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PubMed1995

Some perinatal characteristics of monozygotic twins who are dichorionic.

Zygosity testing of all multiple births allowed the identification of a subgroup of 42 monozygotic twin pairs who have dichorionic placentas, fused and separate. Perinatal outcomes of this group were compared with 110 pairs of monochorionic monozygotic twins and 148 pairs of dizygotic twins. Dichorionic monozygotic twins had the lowest incidence of preterm birth, perinatal mortality, and birth weight discordance. There was an excess of like-sexed over unlike-sexed pairs among the dizygotic twins.

Birth Weight↗
PubMed2004

Familial symptom domains in monozygotic siblings with autism.

Autism is characterized by a triad of symptom domains (impaired social interaction, communication deficits, and repetitive behaviors) that vary significantly in their clinical presentation across the population. Within families with more than one affected member, however, discrepant findings exist with regard to symptom variability. Reduced intrafamily variance is of particular importance because it supports an underlying model of genetic heterogeneity in the transmission of autism, and the identification of familial clinical subtypes can be used to select more homogeneous samples for linkage analysis in the future. This study examines whether there are specific features of autism that show decreased variance within 16 families with monozygotic siblings concordant for autism. Evidence for familiality was defined as significantly decreased variance of symptom levels within monozygotic siblingships as compared to between siblingships. Using regression analysis, we demonstrated significant aggregation of symptoms within monozygotic siblingships for two of the three main symptom domains in autism: impairments in communication and social interaction showed significant familiality. Within the repetitive behavior domain, only the categories of circumscribed interests and preoccupation with part-objects showed reduced variance within siblingships. In addition, with the exception of a negative association between the social and behavior domains, partial correlation coefficients did not reveal significant associations between the levels of different symptom domains within families, suggesting that the levels of clinical features seen in autism may be a result of mainly independent genetic traits. Because of presumed genetic heterogeneity and the wide clinical variation seen in autism and other pervasive developmental disorders, selecting probands according to specific features known to show reduced variance within families may provide more homogeneous samples for genetic analysis and strengthen the power to detect the specific genes involved in autism.

Autistic Disorder↗
PubMed1997

Monozygotic twins discordant for congenital complete heart block.

OBJECTIVE: Isolated congenital complete heart block (CCHB) occurs in 1/20,000 live births. More than 85% of mothers giving birth to affected infants are anti-Ro antibody positive, but only approximately 1% of babies with anti-Ro-positive mothers develop CCHB. We studied 2 sets of monozygotic twins discordant for CCHB. METHODS: Monozygosity was determined using placental examination and DNA microsatellite analysis. HLA typing was performed. Autoantibody studies were performed using counterimmunoelectrophoresis, immunoblotting, Ro 52 and Ro 60 enzyme-linked immunosorbent assay (ELISA), and indirect immunofluorescence (IIF) on Ro 60- and Ro 52-transfected HEp-2 cells. RESULTS: Both sets of twins were monozygotic. They had similar birth weights. Twin 2 in the second set required a pacemaker at age 2 months. Both mothers were positive for anti-Ro 52 and anti-Ro 60 antibody, and neither had anti-La antibody on immunoblot. One set of twins was studied at birth. Similar titers of anti-Ro 52 and anti-Ro 60 antibody were found by IIF and ELISA. CONCLUSION: There are no previous well-documented reports of monozygotic twins discordant for CCHB. These cases demonstrate that there is still discordance in the development of CCHB despite identical genetics and environmental exposure to anti-Ro antibody.

Adult↗
PubMed1990

Fetal blood sampling demonstrating chimerism in monozygotic twins discordant for sex and tissue karyotype (46,XY and 45,X)

Fetal blood sampling has been used in the genetic work-up of twin gestations for rapid karyotyping. We present a case of twins which on ultrasound evaluation revealed hydrops fetalis in one twin and a normal second twin. Fetal blood sampling revealed the presence of mosaicism for 46,XY/45,X in both twins. HLA antigen testing showed the twins to be identical. The patient elected pregnancy termination. Blood chromosomal analysis after delivery revealed both twins to have 46,XY/45,X mosaicism, but the twin with signs of hydrops fetalis had tissue chromosomes of 45,X and the normal twin had tissue chromosomes of 46,XY. Amniotic fluid chromosomal analysis revealed 46,XY in twin A and 45,X in twin B. This represents a case of identical (monozygotic) twins with sex discordance. In this case, there was the probable occurrence of post-zygotic chromosomal non-disjunction leading to the discordancy of the sex in this set of twins. With the presence of vascular communication in monozygotic twins, there is the possibility of exchange of blood in monozygotic twins and the result of blood chimerism in twins.

