Background Huntington Disease (HD) is a dominant disorder caused by a CAG repeat expansion in the HTT gene, characterised by progressive basal ganglia and cortex degeneration, leading to motor, psychiatric, and cognitive disturbances. While there are international guidelines for predictive genetic test in subjects at risk, no statement exists for diagnosis of HD. Aspecific abnormalities may be present many years before disease onset, but the presence of unequivocal motor signs, usually chorea, is required for clinical diagnosis. Therefore, when chorea is not evident, as in hypokinetic/rigid forms or in patients with cognitive or psychiatric onset, the decision to proceed to diagnostic testing represents a complex ethical issue.

Case history We present two illustrative cases. A parkinsonian syndrome developed in a 40-year-old lady at risk for HD, treated with neuroleptics for psychosis. The short period and the low doses of therapy challenged an iatrogenic origin of parkinsonism and a molecular test for HD diagnosis was considered to guide further treatments and obtain a disability pension and other welfare benefits. On the other hand, an early clinical diagnosis could worsen symptoms and expose to social discrimination. Moreover, the psychiatric illness could raise legal issues about the informed consent for the genetic test. The second case was a 16-year-old mentally retarded at-risk boy who developed behavioural changes and hypokinesia. Juvenile HD was suspected and a molecular test was performed. A 40 repeat expansion was found, which was not likely to explain the early-onset symptomatology and could represent an undesired predictive test in a minor.

Conclusions Several ethical shades should be considered in the diagnosis of HD, as interests of affected patients and society (job or family) may be different and legal problems may arise. For these reasons clinical management of HD patients and their family could benefit from guidelines for making diagnosis and communicating it.