A patient with a short arm deletion of chromosome 18 (46,XY,18p-).

Recent advances in human cytogenetics have provided impetus for the mapping of autosomal genes. Inherited variations in the morphology of the chromosomes, such as translocations and deletions, can be used as markers in identifying chromosomes and possibly in localizing the genes within such chromosomes. Penrose and Delhanty (1961) and Shaw (1962) described two different pedigrees in which a 15/21 translocation chromosome was segregating. Though the MN and Rh loci were eliminated as being located in the translocation chromosomes, the evidence for the ABO locus being located in these chromosomes was not conclusive. The deletion of various segments of a chromosome has been used by geneticists to localize a given gene in many experimental organisms. In the case of man, a valuable 'experiment of nature' is to be found in subjects in whom there is a deletion of a portion of an autosomal chromosome. There are well-defined syndromes, such as the cri du chat, a deletion of a short arm of chromosome No. 5 (Lejeune et al., 1963), and deletions of a segment of the long arm of No. 18 (Destine et al., 1967), that can be suspected or diagnosed clinically. There have been a number of other reports of patients with deleted chromosomes that do not fit into easily diagnosed syndromes (Weleber, Hecht, and Giblett, 1968). An example of the latter category is a ring chromosome that has, in effect, a terminal deletion at both ends of the chromosome (Wolf et al., 1967). This report deals with one of the more poorly defined chromosome deletion syndromes, deletion of the short arm of the chromosome 18. By describing these cases in detail, including the genetic information obtained from family studies, the spectrum of anomalies associated with this chromosome deletion may eventually be clarified.