PARENTAL ORIGIN AND MECHANISMS OF FORMATION OF 3 CASES OF 12P TETRASOMY

Pallister-Killian syndrome is a clinically recognizable syndrome chara cterized by tissue-limited mosaicism for an extra 12p isochromosome. V ery little is known about the underlying mechanism of this rare rearra ngement. Microsatellite markers were studied from three fetuses with P allister-Killian syndrome and their parents to determine the parent of origin and the cell division yielding the additional isochromosome. I n two cases the isochromosome contained the same allele(s) as a normal transmitted chromosome 12, one paternal and one maternal in origin. A third case showed inheritance of two different maternal alleles, indi cating that at least one meiotic error was involved in the ultimate fo rmation of the extra isochromosome.