Risk of Alzheimer disease with the epsilon4 allele for apolipoprotein E in a population-based study of men aged 62-73 years.

The epsilon4 allele at APOE, the polymorphic locus for apolipoprotein E, increases the risk of Alzheimer disease (AD), especially among those with the homozygous epsilon4/epsilon4 genotype. In family studies, epsilon4 homozygotes typically develop AD at 55-75 years, an age range when AD is otherwise relatively infrequent. Population-based studies of the AD risk associated with allele epsilon4 (and especially with genotype epsilon4/epsilon4) are limited in number, and most such studies have included few AD cases between the ages of 55 and 75 years. In a large population-based twin registry, the screening of 12,709 men who were 62-73 years old yielded 38 prevalent cases of AD whose onset age ranged from 54 to 73. Genotype at APOE was determined for 37 of these cases and independently, for a similarly aged probability sample of 344 men from the same registry. The epsilon4 allele frequencies among the AD cases and the population samples were 0.39 and 0.15, respectively. The odds ratios (ORs) for AD were 17.7 for genotype epsilon4/epsilon4 versus epsilon3/epsilon3 and 13.8 for epsilon4/epsilon4 versus all remaining genotypes. By contrast, the ORs with heterozygous epsilon4/epsilon3 were only 2.76 versus epsilon3/epsilon3 and 2.01 versus all genotypes other than epsilon4/epsilon3 (p for homozygote vs. heterozygote ORs=0.002). The estimated etiologic fraction for AD with homozygous epsilon4 among men in their mid-50s to mid 70s is therefore 0.20; for the much more common heterozygous genotype epsilon4/epsilon3, the fraction is 0.18. In combination with other studies that have adjusted statistically for age, these results suggest that the effect of the epsilon4 allele dose is neither linear nor homogeneous for age. Homozygous epsilon4/epsilon4 appears to confer an extreme risk of AD at the age when onset with this genotype is most likely. These results are consistent with the view that individual genotypes modify risk by predisposing to substantially different distributions of AD onsets.

Cognitive functioning in late-life schizophrenia: a comparison of elderly schizophrenic patients and patients with Alzheimer's disease.

OBJECTIVE: Previous studies have suggested that geriatric inpatients with chronic schizophrenia manifest profound cognitive impairments. This study investigated how these cognitive impairments resemble those seen in degenerative dementing conditions. METHOD: The neuropsychological battery of the Consortium to Establish a Registry for Alzheimer's Disease (CERAD), widely used to characterize the cognitive deficits of patients with Alzheimer's disease, was used to compare patterns of cognitive impairment in 66 triads of subjects consisting of one elderly patient with Alzheimer's disease, one elderly, institutionalized patient with chronic schizophrenia, and one elderly, cognitively normal comparison subject who were matched on age, gender, and education. For some analyses, the two groups of patients were divided into subgroups according to the degree of their cognitive impairment (mild, moderate, or severe) as determined by their scores on the Mini-Mental State examination. RESULTS: Relative to the comparison subjects, both groups of patients showed cognitive deficits on each of the neuropsychological measures. The schizophrenic patients performed worse than the patients with Alzheimer's disease on tests of naming and constructional praxis but were less impaired on the test of delayed word recall. These differences were consistent across all levels of severity of globally measured cognitive impairment. CONCLUSIONS: Consistent with earlier findings from postmortem studies, these findings suggest that major differences exist in the neurobiologic mechanisms responsible for cognitive impairment in schizophrenia and Alzheimer's disease. Effects directly attributable to social and environmental differences between these two groups of patients may also play a role.

Interpretation variability of 18FDG-positron emission tomography studies in dementia.

