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1.  Gluteal flap for omphalocele repair in a case of epigastric heteropagus: A novel approach for surgical management 
Epigastric heteropagus is an extremely rare congenital anomaly, in which there is asymmetrical conjoined twinning, with the parasitic twin attached to the epigastrium. A 2-day-old male, with epigastric heteropagus and omphalocele, was operated in our institution. After excision of the parasitic twin, omphalocele was covered with a gluteal skin flap available from the parasitic twin. Post-operative course was uneventful, except for infection along the edges of the skin flaps, which was managed conservatively. Only 44 cases of epigastric heteropagus twins have been reported previously in world literature. We present a novel surgical approach for the repair of the omphalocele in a case of epigastric heteropagus twins, probably the 45th case to be reported in the world literature.
doi:10.4103/0970-0358.113731
PMCID: PMC3745099  PMID: 23960319
Conjoined twins; epigastric heteropagus; gluteal skin flap
2.  Heteropagus Twins—A Tale of Two Cases 
The Indian Journal of Surgery  2011;73(3):217-220.
Heteropagus twinning is a rare occurrence. Parasitic and asymmetric conjoined twins are rarer anomalies of monochorionic monoamniotic twins; which consist of an incomplete twin attached to the fully developed body of the co-twin. We present here two such cases of Heteropagus twinning.
doi:10.1007/s12262-010-0228-8
PMCID: PMC3087066  PMID: 22654336
Heteropagus; Twins; Omphalocele
3.  A Rare Form of Heteropagus Twinning: Three-Armed Infant with Spinal Dysraphism 
Case Reports in Pediatrics  2012;2012:831649.
An ectopic or accessory limb attached to the back is an extremely rare and strange condition, and there are only a few documented cases in the worldwide literature. The first case was described by Jones and Larkin (1889). There are several theories regarding the origin of this condition. Asymmetric conjoined twinning which is located dorsally in the vertebral column (rachipagus) is the most probable diagnosis of our patient. Conjoined twinning is very rare and the incidence is 1 per 50 000 live births. Rachipagus is even rarer, with no more than 30 case reports so far (Chadha et al. (1993, 2006)). In this report, we present a patient who underwent successful surgical excision of a third arm attached to the back in the midline over the low-dorsal region. Differential diagnoses including teratoma and fetus in fetu are discussed.
doi:10.1155/2012/831649
PMCID: PMC3530761  PMID: 23304600
4.  Prenatal diagnosis of pygopagus tetrapus parasitic twin: case report 
Background
Asymmetric and parasitic conjoined twins are rarer anomalies of monochorionic monoamniotic twins, consisting of an incomplete twin attached to the fully developed body of the co-twin.
Case presentation
A 30-year-old multigravid woman referred to maternal fetal unit due to polyhydramnios at 28th week of gestation. Sonographic examination revealed a single fetus and polyhydramnios with amniotic fluid index 30 cm. The fetus had normal apparent single head, spine, thorax, abdomen, two upper and two lower limbs, and two relatively well developed rudimentary parasitic lower limbs at sacral region. Lower limbs of the autosite were moving freelly but no movement was detected at the parasite. The parasite contained irregular lower limbs and left foot with three toes. Short and deformed long bones were also present in the parasitic limbs. A Cesarean section was performed at 38th week of gestation and a live female infant weighing 3600 g was delivered. The parasitic lower limbs were totally excised. Post-operative period was uneventful and the newborn was discharged as healthy. Post-natal follow-up was normal at nine-month-old.
Conclusion
Pygopagus tetrapus parasitic twin is a rare form of conjoined twins and in utero diagnosis with ultrasound assists in prenatal management and counselling with parents.
doi:10.1186/1471-2393-4-13
PMCID: PMC481071  PMID: 15251046
5.  Prenatal diagnosis of conjoined twins: four cases in a prenatal center 
Objective
To assess the findings in conjoined twins diagnosed prenatally.
Material and Methods
Between January 2002 and June 2009, we reviewed the database and medical records of 857 twin pregnancies, including 140 monochorionic twins. Nineteen monochorionic-monoamniotic twin pregnancies were detected, four of which were complicated by conjoined twins.
Results
Of these 4 cases, 2 were complicated by thoracopagus and one had thoraco-omphalopagus; these three cases underwent termination at 16, 11, and 19 weeks gestation, respectively. The last case was diagnosed as a pygopagus tetrapus parasitic twin at 28 weeks gestation. The family decided to continue the pregnancy, and achieved a successful outcome with elective surgery postpartum.
Conclusion
Conjoined twins are an uncommon and complex complication of monozygotic gestations, which is associated with high perinatal mortality. The early prenatal diagnosis of conjoined twins allows improved counseling about the management options, including maintenance of pregnancy with surgery after delivery or termination of pregnancy.
doi:10.5152/jtgga.2010.32
PMCID: PMC3939146  PMID: 24591931
Conjoined twins; prenatal diagnosis
6.  Imperfect twinning: a clinical and ethical dilemma 
Revista Paulista de Pediatria  2013;31(3):384-391.
