The third and thirteenth chromosomes of a 29-year-old man, surnamed Yang, were recently confirmed to be the world's first reported chromosomal abnormality karyotype, according to the National Medical Genetics Key Laboratory in Changchun, capital city of northeast China's Jilin Province.
The chromosome karyotype, the world's first known case of balanced translocation of the third and thirteenth chromosomes, has been listed in the database of China human chromosomal abnormality karyotypes, according to Changchun Maternity Hospital.
Experts say that the discovery of this new chromosomal abnormality karyotype not only enriches the world's chromosome data bank, but is also very helpful to the study of hereditary improvement of the human race, and useful in the clinical studies of genetics.
Yang's wife was pregnant twice, but unfortunately twice suffered a miscarriage within the first two months of pregnancy.
Medical tests showed that Yang's third and thirteenth chromosomes are different from those of normal people.
"The two chromosomes set off a balanced translocation, which means that the two chromosomes became fractured, and they have changed to become two totally new chromosomes after their natural reconstruction," said Du Wei, doctor from Changchun Maternity Hospital's Cytogenetics Lab.
Since there was no record on balanced translocation of human's third and thirteenth chromosomes at home or abroad, the hospital sent Yang's cell sample to the National Medical Genetics Key Laboratory for verification.
Since the quantity of the chromosome has not changed, Yang is no different in appearance, personality or intelligence from a normal human.
However, the couple only have a one in eighteen chance of having a healthy child through regular pregnancy, and the child in turn has a one in eighteen chance of inheriting the chromosomal abnormality.
"A method to treat this kind of disease is still under investigation." Du added.
According to Du, chromosomal abnormality karyotype may be inherited from the parents, or caused by long-term exposure to chemicals, radioactive material or a biological virus.
Yang was found to have no experience of such exposures, leaving inheritance as the only explanation. However, tests on his parents' chromosomes have yet to be conducted.
(China Daily August 15, 2005)
