Adult Male Twins Research Articles

Genetic control of ethanol action on the central nervous system. An EEG study in twins.

The purpose of the investigation is to claify the genetic contribution to the interindividual variability of ethanol action on the central nervous system. The 52 adult male healthy twin pairs (26 MZ, 26 DZ) got 1.2 ml/kg ethanol p.o. under standardized conditions; furthermore, 13 non-twin subjects were repeatedly subjected to the same procedure in order to test the intraindividual variability. The EEG was recorded before and 60, 120, 180, and 240 min after alcohol intake. The EEGs were off-line analyzed by means of a computer program for time domain analysis. As was already known, on the average alcohol led to a better synchronisation of the EEG, i.e., the number of beta-waves decreased whereas the number of alpha- and theta-waves increased. The extent of the alcohol effect on the EEG varied enormously between individuals; however, the EEGs of MZ twins proved to react indentically to alcohol loading, whereas the EEGs of DZ twins became mor dissimilar during the course of the experiment. The low-voltage EEG presumably is resistant to alchohol; furthermore, it is supposed that there exists a special beta-prone EEG-type which is also genetic in origin. The identical EEG reaction of MZ twins to alcohol loading could not be attributed to more similar blood alcohol concentrations. It is hypothesized that the differences in the extent of the alcohol effect on the EEG between individuals might reflect differences in the sensitivity of the ascending reticular activating system. In the literature it has frequently been reported that alcoholics have preferentially brain wave patterns which are poorly synchronized. These findings are discussed in the light of the present results.

Fatty acid variability of plasma lipids and cholesteryl esters in adult male twins and their brothers.

Variation in the fatty acid composition of fasting plasma lipids and of cholesteryl esters was studied in 69 sets of adult male twins and 25 of their brothers. Genetic variances were estimated using the twin model. In general, monozygotic (MZ) twins were characterized by the smallest within-pair variance, and brothers of twins by the largest. Variation within dizygotic pairs fell imtermediate to that of MZ twins and brothers. The present study did not reveal consistent significant (P greater than 0.05) genetic variation in plasma fatty acids from total plasma lipids or cholesteryl esters.

Generalization and dishabituation of the orienting response to a stimulus of lower intensity

An experiment was carried out to investigate generalization and dishabituation of the GSR orienting response by a tonal stimulus of lower intensity than the habituating stimulus. Subjects were 84 young adult male twins. These were divided into two groups, one twin being assigned to each. One group received 32 auditory stimuli at 95 dB intensity with an interstimulus interval of 33 sec. The other group differed only in that the 22nd stimulus was at 65 dB. It was found that the quieter stimulus produced a significantly larger GSR response than did the control group stimulus in the same position. Significant dishabituation of the responses to the subsequent stimuli was also found. No concomitant changes in basal GSR were found. The results were discussed in terms of the habituation theories of Sokolov (1960, 1963) and of Groves and Thompson (1970). It was felt that the best explanation was directly in terms of expectancy rather than of any neurophysiologies theory.

Genetics of plasma cholesterol and triglycerides: a study of adult male twins.

Fasting plasma triglycerides and cholesterol, as well as cholesterol in very low density, low density and high density lipoproteins, were measured in 250 MZ and 264 DZ adult male twin pairs. A new method was used to choose an estimate of genetic variance. This includes an estimate of genetic variance for use when the total variances of MZ and DZ twins are unequal. DZ twins had greater total variance for cholesterol. When genetic variance was estimated by subtracting the within-MZ-sets mean square from the within-DZ-sets mean square, all of the lipids had significant estimates of genetic variance; however, when genetic variance was estimated by a method designed to correct bias due to unequal total variances of MZ and DZ twins, only triglycerides had significant genetic variance. The heritability of plasma triglycerides was calculated to be 0.68.

Heritability of personality traits in adult male twins

Personality test data from the California Psychological Inventory were collected on 99 pairs of identical and 99 pairs of fraternal adult male twins. Heritabilities were comuted for all 18 scales and compared to the heritabilities for "pure" scales with overlapping items omitted. Two of the pure scales, Responsibility and Femininity, had zero heritabilities, whereas all of the full scales had moderate to high heritabilities. It was concluded that item overlap has contributed significantly to previous failures to find evidence for the differential heritability of personality traits as measured by the CPI. CPI items were classified into genetic or environmental categories and separate factor analyses of items in these categories revealed more differences than similarities in factor structure. The genetic personality factors included Conversational Poise, Compulsiveness, and Social Ease. Environmental factors included Confidence in Leadership, Impulse Control, Philosophical Attitudes, Intellectual Interest, and Exhibitionism. Compared to the genetic factors, each of the environmental factors accounted for only a very small percentage of the variance.

Genetic variance in blood pressure.

