CausesThere 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. If the zygote division occurs after 2 weeks of the development of the embryonic disc, it results in the formation of conjoined twins. The second theory is that a fusion of two fertilized eggs occurs earlier in development. Partial splitting of the primitive node and streak may result in 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.
TypesConjoined twins are typically classified by the point at which their bodies are joined. The most common types of conjoined twins are: * ''Thoraco-omphalopagus'' (28% of cases): Two bodies fused from the upper chest to the lower chest. These twins usually share a heart, and may also share the * '' Thoracopagus'' (18.5%): Two bodies fused from the upper chest to lower belly. The heart is always involved in these cases. , separation of a genuinely shared heart has not offered survival to two twins; a designated twin may survive if allotted the heart, sacrificing the other twin. * ''Omphalopagus'' (10%): Two bodies fused at the lower abdomen. Unlike thoracopagus, the heart is never involved in these cases; however, the twins often share a * Parasitic twins (10%): Twins that are asymmetrically conjoined, resulting in one twin that is small, less formed, and dependent on the larger twin for survival. * ''Craniopagus twins, Craniopagus'' (6%): Fused human skull, skulls, but separate bodies. These twins can be conjoined at the back of the head, the front of the head, or the side of the head, but not on the face or the base of the skull. Other, less common types of conjoined twins include: * ''Cephalopagus'': Two faces on opposite sides of a single, conjoined head; the upper portion of the body is fused while the bottom portions are separate. These twins generally cannot survive due to severe malformations of the brain. Also known as janiceps (after the two-faced Roman deity Janus (mythology), Janus) or syncephalus. * ''Syncephalus'': One head with a single face but four ears, and two bodies. * ''Cephalothoracopagus'': Bodies fused in the head and thorax. In this type of twins, there are two faces facing in opposite directions, or sometimes a single face and an enlarged skull. * ''Xiphopagus'': Two bodies fused in the Xiphoid process, xiphoid cartilage, which is approximately from the navel to the lower breastbone. These twins almost never share any vital organs, with the exception of the liver. A famous example is Chang and Eng Bunker. * ''Ischiopagi, Ischiopagus'': Fused lower half of the two bodies, with Vertebral column, spines conjoined end-to-end at a 180° angle. These twins have four arms; one, two, three or four legs; and typically one external set of genitalia and anus. * ''Omphalo-Ischiopagus'': Fused in a similar fashion to ischiopagus twins, but facing each other with a joined abdomen akin to omphalopagus. These twins have four arms, and two, three, or four legs. * ''Parapagus'': Fused side by side with a shared human pelvis, pelvis. Twins that are ''dithoracic parapagus'' are fused at the abdomen and pelvis, but not the thorax. Twins that are ''diprosopic parapagus'' have one trunk and two faces. Twins that are ''dicephalic parapagus'' have one trunk and two heads, and have two (dibrachius), three (tribrachius), or four (tetrabrachius) arms. * ''Craniopagus parasiticus'': Like craniopagus, but with a second bodiless head attached to the dominant head. * ''Pygopagus'' or ''Iliopagus'': Two bodies joined at the human pelvis, pelvis. * ''Rachipagus'': Twins joined along the back of their bodies, with fusion of the vertebral arches and the soft tissue from the head to the buttocks
