Quick teaser: Mosaicism occurs when one of the cells in the early stages of the embryo suffers a copy error or other type of mutation during cell division, ultimately resulting in an individual who has some parts of his body (those composed of cells "descended" from the faulty cell) genetically different from the other parts of his body.
I first found out about this syndrome while researching possible causes for my wife's atypical migraines. Mosaicism can cause all sorts of bizarre medical cases, since the symptoms (if any) depend upon the vast numbers of ways that cells can "fumble" their DNA, multiplied by the vast numbers of ways that the good cells / bad cells can be distributed in the body (causing only certain tissues/organs to be affected, and not others).
As PW's linked article mentions, research is underway to see if mosaicism might be responsible for some cases of autism and alzheimer's, for example.
Any mention of psychiatric disorders in the research you have done on mosaicism?