Mixed-sex human embryo created

[mrz]

Mixed-sex human embryo created
By Martin Hutchinson
BBC News Online health staff in Madrid

Developing embryos can be merged
An experiment in the United States has created a mixed-sex human embryo.
The team involved insists that the creation of an hermaphrodite human embryo was designed to cure illness, but critics say moral and ethical standards have been breached.

The process they used creates what is known as a "chimaera" - a blend of two embryos, each of which would have a distinct genetic identities.

But any attempt to produce such a baby would provoke a worldwide ethical storm.

In experiments using donated embryos, scientists from the Centers for Human Reproduction in New York and Chicago investigated whether healthy cells from one embryo could be implanted into a second defective embryo.

They found that, in some cases, the introduced cells do proliferate and spread throughout the chimaeric embryo.

Their hope is that having even a small proportion of cells from a healthy embryo might prevent certain genetic diseases from arising.

The "merged" embryos were never intended to develop into children, and were destroyed after a few days.

It is not ready for clinical application in humans - I don't want to suggest that.
"But further exploration in animals is warranted


Dr Norbert Gliecher, Centers for Human Reproduction


Has science gone too far?
However, other experts have dismissed the idea as "deeply flawed" - and say research into the issue, even in animals, should not continue.

Any use of chimaeric technology in human reproduction in the UK is illegal.

Dr Norbert Gliecher, who led the research, told the European Society for Human Reproduction and Embryology annual meeting in Madrid: "It is not ready for clinical application in humans - I don't want to suggest that.

"But further exploration in animals is warranted - and who knows where this will take us?"

Joined up

The potential for cells from two different embryos to fuse and become one "combination" individual is well known in nature - there have been examples where this has happened in early pregnancy in humans, with no apparent ill-effects on the resulting baby.

The theory behind Gliecher's work is that some studies have suggested that in certain diseases caused by a single genetic defect, having even as few as 15% of the body's cells free from the defect might be enough to stop the development of the disease.

He said his experiment showed that just a couple of cells injected into the embryo produced an embryo with, in many cases, an even distribution of cells carrying these new genes.

He deliberately injected a male cell into a female embryo - which created an "intersex" embryo, but allowed him to use chemical tests to check the process of the chromosome unique to male cells.

Gleicher said that a couple having embryos screened for a single-gene disease such as Severe Combined Immunodeficiency Disorder (SCID) might end up with two embryos, one of which had the disease and one which did not.

In this instance, he said, it might be possible to take cells from the "good" embryo and put them into the defective one, producing two viable embryos, whereas previously, the defective one would have to be discarded.

However, his experiment was roundly attacked by senior scientists at the conference.

'No logic'

Professor Alan Trouson, a pioneer of IVF in Australia, told BBC News Online: "I really can't see the logic of what he is trying to do - it seems completely flawed to me."

He said that it would be impossible to test whether the correct versions of the genes had been incorporated widely into the embryo before a decision had to be made whether to transfer it back into the woman.

He said that the health risks of producing a chimaeric individual were still uncertain.

"Unless you can be certain you are doing some good, you should not be doing something that could cause harm."

He said that the US team should not even attempt to continue their experiments in animals.

Professor Lyn Fraser, a past president of the society, told the BBC that she shared the disquiet over the technique.

She said: "I don't see how it can be used to treat single gene disorders. It's hard to accept what they have done at all."

http://news.bbc.co.uk/2/hi/health/3036458.stm

[mrz]

'She-male' embryos created in lab
12:18 03 July 03
NewScientist.com news service

The revelation of experiments in which human embryos with both female and male cells were created has been condemned as "flawed" and "revolting" by both fertility scientists and anti-abortion groups.

US researcher Norbert Gleicher and colleagues took cells from three-day-old human male embryos and added them to female embryos, creating what is called a chimera. Gleicher, who unveiled the work at the European Society of Human Reproduction and Embryology's annual conference in Madrid, says the experiments were to test a theoretical alternative to gene therapy.