Adult↗
PubMed1998

[Ventricular septal defect associated with pulmonary hypertension in monozygotic twins--a case report with surgical repair].

This is a report of two-year-old female monozygotic twins, both having a ventricular septal defect (VSD, Kirklin type II) and accompanying moderate pulmonary hypertension (PH). The two patients underwent a patch closure procedure to repair the VSD at the same time, and their postoperative courses were uneventful. Rubenstein and Weaver have reported the only case of surgical treatment for monozygotic twins having both VSD and PH. Our patients are the second such case of surgical treatment of VSD and PH in monozygotic twins.

Cardiac Surgical Procedures↗
PubMed2001

Heterogeneity of type I diabetes: analysis of monozygotic twins in Great Britain and the United States.

AIMS: To determine the risk, hazard rate and factors affecting progression to diabetes in monozygotic twins of patients with Type I (insulin-dependent) diabetes mellitus. METHODS: Prospective analysis was done of two cohorts of non-diabetic monozygotic twins of patients with Type I diabetes from Great Britain (n = 134) and the United States (n = 53). RESULTS: The diabetes-free survival analysis was similar between both cohorts (p = 0.6). The combined survival analysis (n = 187, median follow-up = 17.7 years, range = 0.01-57) at 40 years of discordance estimated a 39% probability of diabetes for the initially discordant twin. Survival analysis with left truncation of data estimated that probability to be 50%. For twins who became concordant (n = 47), the median discordance time was 4.2 years (range 0.4 to 39), exceeding 15 years in 23.4%. Twins of probands diagnosed at 24 years of age or younger had a 38% probability of diabetes by 30 years of discordance, compared with 6% for twins of probands diagnosed after 24 years of age (p = 0.004). The twins of probands diagnosed before 15 years of age had the highest diabetes hazard rate in the first discordance year, decreasing thereafter. By survival analysis, diabetes risk was higher in twins who were heterozygous for DR3-DQ2 and DR4-DQ8 than in twins with neither DR3-DQ2 nor DR4-DQ8 (p < 0.05). CONCLUSION/INTERPRETATION: Monozygotic twins of patients with Type I diabetes from two different countries had similar rates of progression to diabetes. Whereas most twins did not develop diabetes, 25% of the twins who progressed did so after more than 14 years of discordance. An age-related heterogeneity was observed, with higher progression to diabetes for twins of patients diagnosed at a younger age.

Adolescent↗
PubMed2003

Mitochondrial DNA control region diversity in hairs and body fluids of monozygotic triplets.

Length heteroplasmy of the homopolymeric cytosine stretch in the hypervariable region II of the mitochondrial D-loop was investigated in blood, buccal cells and hair shafts of monozygotic triplets. The proportions of length heteroplasmy were determined by cloning and sequencing of multiple independent clones. Blood and buccal cells showed an accumulation of molecules with one and two insertions of cytosine residues in relation to the Cambridge Reference Sequence (CRS). The results did not show statistically significant differences between blood and buccal cells of one and the same individual and also not between the three monozygotic brothers. In the hair samples a loss of cytosine residues was established in all three monozygotic individuals compared to blood and buccal cells, suggesting that this must be a regular process. Furthermore, the hair shaft samples showed significant differences between the frequencies of 7, 8 or 9 Cs in the poly C region comparing the three individuals (p<0.008) and in addition there were highly significant differences (p<0.0001) when comparing the results for six different hairs of each individual separately. From these results it can be assumed that besides a common genetic bottleneck during embryonic development, a post-embryonic bottleneck seems to exist in each hair follicle.

