On the food favoritism of twins

In the present study, there is a continuation of the authors' earlier investigations concerning food preference/refusal patterns in a group of Hungarian adult MZ and DZ twin pairs. A "Food Like/Dislike Chart" (FLDC), adapted to local nutritional habits, was applied. In order to characterize the degree of intra-pair concordance referring to the food favoritism, the concept of the "Taste Concordance Point" (TCP) was introduced. On the basis of the comparison of the TCP values obtained for the MZ and DZ pairs the conclusion can be drawn that gustatory habits are presumably influenced also by genetic factors. The results allow the possibility of applying TCP to testing zygosity.     

Human basophil releasability. III. Genetic control of human basophil releasability

Basophil releasability implies that, in addition to the surface density of IgE molecules, biochemical events determine the capacity to release chemical mediators in response to activating stimuli. We studied the IgE (anti-IgE)-mediated and non-IgE-mediated (f-met peptide and the Ca2+ ionophore A23187) releasability of human basophils obtained from 14 monozygotic (MZ) (ages 25.7 +/- 13.3 yr; mean +/- SDM) and 13 dizygotic (DZ) twin pairs (ages 20.4 +/- 9.9 yr). A significant intrapair correlation coefficient of the maximal percent of anti-IgE-induced histamine release was found in the MZ, whereas no significant correlation was found in the DZ. The mean intrapair variance of anti-IgE-induced histamine release in MZ (VMZ) and in DZ (VDZ) gave an F value equal to 3.84 (p less than 0.01) and a heritability (H) index of 0.74. Similar findings were obtained with respect to the sensitivity to a standard concentration (10(-1) micrograms/ml) of anti-IgE. No correlation between serum IgE level and anti-IgE-induced histamine release was found in either MZ or DZ. A significant intrapair correlation coefficient of f-met peptide-induced histamine release was found in both the MZ and the DZ. The difference between MZ and DZ was not significant. The VMZ and the VDZ of the f-met peptide-induced histamine release gave an F value of 1.52 (NS) and an H value of 0.34. The intrapair correlation coefficient of A23187-induced release was significant in MZ and not significant in DZ. The mean intrapair variance of A23187-induced histamine release gave an F value of 2.33 (NS) and an H index of 0.57. Similar findings were obtained by using suboptimal (3 X 10(-1) micrograms/ml) concentrations of A23187. There was no correlation between the sensitivity of basophils to release in response to anti-IgE and their response to f-met peptide or A23187, in either the MZ or the DZ. We conclude that the ability of basophils to respond to anti-IgE and A23187 is influenced by genetic factors.     

Inheritance of hypodontia in twins

The aim of this study was to establish prevalence of hypodontia in the twin sample and to assess the degree of its heritability. A study was performed in a sample of 96 twin pairs, 38 pairs being monozygotic (MZ) and 58 pairs dizygotic (DZ), from north-west Croatia. The sample included 25.82% of all twins born in the region during a ten-year period. The twin zygosity was determined according to the WHO recommendations (1996). A revised Holzinger's index (Hc') according to Allen was applied to calculate the degree of heritability. Hypodontia was found in 22 out of the total of 192 twins analyzed (11.5%). Among 96 pairs of twins, hypodontia was observed in 17 pairs (7 MZ and 10 DZ pairs). Among the MZ, 4 pairs were found to be concordant for hypodontia, among the DZ one pair only. The heritability index was 0825. A prevalence of hypodontia in twins observed in this study is significantly higher than in the general population. A high index of heritability (Hc' = 0.825) points to a high genetic determination.     

