Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to Pallister-Killian mosaic syndrome ?
    ### Response:
    Pallister-Killian mosaic syndrome is usually caused by the presence of an abnormal extra chromosome called an isochromosome 12p or i(12p). An isochromosome is a chromosome with two identical arms. Normal chromosomes have one long (q) arm and one short (p) arm, but isochromosomes have either two q arms or two p arms.
    