Two related but distinct neurological disorders are Prader-Willi syndrome (PWS) and Angelman syndrome (AS). Children with PWS are obese, have weak muscle tone, and delayed development. Children with AS have severe speech impairment, developmental delay, intellectual disability, and problems with movement and balance. However, both disorders are due to the deletion of the same part of chromosome 15. When the deletion is in the copy of chromosome 15 that came from the father, the child has PWS, but when the deletion is in the copy of chromosome 15 that came from the mother, the child has AS. What hypothesis can explain these observations?

Question

Quizplus · Accepted Answer

Parental imprinting occurs when one copy of a gene is silenced based on its parental origin. This phenomenon explains the difference in phenotype between PWS and AS despite the same genetic deletion on chromosome 15. The genes in the deleted region on chromosome 15 are normally subject to imprinting, with the paternal copy being active and the maternal copy being silenced. In individuals with PWS, the deletion removes the active paternal genes, resulting in the manifestation of PWS symptoms. In individuals with AS, the deletion removes the silenced maternal genes, resulting in the manifestation of AS symptoms.

Two Related but Distinct Neurological Disorders Are Prader-Willi Syndrome (PWS)