RATIONALE AND OBJECTIVES: Functional imaging studies such as 18F-fluoro-18-labeled-deoxyglucose-positron emission tomography (18FDG-PET) are being used increasingly in the evaluation of patients with dementia. The authors evaluate inter- and intraobserver interpretation agreement in a diverse group of patients with clinically diagnosed dementia and subjective memory complaints, as well as two healthy control subjects. METHODS: Ninety-six patients with clinical diagnoses of probable Alzheimer's disease (n = 18), possible Alzheimer's disease (n = 33), dementia (n = 26), and mild memory impairment (n = 17), as well as two healthy control subjects were studied using 18FDG-PET. Three observers graded all studies for regional 18FDG uptake in the temporal, parietal, and frontal regions bilaterally. The studies also were interpreted for the presence of bilateral temporoparietal hypometabolism, which typically is present in Alzheimer's disease. The kappa statistic was used to determine intra- and interobserver agreement for regional 18FDG uptake and bilateral temporoparietal hypometabolism. RESULTS: There was excellent intraobserver (kappa = .56, P < 0.0005) and interobserver (kappa = .51, P < 0.0005) interpretation agreement for bilateral temporoparietal hypometabolism. There also was excellent intraobserver (kappa = .61, P < 0.000) and interobserver (kappa = .55, P < 0.000) interpretation agreement of regional 18FDG uptake. Interobserver agreement was extremely high in those patients who were considered clinically to have possible (kappa = .42, P < 0.001) or probable (kappa = .42, P < 0.01) Alzheimer's disease. CONCLUSIONS: Results confirm that bilateral temporoparietal hypometabolism is the metabolic abnormality associated with the diagnosis of probable Alzheimer's disease. Furthermore, intra- and interobserver agreement of visual interpretation of 18FDG-PET images indicates that 18FDG-PET is acceptable as an imaging technique in the clinical evaluation of the dementia patient.

Neuropsychological test performance in African-American and white patients with Alzheimer's disease.

Little information exists on the performance of black versus white patients with Alzheimer's disease on neuropsychological tests for dementia. In this study, we compared performance on the CERAD (Consortium to Establish a Registry for Alzheimer's Disease) neuropsychological battery between white (n = 830) and black (n = 158) patients with Alzheimer's disease enrolled in the CERAD study at 23 university medical centers in the United States. The black patients were older, had fewer years of formal education, and were more impaired in their activities of daily living than were the white patients. After controlling for these characteristics and for duration of the disease and severity of dementia, there were differences in the performance of black and white patients on several of the cognitive measures. Black patients scored lower than whites on tests of visual naming and constructional praxis and on the Mini-Mental State Examination. There were no statistical differences in performance on tests of fluency and word list memory. These findings suggest that cultural or experiential differences may modify performance on specific neuropsychological tests. These factors, in addition to age and educational background, should be considered when interpreting performance on neuropsychological tests in elderly black patients with dementia.

Reliability of the Rey-Osterrieth Complex Figure in use with memory-impaired patients.

Rater reliability was evaluated for the system most widely used to assess copy and recall of the Rey Complex Figure: the Osterrieth (1944) 18-item scoring system. The study sample consisted of 95 subjects (49 males, 46 females), most of whom were elderly individuals (M = 59.83, SD = 15.21 years) suffering from memory impairment. Four raters rated copy and delayed-recall protocols, and three raters re-rated the protocols after an interval of 3 months. Results revealed excellent inter- and intra-rater reliability coefficients (.85-.97) for total scores. However, reliabilities for the 18 individual items ranged from poor (.14) to excellent (.96). Differences in both reliability and level of subject performance were observed as a function of item and conditions of copy versus recall. It is concluded that the Osterrieth scoring system supports excellent reliability in use with memory-impaired patients using total scores. Nevertheless, individual-item reliability would benefit from enhancement, for example, via amplified delineation of relevant decision criteria.

Intelligence and education as predictors of cognitive state in late life: a 50-year follow-up.

We evaluated the relation of education and intelligence in early adult life to cognitive function in a group of elderly male twins. The Army General Classification Test (AGCT) was administered to US armed forces inductees in the early 1940s. Fifty years later, as part of a study of dementia in twins, we tested the cognitive status of 930 of these men using the modified Telephone Interview for Cognitive Status (TICS-m). TICS-m scores obtained in later life were correlated with AGCT scores (r = 0.457) and with years of education (r = 0.408). Thus, in univariate analyses, the AGCT score accounted for 20.6% and education accounted for 16.7% of variance in cognitive status. However, these two effects were not fully independent. A multivariable model using AGCT score, education, and the interaction of the two variables as predictors of the TICS-m score explained 24.8% of the variance, a slightly but significantly greater proportion than was explained by either factor alone. In a separate analysis based on 604 pairs of twins who took the AGCT, heritability of intelligence (estimated by AGCT score) was 0.503. Although this study does not address the issue of education and premorbid IQ as risk factors for dementia, the findings suggest that basic cognitive abilities in late life are related to cognitive performance measures from early adult life (ie, education and IQ).

