TRUE TELOMERIC TRANSLOCATION IN A BABY WITH THE PRADER-WILLI PHENOTYPE

We report on a baby with a nonreciprocal de novo unbalanced translocat ion between chromosomes 12 and 15. Her karyotype was 45,XX, - 12, - 15 , + der(12) t (12;15) (pter-->qter=q13-->qter). The paternal origin of the 15q11-13 region was shown by DNA marker studies and, consistent w ith this, the baby had the Prader-Willi (PWS) phenotype. The breakpoin t on 12q was distal to D12S11 (lambdaMS43) which maps to 12q24.3-qter. Fluorescent in situ hybridization using the oligonucleotides (TTAGGG) 7 and (AATCCC)7 showed that the 12q telomere was still present within the translocated chromosome. Thus, the translocation was within or ont o the end of the telomere of 12q. This unusual translocation is furthe r evidence of an unexplained instability of the 15q11-13 region. (C) 1 993 Wiley-Liss, Inc.