SeparationSurgery to separate conjoined twins may range from very easy to very difficult depending on the point of attachment and the internal parts that are shared. Most cases of separation are extremely risky and life-threatening. In many cases, the surgery results in the death of one or both of the twins, particularly if they are joined at the head or share a vital organ. This makes the ethics of surgical separation, where the twins can survive if not separated, contentious. Alice Dreger of Northwestern University found the quality of life of twins who remain conjoined to be higher than is commonly supposed. Lori and George Schappell and Abby and Brittany Hensel are notable examples. The first record of separating conjoined twins took place in the Byzantine Empire in the 900s. One of the conjoined twins had already died, so the doctors of the town attempted to separate the dead twin from the surviving twin. The result was partly successful as the remaining twin lived for three days after separation. The next case of separating conjoined twins was recorded in 1689 in Germany several centuries later. The first recorded successful separation of conjoined twins was performed in 1689 by Johannes Fatio. In 1955, neurosurgeon Harold Voris (1902-1980) and his team at Mercy Hospital and Medical Center, Mercy Hospital in Chicago performed the first successful operation to separate craniopagus twins (conjoined at the head), which resulted in long-term survival for both. The larger girl was reported in 1963 as developing normally, but the smaller was permanently impaired. In 1957, Bertram Katz and his surgical team made international medical history performing the world's first successful separation of conjoined twins sharing a vital organ. Omphalopagus twins John Nelson and James Edward Freeman (Johnny and Jimmy) were born in Youngstown, Ohio, on April 27, 1956. The boys shared a liver but had separate hearts and were successfully separated at North Side Hospital in Youngstown, Ohio, by Bertram Katz. The operation was funded by the Ohio Crippled Children's Service Society. Recent successful separations of conjoined twins include that of the separation of Ganga & Jamuna Shreshta, Ganga and Jamuna Shreshta in 2001, who were born in Kathmandu, Nepal, in 2000. The 97-hour surgery on the pair of craniopagus twins was a landmark one which took place in Singapore; the team was led by neurosurgeons Chumpon Chan and Keith Goh. The surgery left Ganga with brain damage and Jamuna unable to walk. Seven years later, Ganga Shrestha died at the Model Hospital in Kathmandu in July 2009, at the age of eight, three days after being admitted for treatment of a severe chest infection. Infants Rose and Grace Attard, conjoined twins from Malta, were separated in Great Britain by court order ''Re A (Children) (Conjoined Twins: Surgical Separation), Re A'' over the religious objections of their parents, Michaelangelo and Rina Attard. The twins were attached at the lower abdomen and spine. The surgery took place in November 2000, at Saint Mary's Hospital, Manchester, St Mary's Hospital in Manchester. The operation was controversial because Rose, the weaker twin, would die as a result of the procedure as her heart and lungs were dependent upon Grace's. However, if the operation had not taken place, it was certain that both twins would die. Grace survived to enjoy a normal childhood. In 2003, two 29-year-old women from Iran, Ladan and Laleh Bijani, who were joined at the head but had separate brains (craniopagus) were surgically separated in Singapore, despite surgeons' warnings that the operation could be fatal to one or both. Their complex case was accepted only because technologically advanced graphical imagery and modelling would allow the medical team to plan the risky surgery. However, an undetected major vein hidden from the scans was discovered during the operation. The separation was completed but both women died while still in surgery. In 2019 Safa and Marwa Ullah were separated at Great Ormond Street Hospital in London, England. The twins, born January 2017 were joined at the top of the head with separate brains and a cylindrical shared skull with the twins each facing in opposite directions to one another. The surgery was jointly led by neurosurgeon Owase Jeelani and plastic surgeon Professor David Dunaway. The surgery presented particular difficulties due to a number of shared veins and a distortion in the shape of the girls brains, causing them to overlap. The distortion would need to be corrected in order for the separation to go ahead. The surgery utilized a team of more than 100 including bio engineers, 3D modelers and a virtual reality designer. The separation was completed in February 2019 following a total of 52 hours of surgery over three separate operations. As of July 2019 both girls remain healthy and the family plans to return to their home in Pakistan in 2020.
