Similarity Of Monozygotic Twins Research Articles

Evaluation of Phenotypes and CLDN16 Variants in 2 Different Familial Hypomagnesemia with Hypercalciuria and Nephrocalcinosis Families: Phenotypic Differences in Siblings and Phenotypic Similarity in Monozygotic Twins

Evaluation of Phenotypes and CLDN16 Variants in 2 Different Familial Hypomagnesemia with Hypercalciuria and Nephrocalcinosis Families: Phenotypic Differences in Siblings and Phenotypic Similarity in Monozygotic Twins

Tight co-twin similarity of monozygotic twins for hTERT protein level of T cell subsets, for telomere length and mitochondrial DNA copy number, but not for telomerase activity.

Our study analyzed lymphocyte subpopulations of 32 monozygotic twins and compared the level of the catalytic reverse transcriptase protein subunit (hTERT) in T lymphocytes (Tly), helper- (Th), cytotoxic- (Tc) and regulatory T cell (Treg) subgroups. Four variables related to telomere and mitochondrial biology were simultaneously assessed, applying multi-parametric flow cytometry, TRAP-ELISA assay and qPCR standard curve method on peripheral blood mononuclear cell (PBMC) samples of genetically matched individuals. Twin data of telomerase activity (TA), hTERT protein level, telomere length (TL) and mitochondrial DNA copy number (mtDNAcn) were analyzed for co-twin similarity. The present study has provided novel information by demonstrating very high intraclass correlation (ICC) of hTERT protein level in T lymphocytes (0.891) and in both Th (0.896), Treg (0.885) and Tc (0.798) cell subgroups. When comparing results measured from PBMCs, intraclass correlation was also high for telomere length (0.815) and considerable for mtDNA copy number (0.524), and again exceptionally high for the rate-limiting telomerase subunit, hTERT protein level (0.946). In contrast, telomerase activity showed no co-twin similarity (ICC 0). By comparing relative amounts of hTERT protein levels in different lymphocyte subgroups of twin subjects, in Treg cells significantly higher level could be detected compared to Tly, Th or Tc cell subgroups. This is the first study that simultaneously analyzed co-twin similarity in MZ twins for the above four variables and alongside assessed their relationship, whereby positive association was found between TL and mtDNAcn.

쌍생아 여아의 유사성 평가 차트의 확립

Twin studies have important implications for verifying the involvement of various genetic and environmental factors in human characteristics. Among these twin studies, many statistical analyses of the similarities of monozygotic and dizygotic twins require twin pair data. To analyze the similarities of growth process in pair data for twin pairs, Fujii described the growth curve with the wavelet interpolation model and proposed a method of analyzing the similarities between the described growth curves based on cross-correlation functions. In this study, an assessment criteria chart was constructed to evaluate the similarities between girls’ monozygotic and dizygotic twins by applying wavelet interpolation model to these growth curve descriptions and cross-correlation functions. Height growth data for random pairs of general girls were taken and the growth processes were described with the wavelet interpolation method. Cross-correlation functions were then applied to the growth velocity curves of the described random pairs. An evaluation chart of similarities was built from the derived cross-correlation functions, and in the cross-correlation functions from those evaluation charts, r ≧ 0.94 was found to be the standard criterion showing the level of similarity. When the cross-correlation functions of height growth of monozygotic and dizygotic twins were applied to these charts, the correlation of monozygotic twins was high and that of dizygotic twins was somewhat high. Thus, the similarity of monozygotic twins was seen to be high.

