Some enzymes convert starch into sugar. Others help the body get rid of excess sugar. Literally thousands of different enzymes are necessary for life. Although the search for the specific FSD-related enzyme continues, that enzyme has not yeat been identified. Each chromosome contains thousands of genes, the carriers of heredity.
Some genes control the body's manufacture of a particular enzyme.
Patients with FSD either lack the special genes that control the manufac- ture of the enzyme, or those genes do not function normally in producing this enzyme. Because of a defective or absent gene, a person with FSD cannot manufacture the enzyme, and his body may not form various fatty substances or may form them abnormally. One type of fatty substance, called myelin, occurs in high concentrations in the brain and other nervous tissues. In FSD, for example, the affected person lacks the enzyme needed for control of the amount of myelin in his nerve and brain cells. Without that enzyme the cells malfunction.