Abstract

Few cases of isochromosomes for the short arm of the X have been reported and all are dicentric with variable portions of the long arms interposed between the two centromeres. This paper reports three cases of complete short arm duplication of one X chromosome in unrelated female patients. All patients also have a 45,X cell line and present with some characteristic features of Turner syndrome. We used conventional cytogenetics, in situ hybridisation, and molecular genetics to describe all three structurally abnormal chromosomes and the parental origin of two of them. We briefly discuss the "inactivation enhancement" theory; however, any genotype-phenotype correlation is complicated by the presence of the 45,X cell line.