History'' (1493) ceramics depicting conjoined twins. 300 CE Larco Museum, Larco Museum Collection Lima, Peru The Moche (culture), Moche culture of ancient Peru depicted conjoined twins in their ceramics dating back to 300 CE. Writing around 415 CE, Augustine of Hippo, St. Augustine of Hippo, in his book, ''City of God (book), City of God'', refers to a man "double in his upper, but single in his lower half--having two heads, two chests, four hands, but one body and two feet like an ordinary man." According to Theophanes the Confessor, a Byzantine historian of the 9th century, around 385/386 CE, "in the village of Emmaus in Palestine (region), Palestine, a child was born perfectly normal below the navel but divided above it, so that it had two chests and two heads, each possessing the senses. One would eat and drink but the other did not eat; one would sleep but the other stayed awake. There were times when they played with each other, when both cried and hit each other. They lived for a little over two years. One died while the other lived for another four days and it, too, died." In Arabia, the twin brothers Hashim ibn Abd Manaf and 'Abd Shams were born with Hashim's leg attached to his twin brother's head. Legend says that their father, Abd Manaf ibn Qusai, separated his conjoined sons with a sword and that some priests believed that the blood that had flowed between them signified wars between their progeny (confrontations did occur between Banu al'Abbas and Banu Ummaya ibn 'Abd Shams in the year 750 AH).The Life of the Prophet Muhammad: Al-Sira Al-Nabawiyya By Ibn Kathir, Trevor Le Gassick, Muneer Fareed, pg. 132 The Muslim polymath Abū al-Rayhān al-Bīrūnī described conjoined twins in his book ''Kitab-al-Saidana''.A. Zahoor (1997)
Born 19th century and earlier*Mary and Eliza Chulkhurst, alleged names of the Biddenden Maids (per tradition, born in the 12th century) of Kent, England. They are the earliest set of conjoined twins whose names are (purportedly) known. *Lazarus and Joannes Baptista Colloredo (1617–1646?) Parasitic twin, autosite-and-parasite pair *Helen and Judith of Szony (Hungary, 1701–1723) pygopagus * Chang and Eng Bunker (1811–1874), from Thailand (formerly Rattanakosin Kingdom, Siam), joined by the areas around their xiphoid process, xiphoid cartilages, but over time, the join stretched; the expression ''Siamese twins'' is derived from their case *Millie and Christine McCoy (July 11, 1851 – October 8, 1912) American conjoined twins who went by the stage names "The Two-Headed Nightingale" and "The Eighth Wonder of the World." (oblique pygopagus) *Giacomo and Giovanni Battista Tocci (1875?–1912?) (dicephalus tetrabrachius dipus)
Born 20th century*Daisy and Violet Hilton of Brighton, East Sussex, Brighton, England (1908–1969), actresses, appeared in the movies ''Freaks (1932 film), Freaks'' and ''Chained for Life''. Pygopagus. *Lucio and Simplicio Godina of Samar, Philippines (1908–1936) *Masha and Dasha Krivoshlyapova of Moscow, Russia (1950–2003), rarest form of conjoined twins, one of few cases of dicephalus tetrabrachius tripus (two heads, four arms, three legs) *Ronnie and Donnie Galyon of Ohio (1951–July 4, 2020), omphalopagus *Tjitske and Folkje de Vries of Mûnein, Netherlands (b. 1953) *Wariboko and Tamunotonye Davies born 25 July 1953 in Kano, Nigeria. Separated in London by team led by Ian Aird. Tamunotonye died postoperatively. Wariboko became a nurse. *Lori and George Schappell born September 18, 1961, in Reading, Pennsylvania, American entertainers, craniopagus *Spider Girls, Ganga and Jamuna Mondal of India, born 1969 or 1970, known professionally as The Spider Girls and The Spider Sisters. Ischiopagus. *Anna and Barbara Rozycki (born 1970), the first conjoined twins successfully separated. * Ma Nan Soe and Ma Nan San (born 1971 in Myanmar), separated in July 1971 at Yangon Pediatric Hospital. They were joined from chest to belly button. Ma Nan San died after