Japanese scientists have documented the second known case of a chimp born with a genetic condition akin to Down’s syndrome in humans.
Kanako, a 24-year-old female chimpanzee born in captivity, has a chromosomal defect known as trisomy 22, as reported in the case study published yesterday in the journal Primates by scientists from Kyoto University in Japan.
The condition is comparable to the human condition Down’s syndrome as they both involve having an extra third copy of one of the chromosomes. Human cells typically contain 23 pairs of chromosomes, making a total of 46. Down syndrome occurs when a person's cells contain a third copy of chromosome 21, hence why it is also known as trisomy 21. Apes normally have 24 pairs of chromosomes, making a total of 48. However, Kanako has three copies of chromosome 22 instead of just two.
Kanako’s condition came to light following a trail of evidence that started with a routine physical examination in 2014. After the vets noted some abnormalities, she received an echocardiogram that revealed she was also suffering from a defect in the wall that separates the top two chambers of the heart. This prompted them to carry out chromosomal analysis, which revealed she actually had a third copy of chromosome 22.
Footage of Kanako in 2014 from Kumamoto Sanctuary, Kyoto University
The chimp has had stunted growth from a young age. She has also been faced with congenital heart disease, underdeveloped teeth, and problems with her sight. At aged one she developed cataracts and was crossed-eye, which eventually led to her going blind by age seven. Since so little is known about the chromosomal condition in chimps, the researchers state it's not possible to say if these symptoms are explicitly caused by it.
"However, the lack of abnormalities noted in her daily care-taking before the age of one, except for neonatal inactivity and limp limbs, suggests that there was no severe retardation in her behavioral development,” lead researcher Satoshi Hirata said in a statement.
Kanako is generally kept separate from the other chimps as the keepers fear the other apes might act aggressively towards her. However, another female chimp called Roman has been especially calm and friendly to Kanako since the pair were both young. The keepers allow these two old friends to interact once a month to help encourage some social stimulation.
The only other confirmed case of trisomy 22 in a chimpanzee was documented in 1969. While the condition is no doubt rare, the researchers aren't yet sure how common this condition would be among the wider chimp population.
"It is difficult to estimate the probability of a rare event using a small population, but given that around 500 chimpanzees have been born in captivity in Japan, the probability of this autosomal trisomy in chimpanzees may be comparable to that of trisomy 21 in humans, which occurs in up to 1 in 600 births," speculates Hirata.