From which parent does the microdeletion on chromosome 15 causing Prader-Willi syndrome typically originate?

Prader-Willi syndrome is associated with a specific type of genetic alteration known as paternal deletion of chromosome 15. This syndrome results from a microdeletion in the region of chromosome 15 that can lead to the loss of function of certain genes that are typically expressed from the paternal allele.

In the majority of cases of Prader-Willi syndrome, the condition arises when the paternal copy of this chromosome is deleted or unexpressed, while the maternal copy is imprinted (silenced), thus leading to a functional deficiency of the genes that are normally active on the paternal chromosome. This observation aligns with the epigenetic mechanism where certain genes are "turned off" in one parent via imprinting, which is crucial for normal development.

Therefore, it can be articulated that the microdeletion causing Prader-Willi syndrome usually and specifically originates from the father, as the presence of an intact maternal chromosome does not compensate for the loss of function caused by the deletion. This genetic mechanism is what distinctly links Prader-Willi syndrome with paternal inheritance patterns.