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PubMed2002

Classical Scheuermann disease in male monozygotic twins: further support for the genetic etiology hypothesis.

STUDY DESIGN: Classic cases of Scheuermann disease in male monozygotic twins are reported. OBJECTIVES: To report classic cases of Scheuermann disease or Scheuermann kyphosis in male monozygotic twins, and to discuss the previous two cases of classic Scheuermann disease in monozygotic twins and the genetic etiology theory of Scheuermann kyphosis. SUMMARY OF BACKGROUND DATA: The etiology of Scheuermann disease remains unclear. Both genetic and mechanical factors or a combination of the two have been postulated to explain Scheuermann disease. The genetic etiology hypothesis has been explained by an autosomal dominant inheritance pattern. In support of this genetic etiology hypothesis, two cases of Scheuermann disease in monozygotic twins have been reported in the English literature. METHODS: The criteria of Sørensen and Sachs et al were used to diagnose Scheuermann kyphosis. Clinical examination and lateral spinal radiographs were performed on a male monozygotic twin. Both parents were clinically investigated for signs of a kyphotic deformity. RESULTS Scheuermann disease was noted in both patients at the same vertebral levels. The Cobb angle of the kyphosis was 74 degrees and 48 degrees, respectively. Clinical examination of both parents did not show any kyphotic abnormality. CONCLUSIONS: These cases of classic Scheuermann disease in monozygotic male twins support the theory that there is a genetic contribution in classic Scheuermann disease.

Adolescent↗
PubMed1988

Ulcerative colitis and Crohn's disease in an unselected population of monozygotic and dizygotic twins. A study of heritability and the influence of smoking.

By running the Swedish twin registry containing about 25,000 pairs of twins of the same sex together with the central national diagnosis register of hospital inpatients, 80 twin pairs suffering from inflammatory bowel disease were found. In the ulcerative colitis group one of 16 monozygotic pairs was concordant for the disease, but all the other 20 pairs (dizygotic or unknown zygosity) were discordant. In the Crohn's disease group eight of 18 monozygotic pairs and one of 26 dizygotic pairs were concordant. The proband concordance rate among monozygotic twins was 6.3% for ulcerative colitis and 58.3% for Crohn's disease. The calculated heritability of liability based on monozygotic pairs was 0.53 and 1.0 respectively. Thus heredity as an aetiological factor is stronger in Crohn's disease than in ulcerative colitis. Monozygotic twins with Crohn's disease were more likely to be smokers than monozygotic twins with ulcerative colitis. Smoking did not explain the discordance of twin pairs with either ulcerative colitis, or Crohn's disease. The combination of identical heredity and similar smoking habit is not sufficient to cause disease.

Adolescent↗
PubMed1996

Prenatal growth markers in schizophrenia: a monozygotic co-twin control study.

OBJECTIVE: This co-twin study investigated monozygotic twins who were discordant for schizophrenia for evidence of prenatal growth differences between the affected and well co-twins. METHOD: Four dermatoglyphic markers of prenatal growth were obtained by established procedures from 26 monozygotic twin pairs discordant for schizophrenia, 13 monozygotic twin pairs concordant for schizophrenia, and several normal monozygotic twin samples. RESULTS: The a-b ridge count differences between the affected and well co-twins were greater than those found for concordant and normal monozygotic pairs. In comparison with their well co-twins, the affected twins, in discordant pairs, had developed fewer epidermal ridges in the a-b interdigital area of their right palms. In contrast, no significant differences were found between the affected twins and their well co-twins on markers associated with fetal development before 13 or after 15 weeks estimated gestational age. CONCLUSIONS: Because the a-b ridges are known to complete development between 13 and 15 weeks estimated gestational age, the results provide physical evidence suggesting that the schizophrenia-affected monozygotic twins alone experienced a time-specific and time-limited dysgenesis during this time. Commonalities in the ontogeny of epidermal and neurological structures are discussed.

Dermatoglyphics↗
PubMed1998

No paternal effect on monozygotic twinning in the Swedish Twin Registry.