Skeletal growth and aging parameters due to heredity at different stages of ontogeny

Two hundred and twenty twins of Ukrainian ethnic group have been examined (89 monozygotic (MZ) and 131 dizygotic (DZ) pairs) during peripubertal (42 MZ and 69 DZ) and mature (47 MZ and 69 DZ) age periods. Of them: 94 are male pairs (31 MZ and 62 DZ) and 126 female (58 MZ and 68 DZ) pairs. The program including 16 anthropometric, 48 osteometric and 8 osteoscopic signs has been performed according to the recommendations suggested by D. G. Rokhlin (1936), V. V. Bunak (1941) and B. A. Nikityuk (1968). The hereditary influence on the longitudinal anthropometric signs decreases in mature age with a simultaneous increase of these influences on weight parameters and transversal dimensions of the trunk. Transition from the peripubertal to the mature age is characterised by a decrease of genetic effects on highly-hereditable osteometric signs and an increasing effect of heredity on the skeletal ageing signs. The degree of hereditarily-dependent skeletal ageing is higher in the I mature than in the II mature age, and in the female it is higher than in the male group.     

A study of lactose absorption capacity in twins

Summary Lactose absorption capacity was determined by lactose tolerance tests with breath hydrogen determination in 102 healthy, adult, Hungarian pairs of twins in order to test monogenic Mendelian inheritance of the absorptive lactase phenotypes, lactose absorber and lactose malabsorber. Of the total, 52 pairs were monozygous (MZ) and 50 dizygous (DZ) twins of indentical sex. All MZ twins were concordant with respect to lactase phenotype. Among DZ twins, the distribution of lactase phenotypes was in agreement with Hardy-Weinberg expectations derived from the frequencies of the hypolactasia gene in DZ and MZ twins, and in the general Budapest population.In the second part of the study, three commonly used methods of lactose tolerance testing, the blood glucose, the blood galactose, and the breath hydrogen tests, were compared in 49 pairs of twins concordant for lactase phenotype. Blood galactose concentration showed the greatest and only significant difference between the intrapair correlation coefficients of MZ and DZ, and no overlap between lactose absorbers and lactose malabsorbers. The intrapair correlation coefficients of peak breath hydrogen concentration in MZ and DZ twins did not significantly differ from zero, but the resolution of lactase phenotypes was satisfactory. Differences in glucose absorption and concentration in lactose absorbers and malobsorbers overlapped considerably, and among lactose absorbers correlation coefficients in DZ were higher than in MZ twins. In MZ and DZ twins, the difference in concordance and constancy of lactose intolerance symptoms was not significant.     

Fourier analysis of facial profiles of young twins

Twins studies provide a powerful approach to determining the relative contribution of genetics and environment to observed variation. Such studies assume trait differences in monozygous (MZ) twins are due to environmental factors and those in dizygous (DZ) twins are due to both genetic and environmental factors. This study quantitated facial profiles of twins using Fourier equations, determining their value in profile analysis and the assessment of the genetic contribution to facial shape. Standardized profile slide photographs of 79 pairs of 4-6 year-old twins (37 MZ pairs, 42 DZ pairs) were scanned and x and y coordinates were extracted from each profile using sellion and Camper's plane as references. The coordinates were subjected to Fourier analysis and the normalised vertex projection coefficients were studied. The means of the differences between coefficients for MZ co-twins did not differ significantly from that of DZ co-twins, although the DZ group showed higher mean differences in the higher harmonics. Subjective examination of superimposed reconstructions showed wider variation between DZ co-twins than MZ co-twins. Correct classification of twins by discriminant function analysis using Fourier coefficients was similar for both groups (MZ: 70.3%; DZ: 73.8%). Fourier analysis could quantitate facial profiles of young children and differentiate some details, but was unable to discriminate between genetic and environmental influences, and any possible interactions between these influences, on their overall facial profiles at this developmental stage.     

Happy families: a twin study of humour.