OBJECTIVE
To review the history, epidemiology, etiology, gestational aspects, diagnosis and prognosis of imperfect twinning.
DATA SOURCES
Scientific articles were searched in PubMed, SciELO and Lilacs databases, using the descriptors "conjoined twins", "multiple pregnancy", "ultrasound", "magnetic resonance imaging" and "prognosis". The research was not delimited to a specific period of time and was supplemented with bibliographic data from books.
DATA SYNTHESIS:
The description of conjoined twins is legendary. The estimated frequency is 1/45,000-200,000 births. These twins are monozygotic, monochorionic and usually monoamniotic. They can be classified by the most prominent fusion site, by the symmetry between the conjoined twins or by the sharing structure. The diagnosis can be performed in the prenatal period or after birth by different techniques, such as ultrasound, magnetic resonance imaging and echocardiography. These tests are of paramount importance for understanding the anatomy of both fetuses/children, as well as for prognosis and surgical plan determination.
CONCLUSIONS
Although imperfect twinning is a rare condition, the prenatal diagnosis is very important in order to evaluate the fusion site and its complexity. Hence, the evaluation of these children should be multidisciplinary, involving mainly obstetricians, pediatricians and pediatric surgeons. However, some decisions may constitute real ethical dilemmas, in which different points should be discussed and analyzed with the health team and the family.
doi:10.1590/S0103-05822013000300017
PMCID: PMC4182971  PMID: 24142323
twins; twins, conjoined; twins, monozygotic; pregnancy, multiple; prognosis
7.  High Risk of Unexpected Late Fetal Death in Monochorionic Twins Despite Intensive Ultrasound Surveillance: A Cohort Study 
PLoS Medicine  2005;2(6):e172.
Background
The rationale for fetal surveillance in monochorionic twin pregnancies is timely intervention to prevent the increased fetal/perinatal morbidity and mortality attributed to twin–twin transfusion syndrome and intrauterine growth restriction. We investigated the residual risk of fetal death after viability in otherwise uncomplicated monochorionic diamniotic twin pregnancies.
Methods and Findings
We searched an electronic database of 480 completed monochorionic pregnancies that underwent fortnightly ultrasound surveillance in our tertiary referral fetal medicine service between 1992 and 2004. After excluding pregnancies with twin–twin transfusion syndrome, growth restriction, structural abnormalities, or twin reversed arterial perfusion sequence, and monoamniotic and high-order multiple pregnancies, we identified 151 uncomplicated monochorionic diamniotic twin pregnancies with normal growth, normal liquor volume, and normal Doppler studies on fortnightly ultrasound scans. Ten unexpected intrauterine deaths occurred in seven (4.6%) of 151 previously uncomplicated monochorionic diamniotic pregnancies, within 2 wk of a normal scan, at a median gestational age of 34+1 wk (weeks+days; range 28+0 to 36+3). Two of the five cases that underwent autopsy had features suggestive of acute late onset twin–twin transfusion syndrome, but no antenatal indicators of transfusional imbalance or growth restriction, either empirically or in a 1:3 gestation-matched case–control comparison. The prospective risk of unexpected antepartum stillbirth after 32 wk was 1/23 monochorionic diamniotic pregnancies (95% confidence interval 1/11 to 1/63).
Conclusion
Despite intensive fetal surveillance, structurally normal monochorionic diamniotic twin pregnancies without TTTS or IUGR are complicated by a high rate of unexpected intrauterine death. This prospective risk of fetal death in otherwise uncomplicated monochorionic diamniotic pregnancies after 32 wk of gestation might be obviated by a policy of elective preterm delivery, which now warrants evaluation.
Despite intensive fetal surveillance, structurally normal monochorionic diamniotic twin pregnancies were found to be complicated by a high rate of unexpected intrauterine death late in pregnancy.
doi:10.1371/journal.pmed.0020172
PMCID: PMC1160580  PMID: 15971947
8.  Twin reversed arterial perfusion (TRAP) sequence in association with VACTERL association: a case report 
Introduction
Twin reversed arterial perfusion (TRAP) sequence is a rare complication of multiple pregnancy caused by defects in early embryogenesis. The pump twin supplies the acardiac recipient twin with blood, and although the pump twin is usually structurally normal, congenital anomalies have sometimes been reported. We report a unique case of twin reversed arterial perfusion sequence with a prenatal diagnosis of VACTERL association in the surviving pump twin.
