P-163: Genetic and environmental influences on cognitive performances in an elderly Italian twin cohort

Abstract

The progressive reduction of cognitive ability that emerge with aging is a result of complex interactions of genetic and environmental factors. The nature and the mechanisms of these interactions remain largely unknown. The aim of the present study is to explore, in a sample of twins belonging to the population-based Italian Twin Registry, the relative contributions of genetic and environmental factors in determining inter-individual variation of neurocognitive abilities. Ninety-three twin pairs (mean age ± SD, 67.6 ± 4.7 years; 35 MZ pairs, 58 DZ pairs), resident in Rome city were enrolled. All subjects underwent the following neuropsychological tests: Mini Mental State Examination (MMSE), Attentional matrices, Story Recall test, Raven's Coloured Progressive Matrices (PM 36), Phonological (F-P-L) and Semantic (animals) Verbal Fluency test, Token test, Copying Drawings. Data on socio-demographic characteristics and medical history were also collected. Standard univariate twin modelling based on linear structural equations was used. The model allows for separation of the total phenotypic variance into the following components: additive genetic variance; nonadditive genetic variance; common (shared) environmental variance; unique (unshared) environmental variance. No significant differences between MZ and DZ twins were observed in demographic and social data. The means of each neuropsychological test were very similar for MZ and DZ pairs. However, all the cognitive tests, except for Token, showed a higher correlation in MZ than in DZ pairs, suggesting the presence of moderate to sizeable genetic influences. The best fitting model was a model incorporating additive genetic and unique environmental sources of variance for the following tests: MMSE, Raven, Attentional Matrix, Copying Drawings and Story Recall. For Phonological and Semantic Verbal Fluency, the best explanation of the data was obtained under a model, including nonadditive genetic effects. Number of packs of cigarettes smoked per year was negatively associated (coefficient=−0.0041) with the score of the Phonological Verbal Fluency test. Our results suggest that most of the individual differences in specific cognitive abilities in the elderly show moderately to substantially genetic origin. The environmental factors that are relevant for these abilities appeared to be those causing within-family differences.