RNASET2 (ribonuclease T2) is an enzyme which belongs to the RNase T2 family. It is highly expressed in the temporal lobe and fetal brain. RNASET2 gene is a novel member of the Rh/T2/S-glycoprotein class of extracellular ribonucleases. It is a single copy gene that maps to 6q27, a region associated with human malignancies and chromosomal rearrangement. Defects in RNASET2 are the cause of leukoencephalopathy cystic without megalencephaly. An infantile-onset syndrome of cerebral leukoencephalopathy. Affected newborns develop microcephaly and neurologic abnormalities including psychomotor impairment, seizures and sensorineural hearing impairment. The brain shows multifocal white matter lesions, anterior temporal lobe subcortical cysts, pericystic abnormal myelination, ventriculomegaly and intracranial calcifications.