Special problems of genetic counseling in adult-onset diseases: Huntington’s disease as a model

Neurological disorders impose a severe burden on affected individuals Inherited neurological disorders of late onset present their own specific difficulties in terms of genetic counseling, management, and patients’ psychological adaptation. Huntington’s disease (HD) is the archetypal late-onset neurogenetic disorder. It is an autosomal-dominant disorder usually of adult onset in which progressive degeneration of the cerebral cortex and basal ganglia result in choreiform movements and progressive mental deterioration. Closely linked genetic markers have been available since 1983 so that presymptomatic testing protocols have been in development longer for this disorder than for any other similar disorder (for further information on HD specifically see ref. 1). In this chapter we highlight the major issues we consider relevant to achieving optimal diagnostic, predictive, and prenatal testing and to the family management of individuals from HD families. We put forward the protocols we have developed to help clinicians and other allied workers approach these difficult areas. One of the mam issues in late-onset disorders relates to diagnostic and presymptomatic testing. It is important to recognize from the outset that these are separate problems and must be treated as such. Clear distinction is implicit in the term “diagnostic” test, in which the patient is referred for specific mutation analysis because of suspicious clinical features of that disorder. Presymptomatic testing, on the other hand, is performed on healthy individuals in the absence of any clinical features of the disorde