Case presentation
A 24-year-old Caucasian woman presented at 11 weeks' gestation with a monochorionic, monoamniotic twin pregnancy. A reversed arterial flow was noted on a Doppler imaging study coming from the larger, apparently normal twin to the smaller, grossly abnormal twin, and a diagnosis of twin reversed arterial perfusion sequence was made. Cardiac activity was undetectable in the recipient twin by 16 weeks' gestation. Further detailed assessment at 18 weeks' gestation revealed multiple congenital anomalies of the surviving pump twin, in keeping with a diagnosis of VACTERL association. A live infant girl was delivered at 39 weeks by elective cesarean section. She underwent extensive surgery with subsequent normal development at the age of two years.
Conclusion
The co-existence of two rare and complex conditions in this unique case raises interesting questions about the role of early defects in embryogenesis and their subsequent effects on fetal development. This case also highlights the importance of prenatal diagnosis of major congenital anomalies to the plan treatment, reduce morbidity and aid the survival of affected children.
doi:10.1186/1752-1947-4-411
PMCID: PMC3022672  PMID: 21176185
9.  Monoamniotic Monochorionic Twins Discordant for Noncompaction Cardiomyopathy 
Occasionally “identical twins” are phenotypically different, raising the question of zygosity and the issue of genetic versus environmental influences during development. We recently noted monochorionic-monoamniotic twins, one of which had an isolated cardiac abnormality, noncompaction cardiomyopathy, a condition characterized by cardiac ventricular hypertrabeculation. We examined the prenatal course and subsequent pathologic correlation since ventricular morphogenesis may depend on early muscular contraction and blood flow. The monochorionic-monoamniotic female twin pair was initially identified since one fetus presented with increased nuchal translucency. Complete heart block was later identified in the fetus with nuchal translucency who did not survive after delivery. In contrast, the unaffected twin had normal cardiac studies both prenatally and postnatally. Pathologic analysis of the affected twin demonstrated noncompaction of the left ventricle with dysplasia of the aortic and pulmonary valves. Dissection of the cardiac conduction system disclosed atrioventricular bundle fibrosis. Maternal lupus studies, amniocentesis with karyotype, and studies for 22q11.2 were normal. To test for zygosity, we performed multiple STR marker analysis and found that all markers were shared even using non-blood tissues from the affected twin. These studies demonstrate that monozygotic twins that are monochorionic monoamniotic can be discordant for cardiac noncompaction. The results suggest further investigation into the potential roles of pathologic fibrosis, contractility, and blood flow in cardiac ventricle development.
doi:10.1002/ajmg.a.35925
PMCID: PMC3664136  PMID: 23636980
Twins; noncompaction; heritability; cardiomyopathy; congenital heart; monozygotic; fibrosis
10.  Differences between the events preceding spina bifida and anencephaly. 
Journal of Medical Genetics  1981;18(1):17-21.
It is usually held that there is a time continuum in the formation of monoxygotic (MZ) twins which is indexed by their placentation, running from dichorionic to monochorionic diamniotic to monochorionic monoamniotic and conjoined pairs. There is good evidence that this continuum is characterised by a continuum of predisposition to anencephaly, slightly raised in dichorionic pairs but very high in some sorts of conjoined pairs. Although MZ twins, especially monoamniotic and conjoined pairs, are peculiarly liable to anencephaly, they are not particularly susceptible to spina bifida. Among twin pairs concordant for anencephaly or spina bifida, there are strikingly few concordant in the sense of one twin having anencephaly and the other spina bifida, in contrast with the numbers of pairs concordant for the same malformation. The prevalence of anencephaly in double monsters varies with the type of monster, being high in diprosopus. These findings may be explained by the timing of embryonic events.
PMCID: PMC1048651  PMID: 7019447
11.  Twin Reversed Arterial Perfusion Syndrome (TRAP or Acardiac Twin)-A Case Report 
Twin reversed arterial perfusion (TRAP) syndrome is a rare condition (0.3:10,000 births) that occurs in monochorionic twin pregnancies, resulting in coexistence of a normal “pump” twin and an acardiac twin. The acardiac twin is dependent upon the normal twin to provide circulation by means of vascular anastomosis. Many of the bizarre defects are felt to be caused by low oxygen tension and this causes dramatic alteration in the twin fetal physiology and high prenatal mortality. The acardiac twin is a parasite, putting the pump fetus at risk of high output cardiac failure. Overall only 50% of pump twins survive. We present a case in a twenty year female, gravida two, para one, living one, full term normal pregnancy, ultrasound showed twin pregnancy. Following delivery, the first fetus survived only for one day and the second fetus showed features of TRAP syndrome.
doi:10.7860/JCDR/2014/7012.3965
PMCID: PMC3939538  PMID: 24596758
Acardiac twin; fetal anomaly; twin reversed arterial perfusion syndrome
12.  Influence of twin-twin transfusion syndrome on fetal cardiovascular structure and function: prospective case–control study of 136 monochorionic twin pregnancies 
Heart  2002;88(3):271-277.
