Materiały źródłowe

• #1 Conjoined twins – Wikipedia

  https://en.wikipedia.org/wiki/Conjoined_twins

  Conjoined twins, popularly referred to as Siamese twins, are twins joined in utero. It is a very rare phenomenon, estimated to occur in anywhere between one in 50,000 births to one in 200,000 births, with a somewhat higher incidence in southwest Asia and Africa. Approximately half are stillborn, and an additional one-third die within 24 hours. Most live births are female, with a ratio of 3:1. […] Two possible explanations of the cause of conjoined twins have been proposed. The one that is generally accepted is fission, in which the fertilized egg splits partially. The other explanation, no longer believed to be accurate, is fusion, in which the fertilized egg completely separates, but stem cells (that search for similar cells) find similar stem cells on the other twin and fuse the twins together.

• #2 Conjoined Twins – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK560839/

  Conjoined twins refers to twins that are physically fused in utero and consequently at birth. […] The condition is proposed to result from either fission or fusion. […] The most commonly believed etiology of conjoined twinning is either partial fission or secondary fusion. […] Both of these processes can be used to explain the embryological and anatomical findings observed in conjoined twins. […] However, the fission and fusion theories do not unequivocally account for every possible conjunction and cannot be applied to the full spectrum of findings in conjoined twins. […] It is proposed that non-dorsal conjunction may be initiated by duplication of the axial primordia, which leads to a change in the axial orientation and/or interaction aplasia. […] Dorsal conjunction may occur because of secondary fusion of initially separate monozygotic twins.

• #3 Conjoined twins – Wikipedia

  https://en.wikipedia.org/wiki/Conjoined_twins

  Conjoined twins, popularly referred to as Siamese twins, are twins joined in utero. It is a very rare phenomenon, estimated to occur in anywhere between one in 50,000 births to one in 200,000 births, with a somewhat higher incidence in southwest Asia and Africa. Approximately half are stillborn, and an additional one-third die within 24 hours. Most live births are female, with a ratio of 3:1. […] Two possible explanations of the cause of conjoined twins have been proposed. The one that is generally accepted is fission, in which the fertilized egg splits partially. The other explanation, no longer believed to be accurate, is fusion, in which the fertilized egg completely separates, but stem cells (that search for similar cells) find similar stem cells on the other twin and fuse the twins together.

• #4 Conjoined Twins: Definition, Causes & Outlook

  https://my.clevelandclinic.org/health/diseases/22895-conjoined-twins

  Conjoined twins are caused by two embryos that are joined together during fertilization, resulting in twins that are physically connected, most commonly at the abdomen, chest or head. […] Experts dont know exactly what causes the condition. But it likely involves splitting or fusion of very early-stage embryos soon after fertilization. […] There are two theories of what causes conjoined twins: Fission: An early embryo, comprising a small sphere of identical cells, splits into two spheres but doesnt separate completely. The two spheres each develop independently into the conjoined twins. […] Fusion: An identical twin pregnancy contains separate early twin embryo spheres that merge together and join at a random point of connection. […] Both of these theories help explain how conjoined twins might form during the first 12-14 days of fertilization. But scientists still dont know why this happens. […] Since the cause of conjoined twins is unknown, theres no way to prevent conjoined twins from occurring during pregnancy.

• #5 Conjoined Twins – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK560839/

  Conjoined twins refers to twins that are physically fused in utero and consequently at birth. […] The condition is proposed to result from either fission or fusion. […] The most commonly believed etiology of conjoined twinning is either partial fission or secondary fusion. […] Both of these processes can be used to explain the embryological and anatomical findings observed in conjoined twins. […] However, the fission and fusion theories do not unequivocally account for every possible conjunction and cannot be applied to the full spectrum of findings in conjoined twins. […] It is proposed that non-dorsal conjunction may be initiated by duplication of the axial primordia, which leads to a change in the axial orientation and/or interaction aplasia. […] Dorsal conjunction may occur because of secondary fusion of initially separate monozygotic twins.

• #6 Conjoined twins – Wikipedia

  https://en.wikipedia.org/wiki/Conjoined_twins

  Conjoined twins, popularly referred to as Siamese twins, are twins joined in utero. It is a very rare phenomenon, estimated to occur in anywhere between one in 50,000 births to one in 200,000 births, with a somewhat higher incidence in southwest Asia and Africa. Approximately half are stillborn, and an additional one-third die within 24 hours. Most live births are female, with a ratio of 3:1. […] Two possible explanations of the cause of conjoined twins have been proposed. The one that is generally accepted is fission, in which the fertilized egg splits partially. The other explanation, no longer believed to be accurate, is fusion, in which the fertilized egg completely separates, but stem cells (that search for similar cells) find similar stem cells on the other twin and fuse the twins together.