Adult↗
PubMed1998

Congenital tracheobronchial stenosis in monozygotic twins.

UNLABELLED: A pair of monozygotic twins suffering from noisy respirations and recurrent wheezes since early infancy were referred for evaluation. Using direct coronal CT and 3-dimensional reconstruction of the airway, congenital tracheobronchial stenosis was found in both twin babies, later confirmed by fibre optic bronchoscopy. The cause of congenital tracheobronchial stenosis remains obscure, but even in monozygotic twins an unidentified environmental factor cannot be excluded and may be responsible for discordant bronchopulmonary abnormalities. CONCLUSION: This case report shows that tracheobronchial stenosis may present in monozygotic twins. The pattern of malformation in twins differs from cases described previously.

Bronchial Diseases↗
PubMed2005

Monozygotic bichorionic twinning after transfer of a single frozen/thawed embryo that has undergone quarter laser-assisted zona thinning: a case report.

PURPOSE: To present the occurrence of a monozygotic bichorionic twinning after the transfer of a single frozen/thawed embryo has undergone assisted zona hatching (AZH), using a non contact laser. METHODS: A 33-year-old woman who underwent single frozen embryo replacement (FER). Before transfer, the patient was treated with GnRH agonist and with substitutive therapy (estrogens and progesterone). CONCLUSIONS: We are absolutely certain that we are reporting a monozygotic bichorionic pregnancy: a single frozen/thawed embryo was transferred and no concomitant spontaneous conception was possible. Moreover, molecular biology assessment for polymorphisms confirmed clinical findings. The possibility of the occurrence of a monozygotic bichorionic twinning after the transfer of a single frozen/thawed embryo should be borne in mind and its incidence will have to be studied further.

Adult↗
PubMed1996

Plasma protein variations in monozygotic twins discordant for schizophrenia.

Monozygotic twins discordant for schizophrenia were analyzed by two-dimensional (2-D) gel electrophoresis to identify extrahereditary factors important in the development of schizophrenia. Plasma protein patterns in 2-D gels of monozygotic twins discordant for schizophrenia were found to be significantly less alike than those of normal control monozygotic twins. Several polypeptide spots were found to be elevated in the plasma of the schizophrenic twin. One of these polypeptides, spot 782, was also found to be significantly (p < .001) elevated when schizophrenic patients were compared to unrelated normal control individuals. Spot 782 may be an isoform of haptoglobin. Quantitative variations in some plasma haptoglobin levels were seen between discordant twins, but not between unrelated schizophrenic and normal control individuals.

Adult↗
PubMed2005

Group 2A idiopathic juxtafoveolar retinal telangiectasia in monozygotic twins.

PURPOSE: To report the clinical and fluorescein angiographic characteristics of monozygotic twins affected by group 2A idiopathic juxtafoveolar retinal telangiectasia. DESIGN: Observational case report. METHODS: Both eyes of identical twins were examined in a clinical practice setting. RESULTS: Two 68-year-old Caucasian, monozygotic, female twins were examined. In one twin, visual acuity was 20/50 in the right eye (OD) and 20/40 in the left (OS). Ophthalmoscopy demonstrated right-angle venules without edema in both eyes (OU). Fluorescein angiography demonstrated areas of leakage temporal to the fovea OU with some nasal leakage OS. In her identical twin sister, with type II diabetes, visual acuity was 20/60 OD and 20/25 OS. Right-angle venules OU, refractile deposits OS, and no macular edema OU were present. Fluorescein angiography demonstrated areas of parafoveal leakage temporal and nasal OD and temporal OS. CONCLUSION: This is the second set of female monozygotic twins with group 2A idiopathic juxtafoveolar retinal telangiectasia reported in the literature. This finding suggests a genetic component in the pathogenesis of this retinal vascular disease.

Aged↗
PubMed2006

The variable expression of keratoconus within monozygotic twins: dundee University Scottish Keratoconus Study (DUSKS).