Objective: To test the hypothesis that identical twins show no inter-twin differences in cardiovascular structure or physiology in fetal life unless there has been twin-twin transfusion syndrome.
Design: Unselected prospective case–control observational study of fetoplacental haemodynamics including echocardiography at a median of 24 (16.7 to 32.3) weeks, with postnatal confirmation of congenital heart disease or normality.
Setting: Fetal medicine unit.
Patients: 136 women with monochorionic diamniotic twin pregnancies, of which 47 fetal twin pairs (35%) had twin-twin transfusion syndrome.
Results: There were no haemodynamic differences between the bigger fetus (twin 1) and the smaller co-twin (twin 2) in uncomplicated monochorionic diamniotic pairs. In twin-twin transfusion syndrome, recipient fetuses had increased aortic and pulmonary velocities compared with their donor co-twins (mean (SD): 0.73 (0.23) m/s and 0.63 (0.14) m/s), respectively, v 0.53 (0.16) m/s and 0.48 (0.10) m/s in donor twins; p = 0.003 (aortic) and < 0.0001 (pulmonary)), and also in comparison with twin 1 and twin 2. The overall prevalence of congenital heart disease was increased above that in singletons (3.8% v 0.56%; 6.9% in twin-twin transfusion v 2.3% in uncomplicated monochorionic diamniotic twins), with inter-twin discordance for defects. The prevalence in recipient twins was 11.9% (p = 0.014 v uncomplicated control twins).
Conclusions: Fetuses with an identical genome but no circulatory imbalance have similar cardiovascular physiology but discordant phenotypic expression of congenital heart disease. The high prevalence of congenital heart disease in monochorionic diamniotic twins merits detailed fetal echocardiography.
PMCID: PMC1767329  PMID: 12181221
monochorionic twins; twin-twin transfusion syndrome; congenital heart disease; fetal echocardiography
13.  Multimodality Imaging in the Assessment of Thoraco-Omphalopagus Conjoined Twin: Lessons to Learn 
Case Reports in Radiology  2012;2012:564036.
Conjoined twins are rare and present a unique challenge to pediatric surgeons and radiologists. An imaging strategy to accurately define anatomic fusion, vascular anomalies, and other associated abnormalities is important for surgical planning and prognostic information. A conjoined female twin with a combined weight of 2.8 kg was born by emergency caeserean. Hence, a computed tomography scan of the thorax and entire abdomen at 1.25 mm slice thickness was performed to delineate the internal structures of the twins. CT-angiography defined specific vascular supply which determined the distribution of shared structures between the twins. An echocardiogram showed four heart chambers with atrioventricular septal defect. To further evaluate the heart chambers, the twin was planned for gated cardiac magnetic resonance imaging. Unfortunately, they succumbed 6 hours apart due to complication of septicemia. Magnetic resonance imaging and CT scan provide excellent anatomic detail, demonstrating organ position, shared viscera, and limited vascular anatomy, whilst angiography defined specific vascular supply, useful in determining the distribution of shared structures between the twins in planning for surgery.
doi:10.1155/2012/564036
PMCID: PMC3390032  PMID: 22792503
14.  Lessons from BWS twins: complex maternal and paternal hypomethylation and a common source of haematopoietic stem cells 
European Journal of Human Genetics  2009;17(12):1625-1634.
The Beckwith–Wiedemann syndrome (BWS) is a growth disorder for which an increased frequency of monozygotic (MZ) twinning has been reported. With few exceptions, these twins are discordant for BWS and for females. Here, we describe the molecular and phenotypic analysis of 12 BWS twins and a triplet; seven twins are MZ, monochorionic and diamniotic, three twins are MZ, dichorionic and diamniotic and three twins are dizygotic. Twelve twins are female. In the majority of the twin pairs (11 of 13), the defect on chromosome 11p15 was hypomethylation of the paternal allele of DMR2. In 5 of 10 twins, there was additional hypomethylation of imprinted loci; in most cases, the loci affected were maternally methylated, but in two cases, hypomethylation of the paternally methylated DLK1 and H19 DMRs was detected, a novel finding in BWS. In buccal swabs of the MZ twins who share a placenta, the defect was present only in the affected twin; comparable hypomethylation in lymphocytes was detected in both the twins. The level of hypomethylation reached levels below 25%. The exchange of blood cells through vascular connections cannot fully explain the degree of hypomethylation found in the blood cell of the non-affected twin. We propose an additional mechanism through which sharing of aberrant methylation patterns in discordant twins, limited to blood cells, might occur. In a BWS-discordant MZ triplet, an intermediate level of demethylation was found in one of the non-affected sibs; this child showed mild signs of BWS. This finding supports the theory that a methylation error proceeds and possibly triggers the twinning process.