Gene therapy aims to repair genetic defects by using vectors, usually viruses, to ferry new DNA into a patient's cells. But the technique has been troubled by safety fears. Gleicher suggests that embryos carrying genetic defects might be cured by injecting early embryonic cells, called blastomeres, which carry healthy versions of the genes. This could even prevent the need to destroy embryos with faulty genes, he claims.

But Alan Trounson, fertility expert and IVF pioneer at Monash IVF in Melbourne, Australia is scathing. "It seems to me completely flawed," he says. "You can't have half of Huntington's disease."

Lynn Fraser, chair of ESHRE's international scientific committee agrees. In chimeric individuals, the "bad genes" would "all still be there", she says. Naturally-conceived human chimeras can exist but the distribution of the cells containing the different genetic profiles is far from uniform.

Trounson adds that the work is damaging to the image of fertility science: "It could cause some harm because it would be difficult to argue why that experiment was done to patients." Gleicher's study is the second from the conference to cause a furore, following a report of work assessing the potential of ovarian tissue from aborted fetuses to provide eggs for IVF.


Feasible or ethical

The embryos were then followed to the blastocyst stage, which occurs five to six days after fertilisation. Male cells were used because the Y chromosome is an easy marker to track in the developing embryos.

"Twelve of the 21 embryos reached what we considered to be perfectly normal blastocysts," says Gleicher. But four of the female embryos stopped developing after the transplantation, while five become "abnormal blastocysts".

"This study was meant in principle to determine whether the [genetic repair] concept is possible," says Gleicher. "It is not meant to support in any way that the clinical application of this kind of concept at the present time is either feasible or ethically acceptable."

However, he says a patent has been filed for the concept and adds: "We believe further investigation is warranted."


Shaoni Bhattacharya, Madrid

http://www.newscientist.com/news/news.jsp?id=ns99993905

[Simon]

Ik begrijp er ook niet veel van. Er bestaat zoiets als het Klinefelter syndroom dat een soort tussenvorm tussen man en vrouw laat ontstaan en dat één op de 500 geboorten voorkomt (eigenlijk best vaak) maar ik heb altijd begrepen dat dat juist tot veel medische complicaties leidt.

Simon

in de encyclopedie dit gevonden:

Klinefelter syndrome:

relatively common (one per 500 live male births) human sex-chromosome disorder. It is characterized by the following: small testes, lack of sperm formation, late puberty with reduced secondary sexual characteristics (but with normal-sized penis), usually a delicate and long-limbed physique, occasionally breast enlargement (gynecomastia), and about a 25 percent frequency of mental retardation but a much higher frequency of behavioral difficulties.

Treatment with male hormone will normalize male appearance and produce a natural sex drive, but the patient will remain sterile.

The majority of Klinefelter individuals have one extra female sex chromosome, resulting in an XXY pattern and a total of 47 chromosomes instead of 46. Other, less frequent, chromosomal patterns include XXXY, XXXXY, XXYY, XXXYY, mixtures (mosaics), and partial losses or deletions. About 40 percent of the diagnosed examples of Klinefelter's syndrome have a normal XY pattern. One variant of Klinefelter's syndrome, the XXXXY type, is characterized by fusion of the forearm bones and other skeletal anomalies, underdevelopment of the penis and scrotum, incomplete descent of the testes, and marked mental retardation.

Diabetes mellitus and goitre incidence are more common, and various cancers may be more prevalent among Klinefelter's syndrome patients. Thyroidal trapping of radioactive iodine and the responses of the thyroid to injections of thyrotropin (TSH; thyroid-stimulating hormone) may be low. Testosterone production tends to be below normal, with urinary 17-ketosteroids in the normal or low-normal range. The serum and urinary gonadotropins follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are usually, but not necessarily, increased.

Copyright © 1994-2002 Encyclopædia Britannica, Inc.