MOLECULAR CHARACTERIZATION OF THE MARKER CHROMOSOME ASSOCIATED WITH CAT EYE SYNDROME

Cat eye syndrome (CES) is associated with a supernumerary bisatellited marker chromosome which is derived from duplicated regions of 22pter- 22q11.2. In this study we have used dosage and RFLP analyses on 10 CES patients with marker chromosomes, by using probes to five loci mapped to 22q11.2. The sequences recognized by the probes D22S9, D22S43, and D22S57 are in four copies in all patients, but the sequences at the m ore distal loci, D22S36 and D22S75, are duplicated only in some indivi duals. D22S36 is present in three copies in some individuals, and D22S 75 is present in two copies in the majority of cases. Only three indiv iduals have a duplication of the most distal locus examined (D22S75), and these individuals have the largest marker chromosomes identified i n this study. From the dosage analysis it was found that the marker ch romosomes are variable in size and can be asymmetric in nature. There is no obvious correlation between the severity of the phenotype and th e size of the duplication. The distal boundary of the CES critical reg ion (D22S36) is proximal to that of DiGeorge syndrome, a contiguous-ge ne-deletion syndrome of 22q11.2.