A de novo unbalanced reciprocal translocation identified as paternal in origin in the Prader-Willi syndrome.

Interstitial cytogenetic deletions involving the paternally derived chromosome 15q11-13 have been described in patients with the Prader-Willi syndrome (PWS). We report a child with PWS and a de novo unbalanced karyotype -45, XY, -9, -15, + der (9) t (9; 15) (q34; q13). Molecular studies with the DNA probe pML34 confirmed that only a single Prader Willi critical region (PWCR  15q11. 2-q12) copy was present.
Hybridisation of patient and parental DNA with the multi-allelic probe CMW1, which maps to pter-15q13, showed that the chromosome involved in the translocation was paternal in origin.
This is the first example of a paternally-derived PWCR allele loss caused by an unbalanced translocation that has arisen de novo.

