Risk for Parkinson's disease: twin studies for the detection of asymptomatic subjects using [18F]6-fluorodopa PET.

Positron emission tomography (PET) studies were carried out with [18F]6-fluorodopa ([18F]6-FD) in monozygotic (MZ) and dizygotic (DZ) twins for the clarification of dopaminergic function. Four MZ and four DZ pairs of twins, each pair consisting of a parkinsonian index case and an asymptomatic co-twin, were collected from the Nationwide Twin Cohort. The control group comprised 14 healthy volunteers. [18F]6-FD PET examinations with a Siemens/CTI 931/08 scanner were performed dynamically over 90 min. The regions-of-interest analysis included the caudate, the putamen and the occipital reference regions. Patlak plots were calculated using occipital tissue input function. The accumulation of [18F]6-FD in the putamen of the asymptomatic co-twins was significantly lower than that in the normal subjects. This result implies that there may be a preclinical stage of Parkinson's disease in the apparently normal co-twins at the time of the PET study.