For only the second known time, a chimp has a disorder similar to Down Syndrome
A 24-year-old chimp in Japan has a genetic disorder similar to Down Syndrome in humans, researchers have found.
Kanako is only the second chimpanzee known to have the chromosomal defect trisomy 22. The disorder has stunted her growth, left her blind and resulted in a congenital heart disease and underdeveloped teeth.
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But she's also lived a surprisingly long time.
The first chimp with a confirmed case of trisomy 22 — which scientists documented in 1969 — didn't live to see its second birthday. That makes Kanako the longest-living chimp with this chromosomal disorder, at least that scientists are aware of, according to a new study in the journal Primates.
Image: Kumamoto Sanctuary, Kyoto University
Trisomy 22 occurs when a chimp's cells have a third copy of chromosome 22. Apes normally have 24 pairs of chromosomes, for a total of 48.
Humans, by contrast, have 23 pairs of chromosomes, or 46 altogether. With Down Syndrome, a person's cells contain a third copy of chromosome 21 — hence the disorder's scientific name, trisomy 21.
Kanako was born in captivity in 1992 at a Japanese wildlife facility. She was later transferred to Kyoto University, where the study's lead author, Satoshi Hirata, works.
Her caretakers didn't initially suspect the chimp had trisomy 22, even though she had stunted growth, developed cataracts as a baby and developed cross eyes and a disorder that causes her corneas to progressively thin, among other issues. These symptoms are also common in humans with Down Syndrome.
Image: National Human Genome Research Institute
But in 2014, during a routine physical exam, an echocardiogram showed a "hole" in the wall of her heart that separated the organ's top two chambers. That prompted researchers to analyze her chromosomes, a step that eventually confirmed Kanako has trisomy 22.
It remains unclear how common the disorder is among chimps, Hirata said in a press release.
A 2015 paper in Primates suggested a baby chimp in Tanzania had symptoms similar to Down Syndrome, but chromosomal tests couldn't be conducted.
The Japanese researcher speculated that the probability of having trisomy 22 in chimpanzees may be comparable to that of trisomy 21 in humans, which occurs in up to 1 in 600 births.