Alzheimer's disease in the National Academy of Sciences-National Research Council Registry of Aging Twin Veterans. III. Detection of cases, longitudinal results, and observations on twin concordance.

OBJECTIVES: To detect cases of Alzheimer's disease (AD) in a large population of twins living throughout the United States and to examine concordance for AD in twins as a function of age and genotype for apolipoprotein E (APOE). SETTING: Nationwide survey. DESIGN: Multistage screening and field evaluation beginning with two telephone interviews and culminating with laboratory tests, longitudinal neuropsychological measures, physician examination, and diagnostic consensus among experts. PARTICIPANTS: Membership in 1990-1991 of intact pairs in the National Academy of Sciences--National Research Council Registry of veteran twins, then aged 62 to 73 years. MAIN OUTCOME MEASURES: Completeness of case detection was examined in collateral studies. Zygosity and APOE genotypes were determined by restriction mapping. Concordance was calculated by the proband method. RESULTS: Ninety subjects who screened positively for AD were studied in person, and 60 whose differential diagnoses included AD were followed up, as were their co-twins. Sensitivity of screening was estimated at greater than 99%, but 24% of subjects refused participation after initial screening. Seven of 38 diagnoses of AD have been confirmed at autopsy, and 31 other subjects eventually met criteria for probable or possible AD (prevalence estimate, 0.42%, 95% confidence interval, 0.29% to 0.56%), with good interrater reliability (intraclass r = .86). Excluding one discordant pair with unknown zygosity, concordance rates were 21.1% (4/19) for monozygotic and 11.1% (2/18) for dizygotic probands. Concordance was 50% for twins sharing the epsilon 4/epsilon 4 genotype at APOE, but there were no affected co-twins of 15 probands with onset before age 70 years, no epsilon 4 allele, and no family history of AD. The mean (SD) period of discordance in the latter pairs was 11.3 (3.3) years. CONCLUSIONS: The multistage case-detection approach achieved reliable and valid diagnoses of AD with high apparent sensitivity but substantial attrition after initial screening. Genetic influences in AD at this age are limited, except among homozygotes for allele epsilon 4 at APOE. Subjects with early-onset AD who lack the epsilon 4 allele are not rare, and their condition appears to have little genetic influence. They should be ideal for studies on environmental cause of AD.

Delayed onset of Alzheimer's disease with nonsteroidal anti-inflammatory and histamine H2 blocking drugs.

Factors that modify onset of Alzheimer's disease (AD) may be revealed by comparing environmental exposures in affected and unaffected members of discordant twin pairs or sibships. Among siblings at high risk of AD, sustained use of nonsteroidal anti-inflammatory drugs (NSAIDs) was associated with delayed onset and reduced risk of AD. After adjustment for use of NSAIDs, there was minimal effect on onset with reported history of any of three common illnesses (arthritis, diabetes, or acid-peptic disease). However, independent of exposure to NSAIDs, onset was unexpectedly delayed in those reporting extended use of histamine H2 blocking drugs. Randomized clinical trials will be needed to affirm the utility of these drugs for prevention, but the present findings may have implications for pathogenesis: because NSAIDs block the calcium-dependent postsynaptic cascade that induces excitotoxic cell death in NMDA-reactive neurons, and because histamine potentiates such events, excitotoxicity may deserve additional investigation in AD.

Diagnosis and management of memory loss and cognitive disorders among elderly persons.

Memory loss and other cognitive dysfunctions, although common in elderly persons, are not universal features of old age. Instead they herald the presence of various neuropsychiatric diseases, which are first recognized as syndromes. The two most common neuropsychiatric syndromes, dementia and delirium, produce global changes in cognition and other capacities. They are differentiated by the patient's level of consciousness, which is impaired in delirium but intact in dementia. Delirium is generally reversible and often indicates serious physical illness. Although dementia is occasionally reversible, the mainstays of its management and treatment are palliative. Comorbid psychiatric symptoms are common in patients with both delirium or dementia, and their recognition and treatment constitute an important task for the geropsychiatrist. The differential diagnosis of primary dementing illness and other psychiatric illnesses such as depression is complex, because symptoms of the two kinds of disorders often coexist and common pathogenetic mechanisms may underlie both syndromes.

Genes and recent developments in the epidemiology of Alzheimer's disease and related dementia.

