Association of sex steroid hormones with brain morphology and cognition in healthy elderly men

BACKGROUND

There is inconsistent evidence of the presence and direction of the relationship between sex hormone concentrations and cognitive function in older men, and there is little published literature on the relationship of sex hormone concentrations and brain volume as measured by MRI.

OBJECTIVE

To examine the hypothesis that midlife total serum concentrations of testosterone (T), estradiol, estrone, and sex hormone binding globulin (SHBG) predict cognitive task performance and regional brain volumes at 10- to 16-year follow-up, in a longitudinal sample of World War II veteran twin men.

METHODS

Treating twins as individuals, linear regression models were used, adjusting analyses for age, education, depressive symptomatology, blood pressure, alcohol consumption, years of cigarette smoking, and APOE epsilon4 allele status.

RESULTS

There were no significant associations between sex hormone or SHBG concentrations and performance on a series of cognitive tasks measuring global and executive function, visual and verbal learning and memory. Higher midlife T concentrations were associated with larger hemispheric, frontal, and parietal regional brain volumes and with smaller left occipital brain volume. Higher estradiol and estrone concentrations were also associated with smaller right (estradiol) and both right and left (estrone) occipital volumes, but with no other brain regions. Owing to the multiple comparisons conducted, some significant associations may have occurred by chance.

CONCLUSIONS

Overall, the pattern of results suggests a role for sex hormones in brain volume that predates potentially observable associations between sex hormones and cognitive task performance.

Heritability of hippocampal size in elderly twin men: equivalent influence from genes and environment

Recent studies have established that environmental factors can modify hippocampal structure and enhance function in adult rodents, but the extent to which genes and the environment exert differential contributions to hippocampal structural integrity in humans is unknown. Here, we applied the twin model in a large sample of elderly twin men to examine in late life the balance of environmental and genetic effects on the size of the hippocampus in comparison with other brain structures. This study provides novel evidence that the volume of the hippocampus, as measured on MRI, is subject to substantially less genetic control than are comparison brain regions also measured: temporal horn volume, midsagittal area of the corpus callosum, and intracranial volume (ICV). In particular, about 60% of the temporal horn variance and 80% of the callosal and ICV variance was attributable to genetic influences, whereas only 40% of the hippocampal variance was attributable to genetic influences. These results suggest that environment, whether by itself or in interaction with genes, has the potential of exerting greater and possibly longer control in modifying hippocampal size than other brain regions that are under greater genetic control. Considering the potential of environmental modification of this structure suggested by lower heritability, the hippocampus appears well-suited to support the dynamic processes of encoding and consolidation of new, declarataive memories.

Differential rates of regional brain change in callosal and ventricular size: a 4-year longitudinal MRI study of elderly men

Brain structure changes in size with normal aging, but the rate at which different structures change is controversial. We used magnetic resonance imaging (MRI) performed twice, 4 years apart, to compare rates of age-related size change of the corpus callosum, which has been inconsistently observed to thin with age, with change in the lateral ventricles, which are well established to enlarge. Subjects were 215 community dwelling, elderly men (70-82 years old at initial MRI), who were participants in a longitudinal study of cardiovascular risk factors. Percent change in size was significant for both the callosal and ventricular measures, but annual rate of ventricular expansion (2.9%) was significantly greater than annual rate of callosal thinning (-0.9%). Callosal regions showed statistically equivalent rates of shrinkage; ventricular dilatation was symmetrical. Neither callosal and ventricular rates of change correlated with each other (r = 0.01), nor did genu and splenium rates of change correlate with each other (r = 0.05). Tests of speeded processing were administered contemporaneously with both MRIs to examine functional ramifications of observed brain changes. Decline in the Mini-Mental State Examination was related to thinning of the splenium, and decline in Stroop test word reading was selectively related to thinning of the callosal body. These longitudinal data support the contentions that differential rates of change occur in different brain regions in normal aging, age-related callosal thinning contributes to functional declines, and rate of change in one region can be independent of rate of change in another region, even within a brain structure.

Genetic factors in self-reported snoring and excessive daytime sleepiness: a twin study

Subjects in this study included 1,560 intact male-male twin pairs (818 monozygotic [MZ], 742 dizygotic [DZ]) of mean age (+/- SD) 74.2 +/- 2.8 yr. The Epworth Sleepiness Scale (ESS) was used to assess daytime sleepiness and standardized questionnaires assessed snoring. Multivariate genetic model fitting was used to estimate the contribution of genetic and nongenetic (environmental) influences to the variation and covariation of obesity with snoring and daytime sleepiness. In this sample, 26% were habitual snorers, 18% reported excessive daytime sleepiness (ESS > or = 11), and 29% were obese (body mass index [BMI] > or = 28). By using structural equation modeling, we estimated that genetic factors accounted for 64% of the variance in obesity, 40% of the variance in daytime sleepiness, and 23% of the variability in self-reports of snoring. We found a significant genetic correlation between obesity and snoring and between obesity and excessive daytime sleepiness (EDS), although for the most part the genetic variance in snoring and sleepiness was nonoverlapping with the genetic variance for obesity. We conclude from these data that self-reported symptoms of snoring and daytime sleepiness in older men have a genetic basis that is largely independent of genes associated with obesity.

Genetic regulation of regional microstructure of the corpus callosum in late life

In order to identify brain structural phenotypes that remain under significant genetic control in late adulthood, we examined the heritability of corpus callosum macrostructure (i.e. size) using MRI and microstructure (e.g. myelin) using diffusion tensor imaging in 15 monozygotic and 18 dizygotic twin pairs of elderly men. The relative proportion of genetic to environmental influences varied considerably by region and structural type and was 5:1 for callosal macrostructure, 3:1 for splenium microstructure, and 1:1 for genu microstructure. This is the first in vivo identification of quantifiable phenotypes of brain white matter microstructure and demonstrates significant and differential genetic regulation in old age, with anterior interhemispheric connecting pathways more susceptible than posterior pathways to environmental influences.

Cerebrovascular and brain morphologic correlates of mild cognitive impairment in the National Heart, Lung, and Blood Institute Twin Study

OBJECTIVE

To evaluate the relative risk (RR) of mild cognitive impairment (MCI) associated with cerebrovascular risk factors and cerebrovascular-related brain changes.

DESIGN

Mild cognitive impairment was determined for the subjects of the prospective National Heart, Lung, and Blood Institute Twin Study. Quantitative measures of brain, white matter hyperintensity, cerebral infarction, apolipoprotein E genotype, and psychometric testing were obtained.

RESULTS

Subjects with MCI were older (73.5 +/- 3.0 vs 72.1 +/- 2.8 years), consumed less alcohol (3.7 +/- 5.8 vs 7.0 +/- 10.7 drinks per week), had greater white matter hyperintensity volumes (0.56% +/- 0.82% vs 0.25% +/- 0.34% of cranial volume), and had an increased prevalence of apolipoprotein E4 genotype (31.4% vs 19.2%) than normal subjects. White matter hyperintensity and the presence of the apolipoprotein E4 genotype were associated with a significantly increased risk for MCI. When all subjects were included in the analysis, alcohol consumption was associated with a reduced risk for MCI (RR = 0.93, P<.05). When subjects with a history of symptomatic cerebrovascular disease were excluded from the analysis, elevated midlife diastolic blood pressure was associated with an increased risk for MCI (RR = 1.70, P<.05).

CONCLUSIONS

Elevated midlife blood pressures, and the resulting increased white matter hyperintensities, increase the risk for MCI in a group of community-dwelling older men to at least the same degree as apolipoprotein E4 genotype. Given the common occurrence of elevations in midlife blood pressure, early and effective treatment may be warranted to prevent late-life brain abnormalities and MCI. Moreover, since many individuals with MCI progress to clinical dementia, longitudinal evaluations of this cohort will be important.

