Clinical, hormonal and sonographic features of the identical twins with Klinefelter syndrome--a case report

A rare case of Klinefelter syndrome in identical twins is reported. Hormonal levels before and after hCG administration and testicular artery Doppler flow measurements are presented.     

A twin study of dental dimension. I. Discordance,asymmetry, and mirror imagery

Bilateral tooth measurements in twins were partitioned into three orthogonal contrasts, each associated with one degree of freedom, to estimate three parameters: discordance, asymmetry, and mirror imagery. The probability levels of the within-pair variance ratios were used to test for significance of these estimates. The results provided strong evidences for the existence of significant genetic determinants of almost all of the individual tooth dimensions, but little or no evidence for a genetic basis of asymmetry. The analysis gave no indication that monozygotic twinning was associated with an increased degree of either fluctuating asymmetry or mirror imagery, when compared to dizygotic twins. The data on monozygotic twins further suggested that for most variables examined, the increment of environmental discordance resulting from the twinning phenomena was greater than the developmental noise that caused asymmetry within individual cotwins.     

Total and Regional Fat Distribution is Strongly Influenced by Genetic Factors in Young and Elderly Twins

Objective: Indirect estimates of obesity such as BMI seem to be strongly influenced by genetic factors in twins. Precise measurements of total and regional fat as determined by direct techniques such as DXA scan have only been applied in a few twin studies. The aim of the present study was to estimate the heritability (h²) of total and regional fat distribution in young and elderly Danish twins. Research Methods and Procedures: Monozygotic (108) and dizygotic (88) twins in two age groups (25 to 32 and 58 to 66 years) underwent anthropometric measurements and DXA scans. Intraclass correlations and etiologic components of variance were estimated for total and regional fat percentages using biometric modeling. Results: The intraclass correlations demonstrated higher correlations for all fat percentages among monozygotic twins as compared with dizygotic twins. The biometric modeling revealed a major genetic component (h²) of total (h²_young = 0.83, h²_elderly = 0.86) and regional fat percentages (trunk, h²_young = 0.82, h²_elderly = 0.85; lower body, h²_young = 0.83, h²_elderly = 0.81; and trunk/lower body, h²_young = 0.83, h²_elderly = 0.71) in both the young and elderly twins. Discussion: The h² estimates emphasize that body fat and distribution as determined by DXA scan are under extensive genetic control.     

A family study of anthropometric traits in a Punjabi community: I. Introduction and familial correlations

Data on 40 anthropometric measurements from 144 nuclear families in Chandigarh, India, are presented. Most families contain a pair of monozygotic or dizygotic twins, one or more singleton siblings, and their parents. Familial correlations for age-sex standardized, normalized measurements are estimated by maximum likelihood for marital, parent-child, sibling, and twin pairs. Heterogeneity tests for sex-specific subtype correlations male-male, male-female, female-female) indicate that the sex of the relative plays no significant role in the magnitude of the familial correlations except for maternal effects and differences among male and female twin pairs for a few of the variables. Marital correlations are high for body measurements, but not for head or face variables. Twin correlations seem to indicate a higher level of heritability than correlations from other family members.     

