Pallister-Killian syndrome

Abstract

Pallister-Killian syndrome (PKS) is a sporadic genetic disorder defined by a characteristic dysmorphic face, pigmentary skin anomalies, hypotonia, developmental delay, intellectual disability, and other systemic abnormalities. PKS is caused by mosaicism for an extra isochromosome 12p. In this chapter, we present two cases of PKS to illustrate and discuss the low frequency of this extra isochromosome 12p in phytohemagglutinin (PHA)-stimulated peripheral blood lymphocytes and the advantage of chromosome microarray using a direct DNA prep from the uncultured blood without PHA. We suggest chromosome microarray analysis be used as first-tier testing when PKS is considered as a differential diagnosis. We also emphasize the importance of genetic testing being performed as early as possible for the individual with PKS since the percentage of cells containing the extra isochromosome 12p also decreases with age.