A genetic analysis of the Epworth Sleepiness Scale in 1560 World War II male veteran twins in the NAS-NRC Twin Registry

Responses to the eight-item Epworth Sleepiness Scale (ESS) obtained from 1560 World War II male veteran twin pairs [818 monozygotic (MZ), 742 dizygotic (DZ)] were analysed to determine the extent to which genetic influences are involved in self-reported daytime sleepiness in the elderly. Average ESS score (+/- SD) in this sample was 7.1 +/- 3.9, range 0--24. More than half of the twins (65%--67%) reported a moderate to high chance of falling asleep while lying down to rest; fewer than 3% admitted that this would occur while sitting and talking to someone or while stopped in traffic. Daytime sleepiness was not associated with age but was significantly and positively associated with obesity. The intraclass twin correlation on ESS scores was 0.39 in MZ pairs and 0.21 in DZ pairs (both P < 0.001). Structural equation modeling of the observed variance-covariance matrices for MZ and DZ twins estimated the heritability of ESS to be 38% (95% confidence interval 33%--44%). Environmental influences not shared by twin brothers accounted for the remaining variance in daytime sleepiness. A reasonable interpretation of the heritability of ESS in this healthy cohort of elderly male twins is a genetic susceptibility for disordered breathing during sleep.

Longitudinal changes in the contribution of genetic and environmental influences to symptoms of depression in older male twins

Genetically informative longitudinal data on self-reported symptoms of depression allow for an investigation of the causes of stability and change in depression symptoms throughout adult life. In this report, the authors investigated the relative contribution of genetic and environmental influences to symptoms of depression in 83 monozygotic and 84 dizygotic male twin pairs from the National Heart, Lung, and Blood Institute (NHLBI) Twin Study. Participants first completed the Center for Epidemiologic Studies-Depression (CES-D) scale in 1985-1986 and again during 1995-1997. Mean age of twins at baseline was 63 years, range 59 to 70. From cross-sectional genetic analyses we estimated the heritability of CES-D to be 25% (95% confidence interval [CI], 11%-39%) at baseline and 55% (95% CI, 40%-71%) at follow-up. Fitting longitudinal genetic models to the two-wave data, we found that stability of symptoms over the 10-year follow-up was due primarily to continuity of genetic influences.

Relationship of 30-year changes in obesity to sleep-disordered breathing in the Western Collaborative Group Study

OBJECTIVE

Obesity is an important etiologic factor in sleep-disordered breathing (SDB), but the extent to which changes in obesity across adult life contribute independently to SDB in old age has not been studied. In this study, we examined the association between changes in obesity from midlife to late adulthood and overnight recording of respiration during sleep.

RESEARCH METHODS AND PROCEDURES

Subjects in this study are from the Western Collaborative Group Study, a longitudinal cardiovascular epidemiological study that began in 1960 through 1961. Overnight sleep recordings were obtained from 281 male participants in the 1995 through 1996 follow-up of the Western Collaborative Group Study. Subjects were 75 to 91 years old when assessed for SDB as indexed by the respiratory disturbance index and an oxygen desaturation index (O2DI). Long-term changes in anthropometrics were evaluated and examined in relation to SDB severity.

RESULTS

Over the 30 years of follow-up, body mass index and waist circumference increased significantly for this sample and were associated with SDB severity as indexed by respiratory disturbance index and O2DI. Waist circumference at baseline and gain in waist circumference over the 30 years of follow-up (both p = 0.01) were significantly and independently associated with SDB severity as assessed by O2DI. However, percentage of variance as accounted for by waist circumference was modest.

DISCUSSION

This study supports the hypothesis that gain in waist circumference over adult life is significantly associated with SDB severity in older men.

Stability and change in genetic and environmental influences on hand-grip strength in older male twins

The aim of this study was to investigate aging-related changes in the contribution of genetic and environmental influences to hand-grip strength in late adulthood. Subjects in this study are 152 intact twin pairs (77 monozygotic and 75 dizygotic pairs) from the National Heart, Lung, and Blood Institute Twin Study assessed repeatedly for hand-grip strength at mean ages of 63 and 73 yr. Structural equation genetic modeling was used to investigate stability and change in the genetic and environmental components of variance of hand-grip strength in late adulthood. Average decline in strength over the 10 yr of follow-up was -1.05+/-6.8 (SD) kg and was highly significant (P = 0.003). The test-retest correlation between baseline and follow-up grip strength was 0.62 (P<0.001). Bivariate genetic modeling found significant genetic and shared environmental stability in hand-grip strength over the 10 yr of follow-up, with genetic and shared environmental influences accounting for 35 and 48%, respectively, of the test-retest phenotypic correlation. We conclude from these results that stability in hand-grip strength in late adulthood is due primarily to continuity of genetic and familial influences.

Longitudinal changes in the contribution of genetic and environmental influences to symptoms of depression in older male twins

Genetically informative longitudinal data on self-reported symptoms of depression allow for an investigation of the causes of stability and change in depression symptoms throughout adult life. In this report, the authors investigated the relative contribution of genetic and environmental influences to symptoms of depression in 83 monozygotic and 84 dizygotic male twin pairs from the National Heart, Lung, and Blood Institute (NHLBI) Twin Study. Participants first completed the Center for Epidemiologic Studies-Depression (CES-D) scale in 1985-1986 and again during 1995-1997. Mean age of twins at baseline was 63 years, range 59 to 70. From cross-sectional genetic analyses we estimated the heritability of CES-D to be 25% (95% confidence interval [CI], 11%-39%) at baseline and 55% (95% CI, 40%-71%) at follow-up. Fitting longitudinal genetic models to the two-wave data, we found that stability of symptoms over the 10-year follow-up was due primarily to continuity of genetic influences.

The effect of apolipoprotein E epsilon4 in the relationships of smoking and drinking to cognitive function

OBJECTIVES

To investigate the joint effect of the apolipoprotein E epsilon4 (APOE epsilon4), smoking and drinking on cognitive performance in a population-based longitudinal study of elderly men.

DESIGN AND SETTING

The NHLBI Twin Study, a longitudinal cardiovascular study of World War II, white, male veterans.

PARTICIPANTS

A total of 589 male participants in the third cardiovascular examination of this panel and aged 59-69 when assessed for cognitive function.

OUTCOME MEASURES

Cognitive function assessed by the Mini-Mental State Examination, the Digit Symbol Substitution Test, the Benton Visual Retention Test, APOE epsilon4 allele frequency and cardiovascular disease (CVD) health status.

RESULTS

For the sample as a whole, after adjustment for age, education and CVD, smoking was significantly associated with poor cognitive function (odds ratio (OR) = 2.0, 95% confidence interval (CI) 1.2-3.2, in current smokers compared with never smokers), whereas light drinking (one or fewer drinks per day) showed a protective effect (OR = 0.6, 95% CI 0.4-0.9 compared with abstainers). Stratification by APOE epsilon4 indicated that the protective effect of light drinking was stronger and the harmful effect of smoking was weaker among APOE epsilon4 carriers than among noncarriers.

CONCLUSIONS

These data suggest a possible mediating effect of the APOE epsilon4 allele in the relation of smoking and drinking to cognitive function in the elderly.

Segregation analysis of drinking problem in elderly men and their first-degree relatives from the Western Collaborative Group Study

PURPOSE

The purpose of this study is to determine the mode of inheritance of alcohol-related drinking problems.

METHODS

Family history was collected by interview from 493 elderly male participants (probands) in a follow-up cardiovascular exam of healthy white men living in the San Francisco Bay Area and Los Angeles. Segregation analysis was used to test for the presence of a major gene effect underlying the liability to develop an alcohol-related drinking problem.

RESULTS

The results showed that the liability to drinking problem is due, in part, to a single major gene with no residual effects from shared familial influences.

