Case report: denovo inherited 18p deletion in a mother-fetus pair with extremely variable expression, confirmed by fluorescence in situ hybridization (FISH) analysis.

Denovo deletions of 18p without other associated rearrangement are uncommon. For such a deletion to profoundly affect the fetus of a near normal phenotypic carrier would be rarer. We present such a case in which the chance of a cryptic rearrangement was ruled out by fluorescence in situ hybridization (FISH) analysis. Possible explanations for wide variations in clinical expression are discussed.