Cat eye syndrome: A constitutional chromosome abnormality (one that is present at or before birth) with multiple malformations characterized by the combination of a cat-like slit of the iris of the eye (vertical coloboma) and no anal opening (anal atresia). Frequently there are also down slanting eye slits (palpebral fissures), tissue tags or pits just in front of the ears, heart malformations and kidney anomalies.
There is usually normal or near-normal development with the cat eye syndrome, unlike the situation with many other constitutional chromosome abnormalities, and intelligence may be normal or near-normal in cat eye syndrome.
The syndrome is due to the presence of an extra small chromosome that is smaller than chromosome 21, the smallest chromosome in humans. This extra abnormal chromosome is derived from chromosome 22. (In technical terms, this chromosome represents an inversion and duplication of chromosome band 22q11p.)
The name comes from the cat-like appearance of the iris of the eye.