Cytogenetic analysis of the proband and his parents. A) GTG banding revealed a normal male karyotype in 50% of the cells. In the remainder, one deleted and one apparently normal chromosome 18 were present (partial karyotype in blue frame). B) FISH confirmed that both chromosomes 18 were normal in 50% of the cells. However, in the remaining cells both chromosomes 18 turned out to be rearranged. One had a terminal deletion del(18)(q21.32-qter), and the second showed a duplication/insertion of 18q21.2 material adjacent to the original location of the RP11-160B24 probe. C) No such duplication in 18q21.2 was present in any of the parents.