Maternally Derived Complex Small Supernumerary Marker Chromosome 22 Associated with Cat-Eye Syndrome Like Features

Cat-eye syndrome (CES) is a rare genetic disease first reported in 1965. The estimated prevalence of CES is 1:50,000 to 1:150,000, and it is typically associated with an inverted duplicated small supernumerary marker chromosome (sSMC) derived from chromosome 22. The specific chromosomal band involved in CES causing partial tetrasomy is 22q11.21, where chromosomal rearrangements occur due to the presence of low-copy repeats (LCR22). The phenotype of CES is extremely diverse, ranging from normal to multiple abnormalities including intellectual disabilities and dysmorphic features. To our knowledge, over 340 patients with CES have been reported to date. This study reports a patient displaying a duplication of chromosome 22pter-22q12 involving band 22q11.21 where the CES critical region is located, and 18pter to 18p11. The propositus is a three-year-old girl, born to an unrelated and healthy couple. She was referred for facial dysmorphism and psychomotor delay. Banding cytogenetic analysis revealed an sSMC resulting from abnormal 3:1 segregation of the maternal balanced translocation t(18;22). Furthermore, the origin of the sSMC was confirmed by fluorescence in situ hybridization technique. The current study emphasized the importance of molecular cytogenetic techniques such as FISH in apprehending chromosomal abnormality. In addition, it shows that partial trisomy 22q11.2 to 22q12 may lead to CES-like symptoms.