G E McClearn

A Quantitative Genetic Analysis of Cognitive Abilities During the Second Half of the Life Span

Little is known about the importance of genetic effects on individual differences in cognitive abilities late in life. We present the first report from the Swedish Adoption/Twin Study of Aging (SATSA) for cognitive data, including general cognitive ability and 13 tests of specific cognitive abilities. The adoption/twin design consists of identical twins separated at an early age and reared apart (46 pairs), identical twins reared together (67 pairs), fraternal twins reared apart (100 pairs), and fraternal twins reared together (89 pairs); average age was 65 years. Heritability of general cognitive ability in these twins was much higher (about 80%) than estimates typically found earlier in life (about 50%). Consistent with the literature, heritabilities of specific cognitive abilities were lower than the heritability of general cognitive ability but nonetheless substantial. Average heritabilities for verbal, spatial, perceptual speed, and memory tests were, respectively, 58%, 46%, 58%, and 38%.

Familial resemblance for specific cognitive abilities

Measures of familial resemblance (spouse correlations, regressions of offspring on midparent, single-parent/single-child correlations, and sibling correlations) are presented for members of the two largest ethnic groups tested in the Hawaii Family Study of Cognition. Median spouse correlations (corrected for differences in test reliability) for 15 individual tests of specific cognitive abilities are 0.15 and 0.12 for Americans of European and of Japanese ancestry, respectively. With regard to the regressions of offspring on midparent value, corresponding median values are 0.50 and 0.35. Results of hierarchical multiple regression analyses, as well as the ordering of single-parent/single-child and sibling correlations, provide no evidence to support the hypothesis that spatial ability is influenced by a sex-linked, recessive gene.

Effect of hypnotics on mice genetically selected for sensitivity to ethanol

It was previously shown that the rate of disappearance of blood ethanol was identical for two lines of mice selectively bred for differences in sleep-time after ethanol administration. The ED50 values for the loss of righting response with ethanol were significantly different at 3.64 g per kg for the SS line and 1.65 g per kg for the LS line. In the present study the mean sleep time is 367 sec for SS mice and 9342 sec for LS mice. The ED50 values remain essentially the same as previously reported. Unchanged LD50 values for ethanol, however, are not different at 4.8 g per kg for the SS and 4.5 g per kg for the LS line of mice. The ED50 value for loss for righting response following administration of methanol, butanol and t-butanol is approximately 2 fold greater for the SS line of mice than for the LS line. The ED50 values for sodium pentobarbital or ether in the 2 lines of mice for loss of righting response are virtually identical. In addition, the sleep-time values obtained after the administration of pentobarbital, chloral hydrate, trichloroethanol and paraldehyde are not significantly different. These data indicate that while the SS and LS lines of mice differ in central nervous system sensitivity to ethanol, methanol, butanol and t-butanol it is implied that they do no differ in central nervous system sensitivity to other hypnotic agents tested. Proof of this latter suggestion awaits determination of metabolic rates, and brain levels of these other depressants.

Near Identity of Cognitive Structure in Two Ethnic Groups

As part of a large-scale family study in Hawaii, Americans of either Japanese or European ancestry were administered a battery of 15 cognitive tests. Principal component analyses (varimax rotations) yielded the same four major cognitive factors for each of the two ethnic groups, and these factors are defined by strikingly similar factor loadings.

Ethanol-induced depressions in cerebellar and hippocampal neurons of mice selectively bred for differences in ethanol sensitivity: An electrophysiological study

The recently discovered profound differential sensitivity of cerebellar Purkinje (P) cells in long-sleep (LS) verus short-sleep (SS) mice to the depressant effects of locally applied ethanol was extended in this study. First, the sensitivity of Purkinje neurons from HS mice (an outbred stock of mice from which the LS and SS lines were derived), was found to be almost exactly intermediate between the values for the long-sleep and short-sleep animals. Second, no differential sensitivity in long-sleep versus short-sleep hippocampal pyramidal neurons was observed. This was true using both spontaneous and evoked activity. Third, no differential sensitivity of P cells was seen in long- versus short-sleep mice with local application of halothane. Taken together with previous reports, these data strongly suggest that whatever genetically determined central nervous alterations result in the differential soporific effects of ethanol in the two (LS and SS) mouse lines, such alterations are brain region- and depressant drug-specific rather than generalized.