• #7 Conjoined twins // Middlesex Health

  https://middlesexhealth.org/learning-center/diseases-and-conditions/conjoined-twins

  Conjoined twins develop when an early embryo only partially separates to form two individuals. […] It’s believed that when the embryo splits later than this usually between 13 and 15 days after conception separation stops before the process is complete. The resulting twins are conjoined. […] An alternative theory suggests that two separate embryos may somehow fuse together in early development. […] What might cause either chain of events to occur is unknown.

• #8 Conjoined Twins | Children’s Hospital Colorado

  https://www.childrenscolorado.org/conditions-and-advice/conditions-and-symptoms/conditions/conjoined-twins/

  In rare cases, twins develop so closely that their body parts are joined together. Conjoined twins can be connected through a variety of body parts, including the head, chest, abdomen, pelvis and buttocks. Twins joined at the chest or abdomen are the most common type of conjoined twins, comprising 75% of all cases. […] The dominant theory on the origin of conjoined twins suggests that when the single embryo splits later, separation stops before the process is complete, leaving the babies joined. Alternatively, another theory holds that two separate embryos fuse in early development. What would cause either scenario remains unknown. […] Maternal age and the number of prior pregnancies do not appear to be factors that influence the occurrence of this type of twins. However, use of assisted reproductive techniques (for example, in vitro fertilization) may result in an increased risk for conjoined twins.

• #9 Twins Conjoined at Head Now Separated: What Causes Rare Condition? | Live Science

  https://www.livescience.com/56501-conjoined-twins-causes.html

  Twin boys who were born joined at the head are now successfully separated after they underwent a rare surgery that took more than 20 hours, doctors announced today. […] The 13-month-old boys, Jadon and Anias McDonald, were born with a condition called craniopagus, which means they shared a portion of their skull and brain tissue. […] Conjoined twins are identical twins who are physically connected. Normally, identical twins form when an embryo splits in two shortly after fertilization. But with conjoined twins, this separation process stops before it is completed, according to the University of Maryland Medical Center. […] The embryos of identical twins start to separate around eight to 12 days after forming. It’s thought that if this separation process starts later than this, between 13 and 15 days after fertilization, it results in conjoined twins, according to the Mayo Clinic.

• #10 Conjoined twins // Middlesex Health

  https://middlesexhealth.org/learning-center/diseases-and-conditions/conjoined-twins

  Conjoined twins develop when an early embryo only partially separates to form two individuals. […] It’s believed that when the embryo splits later than this usually between 13 and 15 days after conception separation stops before the process is complete. The resulting twins are conjoined. […] An alternative theory suggests that two separate embryos may somehow fuse together in early development. […] What might cause either chain of events to occur is unknown.

• #11 Conjoined twins – Wikipedia

  https://en.wikipedia.org/wiki/Conjoined_twins

  Conjoined twins, popularly referred to as Siamese twins, are twins joined in utero. It is a very rare phenomenon, estimated to occur in anywhere between one in 50,000 births to one in 200,000 births, with a somewhat higher incidence in southwest Asia and Africa. Approximately half are stillborn, and an additional one-third die within 24 hours. Most live births are female, with a ratio of 3:1. […] Two possible explanations of the cause of conjoined twins have been proposed. The one that is generally accepted is fission, in which the fertilized egg splits partially. The other explanation, no longer believed to be accurate, is fusion, in which the fertilized egg completely separates, but stem cells (that search for similar cells) find similar stem cells on the other twin and fuse the twins together.

• #12 Conjoined Twins: Types, Causes, Survival & Life Expectancy

  https://www.webmd.com/baby/what-are-conjoined-twins

  What Causes Conjoined Twins? […] Scientists aren’t sure how it happens. But there are a few theories: […] Fission: This idea suggests that an early embryo contains a sphere of identical cells. The sphere splits into two, but never completely separates, developing into conjoined twins. […] Fusion: This theory says that conjoined twins are monozygotes, meaning they begin as one fertilized egg that splits into two embryos identical twins. But early on, the twin embryos join at some random point and become conjoined twins. […] Conjoined twins are very rare, and happen in about one in every 50,000 to 60,000 births. […] Conjoined twins aren’t linked to any specific race or maternal age.

