Does Higher Concordance in Monozygotic Twins Than in Dizygotic Twins Suggest a Genetic Component?

Abstract Aim: To assess the dentofacial characteristics of a mystery village of twins in South India. Materials and methods: A descriptive cross-sectional study was carried out among of 22 twin pairs (10 monozygotic twins and 12 dizygotic twins). The evaluation was done in terms of height, weight, dentofacial profile, and occlusion status based on anthropometric, photographic, and dental cast analysis. Results: Data obtained upon analysis of anthropometric measurements, photographic data, and dental cast evaluation revealed a set of characteristics peculiar to the twins of this unique village. Conclusion: Twin studies are a fascinating method of research because of their ability to correctly isolate a characteristic and determine its impact, especially in terms of dentofacial characteristics. Clinical significance: Twin research design involving the comparison of variables among monozygotic (identical) and dizygotic (fraternal) twins is a method by which researchers quantify and classify the contribution of genes and other extraneous factors influencing heredity on the dentofacial complex and dentition.

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Evidence for Genetic Factors Explaining the Association Between Birth Weight and Low-Density Lipoprotein Cholesterol and Possible Intrauterine Factors Influencing the Association Between Birth Weight and High-Density Lipoprotein Cholesterol: Analysis in Twins

The Journal of Clinical Endocrinology & Metabolism ◽

10.1210/jcem.86.11.7996 ◽

2001 ◽

Vol 86 (11) ◽

pp. 5479-5484 ◽

Cited By ~ 16

Author(s):

Richard G. IJzerman ◽

Coen D. A. Stehouwer ◽

Mirjam M. van Weissenbruch ◽

Eco J. de Geus ◽

Dorret I. Boomsma

Keyword(s):

Birth Weight ◽

Total Cholesterol ◽

Apolipoprotein B ◽

Genetic Factors ◽

Ldl Cholesterol ◽

Low Density Lipoprotein ◽

Monozygotic Twins ◽

Density Lipoprotein ◽

Hdl Cholesterol ◽

Dizygotic Twins

Recent studies have demonstrated an association between low weight at birth and an atherogenic lipid profile in later life. To examine the influences of intrauterine and genetic factors, we investigated 53 dizygotic and 61 monozygotic adolescent twin pairs. Regression analysis demonstrated that low birth weight was associated with high levels of total cholesterol, low-density lipoprotein (LDL) cholesterol and apolipoprotein B (−0.17 mmol/liter per kg, P = 0.07; −0.18 mmol/liter per kg, P = 0.04; and− 0.07 g/liter per kg, P = 0.02, respectively) and with low levels of high-density lipoprotein (HDL) cholesterol (+0.04 mmol/liter per kg, P = 0.1), after adjustment for age, sex, and body mass index. Intrapair differences in birth weight were significantly associated with differences in total cholesterol, LDL cholesterol, and apolipoprotein B in dizygotic twins after adjustment for differences in current body mass index (−0.49 mmol/liter per kg, P = 0.02; −0.51 mmol/liter per kg, P = 0.01; and −0.10 g/liter per kg, P = 0.04, respectively), demonstrating that the larger the difference in birth weight, the higher these risk factors in the twin with the lower birth weight, compared with the cotwin with the higher birth weight. In monozygotic twins, however, the associations between intrapair differences in birth weight and differences in total cholesterol, LDL cholesterol, and apolipoprotein B were in the opposite direction (+0.32 mmol/liter per kg, P = 0.03; +0.23 mmol/liter per kg, P = 0.08; and +0.06 g/liter per kg, P = 0.04, respectively). The association between intrapair differences in birth weight and differences in HDL cholesterol was not significant in dizygotic twins (+0.04 mmol/liter per kg, P = 0.6) and of borderline significance in monozygotic twins (+0.11 mmol/liter per kg, P = 0.05). These data suggest that genetic factors account for the association of low birth weight with high levels of total cholesterol, LDL cholesterol, and apolipoprotein B, whereas intrauterine factors possibly play a role in the association between birth weight and HDL cholesterol.

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Electroencephalographic Study of Mentally Retarded Twins

Australian & New Zealand Journal of Psychiatry ◽

10.3109/00048677609159494 ◽

1976 ◽

Vol 10 (2) ◽

pp. 157-162

Author(s):

Takao Hattori

Keyword(s):

Mental Retardation ◽

Brain Damage ◽

Monozygotic Twins ◽

Mentally Retarded ◽

Concordance Rate ◽

Dizygotic Twins ◽

Electroencephalographic Study

The EEGs of twenty-five pairs of twins, one or both of whom were mentally retarded, were studied. The concordance rate for mental retardation in monozygotic twins was higher than that in dizygotic twins. The vast majority of cases of mental retardation were considered to be caused by genotype but some exogenous causes were observed in discordant monozygotic twins. Paroxysmal discharges in the EEG especially those of centrencephalic type were suspected to be bio-electrical expressions of a transmissible cerebral susceptibility which may easily lead to intellectual deterioration by brain damage or epilepsy.

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The genetic background of circadian and ultradian rhythm patterns of 17-hydroxycorticosteroids: a cross-twin study

Journal of Endocrinology ◽

10.1677/joe.0.1050247 ◽

1985 ◽

Vol 105 (2) ◽

pp. 247-253 ◽

Cited By ~ 23

Author(s):

A. Reinberg ◽

Y. Touitou ◽

A. Restoin ◽

C. Migraine ◽

F. Levi ◽

...

