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a congenital condition caused by the presence of an extra chromosome 22 in the G group, characterized by psychomotor retardation and various developmental anomalies. Common defects include microcephaly, micrognathia, hypotonia, hypertelorism, abnormal ears with preauricular tags or fistulas, and congenital heart disease. In partial trisomy 22 the extra chromosome is much smaller than the normal pair and causes coloboma of the iris, anal atresia, or both, as well as various other defects. See also cat-eye syndrome.