A subtelomeric cryptic unbalanced translocation der (1)t(1;18)(q44;q23) in a severely retarded girl: similarities and differences to the deletion 1q42/43-ter syndrome

Abstract

We studied a girl with severe mental retardation, dysmorphic features (metopic ridging, mongoloid slant of palpebral fissures, short nose, thin vermilion, retrogenia, and deep-set ears) and multiple congenital abnormalities (microcephaly, agenesis of corpus callosum, flattened gyri, postaxial hexadactyly, and gastro-oesophageal reflux) for subtelomeric deletions using fluorescent in-situ-hybridization (FISH). Only one signal was found with the 1q probe and three signals with the 18q probe. Two of the 18q signals hybridized to the normal chromosome 18 and the third was found on 1q. Therefore, the patient has an unbalanced translocation t(1;18) resulting in monosomy 1q44 and trisomy 18q23-qter. The translocation was not detectable with classical cytogenetics. Comparison of the phenoytpe of patients with the 1q42→qter and 1q43→qter deletion syndrome, respectively, and our patient with a much smaller deletion revealed phenotypical and neurological similarities. This would suggest that the 1q- syndrome phenotype is due to deletions of genes present in the smaller deletion described here. Therefore, patients with a similar phenotype should be analyzed for submicroscopic deletions with the 1qtel probe.