Keyword(s):

Twin Study ◽

Genetic Background ◽

Monozygotic Twins ◽

Power Spectra ◽

Young Male ◽

Ultradian Rhythm ◽

Ultradian Rhythms ◽

Dizygotic Twins ◽

Best Fitting ◽

Time Series Analyses

ABSTRACT Circadian and ultradian rhythms in urinary excretion of 17-hydroxycorticosteroids were documented individually during an 8-day span in two pairs of young male twins. Studies were performed once at the age of 6 years for dizygotic twins and twice at the ages of 4·3 and 10·3 years for monozygotic twins. Four different methods were used for time-series analyses: chronograms (raw data), best-fitting curves resulting from cosinor analyses, power spectra and correlations of time-qualified data. Estimates of rhythm parameters (prominent periods, acrophases, etc.) as well as shapes of curves were closer in mono- than in dizygotic twins. Both similarities and small differences in rhythm characteristics of monozygotic twins were detected at both ages considered. J. Endocr. (1985) 105, 247–253

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Genetic risk of depression and stress-induced negative affect in daily life

The British Journal of Psychiatry ◽

10.1192/bjp.bp.106.032201 ◽

2007 ◽

Vol 191 (3) ◽

pp. 218-223 ◽

Cited By ~ 106

Author(s):

Marieke Wichers ◽

Inez Myin-Germeys ◽

Nele Jacobs ◽

Frenk Peeters ◽

Gunter Kenis ◽

...

Keyword(s):

Negative Affect ◽

Genetic Risk ◽

Daily Life ◽

Monozygotic Twins ◽

Dizygotic Twins ◽

Dsm Iv ◽

Current Mood ◽

Minor Stressors ◽

Related Stress ◽

Trait Associations

BackgroundA bias to develop negative affect in response to daily life stressors may be an important depression endophenotype, but remains difficult to assess.AimsTo assess this mood bias endophenotype, uncontaminated by current mood, in the course of daily life.MethodThe experience samping method was used to collect multiple appraisals of daily life event-related stress and negative affect in 279 female twin pairs. Cross-twin, cross-trait associations between daily life mood bias and DSM – IV depression were conducted.ResultsProbands whose co-twins were diagnosed with lifetime depression showed a stronger mood bias to stress than those with co-twins without such a diagnosis, independent of probands' current depressive symptoms and to a greater extent in monozygotic twins than in dizygotic twins.ConclusionsGenetic liability to depression is in part expressed as the tendency to display negative affect in response to minor stressors in daily life. This trait may represent a true depression endophenotype.

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Genetic factors in anorexia nervosa

European Psychiatry ◽

10.1016/s0924-9338(99)80741-x ◽

1999 ◽

Vol 14 (4) ◽

pp. 189-198 ◽

Cited By ~ 35

Author(s):

A. Kipman ◽

P. Gorwood ◽

M.C. Mouren-Siméoni ◽

J. Adès

Keyword(s):

Anorexia Nervosa ◽

Genetic Factors ◽

Monozygotic Twins ◽

Twin Studies ◽

Vulnerability Factors ◽

Adoption Studies ◽

Complex Disorder ◽

Dizygotic Twins ◽

The One ◽

Familial Environment

SummaryAnorexia nervosa is a severe and complex disorder with incompletely known vulnerability factors. It is generally recognized that anorexia nervosa is a familial disorder, but the majority of twin studies have shown that the concordance rate for monozygotic twins is higher (on average 44%) than for dizygotic twins (on average 12.5%). This difference in concordance rates shows that genetic factors, more than common familial environment, may explain why the `anorexia nervosa' phenotype runs in families. In order to estimate the heritability in the broad sense of anorexia nervosa according to published familial and twin studies, we first assessed the intrapair correlation between monozygotic and dizygotic twins, and secondly calculated the deviation threshold of relatives of affected probands from the relative mean. In this review, we obtained an estimation of the heritability at 0.72 according to all published controlled familial studies (six references quoted in MEDLINE®), and 0.71 for all published twin studies (59 references quoted in MEDLINE®). This estimation is close to the ones previously proposed, between 0.5 and 0.8.Familial and twin studies may also help to define the boundaries of the phenotype, shedding light on the complex relationship between anorexia nervosa on the one hand, and bulimia nervosa, mood disorders, and alcoholism on the other. Demonstrating the importance of genetic factors in anorexia nervosa, and more specifically for anorexia of the restrictive type, requires not only prospective and adoption studies (which are still lacking), but also genetic polymorphisms analyses, which began very recently.

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Effects of Type of Placentation on Birthweight and its Variability in Monozygotic and Dizygotic Twins

Acta geneticae medicae et gemellologiae twin research ◽

10.1017/s0001566000009326 ◽

1979 ◽

Vol 28 (1) ◽

pp. 41-50 ◽

Cited By ~ 58

Author(s):

L.A. Corey ◽

W.E. Nance ◽

K.W. Kang ◽

J.C. Christian

Keyword(s):

Monozygotic Twins ◽

Total Variance ◽

Dizygotic Twins ◽

Chorion Type

Birthweight was measured on 188 monochorionic monozygotic, 54 dichorionic monozygotic, 102 like-sexed dizygotic, and 94 unlike-sexed dizygotic liveborn twin pairs. Overall, males were found to be significantly heavier than females. These differences were not significant, however, when birthweights were compared within zygosity/chorion-type categories. Males were also characterized by a slightly greater overall total variance. Comparisons of intrapair variation of monochorionic and dichorionic monozygotic twins revealed significant differences between monochorionic pairs and dichorionic separate pairs and no significant differences between monochorionic pairs and dichorionic fused pairs. The results of this study suggest that placental proximity may have as important an influence on variation in birthweight as does the presence or absence of vascular anastomoses.

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