The objective of this study was to estimate how much of an individual's appreciation of humour is influenced by genetic factors, the shared environment or the individual's unique environment. A population-based classical twin study of 127 pairs of female twins (71 monozygous (MZ) and 56 dizygous (DZ) pairs) aged 20-75 from the St Thomas' UK Adult Twin Registry elicited responses to five 'Far Side' Larson cartoons on a scale of 0-10. Within both MZ and DZ twin pairs, the tetrachoric correlations of responses to all five cartoons were significantly greater than zero. Furthermore, the correlations for MZ and DZ twins were of similar magnitude and in some cases the DZ correlation was greater than that of the MZ twins. This pattern of correlations suggests that shared environment rather then genetic effects contributes to cartoon appreciation. Multivariate model-fitting confirmed that these data were best explained by a model that allowed for the contribution of the shared environment and random environmental factors, but not genetic effects. However, there did not appear to be a general humour factor underlying responses to all five cartoons and no effect of age was seen. The shared environment, rather than genetic factors, explains the familial aggregation of humour appreciation as assessed by the specific 'off the wall' cognitive type of cartoons used in this study.     

Contribution of familial factors to the occurrence of cancer before old age in twin veterans

In an earlier report, we evaluated familial factors in deaths from all causes before age 62 among the 31,848 white male twin veterans who were followed during 1946–1978 through the National Academy of Sciences-National Research Council Twin Registry. We now report data for this group on twin concordances and heritabilities of cancer recorded on the death certificate as an underlying or associated cause. The study subjects have a mortality from cancer 0.88 times, and one from all causes 0.84 times, that of U.S. white males [12], but this is very similar to the mortality of other U.S. veterans [9].

Among 11,350 monozygotic (MZ) and 14,450 dizygotic (DZ) individuals in twin pairs alive on January 1, 1946, 1,162 MZ and 1,646 DZ individuals died before January 1, 1979. Cancer was diagnosed for 223 MZ and 323 DZ twins as an underlying or associated cause of death. Among the latter were 176 MZ and 274 DZ pairs with the only death in the pair a cancer death, 10 MZ and eight DZ pairs concordant for cancer, and 12 MZ and 14 DZ pairs in which the first death in the pair from cancer was followed by death of the other twin from another cause. When account is taken of the three MZ and two DZ pairs concordant for lung cancer, most likely related to cigarette smoking, the twin cancer death concordance rates are very low, and they are not appreciably different between the two zygosity groups.

Genetic factors may be important in some specific forms of cancer. However, these data suggest that genetic factors and early familial environment, generally shared by twin-pair members, do not contribute much to mortality from most cancers between 30 and 60 years of age.

     

Potential bias regarding birth weight in historical and contemporary twin data bases.

In this study we examine the hypothesis that monozygotic (MZ) twins in historical databases are less discordant for birth weight due to negative selection of severely discordant MZ twins. Furthermore, we test the hypothesis that MZ twins are less discordant for birth weight when comparing a volunteer based twin registry with a population based twin registry, due to selective registration. Data were available on 3927 twin pairs from the volunteer Australian Twin Registry born before 1964, 3059 volunteer twin pairs from the Netherlands Twin Register born 1987-1989 and 454 Belgian twin pairs from The East Flanders Prospective Twin Survey born 1987-1989. Intrapair relative birth weight differences (RBWD) were computed for MZ and dizygotic (DZ) twins from each twin registry. Comparing birth weight differences between MZ and DZ twins provides support for the hypothesis that MZ twins are subject to a negative selection in historical databases. Furthermore, Australian MZ twins have a lower RBWD compared to Dutch MZ twins when corrected for the RBWD of Australian and Dutch DZ twins, indicating circumstances which only affect MZ twins. Our hypothesis that MZ twins are less discordant for birth weight in a volunteer based twin registry compared to a population based twin registry had to be rejected. We suggest that investigators using historical databases to test the fetal origins hypothesis should be aware of this increased likelihood of selective exclusion of individuals with extreme morphometric parameters at time of birth.     

