Causes of UCMD
UCMD is caused by mutations in the COL6A1, COL6A2, and COL6A3 genes that encode for portions of a large structural protein called collagen type 6. These mutations result in either abnormal collagen type 6 protein being produced or less of it. The effect that a particular mutation will have on the protein complex is difficult to predict, but, generally, mutations that cause less collagen type 6 to be produced are associated with more severe symptoms.
How is autosomal recessive UCMD inherited?
Most cases of UCMD are inherited in an autosomal recessive manner. Autosomal means that the mutations are carried on chromosomes that do not determine gender, and so affect both genders equally. Recessive means that a child must inherit two copies of a disease-causing mutation to develop the disease. In most cases, this happens when both parents are carriers of the disease-causing mutation, but they themselves have no symptoms of the disease. The children of carriers have a one-in-two chance of inheriting only one copy of the disease-causing mutation and being carriers like their parents. They have a one-in-four chance of inheriting two copies of the disease-causing mutation and developing the disease, or of inheriting no copies of the mutation and being healthy.
How is autosomal dominant UCMD inherited?
A small number of UCMD cases can be inherited in an autosomal dominant manner — meaning that a single copy of a mutated gene is sufficient to cause the disease. This type of mutation is usually a new mutation in the gene, affecting people with no family history of the disease, although, occasionally, UCMD patients can transmit this type of mutation to their children. Patients with a single copy of the disease-causing mutation have a one-in-two chance of transmitting it to their children, who would then inherit the disease as well.
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