Pallister-Killian syndrome. 
Pallister-Killian syndrome (PKS) is characterized by craniofacial dysmorphism, pigmentary skin anomalies, congenital heart defects, congenital diaphragmatic hernia, hypotonia, intellectual disability, and epilepsy.  PKS is caused by extra copies of chromosome 12p, most characteristically a marker isochromosome 12p that demonstrates tissue-limited mosaicism.  The cytogenetic diagnosis of PKS is often cumbersome due to the absence of the isochromosome in lymphocytes requiring sampling of other tissues.  The mechanism by which the isochromosome 12p results in the constellation of multiple congenital anomalies remains largely unknown.  In this review, we summarize the background of, and recent advances in, the clinical and molecular understanding of PKS.