ISOCHROMOSOME 15Q OF MATERNAL ORIGIN IN 2 PRADER-WILLI-SYNDROME PATIENTS PREVIOUSLY DIAGNOSED ERRONEOUSLY AS CYTOGENETIC DELETIONS

Since our previous report on two Prader-Willi syndrome (PWS) patients with t(15q;15q) (Niikawa and Ishikiriyama; Hum Genet 69:22-27, 1985) w as erroneous, we report here new data and a corrected interpretation. Reexamination of the parental origin of their t(15q;15q) using polymor phic DNA markers that are mapped to various regions of 15q documented no molecular deletions at the 15q11-q13 region in either patient. Both patients were homozygous at all loci examined and their haplotypes on 15q coincided with one of those in their respective mothers. These re sults indicate that the presumed t(15q;15q) in each patient was actual ly an isochromosome 15q producing maternal uniparental disomy, consist ent with genomic imprinting at the PWS locus. (C) 1994 Wiley-Liss, Inc .