However, almost 50% of children diagnosed with NF1 appear to be the first members of their family to have the disorder. There are two possible explanations for this situation: One of the parents actually does have NF1, only its manifestations are so mild that he or she is unaware of it, or neither parent has the disorder. The genetic alteration, or mutation, occurred in the sperm or egg cell that formed the child. The animation below illustrates how this occurs.