Fukuyama congenital muscular dystrophy (FCMD) is a rare form of muscular dystrophy that is seen almost exclusively in the Japanese population. Infants with FCMD have hypotonia (weak muscle tone), weak crying and suckling, impaired brain development, and show delayed milestones like standing, sitting, and walking.
The genetic cause of FCMD
FCMD is caused by mutations in the FKTN gene. This gene is responsible for the production of a protein called fukutin. Fukutin is especially abundant in heart muscles, skeletal muscles, and the brain. It helps in the proper function of another protein called alpha-dystroglycan by aiding in a process called glycosylation (addition of sugar molecules to proteins). Glycosylated alpha-dystroglycan stabilizes muscle fibers and also is required for proper nerve cell development.
The FKTN gene is located on chromosome 9, which is an autosomal (non-sex) chromosome. Chromosomes store genetic information in the cell. All humans have 22 pairs of autosomal chromosomes and one pair of sex chromosomes. Mutations in genes in autosomal chromosomes can affect both males and females.
How is FCMD inherited?
FCMD is inherited in an autosomal recessive manner. Genes occur in pairs with one copy coming from the father and one from the mother. In autosomal recessive diseases such as FCMD, symptoms are seen when both copies of the gene are mutated. People with only one mutated copy are designated as “carriers” and do not usually show symptoms of the disease. However, carriers can still pass the mutation to their children.
If one copy of the FKTN gene is mutated in each parent, for each pregnancy the predicted outcome is as follows:
- A 25% chance of the child being born without FCMD.
- A 50% chance of the child being a carrier.
- A 25% chance of the child being affected by FCMD.
Last updated: Aug. 26, 2019
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