Clinical description of an adult male with psychosis who showed FMR1 gene methylation mosaicism.

Unstable trinucleotide repeat DNA contained in numerous genes has been proposed as the underlying mechanism in the clinical phenomenon of genetic anticipation in fragile X syndrome and other neurodegenerative diseases. No clear evidence has been found for the role of these abnormal trinucleotide repeat expansion-containing genes in schizophrenia or other psychiatric disorders. This report describes an adult male with psychosis who was later found to have methylation mosaicism of the FMR1 gene. We discuss history, examination, and investigation which led to the diagnosis and treatment response of this patient.