Hereditary neuromuscular disease

Most of these myopathies are inherited in an autosomal dominant pattern, which means that a child need only inherit the defective gene from one parent in order to have the disease. The parent transmitting the gene also has the disorder, and each of his or her children has a 50 percent chance of inheriting the disease. With an autosomal inheritance pattern, male and female children are equally affected. In rare instances, some forms of these diseases appear to follow an autosomal recessive pattern or an X-linked recessive pattern. A disease governed by the recessive pattern requires that both parents, who usually do not have the disease, pass on the defective gene in order for a child to be affected by the disease. Each child of such parents has a 25 percent chance of inheriting and showing signs of the disease. A 50 percent chance exists that such a child will inherit the defective gene from only one parent and, therefore, will be a carrier of the flawed gene and will usually not show signs of the disease. X-linked refers to a gene that is on the X chromosome, which along with the Y chromosome determines sex. Male children have one X chromosome and one Y chromosome, while females have two X chromosomes. Therefore, inheritance of a gene on the X chromosome is different from that for one on an autosomal chromosome. In the X-linked recessive pattern, the disease develops mostly in males. Females who inherit the defective gene are usually carriers like their mothers and can pass the disease on to their sons but rarely show signs of the disease themselves.

Central core disease, some forms of myotonia congenita, myotubular myopathy (possibly), some forms of nemaline myopathy, paramyotonia congenita and periodic paralysis follow the autosomal dominant pattern. One form of myotonia congenita and some forms of nemaline myopathy follow the autosomal recessive pattern. Some forms of myotubular myopathy follow the X-linked recessive pattern.