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Conjoined Twins

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Nathan Tan

on 9 May 2013

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Transcript of Conjoined Twins

Conjoined Twins By Nathan Tan Conjoined Twins Definition Same gender (determined through DNA testing) In the same amniotic cavity and placenta Sharing tissue ranging from band of flesh to major organs " Two babies that are born physically connected to each other." Will always be genetically identical Causes/Risk Factors Genetics Environmental Factors Age/Medical Conditions (note: Causes/Risks that contribute to the formation of conjoined twins are not exactly known/understood) The genetic code is like an instructions manual for building and running things in the our body. Even a small change or abnormality can set off a chain reaction which could result in conjoined twins. Transcription Factors (TFs) stick to a gene and control how often the gene is read. Some TFs called activators make cells make extra proteins. And some TFs called repressors cause cells to make less protein. When TFs don't do it's job(due to mutations in genes), an imbalance of proteins being produced can result in conditions such as polydactyly shown above. Environmental factors are factors that come from external conditions or surroundings that influence living organisms.
It can be anything living or non-living. Notable environmental factors that affect humans include: Stress, physical and mental abuse, diet, exposure to toxins, pathogens, radiation and chemicals. Radiation can severely damage DNA Drugs & Alcohol can affect development of fetuses Lack of nutrients or overload of chemicals
will have negative affects on the fetuses Aging can weaken the body which means a lower ability for a successful pregnancy. This is especially, true for women over 40. The body's reproductive system may not be able to function well enough during pregnancy at such an age, resulting in damage to the pregnant woman and her babies. Certain medical conditions or diseases like STDs may have damaged the reproductive system. Other conditions may also make the body inefficient for the pregnancy like high blood pressure, being overweight, and diabetes. These medical conditions plus age increase the chances of having conjoined twins. Being 40+ yrs old can increase chances of conjoined twins because an older (weakened) body may not be able to support a stable process of twin pregnancy. Certain medical conditions may contribute to forming conjoined twins because they can make the reproductive system inefficient or damaged. STDs like chlamydia and gonorrhea can severely damage a woman's reproductive system which increases the chance of conjoined twins. Part 2 Part 3 Normal Identical Twins Formation Processes of Identical Twinning ( Normal & Conjoined ) Sperm and egg cell meet to become a fertilized egg (also called a zygote). Part 1 The zygote then splits into two separate embryos. What stage at which the cell splits(cleavage) determines how the twins will implant on the uterine lining. Splitting at these two stages are ideal Dangerous for twins because of danger of TTTS and cord entanglement. Splitting beyond 13 days has the highest risk for conjoined twins to occur. Eggs attach to the uterine lining and develop to birth. There are two main theories on how conjoined twins form. Instead of splitting in 1 to 13 days, the zygote tries to split beyond 13 days. This occurs after implantation of egg. However, separation stops before the process can be completed. This results in conjoined twins. The babies develop, but share now share some organs, skin, and bones. The degree to which the egg splits and when the split happens determines how and where the twins will be joined. Part 1 Sperm and egg cell meet to become a fertilized egg (also called a zygote). Part 2 Part 3 Conjoined Twins Fission Theory Around 1-8 days after conception, the embryo splits in the cell stage of either morula or blastocyst. This leads to the formation of conjoined twins. Where the cells join determine what type of conjoined twin will be formed. Part 1 Sperm and egg cell meet to become a fertilized egg (also called a zygote). Part 2 Part 3 Part 4 1-4 days 4-8 days It's unclear which stage this occurs on but the at these early stages the human embryo contains three layers of cells including stem cells. these cells seek out other cells that are alike and bind with them. When newly-separated identical twin embryos lie close to each other, signals get mixed up and cells from one twin binds with the other. Conjoined Twins Fusion Theory Ventral Union I Cephalopagus Cephalothoracopagus Connected at the upper chest to belly. Combination of thoracopagus & omphalopagus. Joined at the xiphoid cartilage (approx navel to the lower breastbone). Joined at the pelvis and can can vary in leg number ( 2, 3, 4 ). Spines are conjoined end-to-end. Ventral Union II Twins joined at the front Twins joined at the front Two faces on opposite sides of a single, conjoined head.
