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Cat-eye syndrome is characterized by two major features: anal atresia and coloboma of the iris, from which the name of the syndrome derives. However, patients present with a very heterogeneous range of symptoms: only 41% present with the classic triad of anal anomalies, coloboma of the iris and preauricular skin tags or/and pits. Other inconstant features include mild hypertelorism with downslanting palpebral fissures, cardiac defects, cleft palate and urinary tract or skeletal anomalies. Moderate intellectual deficit is present among 32% of patients. The estimated prevalence in the general population is 1 in 74 000. In 5/6 cases, the karyotype shows the presence of a small supernumerary chromosome derived from the proximal part of chromosome 22. Typically, this marker is bicentric and bisatellited, and results from an inverted duplication [invdup(22)].It is often present in a mosaic state. The presence of this extra marker chromosome is the most reliable diagnostic criterion for this syndrome. No correlations have been identified between the severity of the intellectual deficit and the presence of malformations, and the degree of the mosaicism or the size of the duplication. However, patients carrying small chromosome 22 markers containing no euchromatin display no associated phenotype. The inverted duplication of chromosome 22 usually occurs de novo and transmission is possible through both sexes, with a risk of transmission to the offspring of about 50%. Antenatal diagnosis is possible through karyotyping and Fluorescence In Situ Hybridization (FISH) analysis of prenatal samples. Surgery is required for patients with anal atresia and severe cardiac complications. A few patients with severe multiple malformations have died during infancy, but life expectancy is not significantly reduced for patients with few or mild manifestations. |