Atypical inheritance: new horizons for neurology.
Rediscovery of Mendel's laws produced an enthusiastic new discipline at the turn of this century. The eugenics movement had many disciples in the United States, and it should be noted that the term "final solution" was first used by the National Association of Charities and Corrections in the 1920s. American advocates of eugenics accomplished mass sterilization of retarded individuals and the prohibition of Jewish immigration from Germany during World War II. It is interesting that the close of this century has produced a similar revolution in genetics. These newer genetic mechanisms expose the major fallacy of eugenics: traits may be genetic without showing obvious familial transmission. Sanctions against reproduction or immigration thus will have little effect on the gene pool. The clinical implications of atypical inheritance are enormous. Almost every medical disorder must be reinvestigated for evidence of subtle chromosome changes, for worsening in progressive generations, and for influence of parental origin. The classical Mendelian model taught that extreme and rare phenotypes shed light on more frequent ones, hence the definition of genes responsible for hypercholesterolemia, for Alzheimer disease, and for amyotrophic lateral sclerosis. Atypical inheritance mechanisms further enhance this approach, bringing all of neurology under the light of genetic technology. The lure for the practitioner, then, is not the hyperbole of molecular biology; it is the need for a seasoned hand so emphasized by Huntington's disease and the duty to protect the next century from disasters of the current one.