Canine inherited hypertrophic neuropathy.

A recessively inherited hypertrophic neuropathy was discovered in Tibetan Mastiff dogs. Affected pups developed a generalized weakness with hyporeflexia shortly after weaning. Diagnostic findings in 10-18-week-old pups included: moderate to severe reduction in nerve conduction velocities, infrequent denervation potentials, and inconstant elevation in CSF protein. Light- and electron-microscopic studies of peripheral nerves and roots revealed widespread demyelination and primitive onion bulb formation with relatively little degeneration of axons. Myelin changes often were most striking in the cytoplasmic regions of the sheaths and consisted of separations at the major dense lines, anomalous incisure patterns, and marked filamentous accumulations in the inner spirals and adaxonal cytoplasm. The results of these initial studies suggest an inborn defect in the Schwann cell's ability to form or maintain a stable myelin sheath.