doi:10.1038/ejhg.2009.77
PMCID: PMC2987023  PMID: 19513094
twinning; Beckwith–Wiedemann syndrome; methylation defect; chromosome 11p15; hypomethylation of imprinted loci; vascular connections
15.  Occurrence of Different External Ear Deformities in Monozygotic Twins: Report of 2 Cases 
Summary:
Microtia is a spectrum of congenital deformities, which varies from barely discernable to anotia. Twinning is a well-known risk factor for congenital defects including external ear deformities. Monozygotic twins usually show identical appearances as well as congenital malformations. In special conditions as ear deformities, “mirror-image” may also occur. We report 2 cases of monozygotic twins with different ear deformities. The 8-year-old propositus with lobule type microtia and her identical female twin presented with facial symmetry. Patient A had sausage-type right microtia with absence of external auditory canal. The left external ear showed normal appearance. Patient B presented with left-sided preauricular skin tag and right-sided malformation of tragus with skin tag combined with hyperplasia of underlying cartilage. A granule-size skin tag was also noticed at crus of right helix. A 7-year-old male patient with right-sided conchal type microtia presented to an ear reconstruction center. The patient’s mother showed normal auricular appearance. Her monozygotic twin sister, whose son and daughter had normal ear appearance, was diagnosed with a leftsided lobule type microtia.
doi:10.1097/GOX.0000000000000142
PMCID: PMC4229265  PMID: 25426389
16.  Global Transcript Profiles of Fat in Monozygotic Twins Discordant for BMI: Pathways behind Acquired Obesity  
PLoS Medicine  2008;5(3):e51.
Background
The acquired component of complex traits is difficult to dissect in humans. Obesity represents such a trait, in which the metabolic and molecular consequences emerge from complex interactions of genes and environment. With the substantial morbidity associated with obesity, a deeper understanding of the concurrent metabolic changes is of considerable importance. The goal of this study was to investigate this important acquired component and expose obesity-induced changes in biological pathways in an identical genetic background.
Methods and Findings
We used a special study design of “clonal controls,” rare monozygotic twins discordant for obesity identified through a national registry of 2,453 young, healthy twin pairs. A total of 14 pairs were studied (eight male, six female; white), with a mean ± standard deviation (SD) age 25.8 ± 1.4 y and a body mass index (BMI) difference 5.2 ± 1.8 kg/m2. Sequence analyses of mitochondrial DNA (mtDNA) in subcutaneous fat and peripheral leukocytes revealed no aberrant heteroplasmy between the co-twins. However, mtDNA copy number was reduced by 47% in the obese co-twin's fat. In addition, novel pathway analyses of the adipose tissue transcription profiles exposed significant down-regulation of mitochondrial branched-chain amino acid (BCAA) catabolism (p < 0.0001). In line with this finding, serum levels of insulin secretion-enhancing BCAAs were increased in obese male co-twins (9% increase, p = 0.025). Lending clinical relevance to the findings, in both sexes the observed aberrations in mitochondrial amino acid metabolism pathways in fat correlated closely with liver fat accumulation, insulin resistance, and hyperinsulinemia, early aberrations of acquired obesity in these healthy young adults.
Conclusions
Our findings emphasize a substantial role of mitochondrial energy- and amino acid metabolism in obesity and development of insulin resistance.
Leena Peltonen and colleagues uncover the metabolic changes that result from obesity through an analysis of genetically identical twin pairs in which one was obese and the other was not.
Editors' Summary
Background.
Around the world, the proportion of people who are obese (people with an unhealthy amount of body fat) is increasing. In the US, for example, 1 adult in 7 was obese in the mid 1970s. That is, their body mass index (BMI)—their weight in kilograms divided by their height in meters squared—was more than 30. Nowadays, 1 US adult in 3 has a BMI this high and, by 2025, it is predicted that 1 in 2 will be obese. This obesity epidemic is being driven by lifestyle changes that encourage the over-consumption of energy-rich foods and discourage regular physical activity. The resultant energy imbalance leads to weight gain (the excess energy is stored as body fat or adipose tissue) and also triggers numerous metabolic changes, alterations in the chemical processes that convert food into the energy and various substances needed to support life. These obesity-related metabolic changes increase a person's risk of developing adverse health conditions such as diabetes, a condition in which dangerously high levels of sugar from food accumulate in the blood.
Why Was This Study Done?
The changes in human fat in obesity have not been completely understood, although the abnormal metabolism of adipose tissue is increasingly seen as playing a critical part in excessive weight gain. It has been very difficult to decipher which molecular and metabolic changes associated with obesity are the result of becoming obese, and which might contribute towards the acquisition of obesity in humans in the first place. To discover more about the influence of environment on obesity-induced metabolic changes, the researchers in this study have investigated these changes in pairs of genetically identical twins.