one month and seven days after operation. *Elisa and Lisa Hansen, Ogden, Utah. Born by Caesarean section on 18 October 1977, were conjoined at the top of their head (craniopagus). They were separated 1979 after 16 hour surgery, were first to both survive surgery. *Ladan and Laleh Bijani of Shiraz, Iran (1974–2003); died during separation surgery in Singapore. Craniopagus. * Baby Girl A and Baby Girl B (born 1977 in New Jersey) shared a single six-chambered heart. Separation surgery, led by C. Everett Koop, involved the instant death of Baby Girl A; the difficult ethical and religious concerns generated significant local newspaper coverage. Baby Girl B survived for 6 months. *Viet and Duc Nguyen, born on February 25, 1981, in Kon Tum Province, Vietnam, and separated in 1988 in Ho Chi Minh City. Viet died on October 6, 2007. Ischiopagus. *Maria and Consolata Mwakikuti of Tanzania (1986?–2018); conjoined by the abdomen; died of respiratory problems resulting from an abnormal, inoperable chest deformity. *Patrick and Benjamin Binder, separated in 1987 by team of doctors led by Ben Carson. Craniopagus. *Andrew and Alex Olson, born in 1987, separated in April 1988 at the University of Nebraska Medical Center. Omphalopagus. * Katie and Eilish Holton, born August 1988 in Ireland *Abby and Brittany Hensel, Abigail and Brittany Hensel are dicephalus, dicephalic parapagus twins born on March 7, 1990 in Carver County, Minnesota. Both graduated in 2012 from Bethel University (Minnesota), Bethel University, St. Paul, hired as teachers. *Tiesha and Iesha Turner (born 1991 in Texas) separated in 1992 at Texas Children's Hospital in Houston, Texas. Omphalopagus. *Ashley and Ashil Fokeer, born on 2 November 1992 in Mauritius *Joseph and Luka Banda (born January 23, 1997, in Zambia) separated in 1997 in South Africa by Ben Carson (with a later intervention in 2001 to artificially close their skulls). Craniopagus. *Carmen and Lupita Andrade were born in June 2000 in Veracruz, Mexico. They later moved to the United States for healthcare with their parents.
Born 21st century*Carl and Clarence Aguirre, born with vertical craniopagus in Silay City, Negros Occidental, on April 21, 2002. They were successfully separated on August 4, 2004. *Tabea and Lea Block, from Lemgo, Germany, were born as craniopagus twins joined on the tops of their heads on August 9, 2003. The girls shared some major veins, but their brains were separate. They were separated on September 16, 2004, although Tabea died about 90 minutes later. *Anastasia and Tatiana Dogaru born outside Rome of Lazio, Italy, on January 13, 2004. As craniopagus twins, the top of Tatiana's head is attached to the back of Anastasias's head. *Lakshmi Tatma (born 2005) was an ischiopagus conjoined twin born in Araria district in the state of Bihar, India. She had four arms and four legs, resulting from a joining at the pelvis with a headless undeveloped parasitic twin. * On 2005 a set of conjoined triplets was detected, characterized as tricephalus, tetrabrachius, and tetrapus parapagothoracopagus, and the pregnancy interrupted at 22 weeks. * Kendra and Maliyah Herrin, ischiopagus twins separated in 2006 at age 4 *Krista and Tatiana Hogan, Canadians, Canadian twins conjoined at the head. Born October 25, 2006. Share part of their brain and can pass sensory information and thoughts between each other. * Moira Kelly, AO#Twins, Trishna and Krishna from Bangladesh were born in December 2006. They are craniopagus twins, joined on the tops of their skulls and sharing a small amount of brain tissue. In 2009, they were separated in Melbourne, Australia. *Maria and Teresa Tapia, born in the Dominican Republic on April 8, 2010. Conjoined by the liver, pancreas, and a small portion of their small intestine. Separation occurred on November 7, 2011 at Children's Hospital of Richmond at VCU. * Aung Myat Kyaw and Aung Khant Kyaw (born in May 2011, Mandalay, Myanmar) connected at