The National Heart and Lung Institute Twin Study has examined 514 white adult male twin sets aged 42-56 with respect to blood pressure. The data were analyzed by a method of Christian et al. which eliminates possible biases in estimated genetic variances that could result from different total variances in MZ and DZ twins. Results of the test for the presence of genetic variance indicate that both systolic and diastolic blood pressure are to a considerable extent genetically controlled with an estimated heritability of 0.8 for systolic and 0.6 for diastolic pressure. Although these findings are at variance with some previous reports, it is thought that much of the discrepancy results from application of different analytic techniques, not in the data themselves. The application of these findings to our understanding of hypertension epidemiology and community hypertension control programs are discussed.

Genetic effects in the cortical auditory evoked potential: A twin study

An experiment was carried out on 40 pairs of adult male twins to investigate the extent of genetical determination in the cortical auditory evoked potential. Tonal stimuli of 1 sec duration, at an intensity of 95 dB and a frequency of 1000 c/sec, were used. The inter-stimulus interval was 33 sec and the bipolar evoked potential was measured between the Cz and T3 scalp positions. the reliability of the seven latency and amplitude measures was also calculated and this was taken into account in the subsequent genetic analysis. The biometrical genetical approach, which gives maximal information particularly on small samples, was used to analyse the data. A strong genetic influence was found on all the amplitude scores. The environment made no significant contribution to these. For the latencies there was some evidence for a genetic effect; however, this was not very strong and can well be interpreted as being due to between family environmental effects.

Genetics of Plasma Cholesterol and Triglycerides: A Study of Adult Male Twins

Genetics of Plasma Cholesterol and Triglycerides: A Study of Adult Male Twins

Blood Coagulation Factors I, II, V, VII, VIII, IX, X, XI and XII in Twins

Sources of variation in blood clotting factors I, II, V, VII, VIII, IX, X, XI and XII have been investigated in a series of adult male twin pairs. Estimates of components of variation are presented, t

The National Heart Institute Twin Study.

During the past two decades prospective epidemiologic studies have established the association between several risk factors and coronary heart disease. Elevations of serum cholesterol and blood pressure, obesity, lack of physical activity and cigarette smoking are among the factors which have been related to an increased risk of heart disease. We are now entering a period in which vigorous efforts will be made to modify these factors in order to prevent the occurrence of heart disease. An important part of this effort will be to determine to what extent these factors are genetically controlled and to what extent they can be modified by manipulation of the individual environment. Recognizing this need, the Field Epidemiological Research Section, National Heart Institute, NIH, has recently embarked on a study of cardiovascular disease risk factors in a large sample of adult male twins. The purpose of the present report is to describe the protocol and methods to be used and the importance of this study to current research in cardiovascular disease.

Glycogenic myopathy: A case of skeletal muscle-glycogenosis in twins

With two adult male twins aged 29, severe muscle fatigue was noted after every effort of a rhythmical nature, which in the last 2 years had worsened and then continued unchanged. Both men are well-developed and muscular, and without either atrophy or hypertrophy. They never passed brownish or dark urine. Muscular fatigue was checked by various exercises, while in connection with ischaemic exercises exhaustion ensued much sooner than in the absence of ischaemia and with healthy controls. Neurological investigation did not reveal any abnormality in our patients. Thorough laboratory, biochemical, and biopsy investigations yielded the folllowing findings in the case of one twin (Peter E.): 1. (1) Quiescent values of serum-pyruvic acid were found to be raised; at the end of the ischaemia effort experiment the serum pyruvic acid content rose to less than twice the initial value. 2. (2) With serum lactic acid, the quiescent value was at the normal upper limit; by the end of the ischaemic effort experiment, only a slight rise was noticeable. The relatively slight increase of serum pyruvic acid and serum lactic acid levels at the end of the ischaemic effort test indicated that anaerobic breakdown of muscles glycogen was partially inhibited. Biopsy was performed on bilateral samples from the quadriceps femoris muscle. Staining with haematoxylin-eosin and the Van Gieson and Mallory methods, revealed the presence of a strikingly large number of vacuoles filled, not with neutral fats or lipid substances, but with glycogen, acid mucopolysaccharides, perhaps mixed with other substances. The amount of muscle-glycogen was found histochemically to be increased, while muscle-phosphorylase activity remained approximately normal on the histochemical slides. With one twin (Peter E.) erythrocyte glycogen concentration was normal; with the other it was slightly increased. In the case of both patients, the glycogen isolated from the red blood cells was of pathological structure. Judged by the above histological and histochemical evidence, our case stands nearest to case No. 2 of Thomson et al. [ J. Neurol. Neurosurg. Psychiat. (1963) 26: 20]. With reference to the clinical findings, effort tests and ischaemic exercises, to serological, biopsy-histological and -histochemical findings, our case can be probably placed within the “type-5” group of the glycogenosis table of Stetten and Stetten [ Physiol. Rev. (1960) 40: 505] and Thomson et al., where no enzyme deficiency has been found to occur, but where numerous partial enzyme deficiencies may be deemed responsible. However, since glycogen structure has proved to be pathological in our cases, they may constitute a new, so far unknown subgroup of “type 5”. This is the first occasion in the literature, where glycogen myopathy has been observed in twins.