Twins: And What They Tell Us About Who We Are (15 page)

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Authors: Lawrence Wright

Tags: #Family & Relationships, #Siblings, #Science, #Life Sciences, #Genetics & Genomics, #test

BOOK: Twins: And What They Tell Us About Who We Are
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two of them were kissing as clear as day. Among multiples, there is intrauterine life. They do fight. They do kiss."
There is considerable evidence that when one twin dies the survivor can suffer lifelong feelings of guilt. The loss may be felt most deeply by those whose twin died at birth or shortly afterward. Elvis Presley's twin brother, Jesse, was stillborn, a deeply affecting event in Elvis's life; one has to wonder how American popular culture might have been different had his twin survived. Elizabeth Bryan, who is director of the Multiple Births Foundation in London, set up the Lone Twin Network to provide support for survivors coping with their grief. She says, "I've met quite a number of people who only discovered their twin was stillbornthat is, they only discovered that they were a twin at allat some adult occasion such as they were about to get married, or their first child was on the way, and their mother suddenly said, 'Your twin died and I never told you.' Several of them said that the news came as a profound relief. For the first time they understood the loss they had felt all their lives. Of course, one could argue that their loss could be explained by being brought up by bereaved parents who were hiding something." Lately Bryan reports seeing a number of people who claim to be survivors of vanished twins. Already, as one might have guessed, there are psychotherapies designed to regress patients into the womb so that they can get in touch with their vanished twin. Elizabeth Noble, founder of the Maternal and Child Health Center in Cambridge, Massachusetts, and author of
Having Twins
, underwent primal therapy in Australia and claims to have discovered that her interest in twins came from being a surviving twin. "To this day I hold a clear image and feeling of a disappearing embryo," she writes. She has now written a memoir of
 
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her intrauterine life called
Inside Experiences: From Conception through Birth
.
David Teplica, a plastic surgeon in Chicago, also has come to believe that he might be the survivor of a twin pair, although he tells his story with evident embarrassment. "It just seems so
National Enquirer
'Doctor Searches for Dead Twin,'" says Teplica, who is also an acclaimed photographer. "It's been since my early teens that I was obsessed with the idea of twinning. I would read everything about twins. I started photographing twins in about 1988. At first it was not an obsession, it was just fun." He got to know Louis Keith and his identical twin, Donald, who is a defense contractor in Washington. Through them he turned his hobby into a more formal project. The following year, he went with the Keiths to the annual twin festival in Twinsburg, Ohio. "It was incrediblefor the first couple of hours. Perhaps if you're a twin, it's incredible for a couple of days. You very quickly start feeling like you're alone. It's weird. Of course, it's a gold mine for researchers, but after a while I thought, Boy, I'm just a singleton."
Since then, Teplica has compiled an archive of approximately 6,000 twin portraits, while conducting his own twin study. As a plastic surgeon, he is professionally interested in the aesthetics of the human face. In every twin pair, one is usually considered more attractive than the other. (How that could be is a fascinating subject in itself. Because of their genetic identity, the nuances that make twins look different must be largely environmental in originfor instance, subtle differences in fetal development and the birth process.) By having students pick the more attractive twin from various pairs of photos, Teplica hopes to measure the anatomic variances that make up the standards of beauty. "There have been fascinating things that have come up as a part of the
 
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whole process of collecting these images," he says. "It's now clear to me that almost all secondary skin characteristics on the head and face, and probably elsewhere, are genetically predetermined. For example, freckle patterns, hair whorls, the first gray hairs, the first wrinkles on the human face, even the development of acne on the same location on the nose at exactly the same timeall these things seem to be in some way genetically predetermined. It's frightening. Why else would two identical twins from upstate New York get exactly the same three little crow's-feet at the corners of the eyes? Why would two women from Texas develop basal-cell carcinoma in exactly the same spot on their left ears within a year of each other? Why would two young men from Ohio have the same extra hairs on their cheeks and the same cupped-ear deformities? How can it be that two cell clusters that were separated fifty years ago have enough information to determine where your blackheads would develop when you are fifty or sixty years old? It's really very scary."
After a year or so of Teplica's collaboration with the Keith twins, Donald Keith asked him, "David, why are you so fascinated with twins? Maybe you
are
one."
Teplica laughed. "Donald, I'm
not
a twin," he responded.
But the next time his mother came to visit, Teplica asked if there was any chance that he was a twin. "She turned white," he recalls. "She paused, and said, 'David, I'd never thought you'd hear this.' She proceeded to tell me how she had tried to get pregnant for many years, and when she finally became pregnant she was so large, put on so much weight so quickly, that her physician told her she would be delivering twins. But then in the fourth month, she had some cramping, passed some tissue, had some bleeding, was put on bed
 