INTRODUCTION: As part of a longitudinal observational prospective study (Dundee University Scottish Keratoconus Study, DUSKS) a caucasian female subject was identified with keratoconus affecting both corneas. Of interest was that the subject's mother was a monozygotic twin, however, the mother was reportedly unaffected by keratoconus, although her sister (the subject's aunt) had been diagnosed with keratoconus. METHOD: Computer video-keratoscopy (CVK) was undertaken was on this family to clarify this apparent discordance. RESULTS: CVK demonstrated the variable expression of the keratoconic phenotype, by identifying evidence of subclinical keratoconus in the 'unaffected' twin. CONCLUSION: So far only one set of monozygotic twins with keratoconus have been reported within the UK, this paper reports a second. Since CVK has been available the majority agree on concordance of keratoconus expression but not all, including this study. If monozygotic twin studies demonstrate heterogeneity of keratoconus this may at least explain the contradictory data that exists within the literature and why the inheritance pattern of keratoconus is still unclear in 2005.

Corneal Topography↗
PubMed2005

Arrhythmogenic right ventricular cardiomyopathy in two pairs of monozygotic twins.

UNLABELLED: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inheritant disease with an autosomal dominant mode of transmission with incomplete penetrance and variable expression. Linkage analysis in affected families succeeds in identifying 9 loci determining 9 subtypes of the disease. Genotype phenotype correlation is unclear and the influence of various environmental factors is discussed. OBJECTIVES: Genotype phenotype correlation in 2 pairs of monozygotic twins with ARVC and the role of environmental factors are analyzed. PATIENTS AND METHODS: Among 40 pts with ARVC and their 195 relatives there were 2 pairs of monozygotic twins: brothers, age 47 y; and sisters, age 48 y. History, ECG, Holter monitoring, 2D and Doppler Echo, and MRI were analyzed. RESULTS: Twin brothers: ARVC was diagnosed in the proband after the episode of VT with LBBB morphology (enlarged right ventricle, focal hypokinesia of apex, MR evidence of adipose tissue in RV wall). Identical morphology of RV was seen in asymptomatic twin brother. The patient presenting arrhythmia has been rowing for 4 years. Twin sisters: diagnosis was done during family screening. Both were asymptomatic. RV morphology typical for ARVC was found discrete in one of them (bulges adipose tissue in the RV apex); the latter showed changes suggesting RV abnormality (mild segmental dilatation of infundibulum, adipose tissue in a free wall of the RV). No differences in previous viral infections and sports involvement were observed. CONCLUSIONS: 1. Clinical picture of ARVC in monozygotic twins is not identical. 2. Strenuous effort may be a factor triggering the arrhythmia in pts with ARVC.

Arrhythmogenic Right Ventricular Dysplasia↗
PubMed2005

Isolated imperforate anus in monozygotic twins: case report and implications.

The authors report a case of isolated imperforate anus with perineal fistula in monozygotic twins. Only 4 other well-documented cases of monozygotic twins concordant for isolated anorectal malformation have been reported in the literature. In all these cases the defect occurred below the levator ani muscle. This case confirms previous reports on the incidence of low anorectal anomalies in monozygotic twins where the defect was isolated. A review of the literature relating to this condition in twins and siblings points toward low anomalies and more severe malformations having different genetic backgrounds.

Adult↗
PubMed2006

Gray and white matter density changes in monozygotic and same-sex dizygotic twins discordant for schizophrenia using voxel-based morphometry.

Global gray matter brain tissue volume decreases in schizophrenia have been associated to disease-related (possibly nongenetic) factors. Global white matter brain tissue volume decreases were related to genetic risk factors for the disease. However, which focal gray and white matter brain regions best reflect the genetic and environmental risk factors in the brains of patients with schizophrenia remains unresolved. 1.5-T MRI brain scans of 11 monozygotic and 11 same-sex dizygotic twin-pairs discordant for schizophrenia were compared to 11 monozygotic and 11 same-sex dizygotic healthy control twin-pairs using voxel-based morphometry. Linear regression analysis was done in each voxel for the average and difference in gray and white matter density separately, in each twin-pair, with group (discordant, healthy) and zygosity (monozygotic, dizygotic) as between subject variables, and age, sex and handedness as covariates. The t-maps (critical threshold value mid R:tmid R: > 6.0, P < 0.05) revealed a focal decrease in gray matter density accompanied by a focal increase in white matter density in the left medial orbitofrontal gyrus and a focal decrease in white matter density in the left sensory motor gyrus in twin-pairs discordant for schizophrenia as compared to healthy twin-pairs. Focal changes in left medial (orbito)frontal and left sensory motor gyri may reflect the increased genetic risk to develop schizophrenia. Focal changes in the left anterior hemisphere may therefore be particularly relevant as endophenotype in genetic studies of schizophrenia.