What Did the Researchers Do and Find?
The researchers recruited 14 pairs of genetically identical Finnish twins born between 1975 and 1979 who were “obesity discordant”—that is, one twin of each pair had a BMI of about 25 (not obese); the other had a BMI of about 30 (obese). The researchers took fat and blood samples from each twin, determined the insulin sensitivity of each, and measured the body composition and various fat stores of each. They found that the obese twins had more subcutaneous, intra-abdominal, and liver fat and were less insulin sensitive than the non-obese twins. Insulin sensitivity correlated with the amount of liver fat. Analysis of gene expression in the fat samples showed that 19 gene pathways (mainly inflammatory pathways) were expressed more strongly (up-regulated) in the obese twins than the non-obese twins, whereas seven pathways were down-regulated. The most highly down-regulated pathway was a mitochondrial pathway involved in amino acid breakdown, but mitochondrial energy metabolism pathways were also down-regulated. Finally, mitochondrial DNA copy number in fat was reduced in the obese twins by nearly half, a novel observation that could partly account for the obesity-induced metabolic defects of these individuals.
What Do These Findings Mean?
These and other findings identify several pathways that are involved in the development of obesity and insulin resistance. In particular, they suggest that changes in mitochondrial energy production pathways and in mitochondrial amino acid metabolism pathways could play important roles in the development of obesity and of insulin resistance and in the accumulation of liver fat even in young obese people. The study design involving identical twins has here produced some evidence for aberrations in molecules critical for acquired obesity. The results suggest that careful management of obesity by lifestyle changes has the potential to correct the obesity-related metabolic changes in fat that would otherwise lead to diabetes and other adverse health conditions in obese individuals. In addition, they suggest that the development of therapies designed to correct mitochondrial metabolism might help to reduce the illnesses associated with obesity.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0050051.
The MedlinePlus encyclopedia has pages on obesity and diabetes (in English and Spanish)
The US Centers for Disease Control and Prevention provides information on all aspects of obesity (in English and Spanish)
The UK National Health Service's health Web site (NHS Direct) provides information about obesity
The International Obesity Taskforce provides information about preventing obesity and on diabetes and obesity
The UK Foods Standards Agency and the United States Department of Agriculture provide online tools and useful advice about healthy eating for adults and children
Information is available for patients and carers from the US National Diabetes Information Clearinghouse on diabetes, including information on insulin resistance
doi:10.1371/journal.pmed.0050051
PMCID: PMC2265758  PMID: 18336063
17.  Infantile Perineal Protrusion in Two Monochorionic Twins 
AJP Reports  2014;4(2):e81-e82.
Case Report Two female monochorionic-monoamniotic twins showed the same kind of infantile perineal protrusion (IPP) at birth. Lesions in both twins progressively healed until resolution in 6 weeks' time; none of the twins have manifested, till date, alvus disturbances.
Discussion and Literature Review A literature review numbers approximately 100 reports of IPP. This condition has been classically classified into three categories: congenital/familiar (i.e., female sex, positive parental history of IPP), acquired (mainly due to constipation), and associated with lichen sclerosus et atrophicus.
Conclusions and Final Remarks This case report describes, for the first time, the presence of IPP in monochorionic-monoamniotic twins, supporting the existence of hereditary/genetic factors in the developing of this condition.
doi:10.1055/s-0034-1383853
PMCID: PMC4239147  PMID: 25452887
infantile perineal protrusion; monochorionic twins; congenital disease; neonatology
18.  Perinatal Outcome of Monochorionic in Comparison to Dichorionic
Twin Pregnancies 
Oman Medical Journal  2013;28(3):173-177.
Objective
The aim of this study is to compare the neonatal outcomes of monochorionic and dichorionic twin pregnancies.
Methods
A retrospective cohort study involving 51 twin pregnancies followed and delivered at Sultan Qaboos University Hospital was conducted between January 2006 and December 2011.
Result
Thirty six (71%) pregnancies were dichorionic diamniotic (DCDA), 14 (27%) were monochorionic diamniotic (MCDA), and one (2%) was monochorionic monoamniotic (MCMA). The antepartum complications noted in the 15 monochorionic twins were discordant fetal growth in 2 (14%) cases, low birth weight in 11 (73%) babies, pre-eclampsia in three mothers (21%) and twin to twin transfusion syndrome in four (29%) cases. Fetal respiratory distress affected eight (57%) of the pregnancies. Six (40%) twin sets were delivered before 30 weeks, 4 (27%) sets at 31 to 32 weeks, 2 (13%) sets at 34-35 weeks, 2 (13%) sets at 36-37 weeks, and 1 (7%) at 37-38 weeks. Fifteen mothers delivered 16 live infants, 9 (30%) stillbirths and 5 (17%) died after birth. Most neonatal deaths were due to neonatal sepsis and pulmonary hypoplasia. Dichorioinic twins, (DC) morbidity was seen in 11% and 40% for monochoroinic twins (MC). Mortality rate was 17% for DC and 47% for MC twins.
