Myelin deficiency (md): a neurologic mutant in the Wistar rat.

Myelin deficiency (md), a newly discovered neurologic mutation in the Wistar rat, is transmitted by an X-linked, recessive lethal gene. Male rats are affected, and the first symptom is a head tremor recognizable at 12 to 15 days of age. The tremors become generalized within a few days and disappear when the animal is at rest. In the later stages, from 17 to 21 days of age, the slightest disturbance will precipitate a generalized seizure. Pups die within 30 days after birth. The only gross postmortem change is a gray color of the spinal cord instead of its normally white appearance. Microscopic findings reveal total lack of myelin formation at all levels of the central nervous system.