2 PRADER-WILLI-ANGELMAN-SYNDROME LOCI PRESENT IN AN ISODICENTRIC MARKER CHROMOSOME

We found an abnormal 47,XX,+mar karyotype in a patient with developmen tal delay, hypotonia, microcephaly, failure to thrive, and cognitive d elay. When metaphases were hybridized with Prader-Willi and Angelman l oci-specific probes by the FISH technique, two sites were noted at opp osite positions on the marker chromosome. The alphoid satellite DNA pr obe documented the isodicentric nature while retention of the p arms o n both sides of the marker chromosome was demonstrated by beta satelli te probe. The patient does not exhibit manifestations of either syndro me despite the presence of these loci in tetrasomic dose. The present investigation suggests that other marker chromosomes be reevaluated, a s their clinical manifestations are quite variable. (C) 1994 Wiley-Lis s, Inc.