Tandem triplication of chromosome 13q14 with inverted interstitial segment in a 4 year old girl

EDITOR—Application of chromosome painting has enabled confirmation that an additional segment in a presumed tandem duplication originates from the rearranged chromosome. More recent studies to determine more accurately the exact amount of duplication with cosmid FISH probes have, in a few instances, shown that some of the presumed duplications were in fact triplications of smaller segments.1-7 In some of these patients, unequal distances between the FISH signals showed that the middle segment of the tandemly arrayed three segments was in the opposite orientation to the two flanking segments,1 3 4 thus providing clues to the possible mechanism of formation. Here we report on the clinical, cytogenetic, and molecular analysis of a patient displaying the same type of triplication for segment 13q14 including the retinoblastoma gene, again with opposite orientation of the middle segment.