CONCLUSIONS

These results suggest that at least one major gene is involved in the genetic predisposition to develop drinking problem in late adulthood.

Ten-year follow-up for male twins divided into high- or low-risk groups for ischemic heart disease based on risk factors measured 25 years previously

PURPOSE

To undertake medical follow-up in white males in the National Heart, Lung, and Blood Institute (NHLBI) twin study, previously divided on the basis of cardiovascular disease risk factors.

METHODS

Tree structured survival analysis (TSSA) used at a mean age of 63 years to classify twins into high and low risk subgroups for ischemic heart disease (IHD) found that subjects at a mean age of 48 years were at highest risk with high systolic blood pressures and low high density lipoprotein cholesterol levels. Low risk subjects had lower blood pressures, better pulmonary function tests, and a negative family history for IHD or low post load plasma glucose levels. Medical record review was performed ten years later at the 4th Examination of the NHLBI twin cohort conducted in 1995-1997.

RESULTS

The percentage of men in the NHLBI twin study who died nearly tripled (from 9.3% to 25.8%) in the ten-year period between the ages of 63 and 73 years. Deaths have tended to remain higher in DZ than MZ twins (27.8% versus 23.7%). At Exam 4, the relative risk of IHD (fatal or non-fatal) was 5.24 times higher for those in the high risk group than those in the low risk class (95% confidence limit 2.72-10.07, p < 0.0001 and 5.86 for any cardiovascular disease (95% confidence limit 3.03-11.33). The proportion of deaths from IHD in subjects with a high risk profile at entry was 51.7%, and 70.0% had died from all cardiovascular related disease.

CONCLUSION

The present results indicate TSSA remained effective in classifying subjects into subgroups with greater risk of morbidity and mortality related to cardiovascular disease after ten additional years.

Segregation analysis of cardiovascular reactivity to laboratory stressors

To better understand the contribution of major gene influences to individual differences in cardiovascular reactivity, we performed a segregation analysis on blood pressure responses to two laboratory tasks, mental arithmetic and bicycle exercise. The study population consisted of 1,451 adults (age > or = 18 years) who were members of 81 Utah pedigrees. Only 864 members performed the bicycle task because persons age 60 years or older or with heart disease were excluded. Blood pressure reactivity to mental arithmetic was defined as change from resting values, and reactivity to the bicycle task was defined as the difference between maximum blood pressure during exercise and resting values adjusted for the individual's workload. Complex segregation analysis and likelihood procedures were used to test for a major gene effect controlling blood pressure reactivity to each task. Two modifiers of the penetrance, age and sex, were considered parameters in these models. We found that diastolic blood pressure (DBP) but not systolic blood pressure reactivities to the mental arithmetic and bicycle exercise tasks were controlled by major gene effects. The best-fitting model, however, differed for the two tasks. For DBP reactivity to mental arithmetic, a major codominant model with gene frequency 0.10 was the best-fitting model; for the bicycle task, the best-fitting model was a mixed recessive model with gene frequency 0.21. Sex differences in DBP reactivity were significant in both tasks: the effect of age was significant only for the mental arithmetic task. These results suggest a significant genetic component for DBP reactivity to laboratory stressors.

Biobehavioral characteristics of nondemented older adults with subclinical brain atrophy

OBJECTIVE

To characterize the risk factors and neuropsychological performance of two subgroups of community-dwelling, white elderly men free of severe cognitive impairment (n = 383; mean age, 72.9 +/- 3.0 years) who differ on volumetric measurements of total brain parenchyma and white matter hyperintensity (WMH) volumes.

METHODS

Group comparisons were made of cerebrovascular disease risk factors measured at the time of imaging and at three prior examinations extending over 25 years of adult life. Measures of verbal memory and speed psychomotor processing at the time of imaging and 10 years before imaging were also available.

RESULTS

Compared with those in the "nonatrophy" group, individuals in the subgroup with "atrophy" (defined by low total brain volume and high WMH volume) were older, reported a higher level of depressive symptomatology, experienced a steeper decline in diastolic blood pressure (DBP) and a steeper increase in pulse pressure, were less physically active, had smoked for more years, and had a higher prevalence of several cardiovascular disease indicators, including an ankle/arm systolic blood pressure ratio less than 0.9, and hypertension. After multivariate analysis, the 25-year decline in DBP, the number of years smoked, and an ankle/arm index of less than 0.9 remained significant discriminators of the two groups. Lower levels of speeded performance at the time of imaging and a steeper 10-year decline in cognitive performance on selected tests were also observed in the atrophic group.

CONCLUSION

Community-dwelling older adults with volumetric brain measurements associated with accelerated aging are distinguishable on the basis of several health-related characteristics. These individuals also perform less well on certain tasks involving executive functioning.

Relationship of family history scores for stroke and hypertension to quantitative measures of white-matter hyperintensities and stroke volume in elderly males

White-matter hyperintensities (WMHI) are frequently associated with cerebrovascular risk factors in the elderly, particularly hypertension, and have been interpreted as a subclinical form of ischemic brain damage. WMHI, clinical stroke and blood pressures show significant genetic influences. The objective of this study was to determine whether a relationship exists between family history of stroke and/or hypertension in first degree relatives and WMHI in the elderly. WMHI and stroke (CVA) volumes were quantified from brain MRI performed on 414 white, male twins born between 1917 and 1927 (average age 72.3 +/- 2.9 years). WMHI, adjusted for age and head size, was significantly correlated with the family history score (r = 0.21, p < 0.001). Dividing the family history scores into quintiles revealed significant differences in WMHI by quintile mean (p < 0.05). Subjects in the highest quintile of family history score had the highest mean WMHI. Recalculation of the family history score, by only counting relatives reported to have had a clinical stroke as a positive event, revealed a nonsignificant correlation with WMHI, but the correlation of the family history score with MRI CVA volume was significant (p < 0.05). Stepwise multivariate analysis including ApoE status, current smoking status, smoking packyear history, Doppler ankle/arm blood pressure ratios, current and long term hypertensive status and current systolic and diastolic pressures indicated that the stroke/hypertension family history score was the single best predictor (p < 0.01) of WMHI volumes. Family history was not an independent predictor of CVA volume.

Contribution of genetic and environmental influences to ankle-brachial blood pressure index in the NHLBI Twin Study. National Heart, Lung, and Blood Institute

The ankle-brachial index (ABI) is widely used in the clinical diagnosis of peripheral arterial disease. The contributions of genetic and environmental influences to normal and abnormal ABI values are unknown. In this study, the authors used available data on 94 monozygotic pairs and 90 dizygotic pairs of elderly, White, male twins examined in 1995-1997 to investigate the contributions of genetic and environmental influences to normative ABI values. Within-twin-pair correlations for normative ABI values were statistically significant, and the correlation in monozygotic twin pairs was significantly greater than that in dizygotic pairs. Structural equation modeling of the variance-covariance matrices of monozygotic and dizygotic twins indicated that 48% of the observed variability in ABI values could be attributed to additive genetic effects. In contrast, concordance rates for low ABI values (ABI< or =0.9) for both monozygotic and dizygotic twins were significantly greater than would be expected by chance alone, but within-pair monozygotic similarity was not significantly greater than dizygotic similarity. A matched-cotwin analysis in 21 pairs that were discordant for low ABI values found that twins with low ABI values were physically less active and more likely to be persistent smokers than their normal-control brothers. These findings reinforce the role of individual health practices (e.g., physical activity, smoking) in the manifestation of peripheral arterial disease among subjects matched for age, genetics, and early shared environment.

A genetic analysis of smoking behavior in family members of older adult males

AIMS

To conduct a genetic study of smoking behavior in 493 three-generation families.

DESIGN

Complex segregation analysis and maximum likelihood statistics were used to describe the familial clustering of ever-smoking under several transmission models.

SETTING

The Western Collaborative Group Study, an ageing and health study currently in its 39th year of follow-up.

