Parkinson’s disease affects around 100,000 patients in the United Kingdom and is the most common neurodegenerative condition after Alzheimer’s disease. With an exponential rise in its prevalence with age, the ageing of the UK population over the next 20 years will significantly increase the burden of this neurodegenerative condition. The aetiology of PD is unknown. Family studies continue to suggest a strong genetic component with the possibility of autosomal dominant inheritance with incomplete penetrance. Twin studies have been hampered by the short duration of follow-up of the potentially affected co-twin and thus have given variable results.
Two genes for PD have been identified in a number of large kindreds: a-synuclein has autosomal dominant inheritance and parkin has autosomal recessive inheritance. Other identified loci in familial kindreds are either rare or cause atypical disease.
Most PD is sporadic and genetic defects such as those in a-synuclein and parkin are only very rarely seen in sporadic disease. Thus, most work to date on genetic factors in PD has focussed on studies of genetic markers hypothesised to predispose susceptibility to the disease. Such genetic association studies have, to date, failed to produce replicable results.