Cooperation and Competition as a Function of Zygosity in 7- to 9-Year-Old Twins

A study of 31 monozygotic (MZ) and 24 dizygotic (DZ) Singapore twin pairs (aged 7.6 to 9.7 years) is reported. MZ and DZ twins differed in cooperative and competitive behaviors measured by within-pair reactions to payoff structures designed to elicit simultaneous cooperation (SCO) or reciprocal altruism (RA) on a marble-pull task. Reciprocation entailed turn-taking in rewards. DZ twins showed greater competition than MZ twins when competing for marbles in the RA condition, as predicted. Unexpectedly, however, MZ twins were markedly more competitive than DZ twins under the SCO condition, when success on the task always rewarded both twins. The competition arose over which end of the apparatus was to be used on a given trial. This interaction between condition and zygosity could not be related to differences in parents’ reported treatment of their children or zygosity beliefs, nor did it appear to be related to differences in factors such as time spent together and shared activities. An explanation in terms of uncertain or unstable dominance in MZ twinships is suggested.     

Color perception in twins

The classical twin method was used to examine the genotype--phenotype relationship in color vision. Suprathreshold color differences were assessed by 5 pairs of monozygotic (MZ) and 3 pairs of dizygotic (DZ) twins. The control group included 3 unrelated normal trichromats, a non-twin sibling pair, and a previously diagnosed deuteranomal. Concordance rates were calculated by Spearman's correlation coefficients (rs) and Procrustean distances (gl) between the reconstructed color spaces for each related pair of observers. For 4 pairs of the MZ twins, the rs values were comparable to intraindividual variability in the control normal trichromat; they were significantly higher (0.94-0.97) than those for the DZ twins and siblings (0.72-0.82). The gl values for the MZ twins (0.008-0.029) were lower than for the DZ twins (0.073-0.079) and siblings (0.053). The high concordance between each pair of the MZ twins suggests that their shared photopigment genome constrains a contribution of possible individual variations in nongenetic factors to variability of their color spaces. Lower concordance rates in the DZ twins and siblings can be attributed to differences in the inherited arrays of photopigment genes. Contributions to intrapair variation in color spaces of twins from cognitive factors such as perceptual-cognitive color categorization and decision-process variability are discussed.     

Impact of the genome on the epigenome is manifested in DNA methylation patterns of imprinted regions in monozygotic and dizygotic twins

One of the best studied read-outs of epigenetic change is the differential expression of imprinted genes, controlled by differential methylation of imprinted control regions (ICRs). To address the impact of genotype on the epigenome, we performed a detailed study in 128 pairs of monozygotic (MZ) and 128 pairs of dizygotic (DZ) twins, interrogating the DNA methylation status of the ICRs of IGF2, H19, KCNQ1, GNAS and the non-imprinted gene RUNX1. While we found a similar overall pattern of methylation between MZ and DZ twins, we also observed a high degree of variability in individual CpG methylation levels, notably at the H19/IGF2 loci. A degree of methylation plasticity independent of the genome sequence was observed, with both local and regional CpG methylation changes, discordant between MZ and DZ individual pairs. However, concordant gains or losses of methylation, within individual twin pairs were more common in MZ than DZ twin pairs, indicating that de novo and/or maintenance methylation is influenced by the underlying DNA sequence. Specifically, for the first time we showed that the rs10732516 [A] polymorphism, located in a critical CTCF binding site in the H19 ICR locus, is strongly associated with increased hypermethylation of specific CpG sites in the maternal H19 allele. Together, our results highlight the impact of the genome on the epigenome and demonstrate that while DNA methylation states are tightly maintained between genetically identical and related individuals, there remains considerable epigenetic variation that may contribute to disease susceptibility.     