Genetic determination of the human EEG

Summary In this article, we have discussed recent progress in quantifying the genetically determined component of the resting EEG. This progress has been made possible in particular by the application of advanced information processing techniques such as supervised learning, and the development of a problem-oriented similarity concept. Our work aimed at modeling previous findings regarding the distinct individuality of human brain-wave patterns, the high similarity between the EEGs of monozygotic twins, and the average within-pair similarity of dizygotic twins. Thus, we had three objectives: First, we wanted to improve the quantification of EEG characteristics with respect to reproducibility and specificity by means of adaptive procedures and repeated measurements. Second, we wanted to compare the typical within-subject EEG similarity with the typical within-pair EEG similarity of monozygotic and dizygotic twins brought up together. Finally, we were interested in the degree to which environmental factors affect the characteristics of human brain-wave patterns. Our investigations were based on the empirical data derived from five different populations: (1) 81 healthy subjects, (2) 24 pairs of monozygotic twins brought up together, (3) 25 pairs of dizygotic twins brought up together, (4) 28 pairs of monozygotic twins reared apart, and (5) 21 pairs of dizygotic twins reared apart. Following our similarity conception, repeated measurements on the set of 81 individuals were used as design samples, and new registrations from the same individuals taken 14 days later were referred to as test samples in order to develop the appropriate method and to determine all required calibration parameters. This specific approach allowed us to construct EEG spectral patterns which, with a specificity and reproductibility of>90% each, largely met the requirements of genetic EEG studies. Hence, we were able systematically to investigate the within-pair EEG similarity of our twin samples. Our results provided ample evidence that the individual characteristics of the resting EEG are primarily determined by genetic factors: (1) There exists an almost perfect one-to-one mapping between each individual and his EEG; (2) monozygotic twins proved, with respect to their resting EEGs, to be only slightly less like one another (if there is any difference at all) than each person is to himself over time; (3) the average within-pair EEG similarity estimated from a sufficiently representative sample of dizygotic twins is significantly above the inter-individual EEG similarity between unrelated persons (this finding holds true for both samples of dizygotic twins brought up together and reared apart, and there is also no statistically significant difference in the resting EEG between these two samples) and, (4) the EEGs of monozygotic twins reared apart are obviously as similar to each other as are the EEGs of the same person over time, and there is no statistically significant difference in the resting EEG between the two populations of monozygotic twins brought up together and monozygotic zygotic twins reared apart.     

Does higher concordance in monozygotic twins than in dizygotic twins suggest a genetic component?

It is widely regarded that twins can be used as a natural experiment to subject hypotheses to empirical testing regarding the contributions of genetic factors to phenotypic variability in human traits, especially behavioral traits. In genetic epidemiology, a higher concordance rate in monozygotic (MZ) twins than in dizygotic (DZ) twins is often taken as prima facie evidence for a genetic component. While twins studies have been used to estimate the contributions of genetic factors to phenotypic variability in human traits, the corresponding methodology that allows the estimation entails several crucial assumptions. The most critical is that MZ and DZ twins are equally similar environmentally. Although MZ twins are genetically more similar than DZ twins, they are often environmentally more similar. This paper demonstrates that, even in the complete absence of any genetic factor and of any biases, the greater environmental similarity alone in MZ twins can result in higher concordance rate in MZ twins than in DZ twins. This is especially true when there are multiple environmental factors, which may have multiple exposure levels and/or interact strongly, although each of them may be of low risk. This may serve as a sobering antidote to the uncritical reliance on twin studies without examining the validity of the underlying assumptions.     

A family study of anthropometric traits in a Punjabi community: II. An investigation of familial transmission

Path analysis is used to characterize family resemblance for anthropometrics in twins and nuclear families from the Punjabi population of India. Significant positive assortative mating exists with respect to many body measurements, but not for cranial or facial variables. Evidence of a maternal effect for five measurements of bone diameter is reported. Twin resemblance is increased by a component not found in other pairs of relatives for all variables except nasal height, facial length, ear length, and head breadth. Although all variables have significant transmissible components, many have parameter estimates which are not consistent with strictly polygenic inheritance. Some form of cultural transmission is implicated for such variables, especially for those related to fatness levels.     

Associations of Body Composition Measurements with Serum Lipid,Glucose and Insulin Profile: A Chinese Twin Study

Objectives

To quantitate and compare the associations of various body composition measurements with serum metabolites and to what degree genetic or environmental factors affect obesity-metabolite relation.

Methods

Body mass index (BMI), waist circumference (WC), lean body mass (LBM), percent body fat (PBF), fasting serum high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), triglycerides (TG), total cholesterol (TC), glucose, insulin and lifestyle factors were assessed in 903 twins from Chinese National Twin Registry (CNTR). Homeostasis model assessment of insulin resistance (HOMA-IR) was calculated from fasting serum glucose and insulin. Linear regression models and bivariate structural equation models were used to examine the relation of various body composition measurements with serum metabolite levels and genetic/environmental influences on these associations, respectively.

