The Tiresias complex: Huntington's disease as a paradigm of testing for late-onset disorders.

Huntington's disease represents the first disorder for which positional cloning techniques successfully localized an autosomal gene--in 1983. Events since that time have proved the gene recalcitrant to identification and characterization. Since 1986, presymptomatic and prenatal testing for Huntington's disease has been available internationally, although on a limited basis. Testing for Huntington's disease provides an excellent model for designing service programs for genetic testing for late-onset, fatal disorders, particularly when the gene is not yet in hand and no therapeutic intervention is possible. Special training and precautions must be in place before presymptomatic genetic testing should be offered.