Partial trisomy of chromosome 22 resulting from an interstitial duplication of 22q11.2 in a child with typical cat eye syndrome

Cat eye syndrome (CES) is a rare malformation syndrome with a variable pattern of congenital anomalies. The characteristic features of CES include ocular coloboma, preauricular pits or tags, anal anomalies, and congenital heart and renal malformations. Furthermore, CES may be associated with other craniofacial malformations, skeletal anomalies, and, in some cases, with mental retardation.1,2 In almost all cases CES is associated with the cytogenetic finding of a supernumerary marker chromosome consisting of duplicated material of chromosome 22. The marker is usually bisatellite and dicentric (idic(22)(pter→q11.2::q11.2→pter)) and thus results in tetrasomy of the p arm and a part of 22q11.2.1,3 Cytogenetically detectable intrachromosomal direct or inverted duplications are rare and can arise with equal frequency by rearrangement between sister chromatids or non-sister chromatids both on the maternal or paternal chromosome.4 The proximal part of the long arm of chromosome 22 (22q11.2) has been recognised as a hot spot for chromosomal rearrangements and contains both the cat eye and the DiGeorge critical region (for reviews see Kotzot et al 5 and Edelmann et al 6). Multiple congenital malformations showing overlap with CES can arise from familial translocation t(11;22) in the der(22) syndrome,7,8 and, in rare cases, from interstitial duplication of proximal 22q.9–11 However, none of these patients described so far with interstitial duplications of 22q showed the full CES phenotype including all major clinical features. We report here a patient with an interstitial inverted duplication of 22q11.2 and typical features of cat eye syndrome including coloboma, preauricular anomalies, heart defect, renal anomalies, and anal atresia. ### Key points