Senile dementia of the Lewy body type has an apolipoprotein E epsilon 4 allele frequency intermediate between controls and Alzheimer's disease.

We have examined the apolipoprotein E (ApoE) allele distributions in Alzheimer's disease, Parkinson's disease, senile dementia of the Lewy body type and neurologically normal controls. We have confirmed the strong genetic association between the epsilon 4 allele and Alzheimer's disease, shown that there is no association between the epsilon 4 allele and Parkinson's disease and shown that senile dementia of the Lewy body type has an epsilon 4 allele distribution intermediate between Alzheimer's disease and Parkinson's disease. On this basis, we suggest that senile dementia of the Lewy body type represents the co-occurrence of two syndromes.