It seems that the misspelling "kdd" may have been intended as "kid". Other suggestions include "add" or "odd". However, based on the context, "kid" appears to be the most plausible correction.
MDDMDD is an abbreviation for Major Depressive Disorder, a mental health condition characterized by persistent low mood and loss of interest or pleasure in activities.
ODD It was odd that there were no birds chirping in the morning.
PDDPDD is a disorder that affects social interactions, communication, and behavior of an individual.