human genetics
Has everyone heard of Chimera?
The mythical creature who terrorised parts of Ancient Greece. The head of a lion, body of a goat and tail of a dragon/snake.
Well, some of you may not of heard of the Human Chimera.
Some peoples blood contains cells from a brother or sister, others are two individuals rolled into one. Yet more carry a distinct mutation in only
parts of there bodies.
This arcticle is from the News Features Section of the Journal Nature.
Eight years ago in Britain, a boy was born who was genetically 2 difrent people. He formed when two eggs fertilized by two diffrent sperm, fused into
one embryo inside his mothers womb.
He was an unremarkable baby, but as a toddler doctors discovered that he was a hermaphrodite - what was originally diagnosed as an undescended testis
turned out to be an ovary, a fallopian tube and part of a uterus. Further investigation revealed that some parts of his body were genetically female
but the rest, which contained a different combination of his parents' genes, was male1.
The boy, who was otherwise healthy, is one of only a handful of known true human chimaeras - people carrying tissues that originated in two separate
embryos. More common are mosaics, who have patches of tissue that differ genetically from the rest of their body, thanks to a mutation or chromosomal
anomaly that arose early in embryological development
The frequencies of chimaerism and mosaicism are unknown, but doctors might benefit from a better understanding of both conditions. In recent years,
tantalizing hints have emerged that pockets of genetically mismatched cells may contribute to conditions as common as infertility, autism and
Alzheimer's disease. "I think mosaicism has been neglected as an underlying cause of disease," says Huntington Potter, who works on the genetics of
Alzheimer's at the University of South Florida in Tampa.
And if chimaeras and mosaics are more common than we realize, they will complicate future efforts to tailor drug treatments to people's individual
genetic constitutions. Two genetically different tissues in one body might produce an unpredictable response to a drug, speculates Roland Wolf, who
studies pharmacogenetics at the University of Dundee, UK. "It's completely unknown," he says.
The twin within
Human chimaerism first came to light with the advent of blood typing - some people, it emerged, have more than one blood group. Most are 'blood
chimaeras', non-identical twins who shared a blood supply in the womb. Those who were not born a twin are thought to be pumping around the remnants
of a sibling that died early in gestation and was spontaneously aborted. One British woman, for instance, was unaware that she once had a twin until
routine blood tests during her pregnancy in the early 1980s revealed a population of chromosomally male blood cells2.
Twin embryos often share a blood supply in the placenta, allowing blood stem cells to pass from one embryo and settle in the bone marrow of the other,
seeding a lasting source of blood. As a result, as many as 8% of non-identical twin pairs have chimaeric blood3. And given that most multiple
conceptions that result in live births involve the loss of one twin early in pregnancy4, there may also be significant numbers of blood chimaeras
among single births.
www.nature.com...
Related links
1: stuff of mosaicism
www.medgen.ubc.ca...
2: stuff on Blaschko's lines
www.medical-acupuncture.co.uk...
More info when i find it
"Of all the things I've lost, I miss my mind the most."
Good stuff Gryff, though I'm admittedly still digesting some of it. 
