Researchers in Japan have discovered only the second known chimpanzee born with what is, essentially, Down syndrome, according to a study published in Primates. Kanako, a 24-year-old female chimp, was born with trisomy 22. Her symptoms largely align with the symptoms seen in humans with Down syndrome, also known as trisomy 21, according to a press release. Kanako developed vision problems at a young age that eventually led to her being blind by the time she was 7. She also has congenital heart disease, teeth that are underdeveloped, and stunted growth. While it's unclear how or if trisomy 22 has affected Kanako's behavioral development, researchers say there's evidence against "severe retardation" based on what has been observed in her daily caretaking.
Researchers realized Kanako had trisomy 22 during tests following the discovery of her heart condition in 2014. The only other chimpanzee to have trisomy 22 was confirmed back in 1969, and he died before the age of 2. Researchers say they aren't sure how common trisomy 22 is in chimps, but it is likely similar to the rate at which Down syndrome appears in humans—about one in every 600 births. Researchers have worked to improve Kanako's quality of life. Her blindness has made it hard for her to interact with other chimps, and those interactions have to be managed to keep them from becoming aggressive. She currently gets to interact with another female chimp once a month. (In a rare act of cannibalism, a chimp leader was killed and eaten by his former subjects.)