A number of studies of older twins have been published to inform about the relative contributions of genetic and environmental factors and their interactions in determining cognitive ageing and dementia. This review attempts to collate the salient findings from these studies.
Most data come from eight studies, with the majority being Scandinavian. These studies suggest that cognitive functions have moderate to high heritability in late life, with genetic influences varying for different cognitive domains. The heritability of mild cognitive impairment is, however, low, and that of dementia moderate, suggesting significant environmental influences, and possibly some measurement error. Brain structures continue to have high heritability into late life, although the genetic component of the variance does decrease with age. The co-twin control studies support the role of mid-life lifestyle factors for cognitive ageing and late-life dementia.
The potential of twin studies to understand ageing and dementia is only beginning to be realized. More longitudinal studies are needed, and novel strategies of genomics and epigenetics can further exploit this powerful method to inform the field.
aCentre for Healthy Brain Ageing, School of Psychiatry, University of New South Wales
bNeuropsychiatric Institute, Prince of Wales Hospital, New South Wales, Australia
Correspondence to Teresa Lee, PhD, Centre for Healthy Brain Ageing, School of Psychiatry, UNSW Medicine, University of New South Wales, NPI, Euroa Centre, Prince of Wales Hospital, Randwick, NSW 2031, Australia. Tel: +61 2 9382 3739; fax: +61 2 9382 3774; e-mail: firstname.lastname@example.org