We then assessed in vitro evidence of cell damage (altered trafficking of PLP, and activation of CHOP and the UPR) in cells transfected with plasmids containing the mutant PLP1 sequences occurring in the patient we identified and in the two other reported MS-related PLP1 mutation patients, in order to determine whether the mutations found in the patients were potentially pathogenic. The gene discussed is PLP1; the disease is myeloid sarcoma.