In the search for cause or prevention of Alzheimer's disease, the traditional aims of analytic epidemiology have been hindered by several technical difficulties. The heterogeneous genetic influences on Alzheimer's disease have probably contributed substantially to difficulties in the detection of host or environmental factors associated with modified disease risk. We have discussed five areas of improved technical or theoretical approach, each of which has materially improved the prospects for future success in this endeavor. Improved methods of diagnosis have yielded purer samples of "cases" and have made it more practical to undertake population-based studies. Genetic determinants of Alzheimer's disease risk are being understood with increasing sophistication. A growing recognition of the time-dependent nature of the Alzheimer process has led to new and heuristically valuable ways of thinking about the disease, its causes (genetic and otherwise), and its prevention. While there is a growing consensus that Alzheimer's disease is probably not one disease but several, the limited success of efforts to identify distinguishable phenotypes has largely given way to the identification of those with various measures of disease risk and (probably) mechanisms on the basis of identifiable genotypic variation. Thus, several forms of this disease may soon be segregated for separate analysis. Two of the predisposing genes have apparent implications for disease pathogenesis; others remain identified only as anonymous "loci" implicated by linkage analyses. The greater understanding of genetic mechanisms serves to enable not only studies of gene effects in pathogenesis, but also the influence of various environmental factors that may modify the effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Lower cognitive performance in normal older adult male twins carrying the apolipoprotein E epsilon 4 allele.

OBJECTIVE: Given the strong association of the apolipoprotein E (apoE) allele epsilon 4 with late-onset Alzheimer dementia or multi-infarct dementia, we tested whether normal older adult men with at least one epsilon 4 allele demonstrate subclinical changes in cognition and perform more poorly on tests of cognitive function compared with subjects without the epsilon 4 allele. DESIGN: Matched-pair design of normal adult male (average age, 63 years) fraternal twins. SETTING: Subjects voluntarily participated on an outpatient basis at a research or medical center facility. PARTICIPANTS: Members of the National Heart, Lung, and Blood Institute twin panel third examination previously genotyped for apoE. MAIN OUTCOME MEASURE: Education-adjusted scores on several neuropsychological tests were compared in twins discordant for the apoE epsilon 4 allele. Subjects with documented cerebrovascular disease were excluded. RESULTS: Among 20 fraternal twin pairs discordant for the presence of epsilon 4, twins with the epsilon 4 allele demonstrated poorer mean performance than their co-twins without the epsilon 4 allele. This relationship was also noted cross-sectionally where age- and education-adjusted scores of 50 individual twin subjects with at least one epsilon 4 allele demonstrated poorer performance compared with 138 individual twins without an epsilon 4 allele. CONCLUSIONS: The apoE epsilon 4 allele may be associated with decreased cognitive function in discordant twin pairs. Our results suggest that epsilon 4 may represent a potential marker for accelerated cognitive aging and such individuals may be at greater risk for development of late-onset Alzheimer dementia or multi-infarct dementia.

Characteristics of nonresponders in a community survey of the elderly.

OBJECTIVE: To identify predictors of nonresponse in a community survey of cognitive status in the elderly. DESIGN: Cross-sectional community survey with two stages of recruitment: an initial, less-intensive method, followed by a more aggressive approach that included face-to-face contact. Characteristics of initial nonresponders and responders were compared. SETTING: A close-knit rural community with higher than usual proportions of elderly, especially the very old. Subjects were interviewed in their homes. Collateral informants were subsequently interviewed by telephone. PARTICIPANTS: Utah heads of household aged 75 and older who resided in a noninstitutionalized setting. MEASUREMENTS: Mini-Mental State Examination (MMSE), Dementia Questionnaire, and an autobiographical risk factor and family history questionnaire provided measures for all independent variables. The dependent variable was status as initial responders or initial nonresponders. RESULTS: An initial participation rate of 63% was achieved, but a final rate of 93% was achieved when initial nonresponders were contacted later face-to-face. MMSE score was significantly related to responder status when analyzed alone (beta = -.19, P = 0.02) and remained a significant predictor after adjusting for education and whether born in Cache County (beta = -.16, P = 0.041) or current drinking, diabetes, or "other" health problems (beta = -.18, P = 0.028). After controlling for the informant report of subject's problems with activities of daily living, MMSE score fell just below statistical significance (beta = -.16, P = 0.079). CONCLUSIONS: Nonresponders in community surveys of the elderly appear to be disproportionately cognitively impaired. The increase in participation rates achieved after more persistent recruitment suggests that many initial nonresponders can still be recruited if intensive methods are used.

