Huntington’s disease (HD) is an autosomal dominant inherited, progressive neurodegenerative disorder with motor, cognitive, personality and behavioral changes. The activities of respiratory chain complexes (RC) (I, II, I+III, and IV) and citrate synthase (CS) in platelets in 18 HD patients (8 males and 10 females) and in 29 age related controls (11 males and 18 females) were measured by means of spectrophotometry. In comparison with controls, decreased activity of one or more RCs was found in 7 out of 18 HD subjects: complex IV was decreased in 4 patients, complex III in 3, complex II in 2, and complex I in one. Decreased ratio between complex IV and CS was found in 2 patients and decreased ratio between complex I+III and CS in two. Furthermore, there was found significant negative correlation between the amount of CAG repeats and the activities of complexes I+III (p<0.05). Patients with dominant neurological symptoms did not differ from those with mixed (neurological and psychiatric) symptomatology (p<0.05). Significant negative correlation between the amount of CAG repeats and age at the onset of HD (p<0.01) was confirmed. Mitochondrial dysfunction in HD is probably a secondary process, variably expressed in various peripheral tissues. Changes in platelets RC may not necessarily reflect the pathological process of HD and the findings are often inconsistent.

        Key words: Huntington’s disease, blood plateles, CAG triplet repeats, respiratory chain