Brain↗
PubMed2005

The variability of ovum pick-up response and in vitro embryo production from monozygotic twin cows.

Oocytes were recovered by ovum pick up (OPU) from nine pairs of monozygotic twin German Simmental cows. The hypothesis was that there is less variability between identical twins versus among non-related individuals in the variation in the recovery of oocytes by OPU and in the efficiency of in vitro embryo production. Estrous cycles were synchronized with two doses of cloprostenol, 11 days apart. Beginning 3-4 days after synchronized estrus, OPU was done twice weekly (every 3 or 4 days; total of 11 sessions). The influence of repeated OPU on estrous cyclicity was established by estrus detection, plasma progesterone concentrations, and ovarian ultrasonography. There were no differences among days of collection for the number and quality of cumulus oocyte-complexes (COCs), and rates of cleavage and blastocyst formation. A total of 1,661 COCs, including 657 (39.6%) good-quality COCs, were recovered. From 1,457 (87.7%) cultured COCs, 827 zygotes cleaved and 314 blastocysts were produced on Day 7. The total number of COCs and the blastocyst rates varied among pairs of monozygotic twins; within pairs, only slight differences were observed. In conclusion, recovery of COCs and production of embryos had substantially less variation within pairs of monozygotic twins than among non-related cattle.

Animals↗
PubMed1997

Bilateral congenital optic nerve head pits in monozygotic siblings.

PURPOSE: To report bilateral congenital optic nerve head pits in monozygotic siblings. METHOD: Case reports. RESULTS: Pits were found in abnormally large optic disks in both eyes of two otherwise healthy female monozygotic siblings aged 15 years. Pit size increased and visual acuity decreased with increased optic disk area. In one eye, nonrhegmatogenous retinal detachment developed that eventually necessitated pars plana vitrectomy. The siblings' parents were unremarkable. CONCLUSIONS: Congenital optic nerve head pits can occur bilaterally in otherwise healthy monozygotic siblings with ophthalmologically unremarkable parents. Associated nonrhegmatogenous retinal detachment may be treated by pars plana vitrectomy. Pit size is positively correlated with disk area.

Adolescent↗
PubMed2004

Gray and white matter volume abnormalities in monozygotic and same-gender dizygotic twins discordant for schizophrenia.

BACKGROUND: Whole brain tissue volume decreases in schizophrenia have been related to both genetic risk factors and disease-related (possibly nongenetic) factors; however, whether genetic and environmental risk factors in the brains of patients with schizophrenia are differentially reflected in gray or white matter volume change is not known. METHODS: Magnetic resonance imaging (1.5 T) brain scans of 11 monozygotic and 11 same-gender dizygotic twin pairs discordant for schizophrenia were acquired and compared with 11 monozygotic and 11 same-gender dizygotic healthy control twin pairs. RESULTS: Repeated-measures volume analysis of covariance revealed decreased whole brain volume in the patients with schizophrenia as compared with their co-twins and with healthy twin pairs. Decreased white matter volume was found in discordant twin pairs compared with healthy twin pairs, particularly in the monozygotic twin pairs. A decrease in gray matter was found in the patients compared with their co-twins and compared with the healthy twins. CONCLUSIONS: The results suggest that the decreases in white matter volume reflect the increased genetic risk to develop schizophrenia, whereas the decreases in gray matter volume are related to environmental risk factors. Study of genes involved in the (maintenance) of white matter structures may be particularly fruitful in schizophrenia.

Adult↗