AbstractThe molecular defects responsible for Huntington's disease, the spinocerebellar degenerations, myotonic muscular dystrophy, neurofibromatosis, and tuberous sclerosis, among other major dominant inherited diseases of the nervous system, will be identified using the new techniques of molecular genetics. With synthesized nucleic acid segments complementary to portions of the patient's DNA, known as complementary DNA probes, it will be possible to identify and isolate the mutant gene responsible for a particular disease. These events are referred to as gene cloning. In addition, complex genetic regulatory mechanisms involved in cell differentiation during neuroembryogenesis will be elucidated with the application of these strategies. It is important for the clinician to become familiar with the precision and potential of these new methodologies, because they will soon influence significantly the practice of neurology.