Below is an instruction from Human. Write a response.
    ### Instruction:
    How many people are affected by Pallister-Killian mosaic syndrome ?
    ### Response:
    Pallister-Killian mosaic syndrome appears to be a rare condition, although its exact prevalence is unknown. This disorder may be underdiagnosed because it can be difficult to detect in people with mild signs and symptoms. As a result, most diagnoses are made in children with more severe features of the disorder.
    