PARTICIPANTS

Probands were male participants who were of mean age 71.6 years at the time of the family history interview in 1986-88.

MEASUREMENTS

Data were collected via an interview that focused on the family smoking history of participants. Smoking histories of all first-degree relatives were obtained from probands.

FINDINGS

Evidence for genetic transmission was indicated by rejection of both the environmental and sporadic models in favor of a Mendelian genetic model with residual familial effects from spouses and both parents.

CONCLUSIONS

The best-fitting model was that of a dominant major gene with low estimated frequency and residual familial correlations. This is the first study to date to model the familial transmission of ever-smoking in three-generation families.

The joint effect of apolipoprotein E epsilon4 and MRI findings on lower-extremity function and decline in cognitive function

BACKGROUND

Cognitive decline and poor physical function are risk factors for disability in old age and may occur more often in subjects with the apolipoprotein E epsilon4 (ApoE-epsilon4) allele. The objective of this study was to investigate the joint effect of ApoE-epsilon4 and structural changes detected on MRI brain scans on cognitive decline and lower-extremity function.

METHODS

Brain MRI (1.5 T), neuropsychological tests, and lower-extremity physical function tests were administered to World War II male veteran twins ages 69 to 80. Quantification of MRI scans used a previously published algorithm to segment brain images into total cerebral brain (TCB), cerebrospinal fluid (CSF), and white-matter hyperintensity (WMH) volumes. A short battery of physical performance tests was used to assess lower-extremity function. Ten-year changes in performance on the Mini-Mental State Exam (MMSE), the Benton Visual Retention Test (BVRT), and the Digit Symbol Substitution (DSS) test were used to assess cognitive decline.

RESULTS

For the sample as a whole, the comparison of subjects by median split of total cerebral brain volume found that those with brain volumes below the median performed worse on tests of gait and balance (p < .01) and experienced greater cognitive decline on the MMSE and BVRT cognitive test batteries (both p < .01). In addition, subjects with WMH volumes above the median had poor performance on the standing balance tasks and experienced greater decline on the DSS test (p < .01). Stratified analyses revealed that the joint effect of radiological findings and the ApoE-epsilon4 allele on cognitive decline and lower-extremity function was often greater than that expected from the separate effects combined.

CONCLUSIONS

We conclude that radiological findings in conjunction with ApoE-epsilon4 may single out a group at higher risk for dementia. We speculate that the observed interaction effect may be due to increased susceptibility to brain injury or impaired repair mechanisms in subjects with ApoE-epsilon4.

The contribution of genetic influences to measures of lower-extremity function in older male twins

Tests of balance, gait, and endurance were administered to 95 monozygotic (MZ) and 92 dizygotic (DZ), white male twins aged 68 to 79 years who had been born in the United States. Within-twin-pair correlations were calculated for each individual task and for an overall summary performance score. These were subjected to structural equation modeling to determine the contributions of genetic and environmental influences to individual differences in performance scores. MZ intraclass correlations were significant and greater than DZ correlations for the 8-foot walk and the repeated chair stands task, but not for the standing balance task. The heritability of the lower-extremity summary score was 57%, of which 39% was due to additive genetic effects and 18% due to nonadditive effects. In addition, we found that genetic influences contributed primarily to twin similarity in the poorest quartile of performance, whereas shared environmental influences contributed to twin similarity in the best quartile.

Brain structure in men remains highly heritable in the seventh and eighth decades of life

The midsagittal cross-sectional dimensions of the corpus callosum, the coronal cross-sectional area of the lateral ventricles at the level of the pons, and a three-dimensional estimate of intracranial volume were derived from magnetic resonance brain images obtained from 45 monozygotic and 40 dizygotic male twin pairs aged 68 to 78. Univariate genetic analyses indicated strong genetic influences contributing significantly to the variability of each brain structure. The estimated proportion of genetic variance (i.e. heritability) was 81% for intracranial volume, 79% for the midline cross-sectional area of the corpus callosum, and 79% for lateral ventricle size. There was no evidence that shared environmental influences contributed significantly to twin-pair similarities. We further used bivariate genetic modeling to estimate the genetic and environmental correlation between correlated brain structures. Intracranial volume and corpus callosum area was highly correlated, and this relationship was entirely due to shared genetic effects between these two brain structures. By contrast, the relationship between the height of the corpus callosum and the size of the lateral ventricles was due to both genetic and environmental influences in common. Corresponding genetic and environmental correlations were 0.68 and 0.58, respectively, indicating that more than half of the genetic and environmental influences on these two brain structures were shared. The manner in which the brain responds to the environment with advancing age is highly genetically determined, both for the lateral ventricles, which dilate with aging and disease, and for the corpus callosum, which is deformed in shape by age-related ventricular enlargement, whereas its midline cross-sectional area remains unchanged.

Correlates of the "don't know" response to questions about snoring

Many persons say that they "don't know" whether they snore. The purpose of this study was to investigate the prevalence and correlates of such responses in an elderly population. Subjects were 1715 members (1,155 men, 560 women) of a previously defined cohort (Western Group Collaborative Study) followed prospectively since 1960-1961 with a current mean age of 75.9 (SD = 4.3) for the men and 71.4 (SD = 5.3) for the women. We collected survey questionnaires and reviewed medical records. Results indicated that risk factors for the "don't know" response in this population were similar to those for frequent snoring and included: male sex, higher Body Mass Index, smoking, and use of sinus medication. Between 28 and 44% of the cohort answered questions about snoring with a "don't know" response. These data are compatible with the interpretation that subjects may disavow knowledge of their own snoring and suggest that future studies consider the "don't know" response to questions about snoring as a response of potential interest.

Differential genetic influence for components of memory in aging adult twins

OBJECTIVE

To investigate the relative proportion of genetic and environmental contributions to verbal memory in community-dwelling World War II veteran twins.

DESIGN

The California Verbal Learning Test (CVLT) was administered to 94 monozygotic (MZ) and 89 dizygotic (DZ) elderly male twin pair participants in the fourth examination of the National Heart, Lung, and Blood Institute Twin Study.

SETTING

Subjects voluntarily participated on an outpatient basis at a research or medical center facility in 1 of 4 sites in the United States.

PARTICIPANTS

Subjects had a mean age of 71.8 years (SD, 2.9 years), a mean educational level of 13.6 years (SD, 2.8 years), and no history of stroke and/or a Mini-Mental State Examination score of 23 or greater.

MAIN OUTCOME MEASURES

Twin pair similarity in performance on 4 factor analytically derived components of the CVLT measuring verbal learning and memory, response discrimination, learning strategy, and recognition memory.

RESULTS

The MZ intraclass correlation was significantly larger than the DZ correlation for verbal learning and memory (I<.001) but not for the other 3 components of memory. Using maximum likelihood methods, the best-fitting genetic model indicated that verbal learning and memory has a substantial genetic component (56% of total variance), whereas response discrimination has a much smaller, although still detectable, genetic component (24% of total variance). There is no evidence of genetic influence on learning strategy or recognition memory.

CONCLUSION

Differential contribution of genetic and environmental influences to specific components of memory suggest that, in this group of elderly male twin pairs, some components may be more amenable to intervention than others.

Impact of apolipoprotein E epsilon4 and vascular disease on brain morphology in men from the NHLBI twin study

BACKGROUND AND PURPOSE

Apolipoprotein E epsilon4 genotype (ApoE4) has been associated with increased risk for cardiovascular disease morbidity or mortality. This appears to be mediated by an ApoE4-related increase in cardiovascular atherosclerosis. Given the similarities between risk factors for heart disease and risk factors for stroke, a positive association between ApoE4 and stroke would be expected. Since age-related brain atrophy and the extent of white matter hyperintensities (WMH) share similar risk factors, we examined the combined effect of ApoE4 and history of vascular disease on brain volume, WMH, and MRI evidence of stroke.