Heritability of bone mass: a longitudinal study in aging male twins

Midshaft radial bone mass was first measured from 1970 through 1972 by photon absorptiometry in 42 pairs of monozygotic (MZ) and 38 pairs of dizygotic (DZ) male Caucasian twins (age 44-55 years). The MZ intraclass correlation (rMZ) of .70 was significantly larger (P less than .05) than the DZ correlation (rDZ) of .45, providing evidence for genetic influences (Smith et al. 1973). Radial bone mass measurements repeated 16 years later (1986-87) on 25 of the MZ pairs and on 21 of the DZ pairs revealed an rMZ of .61 and an rDZ of .44, but the difference was not significant (P greater than .05). The twins had an average radial mass loss of 0.49%/year between the two examinations. The rMZ (.52) and rDZ (.49) values for the 16-year loss in radial mass were both significantly different from zero, but their similar size indicated that the correlations were due to nongenetic factors. In a search for the source of genetic influences on adult radial mass, heritability was estimated by the formula 2(rMZ - rDZ) for radial width and was found to be .66 and .76 (P less than .05) for examinations 1 and 2, respectively. An index of radial density (mass/width) was calculated, and the differences between rMZ and rDZ were not significant at either examination. The intraclass correlations (rMZ = .35; rDZ = .43) were both significant for the loss of bone density between examinations but provided no evidence for genetic influences, results similar to the findings for the loss of mass.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sex difference in heritability of BMI in South Korean adolescent twins

Twin studies of BMI on the basis of Asian twins are extremely rare. Eight hundred eighty-eight pairs of twins [279 monozygotic (MZ) and 82 dizygotic (DZ) pairs of male twins, 319 MZ and 82 DZ pairs of female twins, and 126 opposite-sex pairs of DZ twins] completed items concerning height and weight through a mail and a telephone survey. A general sex-limitation model was applied to the data. Heritability estimate was greater among women than among men. However, there was little evidence of sex-specific genes. Under the best-fitting model, additive genetic variances were 82% [95% confidence interval (CI): 72% to 95%] for men and 87% (95% CI: 77% to 99%) for women; shared environmental variances were negligible in both men and women. These estimates of genetic and environmental factors in BMI found among South Korean adolescent twins were broadly in the range of those reported in previous studies of BMI based on Western twin samples.     

Interaction between the ABO and Rh-Hr blood group systems in pairs of monozygotic (MZ) and dizygotic (DZ) twins

Previous studies have revealed significant deviations of twin pairs' blood group distributions. A comparison between monozygotic (MZ) and dizygotic (DZ) pairs in a sample of 688 twin pairs as to interaction between ABO and Rh indicates that the main contribution to total deviation comes from the MZ pairs, thus confirming a different behaviour of the two twin types in this respect.     

The influence of zygosity and chorion type on fat distribution in young adult twins consequences for twin studies.

An adverse intra-uterine environment has been associated with abdominal fat distribution in singletons. Twins often have a low birth weight and a short gestation. Therefore, they may have an increased risk to develop abdominal obesity. Furthermore, monozygotic monochorionic twins (MZ MC) have a larger intra-pair birth weight difference compared to monozygotic dichorionic twins (MZ DC). If adult anthropometry is programmed in utero, this may affect the intra-pair correlations in adulthood and, consequently, also the results from the classic twin method to estimate genetic and environmental influences. In the present study, we compared the absolute values, the intra-pair differences, and the intra-pair correlations of body mass, height, BMI, and abdominal fat distribution of 424 MZ MC, MZ DC and dizygotic (DZ) twin pairs (aged 18-34 yrs). DZ, MZ DC and MZ MC twins did not differ for most anthropometric characteristics. Only MZ women tended (p = 0.03) to accumulate more abdominal fat compared to DZ twins. Overall, the contribution of zygosity and chorion type to adult anthropometry was rather low (< or = 1.7%). Although the intra-pair birth weight difference of MZ MC pairs (10.5% in men, 12.3% in women) was significantly larger compared to that of MZ DC pairs (6.9% and 9.2% resp.), the intra-pair differences in adult anthropometry were similar for both MZ twin types. Also the intra-pair correlations of MZ MC and MZ DC pairs were strikingly alike, suggesting no significant influence of the prenatal environment on adult concordance. In conclusion, the substantial difference in the prenatal environment of MZ MC and MZ DC twins did not result in a difference in intra-pair concordance of adult anthropometry and fat distribution. Therefore, we suggest that the chorion type of MZ twins does not bias the twin design and the estimation of the genetic contribution to adult anthropometry.     

