Chimeras: Transplants, Failed Paternity Tests, and Spider Goats
Mother-Child DNA Mismatch: A Case in Boston
When Karen Keegan needed a kidney transplant, her family rushed to her aid. Keegan had three sons who volunteered to donate a kidney, if only their tissue was a “match” for Karen. Tissue matches are more likely to occur among close relatives, so at least one of Karen’s children was likely to match her tissue type and become a kidney donor. To the Keegan family’s surprise, two of the children had shocking genetic test results. The boys were not a match, and they were also not Karen’s biological sons. Considering Karen Keegan had given birth to all three children, the test results made absolutely no sense. Karen was a beloved teacher working in Boston, and the 1998 medical case caused quite a stir.
Chimeras vs. Mosaicism
Welfare Fraud and False Accusations: When Genetic Testing Goes Wrong
Across the country, in Washington state, another genetic testing drama was unfolding. Welfare fraud occurs frequently in the United States, and states have taken steps to reduce and prevent the abuse of our public welfare system. These measures include genetic testing for those claiming dependents (and thus more money) from the system – if the children are not deemed to be the biological offspring of the applicant, the applicant may lose welfare benefits or be taken to court for fraud.
Such was the case of Lydia Fairchild, who was in an unfortunate financial situation when she applied for welfare for her family. Recently separated from her partner, she took the children in for the required genetic testing to prove that he was, indeed, the biological father of all three children. The DNA tests returned and confirmed that Jamie Townsend was the biological father of all three children.
In a shocking twist, however, the genetic testing showed that Lydia Fairchild was not the children’s mother.
Lydia Fairchild was confused, as she had given birth to all three children (indeed, she was pregnant with her third child as her separation from Jamie Townsend was occurring). Fairchild was accused of welfare fraud and her two older children were taken from her. Her "older" children were only 3 and 4 years old at the time they were forcibly removed from their mother, their births judged as forgeries. Lydia was still pregnant with her third child, and a court-ordered witness was present at the birth as blood was drawn for genetic testing on the third child. This child also had no biological relationship with Fairchild.
The prosecution in the case was relentless, and the court paid no attention to hospital medical records in the case of Fairchild’s older two children. Lydia Fairchild was accused of welfare fraud by using another person’s child (the original premise was through surrogacy, though no medical records of surrogacy existed in the Fairchild case). Genetic testing was considered the “gold standard,” and even Fairchild’s obstetrician was disregarded under the premise that DNA evidence could not tell a lie.
Two Cases Collide: How a Transplant Recipient Solved the Fairchild Case
Lydia’s attorneys were doing a lot of research into problems with genetic paternity testing, and came across the Karen Keegan case. Fortunately, by this point in time, the Keegan case had been closed and the puzzle was solved.
Fortunately for Karen Keegan, the medical doctors involved decided to do an investigation to discover the reason for the genetic mismatch. Karen had a thyroid nodule removed a few years prior, and this tissue was frozen and saved by a nearby lab. Doctors did some testing on the thyroid tissue and discovered that while Karen’s blood did not match the DNA of two of her sons, the thyroid tissue did match their DNA.
After further investigation, doctors realized that Karen Keegan carried two completely different sets of DNA within her body. Some tissues carried one set of genetic material, and other tissues carried a completely different genetic code.
Upon finding this rare case, further testing was immediately ordered on Lydia Fairchild. While Fairchild’s blood did not match her children’s genetic code, tissue from her cervix did match. Lydia Fairchild also carried two completely different genetic codes within her body.
Upon finding this evidence, the case was finally dismissed by the judge and Lydia Fairchild managed to put her family back together. If it wasn't for the Keegan case in Boston, however, her children might have been removed from her custody – permanently.
Blastocysts Are Pluripotent
The Process of Creating Chimeric Mice
Carrying More Than One Genetic Code: Chimeras
How in the world does one person carry more than one genetic code? The answer lies very early in embryonic development.
When an egg is fertilized, it is termed a zygote – and that zygote quickly divides. When it divides into approximately 100 cells, it turns into a hollow spherical form called a blastocyst. The internal cells of a blastocyst are not yet differentiated, and can become any tissue or structure. These cells are called “pluripotent” because they can give rise to any sort of tissue. (insert picture of blastocyst)
If two eggs are released at the time of fertilization, two zygotes would be obtained. In most cases, this simply causes fraternal twins – while fraternal twins share a uterus, they do not share a genetic code. Their DNA is as different as any two siblings.
