Pallister-Killian syndrome: difficulties of prenatal diagnosis.

The first prenatal diagnosis of Pallister-Killian syndrome (PKS) was reported by Gilgenkrantz et al. in1985. Since this report, about 60 prenatal cases have been reported but both sonographic and cytogenetic diagnoses remain difficult. Although ultrasound anomalies such as congenital diaphragmatic hernia, polyhydramnios and rhizomelic micromelia in association with fetal overgrowth are very suggestive of the syndrome, they are inconstant and they may even be absent. The mosaic distribution of the supernumerary isochromosome 12p greatly increases these difficulties. No prenatal cytogenetic technique is sensitive enough to ensure prenatal diagnosis and false-negative results have been described on fetal blood, chorionic villi and amniocentesis. We report here two prenatal cases of PKS which illustrate the great variability of the fetal phenotype. In reviewing the 63 reported cases, we attempt to determine ultrasound indicators of the syndrome and to define a cytogenetic strategy. In cases where ultrasound indicators are present, our proposal is first to perform chorionic villus or placental sampling and then amniocentesis when the first cytogenetic result is normal. Fetal blood sampling is the least indicated method because of the low frequency of the isochromosome in lymphocytes. In this cytogenetic strategy, fluorescent in situ hybridization (FISH) and especially interphase FISH on non-cultured cells increases the probability or identifying the isochromosome. A misdiagnosis remains possible when ultrasound is not contributory; the identification of new discriminating ultrasound indicators would be very helpful in this context.