Results

At individual level, adiposity measurements (BMI, WC and PBF) showed significant associations with serum metabolite concentrations in both sexes and the associations still existed in male twins when using within-MZ twin pair comparison analyses. Associations of BMI with TG, insulin and HOMA-IR were significantly stronger in male twins compared to female twins (BMI-by-sex interaction p = 0.043, 0.020 and 0.019, respectively). Comparison of various adiposity measurements with levels of serum metabolites revealed that WC explained the largest fraction of variance in serum LDL-C, TG, TC and glucose concentrations while BMI performed best in explaining variance in serum HDL-C, insulin and HOMA-IR levels. Of these phenotypic correlations, 64–81% were attributed to genetic factors, whereas 19–36% were attributed to unique environmental factors.

Conclusions

We observed different associations between adiposity and serum metabolite profile and demonstrated that WC and BMI explained the largest fraction of variance in serum lipid profile and insulin resistance, respectively. To a large degree, shared genetic factors contributed to these associations with the remaining explained by twin-specific environmental factors.     

Twin births to mothers who are twins: a registry based study.

OBJECTIVES: To estimate the risk of having twin infants for mothers who are twins; to investigate the genetic influence on twinning. DESIGN: Retrospective study of multiple births in two nationwide registries. SETTING: Sweden. SUBJECTS: Multiple births among 31,586 deliveries between 1973 and 1991 to women who were twins. MAIN OUTCOME MEASURES: Numbers of monozygotic and dizygotic twin births expected and estimated. RESULTS: Women who are dizygotic twins have a moderately increased risk of having twins (relative risk 1.30, 95% confidence interval 1.14 to 1.49) which seems to be completely the result of dizygotic twinning. When a mother is a monozygotic twin, her risk of having twins of the same sex is significantly increased (1.47; 1.10 to 1.97). This is the result of an excess of monozygotic twins (39 pairs estimated, 18 expected). CONCLUSIONS: Women who are twins have an increased risk of giving birth to twins. Genetic components of monozygotic and dizygotic twinning seem to be independent.     

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.     

In detail.

Two families with twins - one in which adult DZ twins continue to face the risk of frontotemporal dementia, and the other in which a mother copes with brittle bones in a newborn infant MZ pair - are featured. The nature and progress of the disorders are reviewed and personal perspectives from the twins and other family members are variously provided. Next, four current twin studies are briefly summarized. Topics include sex differences in social support systems, new reproductive technologies, comparative twin-singleton frequencies of placenta previa, and the nature and complications of heterotopic pregnancies. This article concludes with a brief sampling of human interest stories involving twins: a different looking DZ pair, newborn sextuplets, conjoined twins and opposite-sex twin athletes.     

Behavioral inhibition as a function of relationship in preschool twins and siblings.

Monozygotic (MZ) twins spend more time with each other and are more genetically alike than are dizygotic (DZ) twins or nontwin siblings and therefore probably experience less diversity in their playmates than DZ twins, who in turn may experience less diversity than other-age siblings. Thus MZ twins may be more inhibited than DZ twins, who may in turn be more inhibited than nontwin siblings. To test this, 205 children (42 MZ twins, 94 DZ twins, and 69 nontwin siblings) were assessed in a playroom laboratory during free play with an unfamiliar peer. Children's inhibition was rated based on latency to touch a toy for the first time and amount of time spent interacting with the other child. Additionally, the Child Behavior Checklist (CBCL) withdrawn scale was used to assess inhibition according to parent report. Behavioral ratings showed that MZ and DZ twins did not significantly differ on the inhibition or withdrawn ratings. DZ twins were significantly more inhibited than were nontwin siblings, according to laboratory ratings. Greater inhibition of twins during the free peer play situation can be explained by their relative lack of experience in playing with children who are less genetically and phenotypically like themselves. Parental ratings showed exactly the opposite pattern, suggesting a rater bias effect.     