Previous research has provided evidence for a genetic effect in monozygotic twinning, indicated by an increased risk for monozygotic women to have monozygotic offspring. However, since the biological mechanism for this trait is unknown, it is not clear if there exists a paternal inheritance. In this study we investigated twin pregnancies in offspring born in 1941-1996 to male twins in the Swedish Twin Registry and population controls born in 1926-1980. In total 4,225,331 offspring, of which 89,286 were twins, were studied. There was neither an increase in the probability for monozygotic men to have like-sexed twin offspring risk ratio (RR = 0.95; 95% CI = 0.77-1.13) nor an increase in the estimated number of monozygotic twin births. Thus, there is no evidence for a paternal effect on monozygotic twinning, suggesting that the gene(s) increasing the liability for division of the embryo are expressed in the mother and not in the fertilised egg.

Cohort Studies↗
PubMed1986

The potential use of artificially produced monozygotic twins for comparative experiments.

The uniformity of twins has been examined by assembling estimates of the intraclass correlation coefficient (rho(I)) available in the literature for a variety of parameters studied in cattle monozygotic twins and human dizygotic and monozygotic twins. The values of rho(I) vary considerably between parameters. In human monozygotic twins rho(I) is always larger compared to that found in dizygotic twins. There is insufficient evidence to determine whether artificial monozygotic twins are more uniform than natural monozygotic twins. A new measure of twin uniformity, given by T (3) = 1 (1-rho (I)) , is introduced. In practice 2T(3) gives the number of animals chosen at random that one member of a twin pair can replace without loss of statistical efficiency. A useful class of experimental designs for the exploitation of twin uniformity is incomplete block designs. These designs are defined by (v, k, b), where v is the number of treatments to be compared, k = 2, and b is the number of twin pairs. Each design has an associated efficiency (E). Provided rho(I)>1-E, an incomplete block design will be advantageous. In general, when only a few twin pairs are available, this relation will only hold for monozygotic and not dizygotic twins. Suitable arrangements of treatment comparisons for designs (3,2,8), (4,2,9), (5,2,10), (6,2,11) are presented.

Journal Article↗
PubMed2003

A note on including phenotypic information from monozygotic twins in variance components QTL linkage analysis.

Williams & Blangero (1999) derived closed form expressions for the power of a univariate variance components test of linkage for a variety of pedigree structures. We have extended their results by investigating the effect of including monozygotic twins in the design on the power to detect linkage. Specifically, we determined the power associated with a pedigree of size three, where individuals one and two were monozygotic twins and individual three was a full sibling to the twins. The power of this sampling unit was uniformly greater than the power obtained from a sib-pair under the same genetic model. The reason for this was that addition of a second monozygotic twin provided another estimate of the sibling correlation for the particular IBD class. In addition, when the total heritability of the trait was <50%, the number of individuals that needed to be phenotyped was less than that with sib-pairs alone. However, a pedigree consisting of a monozygotic pair and sibling was never as informative as a sib-trio, presumably because the sib-trio provided information about allele sharing between three individuals, whereas the monozygotic twins and sibling unit only provided one such relationship. We conclude that including a monozygotic twin in the analysis is an economical strategy, since only one twin needs to be genotyped.

Genetic Linkage↗
PubMed1981

Attempts to produce monozygotic quadruplets in cattle by blastomere separation.

The blastomeres of eight-cell cow embryos were separated by micromanipulation into four pairs, inserted in foreign zonae pellucidae, embedded in agar and cultured for approximately four days in ligated sheep oviducts. Of 44 "quarter" embryos (11 monozygotic groups) transferred to sheep, 91 per cent had continued to develop at a normal rate and 77 per cent had formed small blastocysts with a single inner cell mass. Twenty-six blastocysts freed from the agar were transferred to heifers, each heifer receiving two monozygotic embryos, one to the tip of each uterine horn. Nine recipients were diagnosed pregnant by rectal palpation on day 50, six carrying twins. Thus 15 of the embryos had continued to develop including two sets of monozygotic quadruplets and one set of monozygotic triplets. Eight fetuses developed to full term, one set of monozygotic triplets, two sets of monozygotic twins (one set born dead) and one single.

Animals↗
PubMed1996

X-inactivation patterns in monozygotic and dizygotic female twins.

