Analysis of episodic memory, however, typically shows less genetic influence. We therefore analyzed in more detail associations between general and specific cognitive abilities and concluded that genetic factors produce similarities among cognitive abilities, while environmental influences contribute to differences across abilities. In another study we examined the genetic and environmental influences across the distribution of cognitive functioning, from high to low functioning. We are currently expanding these studies for longitudinal analysis. The above analyses were conducted in non-demented twin pairs.
Twins suspected for dementia are all worked-up for a diagnosis and followed to autopsy.
The longitudinal design provides information on the incidence of dementia. Preliminary results confirm findings from younger samples that the genetic effects are more pronounced for Alzheimer's than for vascular type dementia. Also, our sample of old-old demented twins is pooled with younger cases from other ongoing Swedish twin studies to examine potential environmental risk factors for dementia. In one study we found that a history of psychiatric illness, especially depression, may be associated with an elevated risk for Alzheimer's disease. The domain of health and functional capacity is currently investigated for vision and hearing, lung capacity, grip strength, blood pressure, medication use, etc.