Observations on dystrophic mouse indicate that a genetically determined partial deficiency of basement membrane is present in the Schwann cells of the peripheral nervous system, and suggest that the Schwann cells develop basement membrane before establishing a definitive relationship with the axons. A consistent finding in all dystrophic mice was a patchy deficiency of the basement membrane of Schwann cells of fibers which were myelinated. The basement membrane was completely absent in amyelinated zones. In longitudinal sections, myelinated fibers entering an area of amyeliation lost not only their Schwann cell covering and myelin sheath, but also the associated patchy basement membrane. Some of the myelinated fibers had abnormally long bare nodal segments, without the usual basement membrane and Schwann cell pseudopodial covering. The abnormally long bare nodes are probably responsible for the 25% reduction in the sciatic nerve conduction velocity. Skin basal cells, skeletal muscle fibers, and endoneurial blood vessels showed continuous basement membrane of normal thickness. The basement membrane of the normal littermates was normal, and identical to that in the normal C57BL mice. The defect of basement membrane was thus inherited in an autosomal recessive manner in these dystrophic mice, and presumably the gene responsible for the dystrophy is also responsible for the basement membrane defect.
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