Conclusions
Perinatal morbidity and mortality remain high among monochorionic twins. This is likely due to frequent twin-to-twin transfusion syndrome, prematurity, fetal growth restriction and intrauterine fetal death. Improved fetal and neonatal management may result in improved outcomes.
doi:10.5001/omj.2013.49
PMCID: PMC3679607  PMID: 23772282
Twins; Monochorionic; Dichorionic, Outcome
19.  Traces of embryogenesis are the same in monozygotic and dizygotic twins: not compatible with double ovulation 
Human Reproduction (Oxford, England)  2009;24(6):1255-1266.
Common knowledge of over a century has it that monozygotic and dizygotic twinning events occur by unrelated mechanisms: monozygotic twinning ‘splits’ embryos, producing anomalously re-arranged embryogenic asymmetries; dizygotic twinning begins with independent ovulations yielding undisturbed parallel embryogeneses with no expectation of departures from singleton outcomes. The anomalies statistically associated with twin births are due to the re-arranged embryos of the monozygotics. Common knowledge further requires that dizygotic pairs are dichorionic; monochorionicity is exclusive to monozygotic pairs. These are fundamental certainties in the literature of twin biology. Multiple observations contradict those common knowledge understandings. The double ovulation hypothesis of dizygotic twinning is untenable. Girl–boy twins differ subtly from all other humans of either sex, absolutely not representative of all dizygotics. Embryogenesis of dizygotic twins differs from singleton development at least as much as monozygotic embryogenesis does, and in the same ways, and the differences between singletons and twins of both zygosities represent a coherent system of re-arranged embryogenic asymmetries. Dizygotic twinning and monozygotic twinning have the same list of consequences of anomalous embryogenesis. Those include an unignorable fraction of dizygotic pairs that are in fact monochorionic, plus many more sharing co-twins’ cells in tissues other than a common chorion. The idea that monozygotic and dizygotic twinning events arise from the same embryogenic mechanism is the only plausible hypothesis that might explain all of the observations.
doi:10.1093/humrep/dep030
PMCID: PMC2683734  PMID: 19252194
twins; dizygotic; chimera; double ovulation; monozygotic
20.  Discordance of Prenatal and Neonatal Brain Development in Twins 
Early human development  2008;85(3):171-175.
Background
Discordance of birth weight has been observed in twin pairs, though little is known about prenatal and early neonatal discordance of head and brain size, and the role that zygosity and chorionicity play in discordances of early brain development in twins.
Aims
To compare prenatal and neonatal discordances of head size in monozygotic –monochorionic (MZ-MC), monozygotic-dichorionic (MZ-DC), and same-sex dizygotic-dichorionic twin pairs (DZ).
Study Design
Subjects prospectively had ultrasounds at 22 and 32 weeks gestational age, and magnetic resonance imaging (MRI) of the brain MRI after birth.
Subjects
88 twin pairs recruited from two university hospital prenatal diagnostic clinics; 22 MZ-MC, 17 MZ-DC, and 49 same sex DZ pairs.
Outcome measures
Discordance of head circumference (HC) and weight at 22 weeks, 32 weeks and birth, as well as intracranial volume (ICV) on neonatal MRI.
Results
There were no group differences in discordance of head circumference and weight on the 22 or 32 week ultrasounds, or at birth. MZ-MC twins tended to have numerically greater discordances of HC and weight. There was a significant group difference in ICV on neonatal MRI (ANOVA, p = 0.0143), with DZ twins having significantly greater discordance than MZ-MC (p = 0.028) or MZ-DC (p = 0.0131) twins.
Conclusions
This study indicates that zygosity and chorionicity do not contribute to significant discordances of head size in late prenatal development. DZ twins do have significantly greater discordances of ICV on neonatal MRI, suggesting a relatively greater genetic influence on brain growth in the first weeks after birth.
doi:10.1016/j.earlhumdev.2008.07.008
PMCID: PMC2696044  PMID: 18804925
21.  Conjoined Twins in a Triplet Pregnancy: A Case Report 
Background. Conjoined twins are a rare complication of monozygotic twinning and are associated with high perinatal mortality. Case. Here we present a case of conjoined twins in a triplet pregnancy diagnosed at 13 of weeks gestation. With the aid of 3D ultrasound and MRI images, the parents were counseled regarding the management options, including continuation of pregnancy, termination of pregnancy, or selective fetocide. They chose selective fetocide of the conjoined twins and went on to deliver the remaining triplet at term. Conclusion. This case represents to our knowledge the only MRI images of conjoined twins in a triplet pregnancy and demonstrates how 3D imaging can be used to better counsel patients about management options.