• #13 Conjoined Twins – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK560839/

  Conjoined twins refers to twins that are physically fused in utero and consequently at birth. […] The condition is proposed to result from either fission or fusion. […] The most commonly believed etiology of conjoined twinning is either partial fission or secondary fusion. […] Both of these processes can be used to explain the embryological and anatomical findings observed in conjoined twins. […] However, the fission and fusion theories do not unequivocally account for every possible conjunction and cannot be applied to the full spectrum of findings in conjoined twins. […] It is proposed that non-dorsal conjunction may be initiated by duplication of the axial primordia, which leads to a change in the axial orientation and/or interaction aplasia. […] Dorsal conjunction may occur because of secondary fusion of initially separate monozygotic twins.

• #14 Conjoined twins // Middlesex Health

  https://middlesexhealth.org/learning-center/diseases-and-conditions/conjoined-twins

  Conjoined twins develop when an early embryo only partially separates to form two individuals. […] It’s believed that when the embryo splits later than this usually between 13 and 15 days after conception separation stops before the process is complete. The resulting twins are conjoined. […] An alternative theory suggests that two separate embryos may somehow fuse together in early development. […] What might cause either chain of events to occur is unknown.

• #15 Conjoined Twins: A Worldwide Collaborative Epidemiological Study of the International Clearinghouse for Birth Defects Surveillance and Research

  https://pmc.ncbi.nlm.nih.gov/articles/PMC4457318/

  Genetic and environmental risk factors such as consanguinity, familial aggregation, cytogenetic studies, and maternal exposures, and acute and chronic diseases during pregnancy did not reveal any association with the occurrence of CT, in general, or for any particular type of CT. No familial cases were reported and all karyotypes performed were normal. […] Review of variable total prevalence, variable prevalence by occurrence type, predominance in females, a higher prevalence in some ethnic groups such as Blacks and Chinese, geographic variation, socio-demographic variables, genetic and environmental factors, has not helped to advance the understanding of the altered mechanisms that interrupt the normal separation of an inner cell mass leading to the occurrence of a set of CT. Considering the fission theory as currently accepted, a simple molecular disorder at a deep cellular level distorting cell adhesion or apoptosis in a very early stage of embryogenesis could be involved in a etiology of CT that involves incomplete split of the inner mass cell.

• #16 Conjoined Twins: A Worldwide Collaborative Epidemiological Study of the International Clearinghouse for Birth Defects Surveillance and Research

  https://stacks.cdc.gov/view/cdc/33771

  Conjoined twins (CT) are a very rare developmental accident of uncertain etiology. […] The process by which monozygotic twins do not fully separate but form CT is not well understood. […] No genetic, environmental or demographic significant associated factors were identified. […] Further work in epidemiology and molecular research is necessary to understand the etiology and pathogenesis involved in the development of this fascinating phenomenon of nature.

• #17 Conjoined Twins | Children’s Hospital Colorado

  https://www.childrenscolorado.org/conditions-and-advice/conditions-and-symptoms/conditions/conjoined-twins/

  In rare cases, twins develop so closely that their body parts are joined together. Conjoined twins can be connected through a variety of body parts, including the head, chest, abdomen, pelvis and buttocks. Twins joined at the chest or abdomen are the most common type of conjoined twins, comprising 75% of all cases. […] The dominant theory on the origin of conjoined twins suggests that when the single embryo splits later, separation stops before the process is complete, leaving the babies joined. Alternatively, another theory holds that two separate embryos fuse in early development. What would cause either scenario remains unknown. […] Maternal age and the number of prior pregnancies do not appear to be factors that influence the occurrence of this type of twins. However, use of assisted reproductive techniques (for example, in vitro fertilization) may result in an increased risk for conjoined twins.

• #18 Conjoined Twins: Development, Delivery, and Separation

  https://www.healthline.com/health/conjoined-twins

  Conjoined twins are the result of a monozygotic twin pregnancy (identical twin pregnancy) that comes from the fertilization of just one egg. […] Many researchers believe that conjoined twins begin their journey just as other identical twins do. […] An egg becomes fertilized by a sperm and travels down the fallopian tubes to implant into the uterus. Unlike typical identical twins, the embryo doesn’t fully separate into two separate babies. For some reason, the babies stay fused together and continue to develop that way until birth. […] We don’t know why the embryo doesn’t fully separate. And in fact, some researchers believe that the embryos may separate normally but then fuse together early in their development. In either case, more research is needed to determine the exact cause of conjoined twins.

