Tandem Duplication/Deletion in A Maternally Derived Chromosome 9 Supernumerary Derivative Resulting in 9p Trisomy and Partial 9q Tetrasomy

A 19-week stillborn female fetus with bilateral cleft palate, horseshoe kidney, bicornuate uterus, low-set ears, and intrauterine growth retardation (IUGR) was found to have a supernumerary derivative chromosome 9 (der(9)) with an apparent tandem duplication in the long arm. PCR analysis at five polymorphic loci confirmed the duplication and showed an adjacent deletion, while whole chromosome FISH demonstrated only chromosome 9 to be involved. Further FISH studies of der(9) found the 9qh region to be duplicated, telomeric sequences to be intact, and subtelomeric sequences to be absent. Thus, the fetus was determined to be trisomic for 9pter-->9q12 and 9q34.3-->9qter, tetrasomic for 9q12--> 9q33, and disomic for 9q33-->9q34.3. These results are consistent with a tandem duplication of 9q12-->9q33 and adjacent distal deletion as designated by the karyotype, 47,XX,+der(9)dup(9) (q12q33)del(9) (q33q34.3).ish der(9)(WCP9+,D9Z1x2,STP9q-, AHT+) de novo. In addition to characterizing der(9), the combined PCR and cytogenetic studies refined the Genome Database Map of three loci (D9S907, D9S155, and D9S302) approximately to the distal 9q33 region. Without the attempt to refine breakpoints by PCR analysis, the deletion in distal 9q would not have been detected. Tandem direct duplication/deletion chromosomes have been reported in fewer cases than inverted duplication/deletions. We propose mechanisms of origin, consistent with those for recurrent inter stitial microdeletion and microduplication syndromes, shown to arise by recombination at homologous, flanking DNA sequences.