Feb. 21 (UPI) -- Scientists at Kyoto University in Japan have identified another chimpanzee with trisomy 22, a Down syndrome-like chromosomal disorder. It's the second case of chimpanzee Down syndrome known to science.
Healthy human cells contain a total of 46 chromosomes, 23 pairs. The cells of humans with Down syndrome feature an extra chromosome -- a third copy of chromosome 21, or trisomy 21.
Apes have 48 chromosomes, one more pair than humans. When chimpanzees, gorillas or orangutans are born with an extra copy of chromosome 22, they're diagnosed with the disorder known as trisomy 22.
The name of the newly diagnosed chimp is Kanako. She was born in captivity in 1992. In 2011, the facility where she lives was transferred to Kyoto University and renamed the Kumamoto Sanctuary and Wildlife Research Center.
The first case of trisomy 22 was identified in 1969. The male chimp died before he turned two, making Kanako the oldest living chimp diagnosed with Down syndrome.
Kanako has stunted growth, underdeveloped teeth, congenital heart disease and partial blindness stemming from a progressive thinning of her corneas -- all symptoms typical of human Down syndrome.
Kanako is housed separate from other chimps, but is allowed periodic interactions with another female.
Because the behavior of Kanako was, until recently, only periodically monitored, it's unclear to what extent her condition has affected her social and mental capacities.
"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," researcher Satoshi Hirata said in a news release. "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."
Kanako's newly confirmed trisomy 22 diagnosis was detailed in the journal Primates.