Why the healing gods are twins

The association of twins with health-giving powers is widespread in mythology, folklore, and religion. The Ashvins of the Rig-Veda, the classical Dioscuri, and the early Christian saints Cosmos and Damian are among the many examples of twins divinely empowered in the area of health and fertility. A characteristic set of attributes of twins recurs in different mythologies of wide distribution. In addition to healing, divine twins are often empowered with the ability to revive the dead, increase the fertility of man, animals, and crops, influence the weather, predict the future, and insure victory in battle. In some traditional societies these special attributes are thought to extend to all of the twins and their parents in the tribe.Ancient and primitive societies supposed that the birth of twins was associated with divine influence, the mother having been visited or otherwise affected by supernatural powers. A frequent explanation was that twins were the result of superfetation, a divine impregnation occurring along with that by the lawful husband. The specific powers of divine twins appear to be a reflection of the particular form of origin of twins through divine interference with the fertilization process. The twins thus share some of the powers of the divine parent, particularly those pertaining to fertility. Their dual paternity and its inherent competition is related to their martial interests as well as their ability to resolve ambivalent or ambiguous situations and predict outcomes.     

Why zygosity of multiple births is not always obvious: an examination of zygosity testing requests from twins or their parents.

This paper examines why parents of twins or adult twins themselves request zygosity testing. Of 405 multiples including 8 sets of triplets, the majority (93%) were monozygotic. Age of testing ranged from 0 days to 73 years. About 50% of requests came from parents or twins who were curious about, or expressed a need to be certain of, their zygosity. Other reasons included health concerns (current or future), other twins in the family, and misinformation about zygosity, frequently because of the erroneous assumption that all dichorionic twins are dizygotic. Parents of monozygotic twins may expect their twins to be 'identical' and believe their twins to be dizygotic because of minor phenotypic differences between them. Dizygotic twins like other siblings may share a phenotypic resemblance. Health professionals should be aware that zygosity of multiples may not always be obvious to parents and that accurate knowledge of zygosity may be justified.     

母亲年龄对中国双生子出生率的影响

选用全国人口普查时登报的 1 989年 1月 1日至 1 2月 31日期间中国育龄妇女 ( 1 5— 49岁 )的生产记录 ,用 Weinberg差别法进行双生子卵性分类 ,分析了中国总体、DZ和 MZ双生子出生率与母亲年龄之间的关系以及双生子的出生性别比。结果表明 ,中国总体、 DZ和 MZ双生子的出生率分别为 0 .787± 0 .0 0 2 % ,0 .573± 0 .0 0 2 %和 0 .2 1 4± 0 .0 0 1 % ,DZ双生子出生率在 33岁前随母亲年龄增高单调上升 ,随后下降 ,但在 46岁后又随龄上升 ,MZ双生子出生率在 34岁前相对恒定 ,随后随龄上升。中国双生子出生性别比显著性低于同期群体出生性别比 ,1 5— 1 9岁和 45— 49岁年龄组出生的双生子性别比低于其它年龄组出生的双生子性别比 ,1 5— 1 9岁和 45— 49岁年龄组出生的双生子性别比较低可能是较低的 MZ双生子出生性别比造成的。     

Twins and non-twin siblings: different estimates of shared environmental influence in early childhood.

Twin studies typically indicate shared environmental influence for cognitive abilities, especially in early childhood. However, across studies, DZ twin correlations tend to be greater than non-twin sibling correlations, suggesting that twin estimates of shared environment are to some extent specific to twins. We tested this hypothesis in a sample of more than 1800 MZ and 1800 same-sex DZ pairs from the Twins Early Development Study (TEDS), a study of twins born in England and Wales in 1994 and 1995. For this analysis, we obtained comparable data from more than 130 same-sex younger siblings of the twins. Twins and their younger siblings were assessed for language, cognitive abilities and behavior problems by their parents at 2 and 3 years of age. For language and cognitive measures at both 2 and 3 years, but not for behavior problems, estimates of shared environment were more than twice as large for twins as compared to non-twin siblings. We conclude that about half of twin study estimates of shared environment for cognitive abilities in early childhood are specific to twins. Although many possibilities exist for explaining the special shared environment effect for twins, we suggest that cognitive-relevant experiences that are not shared by siblings are shared by twins because they are exactly the same age.     