Often called Janus twins after the Roman god. Considered non-viable due to severe malformations of the brain. Bodies are fused in the head and thorax. More likely to be single-faced with enlarged skull, also non-viable. Thoracopagus Connected at upper chest to near the belly. Almost always has a shared heart or conjoined hearts. Omphalopagus Connected at lower chest to the belly area. Often share digestive system & other organs in the area but always have two distinct hearts. Thoraco-omphalopagus Usually share a heart, digestive system, & liver. Xiphopagus Almost never share vital organs, but may likely share liver. Ischiopagus Common to have single external genitalia & external anus. Sometimes genitalia is internal. Omphalo-Ischiopagus Fused at the pelvis like ischiopagus but also face-to-face by connect at abdomen like omphalopagus. This union can also extend upwards towards the chest.
Would add Thoraco-/Xipho- to the name. Connected side-by-side and share a conjoined pelvis. Fused at the abdomen and pelvis but not at the thorax (chest area). United along the thorax, abdomen, and pelvis. However, only one trunk with two heads. Various levels of duplication of the face and brain. Most times is born stillborn. Lateral Union Twins joined side-by-side Parapagus Rarely shares heart by may share the liver, kidneys, and other organs. Dithoracic parapagus Number of arms can vary from 2, 3, to 4 arms. Dicephalic parapagus May share many organs or have two sets of organs. Arms can vary from 2, 3, to 4 arms. Diprosopic parapagus Has single trunk and single head with two faces. Fused on any portion of the skull except the face and base. Joined at the sacral region (near end of spinal cord), so sometimes share that area of spinal cord. Joined along the dorsal aspect but above sacral region. Dorsal union Twins joined at the dorsal aspect (back) Craniopagus Can be joined vertically(show above), occipital (back), forehead, or side of the head. Pygopagus Has one anus, two rectums, four arms, and four legs. Rachipagus Spine maybe joined in some parts. An undeveloped fetus which is encased in the body of it's own twin. Special types Parasitic twin One twin is healthy while the other underdeveloped and is dependent on the healthy twin. Parasitic twin can vary from single extra leg to complete second body. It can be formed in odd places like the back of the head. Having to support the parasitic twin can put a strain on the healthy twin. Fetus in fetu Often presents itself as a cyst. Statistics & Facts I Conjoined twins occur once in every 40,000 births but only once in every 100,000 to 200,000 live births. Around 40%-60% of conjoined twins are stillborn or lost in utero. 35% of conjoined twins die within the first 24 hours. Survival rate is around 5%-25% percent (may be much higher for certain types or non viable). Almost all surviving conjoined twins are female (70%). More likely to occur in India, Africa, and Vietnam. Success of separation depends highly on where the twins are joined and what organs are shared/fused. Parents may have to face the hard choice of either ending or continuing pregnancy. Also, sometimes separation may only leave one survivor. Statistics & Facts II The six most common types are thoracopagus, omphalopagus, parapagus, ischiopagus, pyopagus, and craniopagus. Separation is most successful at the base of the spine while being least successful if it involves the heart. Quality of life as either conjoined or separated depends on the type. Disabilities of mental or physical nature may be present after separation (ex: walking or learning) Great coordination and team work between twins is important. Twins also have distinct personalities. It is possible for conjoined twins to live a normal life and achieve many things like driving and graduating. Notable Conjoined Twins Abigail and Brittany Hensel Born on March 7, 1990 (age 23) Dicephalic parapagus twins Graduated and know how to drive. Lead normal lives and are in good health despite all odds. Have their own show on TLC called "Abby & Brittany" Chang and Eng Bunker Born on May 11, 1811 & died on January 17, 1874(age 62) Born in Carver County, Minnesota Born in Siam (now Thailand). Nicknamed as Siamese twins. Xiphopagus twins Married to Adelaide Yates and Sarah Anne Yates on April 13, 1843. Fathered a total of 21 children, and their descendants - including several sets of non-conjoined twins - now number more than 1,500. Chang died of a stroke and Eng died shortly after before being able to get separation surgery.
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