What causes Prader-Willi syndrome?
PWS is caused by a lack of active genetic material in a particular region of chromosome 15 (15q11-q13). Normally, individuals inherit one copy of chromosome 15 from their mother and one from their father. In PWS, the genetic defect causing inactivity of chromosome 15 can occur in one of three ways: PWS by Deletion Most often, part of the chromosome 15 that was inherited from the person’s father is missing, or deleted, in this critical region. This small deletion occurs in approximately 70% of cases and usually is not detectable with routine genetic analysis such as amniocentesis. PWS by UPD Another 30% or so of cases occur when an individual inherits two chromosome 15’s from their mother, and none from the father. This scenario is termed uniparental disomy (UPD). PWS by Imprinting Mutation Finally, in a very small percentage of cases, a small genetic mutation in the Prader-Willi region causes the genetic material in that area to be inactive.