Neural correlates of dementia: regional brain metabolism (FDG-PET) and the CERAD neuropsychological battery.

The present Investigation examined the biological correlates of the cognitive deficits of Alzheimer's disease and related dementias using the neuropsychological assessment battery of the Consortium to Establish a Registry of Alzheimer's Disease (CERAD) and positron emission tomography (PET). Resting state cerebral glucose metabolism was measured using the labelled radiotracer, [18F] Fluoro-2-deoxyglucose (FDG), in a sample of patients with mild to moderate dementia (n = 66). Specific and predictable relationships were seen between regional brain metabolism (left and right, frontal, temporal, and parietal lobes) and the neuropsychological measures of verbal fluency, constructional praxis, and verbal list learning. On tests of naming and delayed verbal recall only diminished FDG uptake in the left frontal lobe and the left temporal lobe, respectively, approached significance. This study demonstrates the expected relationships between neuropsychological performance and regional cerebral metabolism, thereby providing support for the CERAD battery as a valid measure in the clinical evaluation of dementia and for the use of FDG-PET in brain-behavior studies of dementia.

Discrimination between stages of Alzheimer's disease with subsets of Mini-Mental State Examination items. An analysis of Consortium to Establish a Registry for Alzheimer's Disease data.

OBJECTIVE: To identify minimal sets of Mini-Mental State Examination (MMSE) items that can distinguish normal control subjects from patients with mild Alzheimer's disease (AD), patients with mild from those with moderate AD, and those with moderate from those with severe AD. DESIGN: Two randomly selected equivalent half samples. Results of logistic regression analysis from data from the first half of the sample were confirmed by receiver operating characteristic curves on the second half. SETTING: Memory disorders clinics at major medical centers in the United States affiliated with the Consortium to establish a Registry for Alzheimer's Disease (CERAD). PARTICIPANTS: White, normal control subjects (n = 412) and patients with AD (n = 621) who met CERAD criteria; nonwhite subjects (n = 165) and persons with missing data (n = 27) were excluded. MAIN OUTCOME MEASURES: Three four-item sets of MMSE items that discriminate, respectively, (1) normal controls from patients with mild AD, (2) patients with mild from those with moderate AD, and (3) patients with moderate from those with severe AD. RESULTS: The MMSE items discriminating normal controls from patients with mild AD were day, date, recall of apple, and recall of penny; those discriminating patients with mild from those with moderate AD were month, city, spelling world backward, and county, and those discriminating patients with moderate from those with severe AD were floor of building, repeating the word table, naming watch, and folding paper in half. Performance on the first two four-item sets was comparable with that of the full MMSE; the third set distinguished patients with moderate from those with severe AD better than chance. CONCLUSIONS: A minimum set of MMSE items can effectively discriminate normal controls from patients with mild AD and between successive levels of severity of AD. Data apply only to white patients with AD. Performance in minorities, more heterogeneous groups, or normal subjects with questionable cognitive status has not been assessed.

Caregiver ratings of personality change in Alzheimer's disease patients: a replication.

Caregivers of 26 patients with Alzheimer's disease (AD) rated current and premorbid personality patterns with the NEO Personality Inventory. Results replicated previous findings on the degree of change reported in a previous group of patients with mixed memory disorder diagnoses. After a diagnosis of AD, the patients were rated as significantly more neurotic, less extraverted, less open, and less conscientious. There were no rated differences of changes in the personality domain of Agreeableness. These results strengthen the usefulness of caregiver ratings of personality change of patients with memory problems who cannot be useful informants on their own behalf.

The Consortium to Establish a Registry for Alzheimer's Disease (CERAD). Part V. A normative study of the neuropsychological battery.