We have tested the hypothesis that contrasting X-inactivation patterns could be a trigger for monozygotic twinning in females. X-inactivation patterns were studied in umbilical cord tissue in 43 monozygotic twin pairs and 24 dizygotic twin pairs. Very skewed or non-random X-inactivation patterns were observed in both twins in six of the monozygotic twin pairs and in one of the dizygotic twin pairs. Contrasting X-inactivation patterns occurred in only one of the six monozygotic twin pairs. This does not support the original hypothesis. There is a trend to extreme skewing of X-inactivation pattern occurring more frequently in monozygotic twins.

Base Sequence↗
PubMed1996

Some causes of genotypic and phenotypic discordance in monozygotic twin pairs.

The use of the adjective "identical" rather than monozygotic leads to misunderstandings about the biology of monozygotic twinning. Most monozygotic twin pairs are not identical; there may be major discordance for birth weight, genetic disease, and congenital anomalies. These indicate that postzygotic events may lead to the formation of two or more cell clones in the inner cell mass and early embryo that actually stimulate the monozygotic twinning event. There is also evidence that there may be unequal allocation of numbers of cells to the monozygotic twins; this may have widespread implications for the cascade of developmental events during embryogenesis, formation, and vascularization of the placenta. Large-scale zygosity testing at birth could be the template for analysis of twin outcomes and their biologic causes.

Chorion↗
PubMed1987

Goldenhar complex in discordant monozygotic twins: a case report and review of the literature.

In 1952, Goldenhar described a pair of monozygotic twins who were discordant for epibulbar dermoids, auricular appendages, malformations of the auricle, and hemifacial microsomia. Eighteen twin pairs have subsequently been described in which at least one member exhibited these manifestations. We report on an additional pair of discordant dichorionic monozygotic male twins. All of the 5 monozygotic twin pairs for which placental information is available have been discordant and 2 of these had dichorionic membranes. The failure of discordant monozygotic twins to be limited to monochorionic pairs argues against the hypothesis that developmental abnormalities arising from the placental vascular anastomoses that are commonly found in monozygotic twins is the probable explanation for the discordant expression of these traits in twins.

Female↗
PubMed2004

Olfactory impairment in monozygotic twins discordant for schizophrenia.

OBJECTIVE: Several studies demonstrated olfactory dysfunction in patients with schizophrenia, some reported deficient olfaction in unaffected relatives of schizophrenics as well. This study differentially assessed olfactory acuity as well as smell identification and smell discrimination in monozygotic twins discordant for schizophrenia and healthy, monozygotic control twins, to determine the genetic basis of different olfactory modalities and their association to schizophrenia. METHOD: The Sniffin'Sticks test,a comprehensive and standardized olfactory test, was employed to assess the olfactory function of 10 monozygotic twin pairs discordant for schizophrenia versus 10 age- and sexmatched healthy,monozygotic twin pairs. RESULTS: Olfaction of affected monozygotic twins was globally impaired. Partial olfactory impairment of their unaffected co-twins may point to a genetic cause of olfactory impairment in schizophrenia. The influence of genetic factors was most evident for olfactory acuity and least evident for smell identification. All olfactory functions declined with duration of illness. Side of stimulus presentation did not influence olfactory performance. CONCLUSIONS: Genetic factors associated with olfactory dysfunction may contribute to schizophrenia. The degree of the genetic influence on olfaction depends on the olfactory domain under examination.

Adult↗
PubMed1998

Cerebral ventricle-brain ratio in monozygotic twins discordant and concordant for schizophrenia.

1. Several studies on monozygotic twins discordant for schizophrenia showed that the cerebral ventricle-brain ratio (VBR) was larger in the twins with schizophrenia, as compared with the corresponding normal twins. 2. The results suggest that the difference of the VBR of the discordant twins was larger than that of the concordant twins of schizophrenia. 3. The authors studied the VBR in four monozygotic twin pairs discordant and four monozygotic twin pairs concordant for schizophrenia by computerized tomography. 4. In the discordant twins, all pairs showed that the VBR of the normal twins was smaller than that of the corresponding twins with schizophrenia. 5. The difference of the VBR of the discordant twins and that of the concordant twins of schizophrenia was not statistically different using Mann-Whitney U test. 6. The preliminary results suggest that the VBR enlargement in schizophrenia is not genetically controlled in monozygotic twins either discordant or concordant for schizophrenia. 7. In monozygotic concordant twins, the brain pathology may be heterogeneous.