In very rare circumstances, however, the two different zygotes develop into blastocysts… and then merge. The cells at this stage are undifferentiated, and so the blastocysts simply become one entity and continue developing as normal – creating one child instead of two. The resulting person is entirely healthy, but contains two different strains of DNA. The DNA in any specific tissue will reflect the cell in the blastocyst that gave rise to it.
For example, the liver cells may all contain one genetic code, while the cells in the blood carry different genetic material.
The result of this embryonic fusion is dubbed a “Chimera,” from the Greek creature which had the head of a lion, the body of a goat, and a tail with a snake’s head on the end. Of course, genetic chimeras do not give rise to such obvious physical characteristics as the mythical one, but scientists are putting chimeras to use in the lab.
Sheep + Goat = Chimeric Geep
In the 1980’s, a man named W.H. Dixon created the first geep – an animal that appeared to be a hybrid between a goat and a sheep. geep are unlikely to occur in nature, as goats and sheep have a different number of chromosomes and the fetuses generally perish before birth. There are some (rare) natural hybrids, and all of these are sterile.
Dixon’s geep were created in the laboratory, as chimeras. He fused the blastocysts of a sheep and a goat, which developed into a healthy animal containing the genetic traits of both creatures. Some geep tend to appear goat-like in nature, but have wool. Others appear sheep-like in nature, but have the angora fur of a goat.
Unlike traditional hybrids (like mules), geep chimeras are always fertile – though the offspring will be entirely goat or entirely sheep, depending on which species the geep’s reproductive tract originated from.
Combining a sheep and a goat may not seem that radical, but other interesting (and surprisingly useful) chimeras have been created to produce materials that are difficult to grow in traditional ways.
The BioSteel Spider Goats
BioSteel®: The Rise of the Spider Goat
Spider silk is amazingly strong – and its properties would make an excellent material for defense (very light bullet-proof vests) and medicine (sutures that hold a knot better than nylon). Spider silk is so unbelievably strong that a strand as thick as a man’s thumb could support a fully loaded passenger plane. The problem is in the production: a great quantity of spider silk would be required to produce the raw material proteins necessary for creating items like vests and sutures. Spiders are also difficult to farm – they tend to kill each other when in close contact.
In the early 2000’s, a company called Nexia had an innovative solution to the problem. Why not incorporate the spider’s silk making genes into a goat? The goat’s milk would then contain the protein, which would make the use of spider silk viable for commercial use. The company used “Breed Early Lactate Early” (BELE) goats for the experiment, and was successful in producing transgenic goats: creatures which were mostly goat, but carried some spider DNA. The experiment was a success, and the company dubbed the material BioSteel®. BioSteel® has several targeted commercial applications: artificial ligaments, body armor, fishing lines, and tennis strings. In addition to being unbelievably strong, BioSteel® has another advantage: it is environmentally friendly. While nylon does not biodegrade quickly, BioSteel® is pure spider web protein and will biodegrade when it is discarded.
Nexia sold its BioSteel® technology and assets to the Advanced Foods and Materials Network (AFMNet) in 2009. AFMNet has experience in nanotechnology and the creation of biological materials, and will work with the University of Wyoming to increase spider protein production efficiency.
Natural and Created Chimeras Change Our Understanding of Genetics
Our understanding of genetics is rapidly increasing, and the understanding of naturally occurring chimeras will shed light on the liabilities of DNA testing. Once thought infallible, genetic testing must be properly interpreted prior to closing any case. As the case of Lydia Fairchild highlights, data given from a genetic test cannot be blindly accepted as proof when other evidence strongly indicates a more thorough investigation is required.
Chimeras created in the laboratory have the potential for creating new products for the materials sciences – biodegradable and strong bio-polymers have the ability to revolutionize the medical and defense fields. Through all of this, there are battles over ethics and concerns about genetically modified animals – as our society progresses through the 21st century, the benefits and risks of creating such creatures will have to be carefully weighed.