A CASE OF PRADER-WILLI-SYNDROME ARISING AS A RESULT OF FAMILIAL UNBALANCED TRANSLOCATION T(11-15)(Q25-Q13)

We report on a case of Prader-Willi syndrome (PWS) with a true recipro cal unbalanced translocation, 45,XX,-15,der(11)t(11;15)pat. The propos ita was diagnosed clinically as having severe PWS. Molecular studies r evealed loss of the paternal methylation pattern at locus D15S63 and a deletion encompassing the loci from at least D15S10 to D15S97 of pate rnal chromosome 15. FISH studies confirmed the deletion of 15q11-q13 r egion and the presence of two telomeres on ail chromosomes. The propos ita's father, the father's sister and their mother are all carriers of the same balanced translocation t(11;15)(q25;q13). By genomic imprint ing we would expect that if the father's sister were to give birth to a child with the same unbalanced translocation as the proband, it woul d be affected by Angelman syndrome. To date, a similar familial unbala nced translocation due to loss of the small chromosome15 derivative ha s not been described. (C) Munksgaard, 1998.