Cat eye syndrome

Lore & Background

The abnormalities now recognized as cat eye syndrome were first cataloged in 1899, and the association with a small marker chromosome was described in 1965. Early reports considered possible involvement of chromosome 13, but the condition is now understood to involve trisomy of chromosome 22 material. The small supernumerary marker chromosome usually arises spontaneously, though it may be hereditary, and parents can be mosaic carriers without showing symptoms.

Reader's Guide

Cat eye syndrome is significant as a model for understanding how extra chromosomal material—specifically from the 22pter→q11 region—can produce a recognizable pattern of birth defects. The condition highlights the variability of phenotypic expression: while some patients have classic features such as iris coloboma, preauricular pits, and anal atresia, many do not present with the eye trait that gives the syndrome its name. The presence of heart or kidney abnormalities strongly influences prognosis. Diagnosis relies on ultrasound, amniocentesis, and genetic testing (karyotyping or FISH). The syndrome's rarity and the fact that many individuals have normal intelligence underscore the importance of individualized medical management. The identification of candidate genes (CECR1, SLC25A18, ATP6V1E1) within the critical region offers avenues for future research into the molecular basis of the associated malformations.

Did You Know?

• Over half of CES patients do not have the vertical colobomas that gave the syndrome its name.
• The extra chromosome in CES consists of the entire short arm and a small section of the long arm of chromosome 22.
• About 30% of CES patients have moderately impaired mental development; severe intellectual disability is rare.