Can animals have down syndrome? Some images suggest that yes, but the answer offered by scientists is more complex.
You’ve probably all seen a photograph of Kenny, that particular faceted white tiger. A huge round head almost deprived of a neck, a short muzzle and small blue eyes, very distant under a broad forehead. At first sight, one might well believe in a case of animal trisomy. However, the reality is more nuanced.
What is trisomy?
Trisomy 21, or Down syndrome, is the most common form of trisomy in humans: it affects about 1 birth in 770. This chromosomal anomaly is caused by the presence of a supernumerary chromosome at the level of the 21st pair (the human being has 23 in all). It is associated with a deficit in cognitive development, congenital malformations and the risk of complications that have long shortened the lifespan of sufferers.
Although it is very difficult to predict, this chromosomal anomaly is now much better managed, which has made it possible to extend the life expectancy of patients.
Animals with trisomy?
According to the website of the United States National Institute for Human Genome Research: “Several cases of chimpanzees with Down syndrome have been reported. Since the syndrome is caused by a supernumerary copy of a specific chromosome (chromosome 21 in humans), only animals that are genetically very close to humans can be affected by the syndrome.
Some biologists however argue that “Animals can be born with genetic defects similar to those of Down syndrome, but can not be reached by this specific syndrome, except in the case of large monkeys. [These] are closest to humans because they have 24 pairs of chromosomes. ”
In chimpanzees, the anomaly that is usually found on human chromosome 21 is transferred to chromosome 22. It has been possible to observe it in the chimpanzee known as Kanako, 24 years old, born in captivity. Kanako has several symptoms similar to those seen in Down syndrome: congenital heart disease, growth retardation, underdeveloped teeth, and eye complications.
Other cases of trisomy have been reported in primates such as siamangs or macaques. Cases among cattle, a mare, or a buffalo have also been recorded, but none are related to Down syndrome. The researchers created mice with trisomy 16 to study the pathology in the laboratory. However, more studies are needed to help scientists clearly define the limitations of Down syndrome.