Motor neuron disease in a patient with a monoclonal IgMk directed against GM1, GD1b, and high-molecular-weight neural-specific glycoproteins.

In a patient with motor neuron disease and benign IgMk monoclonal gammopathy, the M protein reacted with the glycolipids GM1, GD1b, and asialo GM1 and, by immunoblot, with some high-molecular-weight neural-specific glycoproteins. The main reactive bands had an approximate molecular weight of 250 and 400 kd, were most concentrated in the spinal cord, and were also bound by the lectin peanut agglutinin. The presence of the Ga1(beta 1-3)Ga1NAc epitope on these neural-specific glycoproteins may help to explain the selective neurological impairment of the patient.