• #19 Conjoined Twins | Children’s Hospital Colorado

  https://www.childrenscolorado.org/conditions-and-advice/conditions-and-symptoms/conditions/conjoined-twins/

  In rare cases, twins develop so closely that their body parts are joined together. Conjoined twins can be connected through a variety of body parts, including the head, chest, abdomen, pelvis and buttocks. Twins joined at the chest or abdomen are the most common type of conjoined twins, comprising 75% of all cases. […] The dominant theory on the origin of conjoined twins suggests that when the single embryo splits later, separation stops before the process is complete, leaving the babies joined. Alternatively, another theory holds that two separate embryos fuse in early development. What would cause either scenario remains unknown. […] Maternal age and the number of prior pregnancies do not appear to be factors that influence the occurrence of this type of twins. However, use of assisted reproductive techniques (for example, in vitro fertilization) may result in an increased risk for conjoined twins.

• #20 Conjoined Twins – Stanford Medicine Children’s Health

  https://www.stanfordchildrens.org/en/services/general-surgery/patient-stories/conjoined-twins.html

  There are two theories about the development of conjoined twins. The first is that a single fertilized egg does not fully split during the process of forming identical twins. The second theory is that a fusion of two fertilized eggs occurs earlier in development. […] Although conjoined twinning has not been linked to any environmental or genetic cause, they occur so rarely it has not been possible to draw firm conclusions.

• #21 Conjoined Twins: A Worldwide Collaborative Epidemiological Study of the International Clearinghouse for Birth Defects Surveillance and Research

  https://pmc.ncbi.nlm.nih.gov/articles/PMC4457318/

  Genetic and environmental risk factors such as consanguinity, familial aggregation, cytogenetic studies, and maternal exposures, and acute and chronic diseases during pregnancy did not reveal any association with the occurrence of CT, in general, or for any particular type of CT. No familial cases were reported and all karyotypes performed were normal. […] Review of variable total prevalence, variable prevalence by occurrence type, predominance in females, a higher prevalence in some ethnic groups such as Blacks and Chinese, geographic variation, socio-demographic variables, genetic and environmental factors, has not helped to advance the understanding of the altered mechanisms that interrupt the normal separation of an inner cell mass leading to the occurrence of a set of CT. Considering the fission theory as currently accepted, a simple molecular disorder at a deep cellular level distorting cell adhesion or apoptosis in a very early stage of embryogenesis could be involved in a etiology of CT that involves incomplete split of the inner mass cell.

• #22 Conjoined Twins: A Worldwide Collaborative Epidemiological Study of the International Clearinghouse for Birth Defects Surveillance and Research

  https://pmc.ncbi.nlm.nih.gov/articles/PMC4457318/

  Genetic and environmental risk factors such as consanguinity, familial aggregation, cytogenetic studies, and maternal exposures, and acute and chronic diseases during pregnancy did not reveal any association with the occurrence of CT, in general, or for any particular type of CT. No familial cases were reported and all karyotypes performed were normal. […] Review of variable total prevalence, variable prevalence by occurrence type, predominance in females, a higher prevalence in some ethnic groups such as Blacks and Chinese, geographic variation, socio-demographic variables, genetic and environmental factors, has not helped to advance the understanding of the altered mechanisms that interrupt the normal separation of an inner cell mass leading to the occurrence of a set of CT. Considering the fission theory as currently accepted, a simple molecular disorder at a deep cellular level distorting cell adhesion or apoptosis in a very early stage of embryogenesis could be involved in a etiology of CT that involves incomplete split of the inner mass cell.

• #23 Conjoined twins – Wikipedia

  https://en.wikipedia.org/wiki/Conjoined_twins

  There are two hypotheses about the development of conjoined twins. A single fertilized egg does not fully split during the process of forming identical twins. If the zygote division occurs after two weeks of the development of the embryonic disc, it results in the formation of conjoined twins. Fusion of two fertilized eggs occurs early in development. […] Partial splitting of the primitive node and streak may result in the formation of conjoined twins. These twins are classified according to the nature and degree of their union. Occasionally, monozygotic twins are connected only by a common skin bridge or by a common liver bridge. The type of twins formed depends on when and to what extent abnormalities of the node and streak occurred. Misexpression of genes, such as goosecoid, may also result in conjoined twins. Goosecoid activates inhibitors of BMP4 and contributes to regulation of head development. Over- or underexpression of this gene in laboratory animals results in severe malformations of the head region, including duplications, similar to some types of conjoined twins.

