FCMD is caused by mutations in the FCMD gene, also known as the Fukutin gene. This gene is responsible for producing a protein essential for the proper development and maintenance of muscle and brain cells. The mutations lead to the production of a defective protein, which disrupts normal cellular functions and results in the symptoms observed in FCMD. The disorder is inherited in an autosomal recessive manner, meaning that both copies of the gene (one from each parent) must be mutated for the disease to manifest.
