Characterization of a heritable partial monosomy 18p by molecular and cytogenetic analysis

This report describes the fourth case of heritable 18p monosomy, which was ascertained by prenatal diagnosis. Cytogenetic analysis of amniotic fluid cells by G-banding showed an apparently distal 18p chromosome deletion and a derivative X chromosome resulting from a translocation between the X and Y chromosomes. Analysis of peripheral blood lymphocytes from the parents by G-banding revealed the same chromosome 18 deletion in the mother, who did not have the X/Y translocation. Comparative genomic hybridization (CGH) studies confirmed the loss of chromosome region 18p11.3-pter previously detected, and eliminated the presence of unbalanced reorganizations of other chromosome regions. No subtle translocation was detected by fluorescence in situ hybridization (FISH) studies using whole chromosome specific painting probes. This is a new report of a heritable 18p monosomy. Although in our case the mother had several minor congenital malformations, the loss of 18p11.3 band was not associated with any obvious phenotypic alteration in the fetus.