Prefrontal cortex gyrification index in twins: an MRI study

Cortical development and folding seems to be under environmental as well as genetic control. The aim of our study was to estimate the genetic influence on gyrification and cortical volumes, comparing prefrontal gyrification index (GI) in monozygotic (MZ) and dizygotic (DZ) twin pairs, and unrelated pairs. Twenty-four subjects (6 pairs of MZ and 6 pairs of DZ twins) were included in this study. Prefrontal cortical folding (gyrification) was measured by an automated and manual version of the gyrification index (A-GI, M-GI) according to previously published protocols. MR-imaging was performed and 3 representative slices were selected from coronar MR-imaging scans. The volumes of the total brain, temporal lobes, prefrontal lobes, and cerebellum were analyzed, too. To evaluate similarity in GI, absolute differences in GI, and brain volumes as well as intraclass correlations of twin pairs were compared with regard to twin status. Finally, a control group of unrelated pairs was assembled from the first two study groups and analyzed. Compared to unrelated pairs, twin pairs exhibited more similarity concerning different brain volumes and a trend to more similarity concerning A-GI. MZ twins did not present more similarity concerning GI (automatically and manually measured) and volume measurements compared to DZ twins. Different factors, like intrauterine factors, postnatal development conditions, and especially environmental factors might account for the differences between related and unrelated pairs. The nonexistence of a pronounced similarity in MZ twins compared to DZ twins concerning prefrontal GI raises questions about the extent of genetic influence on GI.

Underlying heterogeneity: a problem for biological, philosophical, and other analyses of heritability?

Claims that some human trait, say, IQ test score at age 18, show high heritability derive from analysis of data from relatives. For example, the similarity of monozygotic twins (which share all their genes) can be compared with the similarity of dizygotic twins (which do not share all their genes). The more that the former quantity exceeds the latter, the higher the trait’s ‘‘heritability.’’ Researchers and commentators often describe such calculations as showing how much a trait is ‘‘heritable’’ or ‘‘genetic.’’ However, no genes or measurable, transmissable genetic factors (e.g., alleles, tandem repeats, chromosomal inversions) are examined in deriving heritability estimates, nor does the method of analysis suggest where to look for them. Moreover, even if the similarity among twins or a set of close relatives is associated with similarity of yet-to-be-identified genetic factors, the factors may not be the same from one set of relatives to the next, or from one situation to the next. In other words, the underlying factors may be heterogeneous .I t could be that pairs of alleles, say, AAbbcbDDee, subject to a sequence of environmental factors, say, FghiJ, are associated, all other things being equal, with the same outcomes as alleles aabbCCDDEE subject to a sequence of environmental factors FgHiJ. That heritability estimates are not helpful in identifying the specific genetic factors has been noted by prominent researchers (e.g., Rutter 2002, p. 4), but the possible heterogeneity of factors that underlie patterns in observed traits has not been flagged as an issue, either by quantitative geneticists or by critical commentators on heritability research (e.g., Downes 2004 and references therein). A conference session that involved members of three Societies—Social Studies of Science, History of Science, and Philosophy of Science—was held in November 2006 to stimulate interest among a range of scholars in the scientific, philosophical,

Response

Dear Madam: We thank Drs. Samaras and Campbell for their comments regarding our paper ((1)). We appreciate the opportunity to further discuss this interesting and important area of biomedical investigation. In our paper, we focused discussion on the measurements of both whole body and selected regional quantities of fat mass (FM) and lean mass (LM). We analyzed DXA measurements, including % FM, whole body FM, trunk FM, whole body LM, and appendicular LM. BMI was considered as an easily measured phenotype for comparison. We recognize that DXA can be used to estimate central abdominal fat, but central abdominal fat was not the focus of this paper. Rather, we chose to focus on body composition per se (i.e., absolute and relative quantities of adipose tissue and lean mass). Drs. Samaras and Campbell have published a series of papers using a twin study to study the genetic epidemiology of total and central obesity and metabolic syndrome. The Diabetes Heart Study (DHS), on the other hand, is a study of siblings concordant for type 2 diabetics and unaffected family members. It is interesting to note that the twin study provides heritability estimates of similar magnitude to those in our study. This similarity may suggest relatively little effect of non-additivity or gene-gene interaction on the variation in these adiposity phenotypes after adjusting for the covariates. The two study designs (twin and family) have their own advantages and disadvantages. Sampling on multiplex families (e.g., affected sibling pairs) reduces the likelihood of including non-genetic sources of variation. Thus, the sibling pair study design can be used to define the role of genetic factors in disease and, with inclusion of genetic markers, provide gene localization. One potential limitation of the family study is that the heritability estimates may not delineate shared genes from shared environment. The twin study, when including monozygotic (MZ) and dizygotic (DZ) twin pairs, provides an elegant way to delineate genetic from environmental factors; however, in the absence of twins reared apart, the twin design may overestimate heritability due to the inability to separate the effects of shared environment. Even in the absence of any genetic factor, the greater environmental similarity in MZ twins can result in a higher concordance rate in MZ twins than in DZ twins ((2)). The ability to generalize results of twin studies to the non-twin population remains controversial, as twins share environmental factors uniquely, and selection bias may minimize the environmental variation and, hence, inflate the role of genetic factors ((3)). The DHS has extensive data on cardiovascular phenotypes, bone mineral density, and body composition. While our paper focuses on DXA measures, quantitative computed tomography measures exist that further delineate components of body composition. Taking advantage of the family study design, a genome scan is being performed to identify quantitative trait loci that contribute to the observed variation in these phenotypes. The combination of genome scan, candidate gene, and family-based association studies should permit the identification of genes that may contribute to the expression of FM and LM.