METHODS

Subjects were the surviving members of the National Heart, Lung, and Blood Institute Twin Study. This is a longitudinal study of the effects of cardiovascular disease risk factors in community-dwelling male veterans. The fourth and final examination of this cohort included cerebral MRI and was completed in 1997. Apolipoprotein E (ApoE) genotype, quantitative measures of brain volume, WMH, and the presence of stroke on MRI were obtained from the 396 participants in the final examination. The presence or absence of a history of coronary heart disease, cerebrovascular disease, peripheral arterial disease, and ApoE genotype were determined for each subject.

RESULTS

Of the 396 men, 88 (22%) had at least 1 ApoE4 allele. ApoE4 was not associated with differences in age or education. While the prevalence of vascular disease was generally greater in the ApoE4 group, this was only significant for coronary heart disease (29.8% in subjects without ApoE4 versus 40.7% in subject with ApoE4; P=0.03). ApoE4 subjects had significantly smaller brain volumes (942.4+/-34.5 versus 952.2+/-40.1 cm(3); P=0. 02). MRI evidence of stroke was detected in 88 (22%) of the subjects. The distribution of ApoE genotype was marginally different between subjects with MRI-detected stroke compared with those without. Further analysis revealed that the co-occurrence of cerebrovascular disease and ApoE4 was associated with significantly greater brain atrophy and WMH than either ApoE4 or cerebrovascular disease alone. Similar relations were seen for coronary heart disease and peripheral arterial disease.

CONCLUSIONS

We conclude that ApoE4 enhances the extent of brain abnormalities in the presence of various vascular diseases. We speculate that this effect may be mediated by an increased susceptibility to brain injury or impaired repair mechanisms associated with ApoE4.

Midlife cardiovascular risk factors and brain morphology in identical older male twins

OBJECTIVE

Structural changes in the human brain have been reported to a greater extent in subjects with cardiovascular risk factors. We conducted a matched co-twin analysis of elderly monozygotic twins from the National Heart, Lung, and Blood Institute Twin Study to examine the association between midlife cardiovascular risk factors and MRI-based measures of brain atrophy.

METHODS

Brain MRIs (1.5-T) were obtained from 74 monozygotic, white, male, World War II veteran twins born in the United States from 1917 to 1927 and age 68 to 79 at the time of the brain scan. A semiautomated algorithm was used to segment brain images into total brain, CSF, and white matter hyperintensity volumes. Cardiovascular risk factors, medical history variables, and health practices were available from data collected over 25 years of adult life.

RESULTS

Independent of shared genetic or familial influences, within-pair differences in midlife glucose levels, high-density lipoprotein cholesterol, and systolic blood pressure were significantly associated with differences in white matter hyperintensities. Within-pair differences in coronary heart disease history and in current consumption of alcohol and level of physical activity were significantly associated with differences in brain parenchyma. In addition, within-pair differences in white matter hyperintensity volumes were significantly associated with differences in performance on cognitive and physical function tests and self-reports of depression symptoms.

CONCLUSION

Independent of age effects and shared genetic or familial influences, midlife cardiovascular risk factors and lifetime health practices were predictive of structural brain changes in old age.

Predictors of brain morphology for the men of the NHLBI twin study

BACKGROUND AND PURPOSE

Cross-sectional studies show that cerebrovascular risk factors are associated with increased brain atrophy, accumulation of abnormal cerebral white matter signals, and clinically silent stroke. We extend these findings by examining the relationship between midlife cerebrovascular risk factors and later-life differences in brain atrophy, amount of abnormal white matter, and stroke on MRI.

METHODS

Subjects were the 414 surviving members of the prospective National Heart, Lung, and Blood Institute Twin Study, who have been examined on 4 separate occasions, spanning the 25 years between 1969-1973 and 1995-1997. Quantitative measures of brain volume, volume of abnormal white matter signal (WMHI), and volume of stroke, when present, were obtained from those participating in the fourth examination.

RESULTS

The mean+/-SD age of the subjects was 47.2+/-3.0 years at initial examination and 72. 5+/-2.9 years at final examination. Average blood pressure (BP) levels were normal, although 32% of the subjects had received or were currently taking antihypertensive medications. As a group, 31% had symptomatic cardiovascular disease, 11% had symptomatic cerebrovascular disease, and 8% had symptomatic peripheral vascular disease. Both systolic and diastolic BP levels at initial examination were inversely related to brain volume and positively related to WMHI volume. Multiple regression analysis identified BP-related measures and vascular risk factors as significant predictors of brain and WMHI volumes. In addition, the magnitude of orthostatic BP change was significantly associated with WMHI volume. Subjects with extensive amounts of WMHI had significantly higher systolic BP at the final examination and a higher prevalence of symptomatic cardiovascular and cerebrovascular disease, without significant differences in the prevalence of hypertension treatment.

CONCLUSIONS

Midlife BP measures are significantly associated with later-life brain and WMHI volumes and the prevalence of symptomatic vascular disease. Since WMHI share cerebrovascular risk factors and extensive WMHI are associated with symptomatic vascular disease, extensive WMHI may be a subclinical expression of cerebrovascular disease. Careful treatment of midlife BP elevations may diminish these later-life brain changes.

Systolic blood pressure tracking over 25 to 30 years and cognitive performance in older adults

OBJECTIVE

To determine the extent to which individual changes in systolic blood pressure (SBP) over a 30-year interval are associated with differential neuropsychological outcomes in old age.

METHODS

Seven hundred seventeen survivors from the Western Collaborative Group Study, a longitudinal study of cardiovascular risk factors now in its 38th year of follow-up, with blood pressures measured in middle age (mean=45 years) and in old age (mean=75 years) and neuropsychological tests administered at follow-up were included in this analysis. Participants were grouped according to 30-year change in SBP (increased, decreased, or "normal"). Analyses focused on comparisons of neuropsychological performance of "high SBP trackers" (ie, those with persistent SBP>/=140 mm Hg throughout adult life) and of SBP "decreasers" with the performance of those whose SBP was either stable or changed in an expected way over time.

RESULTS

Only 7.5% of participants had elevated SBP in middle age, but 43.8% of participants had elevated SBP in old age. After adjustment for age, education, depression, clinically defined stroke, and use of antihypertensive medications and after exclusion of individuals with impaired cognitive performance at follow-up, high SBP trackers, 5.0% (n=36), performed consistently less well than the "normal" SBP subgroups on a composite measure of verbal learning and memory (P=0.04). When compared with the "normal" SBP subgroup, the SBP decreasers, 5.3% (n=38), performed less well on speeded performance (P=0.03).

CONCLUSIONS

There is a relatively small group of people who maintain elevated SBP throughout their adult lives. These persons are at increased risk for reduced verbal learning and memory function. There is also a group of individuals who experience a decrease in SBP and who are at risk for decreased psychomotor speed. Delineation of these 2 SBP subgroups may lead to further clarification of the effects of SBP on neurobehavioral function in older adults.

Association of midlife blood pressure to late-life cognitive decline and brain morphology

OBJECTIVE

To investigate the association between midlife systolic blood pressure (SBP) and late-life cognitive decline and brain morphology in a sample of community-dwelling elderly men 68 to 79 years of age.

METHODS

Subjects are surviving members from the prospective National Heart, Lung, and Blood Institute Twin Study (intake, 1969 to 1972) who, when examined for a fourth time in 1995 through 1997, underwent brain MRI and repeated assessment of neurobehavioral functioning. Quantification of the MR images determined cerebral volume and total volume of white matter hyperintensities (WMHIs) for 392 subjects. Midlife SBP levels measured in 1970, 1980, and 1985 were used to classify subjects into low, medium, and high midlife SBP categories. A 10-year change in performance on the Mini-Mental State Examination, Digit Symbol Substitution Test, Benton Visual Retention Test, and Verbal Fluency Test was also calculated for these subjects. For all reported analyses, patients were treated as genetically unrelated individuals.

