Timothy syndrome is a disorder that affects the heart, digits (toes and fingers), and nervous system (brain and nerves). It is a type of long QT syndrome. Long QT syndrome refers to a prolonged QT interval measurement seen on the electrocardiogram. Symptoms of Timothy syndrome include fusion of the skin between fingers or toes (syndactyly), distinctive facial features, and congenital heart defects. Additional symptoms may include developmental delay, intellectual disability, and autism spectrum disorders. There are two forms of Timothy syndrome, classified based on signs and symptoms. Type 1, known as classic type, includes all of the symptoms described above. Type 2, or atypical type, causes a more severe form of long QT syndrome and does not appear to include syndactyly. Both types are caused by genetic changes in the CACNA1C gene and are inherited in an autosomal dominant manner.