Comparing sensory experience in bitter taste perception of phenylthiocarbamide within and between human twins and singletons: intrapair differences in thresholds and genetic variance estimates

BACKGROUND: Quantitative genetic studies revealed that not all of the phenotypic variance in PTC taste perception is heritable. AIM: To study quantitative variations in PTC tasting ability in twins and to estimate heritability of PTC taste perception on the taste of twin data on males and females sexes separately. SUBJECTS AND METHODS: The data for PTC taste sensitivity following the classic method of Harris & Kalmus (1949) were collected on a sample of 141 twin pairs (66 MZ and 75 DZ) and 275 singletons (128 males and 147 females) from Chandigarh, India. Genetic analyses were performed following Christian (1979), Donner (1986) and Sham (1998). RESULTS: Frequency of non-tasters was similar in twins (33 %) and singletons (32 %), but significant sex differences were observed. No differences were found between zygosities for mean thresholds. Similarly, no evidence of variance heterogeneity and environmental covariance was seen between zygosities. Since no basic assumption of the twin method was found violated, within-pair estimates of genetic variance would be unbiased. These estimates were highly significant in both males and females. However, dominance and additive components of genetic variance were found to differ between sexes. CONCLUSION: PTC thresholds do not seem to be significantly affected by environmental factors as no variance inequality was observed between twin zygosities. Intensity of bitterness (scalar dimensions) of PTC is a separate trait having no commonality with the genetic basis of recognition threshold for PTC tasting ability. The receptors recognizing bitter taste are different from the receptors determining intensity of taste. The absolute difference between co-twins in PTC thresholds can be used as a simple tool in the twin zygosity diagnosis. The results show that none of the MZ co-twins had manifested difference of more than 3 in their PTC threshold.     

Excess of twins among affected sibling pairs with autism: implications for the etiology of autism

It is widely accepted that genes play a role in the etiology of autism. Evidence for this derives, in part, from twin data. However, despite converging evidence from gene-mapping studies, aspects of the genetic contribution remain obscure. In a sample of families selected because each had exactly two affected sibs, we observed a remarkably high proportion of affected twin pairs, both MZ and DZ. Of 166 affected sib pairs, 30 (12 MZ, 17 DZ, and 1 of unknown zygosity) were twin pairs. Deviation from expected values was statistically significant (P<10(-6) for all twins); in a similarly ascertained sample of individuals with type I diabetes, there was no deviation from expected values. We demonstrate that to ascribe the excess of twins with autism solely to ascertainment bias would require very large ascertainment factors; for example, affected twin pairs would need to be, on average, approximately 10 times more likely to be ascertained than affected non-twin sib pairs (or 7 times more likely if "stoppage" plays a role). Either risk factors (related to twinning or to fetal development) or other factors (genetic or nongenetic) in the parents may contribute to autism.     

The Host Genotype and Environment Affect Strain Types of Bifidobacterium longum subsp. longum Inhabiting the Intestinal Tracts of Twins

To investigate the influences of host genotype and environment on Bifidobacterium longum subsp. longum inhabiting human intestines at the strain level, six pairs of twins, divided into two groups (children and adults), were recruited. Each group consisted of two monozygotic (MZ) twin pairs and one dizygotic (DZ) twin pair. Child twins had been living together from birth, while adult twins had been living separately for 5 to 10 years. A total of 345 B. longum subsp. longum isolates obtained from 60 fecal samples from these twins were analyzed by multilocus sequence typing (MLST), and 35 sequence types (STs) were finally acquired. Comparison of strains within and between the twin pairs showed that no strains with identical STs were observed between unrelated individuals or within adult DZ twin pairs. Eight STs were found to be monophyletic, existing within MZ twins and child DZ twins. The similarity of strain types within child cotwins was significantly higher than that within adult cotwins, which indicated that environment was one of the important determinants in B. longum subsp. longum strain types inhabiting human intestines. However, although these differences between MZ and DZ twins were observed, it is still difficult to reach an exact conclusion about the impact of host genotype. This is mainly because of the limited number of subjects tested in the present study and the lack of strain types tracing in the same twin pairs from birth until adulthood.