The contribution of twins to the study of cognitive ageing and dementia: the Older Australian Twins Study.

The Older Australian Twins Study (OATS) is a major longitudinal study of twins, aged ≥ 65 years, to investigate genetic and environmental factors and their interactions in healthy brain ageing and neurocognitive disorders. The study collects psychiatric, neuropsychological, cardiovascular, metabolic, biochemical, neuroimaging, genomic and proteomic data, with two-yearly assessments, and is currently in its third wave. The initial cohort comprises 623 individuals (161 monozygotic and 124 dizygotic twin pairs; 1 MZ triplets; 27 single twins and 23 non-twin siblings), of whom 426 have had wave 2 assessment. A number of salient findings have emerged thus far which assist in the understanding of genetic contributions to cognitive functions such as processing speed, executive ability and episodic memory, and which support the brain reserve hypothesis. The heritability of brain structures, both cortical and subcortical, brain spectroscopic metabolites and markers of small vessel disease, such as lacunar infarction and white matter hyperintensities, have been examined and can inform future genetic investigations. Work on amyloid imaging and functional magnetic resonance imaging is proceeding and epigenetic studies are progressing. This internationally important study has the potential to inform research into cognitive ageing in the future, and offers an excellent resource for collaborative work.

Genetic influences on five measures of processing speed and their covariation with general cognitive ability in the elderly: the older Australian twins study.

Processing speed (PS) is one of the basic elements of cognitive functions and has been regarded as a "common mechanism" which mediates general cognitive decline in aging. The present study of Australian twins (117 monozygotic pairs, 98 dizygotic pairs, and 42 single twins aged 65 years and over), estimated the genetic influences in five measures of PS: Digit Symbol Coding (DS), Trail Making Test A (TMTA), Stroop color naming and word reading (Stroop), Simple Reaction Time (SRT) and Complex Reaction Time (CRT); and their covariation with general cognitive ability (GCA): reasoning, problem-solving, and memory. Additive genetic factors explained 62% of the variance in DS, 42% in TMTA, 57% in Stroop, and 48% and 35% in SRT and CRT, respectively. Quantitative genetic modeling showed that all of the covariation between the five PS measures and GCA could be explained by one common genetic factor, while the covariation between the PS measures was partly explained by non-shared environmental as well as genetic influences. The genetic correlation among the PS measures was strongest for DS and TMTA, and between the PS measures and GCA was strongest for DS. These findings suggest that the different PS measures, as well as GCA were to a large extent influenced by the same set of genes and that the relationship between PS and GCA is entirely due to shared-genetic influences.

Validation of the Abbreviated Westmead Post-traumatic Amnesia Scale: a brief measure to identify acute cognitive impairment in mild traumatic brain injury.

OBJECTIVE: To validate the use of the Abbreviated Westmead Post-traumatic Amnesia Scale (A-WPTAS) in the assessment of acute cognitive impairment in mild traumatic brain injury (mTBI). METHODS: Data previously collected from 82 mTBI and 88 control participants using the Revised Westmead Post-traumatic Amnesia Scale (R-WPTAS) was converted to A-WPTAS scores and pass/fail classifications were calculated for both scales. RESULTS: The proportion of failures on the R-WPTAS and the A-WPTAS did not differ and a similar number of mTBIs were classified on each. For mTBIs the relationship between the independent memory test and a pass/fail classification was the same for both scales. Bivariate logistic regressions revealed that mTBIs, relative to controls, were around 8 times more likely to fail the assessment (R-WPTAS: 95% CI: 3.70-18.87; A-WPTAS: 95% CI: 3.70-20.14). As verbal learning improved the likelihood of failure was reduced. Greater education was associated with a decreased likelihood of failure. The relationship between education and a fail performance was not sustained when education was adjusted for the effect of age, prior mTBI, blood alcohol level, injury status, verbal learning, and morphine administration. CONCLUSIONS: The A-WPTAS is a valid measure. The A-WPTAS may reduce the risk of failing to classify patients with mTBI by identifying and documenting acute cognitive impairment.

A comprehensive neuropsychiatric study of elderly twins: the Older Australian Twins Study.

The Older Australian Twins Study (OATS) was recently initiated to investigate genetic and environmental factors and their associations and interactions in healthy brain ageing and ageing-related neurocognitive disorders. The study extends the classic MZ-DZ design to include one or two equivalently aged siblings for each twin pair and utilizes the rich resources of the Australian Twin Registry. The study has a number of distinguishing features including comprehensive psychiatric, neuropsychological, cardiovascular, metabolic, and neuroimaging assessments, a longitudinal design and links with a brain donor program. The study measures many behavioral and environmental factors, but in particular lifetime physical and mental activity, physical and psychological trauma, loss of parent early in life, later losses and life events, early-life socioeconomic environment, alcohol and drug use, occupational exposure, and nutrition. It also includes comprehensive cardiovascular assessment, blood biochemistry, genetics and proteomics. The socio-demographic and health data on the first 172 pairs of twins participating in this study are presented. Prevalence of mild cognitive impairment is 12.8% and of dementia 1.5% in the sample. The target sample size is 1000, with at least 400 pairs of twins aged 65-90 years. The cohort will be assessed every two years, with in-depth assessments being repeated. OATS offers an excellent opportunity for collaboration with other similar studies as well as researchers who share the same interests.

Cognitive functioning in older twins: the Older Australian Twins Study.

AIM: To examine the concordance rates of common medical conditions and neurocognitive performance in monozygotic (MZ) and dizygotic (DZ) older twins. METHODS: Twins aged ≥ 65 years and living in the three Eastern states of Australia were recruited through the Australian Twin Registry and underwent detailed neuropsychological and medical assessment. RESULTS: Assessments were conducted on 113 MZ and 96 DZ twin pairs, with a mean age of 70.5 years. MZ twins were more concordant than DZ twins for hypertension and asthma. MZ twins had higher correlations than DZ twins on most neuropsychological tests, with the exception of some tests related to processing speed. The concordance rate for mild cognitive impairment or dementia was 76.2% in MZ twins and 42.9% in DZ twins, a non-significant difference. CONCLUSIONS: Except for some aspects of processing speed, most cognitive functions in older individuals show significant heritability. The heritability of neurocognitive disorders is, however, low.