• #24 Parasitic Twins: Causes, Symptoms, and Treatment

  https://www.webmd.com/baby/what-are-parasitic-twins

  A parasitic twin is a rare condition where a baby is born with an underdeveloped twin attached to its body. […] Because its an extremely rare condition, researchers dont know the exact mechanisms that cause it to appear. But there are two leading theories regarding parasitic twin causes, both relating to the early development of the fetus. […] The first theory suggests that the parasitic twin appears during the early stages of pregnancy, usually at the end of the first two weeks. […] The second theory proposes the inverse mechanism, where the egg successfully separates, but both parts come in contact with each other at a later stage. […] Researchers have also started studying the impact of the Sonic Hedgehog protein (SHH) on the development of parasitic twins. […] Experts suggest that high levels of SHH proteins can lead to parasitic twinning.

• #25 Conjoined Twins: A Worldwide Collaborative Epidemiological Study of the International Clearinghouse for Birth Defects Surveillance and Research

  https://pmc.ncbi.nlm.nih.gov/articles/PMC4457318/

  Genetic and environmental risk factors such as consanguinity, familial aggregation, cytogenetic studies, and maternal exposures, and acute and chronic diseases during pregnancy did not reveal any association with the occurrence of CT, in general, or for any particular type of CT. No familial cases were reported and all karyotypes performed were normal. […] Review of variable total prevalence, variable prevalence by occurrence type, predominance in females, a higher prevalence in some ethnic groups such as Blacks and Chinese, geographic variation, socio-demographic variables, genetic and environmental factors, has not helped to advance the understanding of the altered mechanisms that interrupt the normal separation of an inner cell mass leading to the occurrence of a set of CT. Considering the fission theory as currently accepted, a simple molecular disorder at a deep cellular level distorting cell adhesion or apoptosis in a very early stage of embryogenesis could be involved in a etiology of CT that involves incomplete split of the inner mass cell.

• #26 Conjoined twins – Wikipedia

  https://en.wikipedia.org/wiki/Conjoined_twins

  There are two hypotheses about the development of conjoined twins. A single fertilized egg does not fully split during the process of forming identical twins. If the zygote division occurs after two weeks of the development of the embryonic disc, it results in the formation of conjoined twins. Fusion of two fertilized eggs occurs early in development. […] Partial splitting of the primitive node and streak may result in the formation of conjoined twins. These twins are classified according to the nature and degree of their union. Occasionally, monozygotic twins are connected only by a common skin bridge or by a common liver bridge. The type of twins formed depends on when and to what extent abnormalities of the node and streak occurred. Misexpression of genes, such as goosecoid, may also result in conjoined twins. Goosecoid activates inhibitors of BMP4 and contributes to regulation of head development. Over- or underexpression of this gene in laboratory animals results in severe malformations of the head region, including duplications, similar to some types of conjoined twins.

• #27 Epigastric heteropagus conjoined twins: two case studies and associated DNA analysis | Clinics

  https://www.elsevier.es/en-revista-clinics-22-articulo-epigastric-heteropagus-conjoined-twins-two-S1807593222018336

  Conjoined twins are rarely observed, but heteropagus conjoined twins occur even less frequently. […] The etiology of conjoined twins is complicated. Although monozygotic twins may be induced experimentally following the administration of a variety of teratogenic agents, the mechanism of induction of spontaneous twins remains unknown. […] The mechanism of the spontaneous generation of monozygotic twins is generally considered to derive from an error in blastogenesis by the incomplete fission of a single zygote, which occurs nearly 14 days after fertilization in humans. […] However, Roberto et al. reported a case of heteropagus conjoined twins that originated from the fusion of two embryos, and, along the same lines, Ratan et al. advocated a fusion theory. […] The parents of the patient in case 1 refused permission to perform DNA analysis on the twins, but in case 2, the DNA analysis of the patient indicated that the parasite had a genotype identical to the autosite, which suggested a monozygotic origin. […] The reported incidence of conjoined twins varies between studies. […] Because of the low incidence of heteropagus conjoined twins, statistics on these twins are generally lacking.

• #28 Necropsy of rare bovine conjoined twins – Texas A&M Veterinary Medical Diagnostic Laboratory

  https://tvmdl.tamu.edu/case-studies/necropsy-of-rare-bovine-conjoined-twins/

  Recently, bovine conjoined twin calves were submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL). […] The vast majority of these are considered spontaneous and a cause is seldom identified. Conjoined twins are believed to be the result of partial splitting of a fertilized egg. […] Possible causes could include genetic defects, consumption of teratogenic toxins by the dam, and viral infection.