Similarity of monozygotic twins regarding vocal performance and acoustic markers and possible clinical significance

Auditory similarities in voices of monozygotic twins have already been described in the literature. However, is there a clinical relevance? Thus, the present study was designed to identify parameters of vocal performance and acoustic features which are significantly more similar in monozygotic twins than in non-related persons. In our hypothesis, comparable prerequisites for an increased vocal load in a profession or in an artistic education of the voice could be due to these similarities. We compared intra-pair differences with data from a control group. Moreover, we examined the correlation of intra-pair differences with the age of the monozygotic twins. A greater difference in older twin pairs than in younger pairs could show the effect of an exogene influence. In addition to the few phoniatric studies in twins in the literature, we used current methods for acoustic analysis. We examined seven parameters of vocal performance and three acoustic features in 31 monozygotic twin pairs (median age 36 years, range 18-75 years) and compared them with 30 control group pairs, which consisted of non-related persons of the same age and sex, newly combined from the group of monozygotic twins ("statistical twins"). We found significant differences in seven of ten parameters (vocal range, highest and lowest vocal fundamental frequency, fundamental speaking frequency, maximum voice intensity, number of partials, vibrato of intensity; U-test by Mann-Whitney). No correlation of the differences of the identical twins with age was found in the examined parameters. The voices of identical twins are significantly more similar than those of non-related persons regarding the above mentioned features. Thus, the suitability of the voices of monozygotic twins for professions with a high demand on voice is comparable. Results of the group comparison correlate largely with the literature. The missing correlation with age could be due to the fact that the environmental effects were not measurable, and/or the development of the voice is more influenced by genetic effects.

Parental style. Mothers' and fathers' and perceptions of their relations with twin children.

Mothers and fathers rated their interaction with twin children on the Parent's Report (PR) questionnaire containing two scales-how the parent actually relates and how the ideal parent would relate. Mothers and fathers differed in parental style. Mothers perceived themselves as being profoundly more child-centered; fathers perceived themselves as using more control through arousal of guilt and anxiety. Parents asserted more control through temper and detachment with same-sex children. Boys and girls and monozygotic (MZ) and dizygotic (DZ) twins did not receive distinctly different parenting. Parents described MZ children as much more similar than DZ children but acted similarly with children in both types of twinships. Parental knowledge of zygosity did not affect the way the parents treated children. These findings suggest the relative importance of genetic contributions to behavioral similarity in MZ twins.

Metacarpo-phalangeal and ring creases in twins.

AbstractMetacarpo‐phalangeal creases including the ring crease were studied on the middle finger of Japanese twins. The mean of differences and the correlation coefficient of the ring crease index as well as fine morphological features showed that the similarity between twins is greater in monozygotic twins than in dizygotic ones. The intrapair similarity in monozygotic twins is almost the same as that between right and left hands of an individual. For the diagnosis of zygosity this trait will be available.