The demyelination (dmy) rat is a unique spontaneous myelin mutation that exhibits severe myelin breakdown with a late onset of clinical signs. The causative autosomal recessive mutation has been identified at the MRS2 magnesium transporter (Mrs2) gene, which encodes an essential component of the major Mg2+ influx system in mitochondria. To clarify the pathogenesis of myelin destruction in dmy rats, we performed a microarray analysis using spinal cord samples. Overall design: For the microarray analysis, 6-week-old control and dmy/dmy rats were deeply euthanized. Total RNA was isolated from the cervical spinal cord with the SV Total RNA isolation system. The RNA was then prepared and hybridized to the rat Genome 230 2.0 Array (Affymetrix, Santa Clara, CA) by Bio Matrix Research, Inc. (Nagareyama, Japan.), following the protocols provided by Affymetrix.