Alright, so, sometimes we hear about certain birth defects, who knows from where, and we are horrified at the concept of knowing someone who was affected by it, my choice for this is Spina Bifida.
I am certain you are capable of googling the grotesque pictures that come along with researching this birth defect, and I implore you to post what you think is the most horrifying.
A short summary of spinal bifida from Wikipedia:
Spina bifida (Latin: "split spine") is a developmental birth defect caused by the incomplete closure of the embryonic neural tube. Some vertebrae overlying the spinal cord are not fully formed and remain unfused and open. If the opening is large enough, this allows a portion of the spinal cord to stick out through the opening in the bones. There may or may not be a fluid filled sac surrounding the spinal cord. Other neural tube defects include anencephaly, a condition in which the portion of the neural tube which will become the cerebrum does not close, and encephalocele, which results when other parts of the brain remain unfused.
XI Wiki