doi:10.1155/2011/235873
PMCID: PMC3335527  PMID: 22567498
22.  A Rare Case of Antepartum Spontaneous Septostomy in a Monochorionic Diamniotic Twin Pregnancy 
Spontaneous septostomy in a monochorionic diamniotic twin pregnancy is a rare phenomenon. We present a case of monochorionic diamniotic twin pregnancy with an intact dividing membrane seen in the 1st half of the pregnancy. At 26 weeks, when she was assessed for preterm contractions, the dividing membrane was not documented, which suggested spontaneous septostomy. There had been no invasive procedures during the pregnancy. She subsequently delivered at 29 weeks, secondary to preterm labor. No dividing membrane was noticed at the time of caesarian section. Spontaneous septostomy can complicate the management of monochorionic diamniotic twins by creating a pseudomonoamniotic environment resulting in cord entanglement, and difficulty in the diagnosis and management of twin-twin transfusion syndrome. We believe that such a case should be managed as monochorionic monoamniotic twin gestation.
doi:10.1155/2012/748614
PMCID: PMC3457626  PMID: 23024870
23.  Case Series of Monoamniotic and Pseudomonoamniotic Twin Gestations 
ISRN Obstetrics and Gynecology  2013;2013:369419.
We retrospectively evaluated a series of 18 monoamniotic and 7 pseudomonoamniotic (secondary to rupture in the membrane dividing monochorionic diamniotic twins) twin gestations managed after 20 weeks' gestation. There were no significant differences in the incidence of neonatal death or umbilical cord entanglement between the monoamniotic and pseudomonoamniotic twin gestations (33 versus 21%, P = 0.94 and 72 versus 43%, P = 0.36). Therefore, the same serious management may be needed for pseudomonoamniotic twin gestations as for monoamniotic twin gestations.
doi:10.1155/2013/369419
PMCID: PMC3595717  PMID: 23509635
24.  Cloaca in Discordant Monoamniotic Twins: Prenatal Diagnosis and Consequence for Fetal Lung Development 
AJP Reports  2014;4(1):33-36.
Objective Describe a case of cloaca prenatally diagnosed in one of a set of monoamniotic twins.
Study Design Retrospective review of a case.
Results Cloaca is one of the most complex and severe degrees of anorectal malformations in girls. We present a discordant cloaca in monoamniotic twins. Fetal ultrasound showed a female fetus with a pelvic midline cystic mass, a phallus-like structure, a probable anorectal atresia with absence of anal dimple and a flat perineum, and renal anomalies. The diagnosis was confirmed by fetal magnetic resonance imaging postnatally.
Conclusions The rarity of the malformation in a monoamniotic pregnancy, the difficulties of prenatal diagnosis, the pathogenic assumptions, and the consequences of adequate amniotic fluid for fetal lung development are discussed.
doi:10.1055/s-0034-1370351
PMCID: PMC4078163  PMID: 25032057
prenatal diagnosis; persistent cloaca; monoamniotic twins; fetal lung development; discordant
25.  X chromosome inactivation patterns correlate with fetal-placental anatomy in monozygotic twin pairs: implications for immune relatedness and concordance for autoimmunity. 
Molecular Medicine  1994;1(1):62-70.
BACKGROUND: Monozygotic (MZ) twinning is a poorly understood phenomenon that may result in subtle biologic differences between twins, despite their identical inheritance. These differences may in part account for discordant expression of disease in MZ twin pairs. Due to their stochastic nature, differences in X chromosome inactivation patterns are one source of such variation in female MZ twins. MATERIALS AND METHODS: We investigated X chromosome inactivation patterns in the blood of 41 MZ twin pairs based on methylation of the androgen receptor gene using a Hpa II-PCR assay. Twenty-six female MZ twin pairs with autoimmune disease (rheumatoid arthritis or multiple sclerosis) were studied. In addition, we studied 15 newborn female MZ twin pairs who were characterized at birth with respect to the anatomy of chorionic membranes (dichorionic versus monochorionic). RESULTS: We found a strong correlation between dichorionic fetal anatomy and differences in X chromosome inactivation patterns between members of an MZ twin pair. In contrast, all monochorionic twin pairs had closely correlated patterns of X chromosome inactivation. X chromosome inactivation patterns did not distinguish between MZ twin pairs who were concordant or discordant for autoimmune disease. CONCLUSIONS: The highly similar patterns of X chromosome inactivation among monochorionic twin pairs may result from their shared placental blood supply during intrauterine life. Alternatively, these patterns may indicate that X chromosome inactivation occurs before the twinning event in this anatomic subgroup of MZ twins. The data further suggest that these factors do not make a major contribution to the high discordance rates for autoimmune disease in MZ twin pairs.
Images
PMCID: PMC2229926  PMID: 8790602

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