It affects 5% of the population over 75 years of age,1 and has a greater impact on healthcare provision than Alzheimer's disease (AD).2 The neuropathological hallmark of DLB is widespread α-synuclein-positive neuronal inclusions (Lewy bodies and Lewy neurites) and in addition this is often associated with amyloid deposition.3 Siblings of affected individuals have a 2.3-fold increased risk of developing the disorder,4 but little is known about the genetic aetiology of the disease. This evidence concerns the gene SNCA and Alzheimer disease.