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rest, and delivered only me. Now, that was before the days of ultrasound, but every indication was that she did have a twin pregnancy."
Charles Boklage believes that most malformed children who were born as singletons actually may be the products of twin pregnancies. This may also be true of left-handers, who are more common among twins.
*
He cites another interesting phenomenon, which, although it has rarely been detected, may not be at all uncommon. "It is possible that I am twins. By that I mean that two different embryos went together to make one body. We know that occasionally happens, but it is almost never detected except in blood banks. I think it is actually much more common than that. I can tell you with complete certainty that some of us are twins who are walking around in a single body." Such a creature is called a chimera, after the mythological Greek monster that had the head of a lion, the body of a goat, and the tail of a serpent. Chimeras are easily produced in the laboratory. "We've had thousands of experiments with rats and mice in which we take part of a mouse embryo and stick it in a rat embryo," says Boklage. "We've done it between sexes and between species. They never make twins. They always fuse into single embryos and come out part rat, part mouse; part male, part female; part sheep, part goat. The forces involved in embryogenesis simply overpower the differences in their origins. I'm sure there are creatures too far apart to put together, like a mouse and a chicken. But when these events occur in human development, it simply goes on." Chimeras sometimes happen in nature when littermates
*
Interestingly, the voodoo culture anticipated the vanishing twin idea long before it became a subject of legitimate scientific interest. In Haiti a child is counted as a "twin" if he is born with webbed fingers, a sign, it is believed, that he has "eaten" his sibling in the womb.
 
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fuse together. The fact that this happens in humans was only discovered when donors in blood banks were found to be carrying two different blood types; it could mean that fraternal twins merged in the womb. Most human chimeras are to some extent hermaphrodites, with ambiguous genitalia. Of course, there is no way to discover if identical twins have merged, since their genes and blood types are the same. In these cases, the twins don't vanish, they amalgamate.
When an infant twin girl, a year and a half old, recently appeared in the Department of Pediatrics at the British Columbia Children's Hospital in Vancouver suffering from chronic lung infections, Judith Hall routinely checked for cystic fibrosis. By analyzing the chloride level in her sweat, Dr. Hall got a positive diagnosis. "We then decided it was time to check the twin," says Hall. As it happens, when these twins were born their obstetrician carefully examined the membranes of the placenta to determine their zygosity. There was a single chorionic sac, so the doctor assumed that the girls must be identical. And yet, when Hall tested the eighteen-month-old twin for cystic fibrosis, there was no sign of the disease. "We then decided to do blood studies, looking for common mutations that occur in cystic fibrosisand they weren't there in
either
twin! So we scratched our heads. We then decided to take a bit of skin, and when we did that, the kid with cystic fibrosis had the common mutations and the other didn't." This was a terrific muddle. The other twin was not even a carrier of cystic fibrosisno evidence of the gene at all. DNA tests showed that the girls were not, in fact, MZ twins. Apparently they were the result of two separate acts of conception, but the zygotes implanted so close to each other in the uterus that the placentas fused. Further testing showed that the diseased twin was carrying
 
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the blood of the healthy twin. They had evidently shared the same circulation in the womb, which is common among identicals, but rare among fraternals. "They were two separate creatures, but they shared their blood in the placenta at such an early age that one twin actually took over for the abnormal twin, so its blood was healthy but the rest of its body had cystic fibrosis," says Hall. "That's a chimera."
There does seem to be a connection between birth defects and twinning, but researchers still disagree as to which causes the other and whether the defects are confined mainly to identicals or are characteristic of both kinds of twins. Of course, it could also be true that twinning and birth defects are both caused by some other trait. The malformations most often associated with twins are heart defects, spina bifida, and cystic fibrosis. Boklage has observed that these same malformations are also found at a higher rate than expected in their non-twin siblings and offspring. But the same is true for left-handedness: thirty-five percent of identical twins are left-handed, double the rate of the general population. To add to the mystery, this association of twins, left-handedness, and malformations of other non-twin family members is just as true for fraternal as for identical twins. And yet the most fundamental proposition of twin science is that fraternal and identical twinning are entirely separate processes. Fraternal twins are supposed to happen when two eggs are separately fertilized. They can be conceived at different times during the same menstrual cycle and even by different fathers, which leads to the occasional situation where there are twins of different racial or ethnic origin. Some fraternal twins are so different in their birth weight that it is possible they were conceived during different menstrual cycles. Identical twins happen when a single egg is fer-
 
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tilized, then in the course of the development the zygote divides. The process of fraternal twinning, on the other hand, is not supposed to have anything to do with splitting. Genetically, DZ twins are assumed to be no more alike than ordinary siblings who are born separately. These suppositions are at the heart of twin studies. If, as Boklage was suggesting, the two forms of twinning have something in common, and if both kinds of twins were more like each other than they were like singletons, then the thousands of twin studies that seek to determine which traits are inherited and which are environmental would be called into question.
Boklage decided to do a study on twins' teeth. "I took the teeth as a way to ask questions about building a head," he says. "The teeth are a subsystem of the head. Bike a brain, teeth grow in a highly coordinated fashion between the left and right halves, and they come from the same top layer of the embryo as the whole nervous system. Back when the embryo was a flat disc, they were in the same cells as the future brain. I first found that the teeth of identical and fraternal twins were differentthey were so different I could tell you whether an individual came from an identical twin pair without seeing the other twin. When I first started doing that, I thought fraternal twins were ordinary people." Twins' teeth were on the whole less regular and symmetrical than the teeth of singletons, and the teeth of identical twins were less regular than those of fraternals. The differences in dentition suggest to Boklage that there might be other differences between twins and singletons as well. "The simple fact is we have never known enough about twins and twinning to do such studies right," he says. For instance, there might be a third type of twinning, in which fraternal twins derive from a

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