TETRASOMY 15Q - 2 MARKER CHROMOSOMES WITH NO DETECTABLE ALPHA-SATELLITE DNA

Two patients with specific and similar phenotypes were both found to h ave an unusual marker chromosome present in 70%-80% of their lymphocyt es at routine cytogenetic examination. The marker chromosomes were iso lated by now sorting and were amplified by degenerate oligonucleotide- primed PCR. These libraries and a cosmid probe located at 15q26 were u sed to characterize the marker chromosomes by FISH. Both marker chromo somes were found to consist of duplicated chromosome material from the distal part of chromosome 15q and were identified as inv dup(15) (qte r-->q23::q23-->qter) and inv dup(15) (qter-->q24::q24-->qter), respect ively. Hence, the markers did not include any known centromere region, and no alpha-satellite DNA could be detected at the site of the prima ry constriction. Tetrasomy 15q may be a new syndrome, associated with a specific type of marker chromosome. In addition, further analyses of this type of marker chromosome might give new insight into the struct ure and function of the mammalian centromere.