RESULTS

Subjects with high midlife SBP experienced a greater decline in cognitive performance and had larger WMHI volumes at follow-up in late life than did those with low midlife SBP. Decreased brain parenchyma and increased WMHI volumes were associated with decline in neurobehavioral functioning as measured in late life independent of age, education, and baseline levels of cognition.

CONCLUSIONS

Midlife SBP is a significant predictor of both decline in cognitive function and MR volumetric measures of brain atrophy in late life. Because decline in neurobehavioral functioning was associated with decreased brain volume and increased WMHI volume, we conclude that the long-term impact of elevated SBP on decline in late-life neurobehavioral functioning is likely to be mediated through its chronic, negative effect on structural characteristics of the brain.

Midlife cardiovascular risk factors, ApoE, and cognitive decline in elderly male twins

OBJECTIVE

To investigate the combined effect of the apolipoprotein E epsilon4 (ApoE*4) allele and midlife cardiovascular risk factors on cognitive decline.

METHODS

Data are from the National Heart, Lung, and Blood Institute Twin Study-a longitudinal cardiovascular epidemiologic study of World War II male veteran twins currently in its 27th year of follow-up. Subjects were assessed for cardiovascular risk factors, including BP and glucose levels, at mean ages 48, 58, and 63 years. Participants in the current study are 410 individual twin subjects for whom cognitive function was measured twice, at ages 63 and 73 years. Ten-year change scores in performance on neuropsychological test examinations were adjusted for age, education, baseline score, and incident cardiovascular disease.

RESULTS

For the sample as a whole, we observed a significant decline (p < 0.01) in cognitive performance over the 10 years of follow-up. ApoE*4 carriers with midlife hyperglycemia experienced the greatest decline in performance, which was also greater than expected from the separate effects combined. Midlife hypertension and ApoE*4, were each associated with excess decline in performance on tests of psychomotor speed. Their joint effect, however, was not greater than expected from the separate effects combined.

CONCLUSIONS

ApoE*4 and midlife cardiovascular risk factors may have a synergistic effect on decline in cognitive function. This effect may be due to greater vascular or degenerative damage among subjects with ApoE*4.

Evidence for genetic variance in white matter hyperintensity volume in normal elderly male twins

BACKGROUND AND PURPOSE

White matter hyperintensities (WMHs), as detected by MRI, are common among the elderly and are frequently interpreted as representing a subclinical form of ischemic brain damage. We used volumetric MR techniques to investigate the contribution of genes and the environment to measures of brain morphology in a sample of community dwelling elderly male twins.

METHODS

Brain MR (1.5 T) scans were obtained from 74 monozygotic (MZ) and 71 dizygotic (DZ), white, male, World War II veteran twins born in the United States and age 68 to 79 when scanned. MR quantification used a previously published semiautomated segmentation algorithm to segment brain images into total brain, cerebrospinal fluid (CSF), and WMH volumes. Twin pair covariances were computed for each measure, and structural equation genetic models were fitted to these data.

RESULTS

Total cranial, brain parenchyma, CSF, and WMH volumes were highly correlated in MZ pairs, and correlations in MZ pairs were significantly greater than those in DZ pairs. Structural equation modeling indicated heritabilities of 91%, 92%, and 73%, respectively, for total cranial, brain parenchyma, and WMH volumes. Correction for age and head size reduced the heritability of brain parenchyma to 62% (95% confidence interval, 56% to 68%) and the heritability of WMH volume to 71% (95% confidence interval, 66% to 76%). Proband concordance rates for large amounts of WMH were 61% in MZ pairs and 38% in DZ pairs, compared with a prevalence of 15% in the entire sample.

CONCLUSIONS

This study is the first to quantify the relative contribution of genetic and individual environmental influences to measures of brain morphology in the elderly.

Segregation analysis reveals a major gene effect controlling systolic blood pressure and BMI in an Israeli population

It has been suggested that genetic factors control blood pressure level at all ages. However, the evidence is limited because of the composite nature of blood pressure and the heterogeneity of the studied samples. The purpose of the present study is to test for genetic influences on systolic blood pressure (SBP) level in a community-based Israeli family study. Segregation analysis was performed on 622 adults from 208 pedigrees. Age, sex, and body mass index (BMI) were significant covariates of SBP. Segregation analysis rejected the environmental transmission model but not the mixed Mendelian transmission model. The best-fitting genetic model was the mixed codominant model, with a heritability of 0.32 and an allele frequency of 0.18 for high SBP level. We further tested whether SBP and BMI shared a common major gene effect. Using bivariate segregation analysis involving two traits and a single locus, we found evidence for a single-locus pleiotropic effect on SBP and BMI. The allele frequency of this major locus was 0.24. The residual genetic correlation resulting from additive polygenes and the environmental correlation between these two traits were not different from zero after taking into account the shared major gene effect. The proportion of phenotypic variation attributable to this major gene effect increased with age for SBP but decreased with age for BMI.

Correlates of change in cognitive function in survivors from the Western Collaborative Group Study

Changes in cognitive function were investigated in 566 subjects 65-86 years old at baseline, who are a subsample of the Western Collaborative Group Study, a cardiovascular epidemiologic study of middle-aged men that began in the 1960s. Cognitive function was assessed in 1986-1988 (baseline) and again in 1992-1994 by three standardized measures: the Benton Visual Retention Test, the Controlled Oral Word Association Test, and the Digit Symbol Substitution (DSS) Test. Longitudinal change in performance was defined as the shift over time in a subject's quartile rank ordering, using the baseline distribution of test scores as a standard. 'Decliners' and 'improvers' in cognitive function were subjects who lost or gained, respectively, two or more quartile ranks on all three tests combined. By this definition, 20% (n = 113) of subjects declined, compared with 17% (n = 95) who improved in cognitive performance from 1986-1988 to 1992-1994. After adjustment for age, education, and physical health, decline in cognitive performance was significantly associated with poor self-perceived health ratings, depression scale scores, and self-reports of physical activity. Rank score change in the DSS Test was the single best predictor of cognitive function at follow-up on a diverse battery of neuropsychological tests.

Obesity and 33-year follow-up for coronary heart disease and cancer mortality

We used tree-structured survival analysis (TSSA), a computer-intensive method of classification, to determine prospectively the relation of the body mass index and the waist-to-calf circumference ratio to coronary heart disease and cancer mortality in 3,155 middle-aged men initially free of these diseases. Applied to coronary heart disease mortality, TSSA identified seven subgroups that differed in profile of risk factors and associated survival. Among the seven subgroups, a small subgroup of older, obese, normotensive men (N = 71) experienced an exceptionally high risk of coronary heart disease deaths over the 33 years of follow-up (34%), similar to the risk of 36% experienced by a larger subgroup (N = 387) of men of similar ages who were less obese and had higher blood pressure levels. We also observed a higher overall risk of coronary heart disease deaths during follow-up (10.3% vs 5.3%) in younger centrally obese men who had low blood pressure levels compared with their counterparts of similar age who were less obese. When applied to mortality from cancer of all sites, TSSA identified five subgroups that differed in survival distributions and profile of risk factors. A subgroup of younger, centrally obese, and ever-smoker men experienced a higher risk of cancer deaths than their counterparts who were less obese (14% vs 8%). Results from these analyses demonstrate the usefulness of a tree-structured analysis for classification of subjects into high- and low-risk survival subgroups.

Heavy consumption of cigarettes, alcohol and coffee in male twins

OBJECTIVE

To determine the relative contribution of environmental and genetic influences on the joint distribution of heavy smoking, heavy alcohol use and heavy coffee drinking.

