A CLINICAL, CYTOGENETIC AND MOLECULAR STUDY OF 10 PROBANDS WITH SUPERNUMERARY INV DUP-(15) MARKER CHROMOSOMES

Ten probands with moderate to severe developmental delay were found to have a supernumerary inv dup (15) chromosome, These patients and thei r families were studied by both cytogenetic and molecular methods. Cyt ogenetic polymorphisms associated with the 15p short arm suggested a m aternal derivation for the marker chromosome in all informative cases. One marker was directly maternally inherited. Molecular analysis empl oying Southern blotting and polymerase chain reaction (PCR) of microsa tellite repeats demonstrated the presence of extra alleles in the 15q1 1q13 region. AU ten of the probands demonstrated an extra band at one or more locus without recourse to densitometry. All of the inv dup (15 ) markers were comparable in size to a G group chromosome but there we re differences in the positions of the breakpoints in 15q. There was a n inconsistent relationship between marker size, gene dosage and sever ity of phenotype.