The neuropsychological tests developed for the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) are currently used to measure cognitive impairments of Alzheimer's disease (AD) in clinical investigations of this disorder. This report presents the normative information for the CERAD battery, obtained in a large sample (n = 413) of control subjects (ages 50 to 89) who were enrolled in 23 university medical centers in the United States participating in the CERAD study from 1987 to 1992. We compared separately the performance of subjects with high (> or = 12) and low (< 12) years of formal education. For many of the individual cognitive measures in the highly educated group, we observed significant age and gender effects. Only the praxis measure showed a significant age effect in the low-education group. Delayed recall, when adjusted for amount of material acquired (savings), was relatively unaffected by age, gender, and level of education. Our findings suggest that the savings scores, in particular, may be useful in distinguishing between AD and normal aging.

Alzheimer's disease in the NAS-NRC registry of aging twin veterans. II. Longitudinal findings in a pilot series. National Academy of Sciences. National Research Council Registry.

Over 3 years we followed 8 pairs of male twins one or both of whom had suspected Alzheimer's disease (AD) including 'mild/ambiguous' changes suggestive of incident AD. These pairs were screened in 1988 and 1989 from 339 pairs in the (US) National Academy of Sciences-National Research Council Registry (NASR) of aging veteran twins, then 61-72 years of age. Most of the suspected cases (10 of 12) had mild/ambiguous changes. Including these subjects, we had estimated the prevalence of AD in the NASR as about 2%. We now describe briefly the longitudinal evaluation of these 8 pairs. Only 1 of the 10 individuals with mild/ambiguous changes has progressed to show well-defined clinical symptoms of AD. Two others remain in their original research category, while 7 clearly do not have AD. Thus, we now estimate the 1988-1989 prevalence of AD in the NASR as 0.5%. These results contrast with other follow-up studies of mild cases from a university-based Alzheimer's clinic. We suggest that the contrasting findings reflect the nature of the samples studied, and we show that the present results are predicted by Bayesian reasoning.

Inverse association of anti-inflammatory treatments and Alzheimer's disease: initial results of a co-twin control study.

We conducted a co-twin control study among 50 elderly twin pairs with onsets of Alzheimer's disease (AD) separated by 3 or more years. Twenty-three male pairs (46%) were screened from the (U.S.) National Academy of Sciences-National Research Council Registry (NAS-NRC Registry) of World War II veteran twins; others (mostly women) had responded to advertisements or were referred from AD clinics. Twenty-six pairs (52%) were monozygous. The onset of AD was inversely associated with prior use of corticosteroids or ACTH (odds ratio [OR], 0.25; 95% confidence interval [CI], 0.06 to 0.95; p = 0.04). Similar but weaker trends were present among pairs discordant for history of arthritis or for prior daily use of nonsteroidal anti-inflammatory drugs (NSAIDs) or aspirin. The association was strongest when we combined use of steroids/ACTH or NSAIDs post hoc into a single variable of anti-inflammatory drugs (AIs) (OR, 0.24; CI, 0.07 to 0.74; p = 0.01). The inverse relation was strong in female (volunteer) twin pairs but was not present in the younger men from the NAS-NRC Registry. AIs had typically been taken for arthritis or related conditions, but a similar result was apparent after controlling statistically for the arthritis variable (OR, 0.08; CI, 0.01 to 0.69; p = 0.02). AIs have been proposed as a means of retarding the progression of AD symptoms, and these data suggest that AIs may also prevent or delay the initial onset of AD symptoms. Because of limitations in the case-control method, our results require corroboration with hypothesis-driven research designed to control bias and confounding.

Hereditary influences on cognitive functioning in older men. A study of 4000 twin pairs.

OBJECTIVE: To determine the contribution of genetic factors to cognitive functioning in older men. DESIGN: Cognitive testing by telephone interview in an epidemiologically defined population. PARTICIPANTS: 2077 monozygotic and 2225 dizygotic male twin pairs, all between the ages of 62 and 73 years, recruited from the National Academy of Sciences twin registry. MAIN OUTCOME MEASURES: The Telephone Interview for Cognitive Status--Modified total score and factor scores were analyzed. The Falconer heritability statistic and maximum likelihood estimates of genetic and environmental components were computed. RESULTS: Heritability of the total Telephone Interview for Cognitive Status--Modified score was estimated to be 30%. Shared environmental effects accounted for an additional 18% of the variance; most of this was related to years of education. Of the four cognitive factors derived, the language/attention factor had the highest heritability estimate. CONCLUSIONS: Genetic factors and educational achievement together account for almost half of the variance in the cognitive functioning of older men. Studies of the genetics of dementing illnesses need to consider the degree to which cognitive capacities are themselves under genetic control.