Lethal Pallister-Killian syndrome: phenotypic similarity with Fryns syndrome.

The Pallister-Killian syndrome is a sporadic multiple congenital anomaly syndrome characterized by "coarse" face, profound mental retardation, and epilepsy. Chromosomes of peripheral lymphocytes are usually normal, but tissue cultures show varying degrees of mosaicism for isochromosome 12p. In babies who die neonatally of severe malformations, including diaphragmatic hernia, and who also have a "coarse" face, acral hypoplasia, and other internal anomalies, Fryns syndrome is more likely to be suspected than Pallister-Killian syndrome, especially if karyotyping is unavailable or if peripheral lymphocytes have a normal chromosome constitution. An initial diagnosis of Fryns syndrome had to be modified in 3 successive newborn infants since chromosome analysis or in situ hybridization with a chromosome 12 probe on kidney tissue demonstrated the mosaic aneuploidy characteristic of Pallister-Killian syndrome. These 3 patients confirm that a similar pattern of malformations can be present in both conditions at birth. It consists of "coarse" face, acral hypoplasia, diaphragmatic hernia, and other defects. Newborn infants who present this phenotype, but lack a conclusively normal chromosome test, may not have Fryns syndrome. A diagnosis of Fryns syndrome should be made carefully to avoid the risk of inappropriate genetic counseling.