METHOD

Multivariate structural equation modeling in a large cohort of male twins (N = 2,220 monozygotic and 2,373 dizygotic twin pairs; mean age = 62.1 years) from the National Academy of Sciences-National Research Council's World War II Twin Registry.

RESULTS

The best-fitting model identified two independent (i.e., uncorrelated) sets of genetic and environmental latent factors, with one set underlying joint heavy smoking and heavy alcohol use and the other set underlying joint heavy smoking and heavy coffee drinking (chi 2 = 14,13,22 df, p > .80). Heavy alcohol use and heavy coffee drinking were uncorrelated in this sample. While common genetic factors accounted for 35% to 78% of the total genetic variance in heavy substance use, a substantial amount of genetic variance remained specific to each of the three substances.

CONCLUSIONS

Several hypotheses involving genetic and environmental factors are presented to account for the independent clustering of heavy smoking and heavy alcohol use and of heavy smoking and heavy coffee drinking.

Curiosity and mortality in aging adults: a 5-year follow-up of the Western Collaborative Group Study

Research suggests that curiosity in older people is associated with maintaining the health of the aging central nervous system. We examined prospectively the relationship of curiosity in 1,118 community-dwelling older men to subsequent survival over a 5-year period. Curiosity was measured when the participants were a mean age of 70.6 years. Initial levels of trait and state curiosity were higher in survivors than in those who subsequently died. After adjustment for other risk factors, the state curiosity-mortality association remained significant in the Cox regression model. Ancillary analyses in 1,035 older women (M age at initial examination = 68.6 years) confirmed the pattern found in the men. State curiosity in these women was significantly associated with survival after adjustment for other risk factors. This is the first study to identify a predictive role for curiosity in the longevity of older adults.

Curiosity and mortality in aging adults: a 5-year follow-up of the Western Collaborative Group Study

Research suggests that curiosity in older people is associated with maintaining the health of the aging central nervous system. We examined prospectively the relationship of curiosity in 1,118 community-dwelling older men to subsequent survival over a 5-year period. Curiosity was measured when the participants were a mean age of 70.6 years. Initial levels of trait and state curiosity were higher in survivors than in those who subsequently died. After adjustment for other risk factors, the state curiosity-mortality association remained significant in the Cox regression model. Ancillary analyses in 1,035 older women (M age at initial examination = 68.6 years) confirmed the pattern found in the men. State curiosity in these women was significantly associated with survival after adjustment for other risk factors. This is the first study to identify a predictive role for curiosity in the longevity of older adults.

Twenty-four year mortality in World War II US male veteran twins discordant for cigarette smoking

BACKGROUND

This study was undertaken to test the constitutional hypothesis which attributes the association of tobacco smoking with morbidity and mortality to genetic predispositions to smoking and/or disease.

METHODS

Subjects were World War II veterans, born in the US between 1917 and 1927, and surveyed at mean age 47 for present and past smoking habits. Twenty-four year mortality follow-up data were available for 1515 male twin pairs discordant for lifelong cigarette smoking. Using the first or only death of a smoking-discordant pair, 24-year relative risks of mortality were calculated by zygosity, cause of death, amount smoked, and age at death.

RESULTS

We found that active smokers at baseline, regardless of zygosity, had a higher risk of death than their co-twins who had never smoked or quit smoking (monozygotic pairs: relative risk [RR] = 2.5; 95% confidence interval [CI] : 1.3-6.1 and RR = 1.7; 95% CI : 1.2-2.5; dizygotic pairs: RR = 2.4; 95% CI : 1.4-3.8 and RR = 2.0; 95% CI : 1.7-3.3). The elevated risk of death among smokers was due to deaths from lung cancer (monozygotic pairs: RR = 5.0; 95% CI: 2. 6-15.0; dizygotic pairs: RR = 11.0; 95% CI : 4.3-45.0) or deaths from cardiovascular diseases (monozygotic pairs: RR = 3.9; 95% CI : 1.9-115; dizygotic pairs: RR = 2.8; 95% CI : 1.7-4.9). Apart from these findings the relationship of smoking with all-cause mortality was stronger for earlier/younger deaths and for heavy to moderate smoking.

CONCLUSIONS

The present results, from the largest and longest-studied series of smoking-discordant twins negate the constitutional hypothesis that genetic or early shared familial influences underlie the significant association between tobacco smoking and premature mortality.

The relationship of Type A behavior and its components to all-cause mortality in an elderly subgroup of men from the Western Collaborative Group Study

This study examined prospectively the relationship of Type A behavior and its components to all-cause mortality in 1,118 men (age 60 to 86) who participated in a 27-year follow-up examination of the Western Collaborative Group Study. Global Type A/B behavior was assessed in these subjects using a modified version of the Structured Interview. Additional psychological data that related to this construct were obtained from self-report questionnaires. The relationship of these data, controlling for other biological risk factors, to 6-year all-cause mortality was investigated by means of a tree-structured survival analysis (TSSA). Using age, Type A behavior, Cook-Medley hostility, ever smoking, and cancer status at follow-up, TSSA identified 6 subgroups that differed in survival rates and associated risk factor profiles. The most favorable survival was experienced by 2 subgroups, one composed of older Type A subjects who scored the lowest on anger-hostility and depression, the other consisting entirely of Type B subjects who had never smoked. The worst survival was experienced by subjects with diagnosed cancer at the 27-year follow-up, and intermediate survival rates were experienced by 3 subgroups that differed markedly on age, smoking, Type A/B behavior, and Cook-Medley hostility. The present study is the first to characterize Type A's with favorable and unfavorable survival rates among the elderly.

The consumption of tobacco, alcohol, and coffee in Caucasian male twins: a multivariate genetic analysis

Despite the fact that epidemiologic studies demonstrate a consistent covariation between the use of tobacco, alcohol, and coffee, most previous behavioral genetic-studies have determined the contribution of genetic and environmental influences as if the consumption of these substances occurred independently of each other. In this study, we used multivariate structural equation modeling to determine the genetic and environmental overlap in the observed correlations between tobacco smoking and alcohol and coffee drinking in 173 monozygotic and 183 dizygotic male twin pairs (M age = 59 years; range = 52-66 years) who participated in a follow-up cardiovascular examination of the National Heart, Lung, and Blood Institute's Twin Study. Consistent with hypothesized psychoneurogenetic predispositions for the joint use of these substances, the most parsimonious model fitting these data identified a common genetic latent factor underlying the observed associations between smoking, alcohol, and coffee use in this cohort. This factor, herein called polysubstance use, underscores the role of genetic influence on the clustering of these behaviors in the same individual.

Evidence for a major gene influencing 7-year increases in diastolic blood pressure with age

The contribution of genetic factors to blood pressure levels is well established. The contribution of genes to the longitudinal change in blood pressure has been less well studied, because of the lack of longitudinal family data. The present study investigated a possible major-gene effect on the observed increase with age in diastolic blood pressure (DBP) levels. Subjects included 965 unmedicated adults (age > or = 18 years) in 73 pedigrees collected in Utah as part of a longitudinal cardiovascular family study. Segregation analysis of DBP change over 7.2 years of follow-up identified a recessive major-gene effect with a gene frequency of p = .23. There was also a significant age effect on the genotypic means, which decreased expression of the major gene at older ages. For those inferred to have the genotype responsible for large DBP increases, DBP increased 32.3%, compared with a 1.5% increase in the nonsusceptible group (P < .0001). The relative risk of developing hypertension between the susceptible and nonsusceptible groups after 7.2 years was 2.4 (P = .006). Baseline DBP reactivities to mental arithmetic (P < .0001), and isometric handgrip (P < .0001) stress tests were greatest in those assigned to the susceptible genotype. We conclude that age-related changes in DBP are influenced by a major gene. Characteristics of this major-gene effect for greater age-related blood pressure increases include greater reactivity to mental and physical stressors. The present study thus provides evidence for genetic control of changes in blood pressure, in addition to the previously suggested genetic control of absolute blood pressure level.

