If I have understood it correctly, in summary we so far have been given the following sequence of events :

Gluten > those that are genetically sensitive to gluten > antibodies > proteins in the body that are similar to gluten > ..................> Narcolepsy OR Parkinson's Disease OR Dementia

What we are presently lacking are : (1) the names of those proteins in the body that are similar in structure to gluten and that are therefore liable to be affected, (2) precisely how the effect on each specific protein can result in the relevant medical disorder, and (3) why it causes one medical disorder rather than another.