Genetic and environmental influences for type A-like measures and related traits: a study of twins reared apart and twins reared together

&NA; The relative influences of genetic and environmental factors for Type A‐like behaviors and related traits were examined in the Swedish Adoption/Twin Study of Aging. The sample consisted of 99 pairs of monozygotic twins separated at an early age and reared apart, 229 pairs of dizygotic twins reared apart, 160 monozygotic pairs reared together, and 212 dizygotic pairs reared together. The average age of the Swedish Adoption/Twin Study of Aging twins at the time of data collection in 1984 was 58.6 (SD 13.6); 72% of the pairs were over 50 years of age and 60% were female. The Framingham Type A Scale, three descriptors of the Type A behavior pattern (pressure, hard‐driving, and ambitious), and measures of hostility and lack of assertiveness were assessed in a mailout questionnaire. Heritability (the proportion of total variance due to genetic effects) was 27%, 28%, 43%, 37%, 20%, and 12%, respectively, for the six measures. The most conservative test of significance indicated significant genetic influence for all but the hostility and assertiveness scales. Sharing the same rearing environment was generally unimportant for twin similarity in the Type A behaviors later in life; however, 20% of the variation in the hostility and assertiveness measures could be attributed to shared family environment. Evidence for the effects of correlated post‐rearing environments was found for hostility. Approximately 60% of the variation in each of the measures can be attributed to non‐shared environmental experiences unique to the individual.

Ethnic variation in use and effects of alcohol.

Americans living in Hawaii were questioned about their use of alcoholic beverages. Although alcohol use was widespread in all ethnic groups included in the study, comparisons among groups showed that (a) a larger proportion of Orientals than Caucasians reported no use of alcohol, (b) Caucasians reported heavier use, and (c) a larger proportion of Oriental users reported facial flushing as a sequel to alcohol consumption. Persons with one Oriental and one Caucasian parent were intermediate with respect to (a) and (b), but were more similar to Orientals on (c). Other symptomology reported appeared to be associated with amount imbibed, not with ethnicity per se. Compared to current users, former users reported a larger number of problems and symptoms associated with alcohol use.

Parent-offspring resemblance for specific cognitive abilities in Korea

Regressions of offspring on midparent value for tests of specific cognitive abilities in Korea were considerably higher than those for Americans of Japanese ancestry or Americans of European ancestry tested in Hawaii. This greater parent-offspring resemblance in Korea may be due to the particular method of test administration or to an increased genetic variance resulting from assortative mating. The pattern of parent-child correlations for three relatively pure tests of spatial ability and for the spatial factor did not conform to that of a sex-linked recessive character.

Genotype€nvironment interaction in personality development: Indentical twins reared apart.

The focus of this study is to identify specific genotype-environment (GE) interactions as they contribute to individual differences in personality in later life. In behavioral genetics, GE interaction refers to the possibility that individuals of different genotypes may respond differently to specific environments. A sample of 99 pairs of identical twins reared apart, whose average age is 59 years, has been studied as part of the Swedish Adoption/Twin Study of Aging (SATSA). Hierarchical multiple regression was used to detect interactions between personality and environmental measures after the main effects of genotype and environment were removed. Analyses yield evidence for 11 significant interactions that provide the first evidence for GE interaction in human development using specific environmental measures. Thus, in addition to the main-effect contributions of heredity and environment, GE interactions contribute to individual differences in personality as measured in the second half of the life course.

Assortative marriage for specific cognitive abilities in Korea

Abstract Age‐adjusted spouse correlations for performance on tests of specific cognitive abilities were substantially higher for couples tested in Korea than for Americans of European or Japanese ancestry tested in Hawaii. It was hypothesized that this greater spouse resemblance in Korea may be due to cultural factors such as the Korean practice of arranged marriages.