<s>[INST] <<SYS>> This is a medical question of type : frequency <</SYS>> How many people are affected by Pallister-Killian mosaic syndrome ? [/INST] 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. More than 150 people with Pallister-Killian mosaic syndrome have been reported in the medical literature. </s>