Cephalopagus conjoined twins in a leopard cat (Prionailurus bengalensis)

Case reports of conjoined twins ("Siamese twins") in wild mammals are scarce. Most published reports of conjoined twins in mammals concern cases in man and domestic mammals. This article describes a case of cephalopagus conjoined twins in a leopard cat (Prionailurus bengalensis) collected on the island of Sumatra, Indonesia, in the period 1873-76. A review of known cases of conjoined twinning in wild mammals is given.     

Genetic basis of human female pelvic morphology: a twin study

To examine the relative role of genetic and environmental factors on pelvic morphology, data on 60 pairs of female twins (30 monozygotic (MZ) and 30 dizygotic (DZ)) were analyzed. Fourteen pelvic measurements were normally distributed, and two were not. Association of twin type with the mean value of a trait was found in only 1 out of 8 traits. Heterogeneity of variance between zygosities was observed in 4 pelvic traits (50%), invalidating within-pair estimates of genetic variance for these traits. Evidence of stronger environmental covariance for MZ than DZ twins was observed for only one trait (sitting height iliocristale). A significant genetic component of variation was observed for age at menarche and in the pelvic area. In instances where inequality of variances between zygosities was demonstrated, total among-pair and within-pair mean squares were larger for dizygotic than for monozygotic twins. This is interpreted as evidence of greater environmental influence between zygosities. Environmental modification was not of the same magnitude in various pelvic traits. Bitrochanteric breadth had the highest magnitude of cultural heritability, indicating that cultural factors played an important role in determining hip breadth.     

Resemblance for age at menarche in female twins reared apart and together

Menarche is a significant developmental event in the lives of young females. Genetic and family environmental influences on the timing of its occurrence are explored in the first formal analysis using reared-apart and reared-together monozygotic (MZA, MZT) and dizygotic (DZA, DZT) twin pairs. Mean age at menarche was 12.50 years (SD = 1.67) for the reared-apart pairs and 12.86 years (SD = 1.49) for the reared-together pairs. Intraclass correlations for age at menarche were 0.56 for MZA twins, 0.16 for DZA twins, 0.70 for MZT twins, and 0.41 for DZT twins. The mean within-pair difference was 1.07 years (SD = 1.04) for MZA twins, 1.67 years (SD = 1.59) for DZA twins, 0.64 year (SD = 0.86) for MZT twins, and 1.43 years (SD = 1.34) for DZT twins. These results are consistent with genetic influence, although the lower correlations for reared-apart twins and their larger within-pair differences suggest that age at menarche is partly affected by common rearing environments. Feeling understood by one's father during the growing-up years was significantly associated with earlier age at menarche, and a comparable trend was found for feeling understood by one's mother. These findings are considered with reference to current theories of pubertal timing.     

A case of true hermaphroditism reveals an unusual mechanism of twinning

Traditionally twins are classified as dizygous or fraternal and monozygous or identical (Hall Twinning, 362, 2003 and 735-743). We report a rare case of 46,XX/46,XY twins: Twin A presented with ambiguous genitalia and Twin B was a phenotypically normal male. These twins demonstrate a third, previously unreported mechanism for twinning. The twins underwent initial investigation with 17-hydroxyprogesterone and testosterone levels, pelvic ultrasound and diagnostic laparoscopy. Cytogenetic analysis was performed on peripheral blood cells and skin fibroblasts. Histological examination and Fluorescence in situ hybridization studies on touch imprints were performed on gonadal biopsies. DNA analysis using more than 6,000 DNA markers was performed on skin fibroblast samples from the twins and on peripheral blood samples from both parents. Twin A was determined to be a true hermaphrodite and Twin B an apparently normal male. Both twins had a 46,XX/46,XY chromosome complement in peripheral lymphocytes, skin fibroblasts, and gonadal biopsies. The proportion of XX to XY cells varied between the twins and the tissues evaluated. Most significantly the twins shared 100% of maternal alleles and approximately 50% of paternal alleles in DNA analysis of skin fibroblasts. The twins are chimeric and share a single genetic contribution from their mother but have two genetic contributions from their father thus supporting the existence of a third, previously unreported type of twinning.