• #29 List of Drugs that may cause 'Conjoined twins’

  https://www.medindia.net/drugs/side-effects/conjoined-twins.htm

  This page lists all known medications that could potentially lead to 'Conjoined twins’ as a side effect. […] If you’re concerned about 'Conjoined twins’, it is advisable to consult a healthcare professional. […] Clomiphene […] Birth Disorder | Cloacal exstrophy | Foramen ovale patent | Pulmonary hypoplasia

• #30 Parasitic Twin: Causes, Diagnosis & Removal

  https://my.clevelandclinic.org/health/diseases/23513-parasitic-twin

  A parasitic twin is a type of conjoined twin where one fetus stops developing but remains attached to its twin. […] A parasitic twin is a rare condition that happens when a conjoined twin stops developing. […] A parasitic twin happens early in embryonic development, so its organs or limbs can be nearly unrecognizable. […] A parasitic twin is a type of conjoined twin. It accounts for about 10% of all conjoined twins. […] No one is entirely sure, but researchers point to two main theories the fission theory and the fusion theory. […] The fission theory describes an incomplete separation of one fertilized egg. […] A parasitic twin happens when one of the fetuses in a conjoined twin stops developing. […] The fusion theory suggests two separate fertilized eggs grow or fuse together during development.

• #31 Parasitic Twin: Causes, Diagnosis & Removal

  https://my.clevelandclinic.org/health/diseases/23513-parasitic-twin

  A parasitic twin is a type of conjoined twin where one fetus stops developing but remains attached to its twin. […] A parasitic twin is a rare condition that happens when a conjoined twin stops developing. […] A parasitic twin happens early in embryonic development, so its organs or limbs can be nearly unrecognizable. […] A parasitic twin is a type of conjoined twin. It accounts for about 10% of all conjoined twins. […] No one is entirely sure, but researchers point to two main theories the fission theory and the fusion theory. […] The fission theory describes an incomplete separation of one fertilized egg. […] A parasitic twin happens when one of the fetuses in a conjoined twin stops developing. […] The fusion theory suggests two separate fertilized eggs grow or fuse together during development.

• #32 Parasitic Twin: Causes, Diagnosis & Removal

  https://my.clevelandclinic.org/health/diseases/23513-parasitic-twin

  A parasitic twin occurs when one of these two fertilized eggs stops developing but remains attached to its twin. […] Another theory suggests that it occurs due to vascular problems within your uterus during fetal development. […] Parasitic twins are unpreventable. It occurs during fetal development. […] A parasitic twin isn’t alive and dies in the womb while attached to the dominant twin. […] The parasitic twin doesn’t survive the pregnancy. The dominant twin is fully developed and typically survives. […] A parasitic twin is a rare type of conjoined twin. It occurs when a partially formed fetus attaches to another fetus (its twin) very early in development.

• #33 Epigastric heteropagus conjoined twins: two case studies and associated DNA analysis | Clinics

  https://www.elsevier.es/en-revista-clinics-22-articulo-epigastric-heteropagus-conjoined-twins-two-S1807593222018336

  Conjoined twins are rarely observed, but heteropagus conjoined twins occur even less frequently. […] The etiology of conjoined twins is complicated. Although monozygotic twins may be induced experimentally following the administration of a variety of teratogenic agents, the mechanism of induction of spontaneous twins remains unknown. […] The mechanism of the spontaneous generation of monozygotic twins is generally considered to derive from an error in blastogenesis by the incomplete fission of a single zygote, which occurs nearly 14 days after fertilization in humans. […] However, Roberto et al. reported a case of heteropagus conjoined twins that originated from the fusion of two embryos, and, along the same lines, Ratan et al. advocated a fusion theory. […] The parents of the patient in case 1 refused permission to perform DNA analysis on the twins, but in case 2, the DNA analysis of the patient indicated that the parasite had a genotype identical to the autosite, which suggested a monozygotic origin. […] The reported incidence of conjoined twins varies between studies. […] Because of the low incidence of heteropagus conjoined twins, statistics on these twins are generally lacking.