pelvis. *Jesus and Emanuel de Nazaré are dicephalus, dicephalic parapagus twins born in Pará, Brazil on December 19, 2011. *Zheng Han Wei and Zheng Han Jing, born in China on August 11, 2013. Conjoined by their sternum, pericardium, and liver. In 2014, they were separated in Shanghai, China, at the Shanghai Children's Medical Center. *Asa and Eli Hamby were born in 2014 in Georgia (U.S. state), Georgia but died less than two days after birth due to heart failure. The twins were Dicephalic parapagus twins, dicephalic parapagus having two heads but being conjoined at the torso, arms and legs. They had separate spinal columns but one heart making postnatal operations impossible. *Jadon and Anias McDonald, born in September 2015. Conjoined by the head. Successfully separated at Children's Hospital of Montefiore Medical Center by James T. Goodrich in October 2016. *Erin and Abby Delaney, born in Philadelphia, Pennsylvania USA on July 24, 2016. Conjoined by the head. They were successfully separated at Children's Hospital of Philadelphia on June 16, 2017. *Marieme and Ndeye Ndiaye, twin girls born in Senegal in 2017, living in Cardiff, UK in 2019 *Safa and Mara Bibi, twin girls born in Hayatabad, Pakistan on January 17, 2017, coinjoined by the head. Successfully separated at Great Ormond Street Hospital in February 2019. *Callie and Carter Torres, born 30 January 2017 in Houston Texas, from Blackfoot Idaho. They are Ischiopagi, Omphalo-Ischiopgagus conjoined twins, attached by their pelvic area and sharing all organs from the belly button down with just one leg each. *Yiḡit and Derman Evrensel, twin boys born on 21 June 2018, Antalya, Turkey. They are Craniophagus twins and were separated at Great Ormond Street Hospital in 2019 by the same surgeons that separated Safa and Mara Bibi. *Ervina and Prefina, born June 29, 2018 in the Central African Republic. They were separated on June 5, 2020 at the Bambino Gesù Pediatric Hospital in Rome, Italy. *Mercy and Goodness Ede, born August 13, 2019, conjoined by the chest and abdomen. Successfully separated at the National Hospital in Abuja, Nigeria in November 2019. *Marie Cléa and Marie Cléanne Papillon, born in Mauritius in 2019
In fiction* Alone (2007 film), ''Alone'', Thai horror film about Pim and Ploy life. * ''Sisters (1973 film), Blood Sisters'' focuses on a French Canadian model who has a separated conjoined twin. * ''Tarot: Witch of the Black Rose'' graphic novel debut the ghost twin, She/they are constant companion(s) of Skeleton Man, her protector. * ''Reiko the Zombie Shop'', 1990s woman horror manga, bonus chapters focus on unexpectedly life of Noriko and her "sister". Summoners Dr. Zero can resurrect and control fuse zombies called medicinal death. * In the TV series ''The Addams Family (1964 TV series), The Addams Family'', there are extended family members of the Addams Family who are mentioned to have two heads. In "Mother Lurch Visits the Addams Family," Morticia Addams mentions that she has a Cousin Slimy who has two good heads on his shoulder. In "Progress and the Addams Family," Morticia was making a knitted hat for Cousin Plato where Gomez Addams has stated that his left head is size 6 and his right head is size 8 3/4. In "Lurch's Little Helper," Morticia made a portrait of Cousin Crimp who has a male head and a female head. * Tamil language, Tamil actor Suriya portrays Vimalan and Akilan, conjoined twins in the 2012 film, ''Maattrraan''. * The book ''The Girls (Lansens novel), The Girls'', by Canadian novelist Lori Lansens, published in 2005, is the fictional autobiography of Canadian craniopagus twins Rose and Ruby Darlen with Slovakian background. * Irish author Sarah Crossan won the Carnegie Medal (literary award), Carnegie Medal for her verse novel, One (Crossan novel), ''One''. The story follows the life and survival of conjoined twin sisters. The book also won ''The Bookseller''
See also* Medical law * Monoamniotic twins * Polycephaly