't contracting. This means that there is less calcium available for the "burst" when the signal to contract is received and that the constant presence of calcium in the muscle cell may destroy the mitochondria there. This may be the origin of the "cores" in the muscles of people with CCD.
In many ways, Central Core Disease is similar to the other congenital myopathies. Each of them, however, has their own specific appearance on biopsy and metabolic mechanisms. Research into any neuromuscular disorder has implications for others, and the myopathies are no different. Hopefully the current research into CCD will lead to further advances in our knowledge of these disorders.
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