Adolescent↗
PubMed2002

Gastroesophageal reflux disease in monozygotic and dizygotic twins.

BACKGROUND & AIMS: Gastroesophageal reflux disease (GERD) interferes with the quality of life and carries an increased risk for esophageal adenocarcinoma. We investigated genetic influence in the development of reflux. METHODS: We compared concordance for reflux in monozygotic (MZ) and dizygotic (DZ) twins. All twins age 55 and older in the nationwide Swedish Twin Registry were invited to participate. Data were collected by computer-assisted telephone interviews. Reflux disease was defined by symptomatic heartburn or acid regurgitation occurring at least weekly. RESULTS: A total of 2178 monozygotic, 3219 same-sex dizygotic, and 3014 unlike-sex dizygotic twin pairs provided information. Overall, 15.3% of the twins had reflux. In men, the intraclass correlation for reflux was 0.29 (95% confidence interval [CI], 0.15-0.43) for monozygotic and 0.13 (95% CI, 0.02-0.25) for dizygotic pairs. In women, the correlation was 0.33 (95% CI, 0.22-0.44) for monozygotic and 0.14 (95% CI, 0.04-0.24) for dizygotic pairs. For unlike-sex dizygotic pairs, the correlation was 0.06 (95% CI, -0.01 to 0.14). Concordance for reflux was not caused by inherited obesity or alcohol use; inherited smoking may be a minor factor. CONCLUSIONS: The increased concordance for reflux in monozygotic pairs, compared with dizygotic pairs, indicates genetic rather than shared environmental effects. Heritability accounted for 31% (23%-39%) of the liability to reflux disease in this population.

Aged↗
PubMed2005

Is there increased monozygotic twinning after assisted reproductive technology?

Over the past two decades there has been an association between assisted reproductive technologies and increased monozygotic twinning. The association is not clear nor are the causes of assisted reproductive technology-related monozygotic twinning understood, although there are several theories as to the possible mechanisms involved. This review looks at some of the assisted reproductive technologies which may be associated with an increased risk of monozygotic twinning such as intracytoplasmic sperm injection, assisted hatching and blastocyst transfers. Determining the true incidence of monozygotic twinning after assisted reproductive technologies is important as there is a well-documented increase in perinatal morbidity and mortality of monozygotic twins compared to singleton and dizygotic pregnancies.

Adult↗
PubMed2006

New chromosome 11p15 epigenotypes identified in male monozygotic twins with Beckwith-Wiedemann syndrome.

Beckwith-Wiedemann syndrome (BWS) is an overgrowth syndrome demonstrating heterogeneous molecular alterations of two imprinted domains on chromosome 11p15. The most common molecular alterations include loss of methylation at the proximal imprinting center, IC2, paternal uniparental disomy (UPD) of chromosome 11p15 and hypermethylation at the distal imprinting center, IC1. An increased incidence of female monozygotic twins discordant for BWS has been reported. The molecular basis for eleven such female twin pairs has been demonstrated to be a loss of methylation at IC2, whereas only one male monozygotic twin pair has been reported with this molecular defect. We report here two new pairs of male monozygotic twins. One pair is discordant for BWS; the affected twin exhibits paternal UPD for chromosome 11p15 whereas the unaffected twin does not. The second male twin pair is concordant for BWS and both twins of the pair demonstrate hypermethylation at IC1. Thus, this report expands the known molecular etiologies for BWS twins. Interestingly, these findings demonstrate a new epigenotype-phenotype correlation in BWS twins. That is, while female monozygotic twins with BWS are likely to show loss of imprinting at IC2, male monozygotic twins with BWS reflect the molecular heterogeneity seen in BWS singletons. These data underscore the need for molecular testing in BWS twins, especially in view of the known differences among 11p15 epigenotypes with respect to tumor risk.

Beckwith-Wiedemann Syndrome↗
PubMed1994

Are neurological abnormalities in well discordant monozygotic co-twins of schizophrenic subjects the result of perinatal trauma?