• #34 Biamniotic Parasitic Conjoined Twins with Discordant Genotype

  https://clinmedjournals.org/articles/ogcr/obstetrics-and-gynaecology-cases-reviews-ogcr-5-112.php?jid=ogcr

  As an alternative for the incomplete fission theory a fusion theory was formulated by Spencer, et al. The latter theory is based on the idea that two separate embryonic discs exist in two different amniotic sacs from early on. These two embryonic discs fuse during development forming the diamniotic conjoined twin. The non-mosaic chromosomal discordance would indicate an early separation in the postzygotic stage and supports the fusion theory in our case. […] The occurrence of a biamniotic conjoined twin pregnancy in combination with a discordant genotype was never published so far. This occurrence supports the fusion theory as an etiologic explanation for conjoined twins.

• #35 Biamniotic Parasitic Conjoined Twins with Discordant Genotype

  https://clinmedjournals.org/articles/ogcr/obstetrics-and-gynaecology-cases-reviews-ogcr-5-112.php?jid=ogcr

  As an alternative for the incomplete fission theory a fusion theory was formulated by Spencer, et al. The latter theory is based on the idea that two separate embryonic discs exist in two different amniotic sacs from early on. These two embryonic discs fuse during development forming the diamniotic conjoined twin. The non-mosaic chromosomal discordance would indicate an early separation in the postzygotic stage and supports the fusion theory in our case. […] The occurrence of a biamniotic conjoined twin pregnancy in combination with a discordant genotype was never published so far. This occurrence supports the fusion theory as an etiologic explanation for conjoined twins.

• #36 Conjoined Twins – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK560839/

  Conjoined twins refers to twins that are physically fused in utero and consequently at birth. […] The condition is proposed to result from either fission or fusion. […] The most commonly believed etiology of conjoined twinning is either partial fission or secondary fusion. […] Both of these processes can be used to explain the embryological and anatomical findings observed in conjoined twins. […] However, the fission and fusion theories do not unequivocally account for every possible conjunction and cannot be applied to the full spectrum of findings in conjoined twins. […] It is proposed that non-dorsal conjunction may be initiated by duplication of the axial primordia, which leads to a change in the axial orientation and/or interaction aplasia. […] Dorsal conjunction may occur because of secondary fusion of initially separate monozygotic twins.

• #37 Conjoined Twins: A Worldwide Collaborative Epidemiological Study of the International Clearinghouse for Birth Defects Surveillance and Research

  https://pmc.ncbi.nlm.nih.gov/articles/PMC4457318/

  Conjoined twins (CT) are a very rare developmental accident of uncertain etiology. Prevalence has been previously estimated to be 1 in 50,000 to 1 in 100,000 births. The process by which monozygotic twins do not fully separate but form CT is not well understood. […] Conjoined twins (CT) are a rare embryologic developmental accident of uncertain etiology. Prevalence, although variable, has been estimated to be 1 in 50,000 to 1 in 100,000 births. […] The exact mechanisms of CT remain obscure. […] Currently, it is accepted that CT originate from a failure in the development of primitive structures at later stages of development, that is, Carnegie stage 6 (days 12-15), or the primitive streak stage of human development. […] However, the exact mechanisms of CT remain obscure. […] No genetic, environmental or demographic significant associated factors were identified. Further work in epidemiology and molecular research is necessary to understand the etiology and pathogenesis involved in the development of this fascinating phenomenon of nature.

• #38 Conjoined Twins: A Worldwide Collaborative Epidemiological Study of the International Clearinghouse for Birth Defects Surveillance and Research

  https://pmc.ncbi.nlm.nih.gov/articles/PMC4457318/

  Conjoined twins (CT) are a very rare developmental accident of uncertain etiology. Prevalence has been previously estimated to be 1 in 50,000 to 1 in 100,000 births. The process by which monozygotic twins do not fully separate but form CT is not well understood. […] Conjoined twins (CT) are a rare embryologic developmental accident of uncertain etiology. Prevalence, although variable, has been estimated to be 1 in 50,000 to 1 in 100,000 births. […] The exact mechanisms of CT remain obscure. […] Currently, it is accepted that CT originate from a failure in the development of primitive structures at later stages of development, that is, Carnegie stage 6 (days 12-15), or the primitive streak stage of human development. […] However, the exact mechanisms of CT remain obscure. […] No genetic, environmental or demographic significant associated factors were identified. Further work in epidemiology and molecular research is necessary to understand the etiology and pathogenesis involved in the development of this fascinating phenomenon of nature.