Cognition and depression in a cohort of aging men: results from the Western Collaborative Group Study

Relationships between cognitive performance and self-ratings of depression on the Center for Epidemiologic Studies Depression scale (CES-D; L.S. Radloff, 1977) were examined for 1,217 older men. After controlling for demographic variables and both objective and subjective measures of health, significant associations were observed between several CES-D variables and measures of cognitive mental status, memory, and psychomotor speed. The Well-Being factor of the CES-D was the most robust predictor of cognitive scores. Therefore, for older adults with generally favorable health and socioeconomic resources, there may be a link between positive affect and maintenance of cognitive effectiveness.

Genetic mediation in the relationship of education to cognitive function in older people

We used data from 136 monozygotic and 125 dizygotic human, male twin pairs (M age = 64 years, range = 59 to 70 years) to test whether the previously observed association (r = .30, p < .01) between cognitive performance and education in this sample is genetically mediated. Biometric genetic modeling found that a common genetic latent variable accounted for 44% of the total variance in the Mini-Mental State Exam (MMSE: M. F. Folstein, S. E. Folstein, & P. R. McHugh, 1975), 40% of the variance in the Iowa Screening Battery for Mental Decline (P. J. Eslinger, A. R. Damasio, & A. L. Benton, 1984), and 21% of the variance in educational attainment. In addition, specific genetic and environmental variables contributed significantly to individual differences in education and cognitive performance of the participants.

Self-reported alcohol intake and cognition in aging twins

OBJECTIVE

To determine the relationship between long-term alcohol intake and cognitive functioning in aging Caucasian men.

METHOD

A retrospective cohort and co-twin-control study of self-reported alcohol intake and cognitive testing using the National Academy of Sciences-National Research Council (NAS-NRC) Twin Panel of U.S. veterans (born between 1917 and 1927). The study included 4,739 twins with two self-reported drinking histories (1970s and 1980s) and a telephone mental status interview (1990 and 1991) that also included 145 individuals with a diagnosis of alcoholism.

RESULTS

Age and education adjusted cognitive scores were lower (p < .05) in diagnosed alcoholics than in the remainder of the subjects. To compare age and education adjusted cognitive scores in alcohol intake, the 4,739 twins were divided, based upon questionnaire data, into nondrinkers and 5 quintiles of drinkers by average reported drinks of alcohol weekly (< 1.0, 1-3.3, 3.4-8.1, 8.2-16.0, > 16.0). Past drinkers had scores lower (p < .05) than nondrinkers and all but quintiles 1 and 5 of the drinkers. The light drinkers in quintile 1 and the heavy drinkers in quintile 5 scored lower (p < .05) than the moderate drinkers in quintile 4. Monozygotic twins in quintile 4 scored higher (p < .05) than their co-twins in quintiles 1-3.

CONCLUSIONS

No evidence was found to indicate an association between moderate long-term alcohol intake and lower cognitive scores in aging individuals. There was a suggestion of a small protective effect of past moderate alcohol intake on cognitive function with aging.

Cognition and depression in a cohort of aging men: results from the Western Collaborative Group Study

Relationships between cognitive performance and self-ratings of depression on the Center for Epidemiologic Studies Depression scale (CES-D; L.S. Radloff, 1977) were examined for 1,217 older men. After controlling for demographic variables and both objective and subjective measures of health, significant associations were observed between several CES-D variables and measures of cognitive mental status, memory, and psychomotor speed. The Well-Being factor of the CES-D was the most robust predictor of cognitive scores. Therefore, for older adults with generally favorable health and socioeconomic resources, there may be a link between positive affect and maintenance of cognitive effectiveness.

Genetic mediation in the relationship of education to cognitive function in older people

We used data from 136 monozygotic and 125 dizygotic human, male twin pairs (M age = 64 years, range = 59 to 70 years) to test whether the previously observed association (r = .30, p < .01) between cognitive performance and education in this sample is genetically mediated. Biometric genetic modeling found that a common genetic latent variable accounted for 44% of the total variance in the Mini-Mental State Exam (MMSE: M. F. Folstein, S. E. Folstein, & P. R. McHugh, 1975), 40% of the variance in the Iowa Screening Battery for Mental Decline (P. J. Eslinger, A. R. Damasio, & A. L. Benton, 1984), and 21% of the variance in educational attainment. In addition, specific genetic and environmental variables contributed significantly to individual differences in education and cognitive performance of the participants.

Performance on the digit symbol substitution test and 5-year mortality in the Western Collaborative Group Study

The relation between performance on the digit symbol substitution test and subsequent 5-year mortality was examined in 1,118 male participants in the Western Collaborative Group Study (mean age at time of examination = 70.6 years). Cox regression analyses revealed that the unadjusted relative risk from all-cause mortality was 1.79 (95% confidence interval 1.45-2.21) for subjects who scored 10 points (1 standard deviation) lower on the digit symbol substitution test. The relative risk remained significant at 1.44 (95% confidence interval 1.12-1.86) after adjustment for age, education, baseline serum cholesterol, and systolic blood pressure levels and for the prevalence of cancer, cardiovascular/cerebrovascular disease, and ever smoking. Tree-structured survival analysis revealed the presence of a subgroup of subjects (n = 130) with low digit symbol substitution performance (mean = 26.3) who experienced a mortality rate of 34.9 deaths per 1,000 person-years. This mortality rate was not significantly different from that encountered by another subgroup of subjects with a history of cancer (n = 128; 45.7 deaths per 1,000 person-years). If age-related slowing of information processing is a marker for aging of the central nervous system, then people with lower digit symbol scores may be "older" physiologically than similarly aged persons with higher digit symbol scores. Aging of the central nervous system might be expected to reduce adaptive capacity in a general way, thereby increasing susceptibility to death from a variety of causes.

Characteristics associated with excessive weight gain after smoking cessation in men

OBJECTIVES

Data from two surveys of the National Academy of Sciences-National Research Council Twin Registry, conducted 16 years apart, were used to determine characteristics of individuals that were predictive of excessive weight gain after smoking cessation.

METHODS

Over the follow-up, 2179 men quit smoking and averaged a weight gain of 3.5 kg. Quitters were grouped into four categories of weight change: lost weight, no change, gained weight, and excessive weight gain ("super-gainers").

RESULTS

In comparison with quitters reporting no change in weight, super-gainers were younger, were of lower socioeconomic status, and differed on a number of health habits before quitting (all Ps < .05). At follow-up, super-gainers reported changes in health habits that were significantly different from those seen in quitters reporting stable weight (all Ps < .05). Pairwise concordance for weight change in 146 monozygotic and 111 dizygotic twin pairs in which both twins quit smoking was significantly greater in monozygotic than dizygotic pairs (P < .01).

CONCLUSIONS

These results indicate that super-gainers differ in important ways from those who do not gain weight after smoking cessation and that these weight changes may be influenced by underlying genetic factors.

World War II-veteran male twins who are discordant for alcohol consumption: 24-year mortality

The role of genetic and shared environmental influences in the association of alcohol with mortality was studied by using the National Academy of Sciences-National Research Council World War II-veteran male twin registry. An epidemiologic questionnaire administered from 1967 through 1969 permitted identification of twin pairs discordant for alcohol consumption. The subsequent 24 years of mortality follow-up yielded data on time and cause of death. Analyzing the first or only death in drinking-discordant pairs, we observed 27 deaths in abstainer twins and 14 deaths in their light- to moderate-drinker cotwins (relative risk [RR] = 1.93). Excess mortality in twin abstainers was also indicated for deaths from cardiovascular diseases (RR = 2.0) and other causes of death excluding cancers (RR = 3.2). The protective effect, however, of light to moderate drinking did not persist in twins who were smokers at baseline.

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.