OBJECTIVE: Neurological abnormalities found in schizophrenic subjects and their healthy relatives have raised questions concerning etiology. The aim of the present study was to investigate the genetic and environmental antecedents of neurological impairment in monozygotic twins discordant for schizophrenia, with particular focus on the well discordant twins. The etiological factors of interest were history of obstetric complications, family history of psychosis, history of substance abuse, and history of postnatal cerebral trauma. METHOD: History of obstetric complications, including information from pregnancy through the neonatal period, and data on neurological "hard" and "soft" signs were obtained blindly and separately for each member of 22 monozygotic twin pairs discordant for schizophrenia and seven normal comparison monozygotic twin pairs. Clinical and family interviews provided information about background factors. RESULTS: Degree of neurological impairment in the well discordant monozygotic twins was significantly positively related to history of both neonatal and total obstetric complications. None of the three other background factors investigated was related to degree of neurological impairment in the ill or well co-twins. CONCLUSIONS: The contribution of obstetric complications to the current level of neurological impairment in well discordant co-twins suggests that the spectrum of neuroabnormality, ranging from neurological signs to schizophrenia, in monozygotic discordant twins may be the result of subtle gene-environment interaction.

Adult↗
PubMed2002

Discordance of monozygotic twins for thyroid dysgenesis: implications for screening and for molecular pathophysiology.

Since the advent of biochemical screening for congenital hypothyroidism, the majority of monozygotic twins reported with thyroid dysgenesis have been discordant, and most were missed on neonatal screening, presumably due to fetal blood mixing. We hypothesized that there may be bias leading to preferential reporting of discordant twins and/or of false negative screening results. Therefore, we performed a systematic search for twins in two congenital hypothyroidism screening centers, Quebec and Brussels, that use a primary TSH approach. In Quebec, 10 pairs of twins were identified, all discordant for congenital hypothyroidism due to thyroid dysgenesis (4 monozygotic and 4 dizygotic pairs) and dyshormonogenesis (2 dizygotic pairs). The 6 pairs identified in the Brussels database were also all discordant for congenital hypothyroidism due to thyroid dysgenesis (1 monozygotic and 3 dizygotic pairs) and dyshormonogenesis (2 dizygotic pairs). The median increase in TSH between screening and diagnosis was 7-fold in the monozygotic twins vs. 2-fold in matched singletons (P = 0.02), suggesting fetal blood mixing between the twins. In summary, discordance for thyroid dysgenesis is the rule in monozygotic twins, and fetal blood mixing may result in delayed or missed diagnoses. We therefore conclude that 1) a second sample for congenital hypothyroidism screening at 14 d of age should be considered for all same-sex twins; and 2) thyroid dysgenesis generally results from epigenetic phenomena, early somatic mutations, or postzygotic stochastic events.

Adult↗
PubMed2000

A novel mutation of the KAL1 gene in monozygotic twins with Kallmann syndrome.

OBJECTIVE: Kallmann syndrome is defined by the association of hypogonadotropic hypogonadism and anosmia. The KAL1 gene is responsible for the X-linked form of Kallmann syndrome. In this study we describe monozygotic twins with Kallmann syndrome due to the same mutation in the KAL1 gene. DESIGN: We studied male monozygotic twins with Kallmann syndrome. METHODS: We analyzed the KAL1 gene using the PCR-direct sequencing method. The twins' mother was examined for the identified mutation. RESULTS: We identified a 14 bp deletion from codon 419 in exon 9 (Pro419del14) in both KAL1 genes of the twins. This was a novel mutation in the KAL1 gene and was responsible for Kallmann syndrome. As Pro419del14 was not detected in the mother of the twins, Pro419del14 was a germline mutation originating from them. These monozygotic twins showed different LH and FSH responses to LH-RH stimulation and different phenotypes such as complications, physiques and psychiatric characters. CONCLUSIONS: We report an identical KAL1 gene mutation in the monozygotic twins with Kallmann syndrome. As these monozygotic twins showed different phenotypes in some respects, we suggest that factors other than mutations in the KAL1gene affect the symptomatic features of Kallmann syndrome.

Adult↗