• #39 Conjoined Twins: A Worldwide Collaborative Epidemiological Study of the International Clearinghouse for Birth Defects Surveillance and Research

  https://pmc.ncbi.nlm.nih.gov/articles/PMC4457318/

  Conjoined twins (CT) are a very rare developmental accident of uncertain etiology. Prevalence has been previously estimated to be 1 in 50,000 to 1 in 100,000 births. The process by which monozygotic twins do not fully separate but form CT is not well understood. […] Conjoined twins (CT) are a rare embryologic developmental accident of uncertain etiology. Prevalence, although variable, has been estimated to be 1 in 50,000 to 1 in 100,000 births. […] The exact mechanisms of CT remain obscure. […] Currently, it is accepted that CT originate from a failure in the development of primitive structures at later stages of development, that is, Carnegie stage 6 (days 12-15), or the primitive streak stage of human development. […] However, the exact mechanisms of CT remain obscure. […] No genetic, environmental or demographic significant associated factors were identified. Further work in epidemiology and molecular research is necessary to understand the etiology and pathogenesis involved in the development of this fascinating phenomenon of nature.

• #40 Conjoined Twins: A Worldwide Collaborative Epidemiological Study of the International Clearinghouse for Birth Defects Surveillance and Research

  https://stacks.cdc.gov/view/cdc/33771

  Conjoined twins (CT) are a very rare developmental accident of uncertain etiology. […] The process by which monozygotic twins do not fully separate but form CT is not well understood. […] No genetic, environmental or demographic significant associated factors were identified. […] Further work in epidemiology and molecular research is necessary to understand the etiology and pathogenesis involved in the development of this fascinating phenomenon of nature.

• #41 Phenotypically Discordant Anomalies in Conjoined Twins: Quirks of Nature Governed by Molecular Pathways?

  https://www.mdpi.com/2075-4418/13/22/3427

  The pathogenesis of symmetrical conjoined twins is still disputed but can potentially be etiologized by the formation of two—instead of one—embryonic primordia in a single embryoblast. […] The type, severity and overall morphology of conjoined twins are determined by the original and mutual localization, and potential mutual interactions of the duplicated primordia. […] Although the etiology of concordant concomitant and mirror-image anomalies is still disputed, the focus in this paper lies in discordant anomalies, as they are among the rarest and most elusive phenotypes that can be found in conjoined twins. […] However, focusing on discordant anomalies could potentially give insights into different developmental pathways, as it is a fact that conjoined twins share identical intra-uterine and presumed genetic footprints and thus parallel developmental pathways.

• #42 Phenotypically Discordant Anomalies in Conjoined Twins: Quirks of Nature Governed by Molecular Pathways?

  https://www.mdpi.com/2075-4418/13/22/3427

  The cause of the unilateral appearance of anomalies in conjoined twins is, therefore, one of the biggest questions as to why and how they arose. […] This paper tries to place discordant phenotypes into a broader molecular and developmental perspective in order to shed some hypothetical and philosophical thoughts on the etiology of the anomalies itself but also potentially giving insight into the genesis of conjoined twins itself.

• #43 Phenotypically Discordant Anomalies in Conjoined Twins: Quirks of Nature Governed by Molecular Pathways?

  https://www.mdpi.com/2075-4418/13/22/3427

  The cause of the unilateral appearance of anomalies in conjoined twins is, therefore, one of the biggest questions as to why and how they arose. […] This paper tries to place discordant phenotypes into a broader molecular and developmental perspective in order to shed some hypothetical and philosophical thoughts on the etiology of the anomalies itself but also potentially giving insight into the genesis of conjoined twins itself.

• #44 Conjoined Twins: A Worldwide Collaborative Epidemiological Study of the International Clearinghouse for Birth Defects Surveillance and Research

  https://pmc.ncbi.nlm.nih.gov/articles/PMC4457318/

  Conjoined twins (CT) are a very rare developmental accident of uncertain etiology. Prevalence has been previously estimated to be 1 in 50,000 to 1 in 100,000 births. The process by which monozygotic twins do not fully separate but form CT is not well understood. […] Conjoined twins (CT) are a rare embryologic developmental accident of uncertain etiology. Prevalence, although variable, has been estimated to be 1 in 50,000 to 1 in 100,000 births. […] The exact mechanisms of CT remain obscure. […] Currently, it is accepted that CT originate from a failure in the development of primitive structures at later stages of development, that is, Carnegie stage 6 (days 12-15), or the primitive streak stage of human development. […] However, the exact mechanisms of CT remain obscure. […] No genetic, environmental or demographic significant associated factors were identified. Further work in epidemiology and molecular research is necessary to understand the etiology and pathogenesis involved in the development of this fascinating phenomenon of nature.

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