Plasma lysosomal enzyme levels in patients with motor neuron disease.

beta-Hexosaminidase and acid-alpha-mannosidase were estimated in 17 adult patients with motor neuron disease. Normal plasma levels of beta-hexosaminidase ((A+B) and A) were found in all patients studied. Plasma acid alpha-mannosidase levels were normal in all but two patients with the spinal muscular atrophy type of the disorder. In addition, altered biochemical properties of acid alpha-mannosidase (i.e. Km, thermal stability) were found in the low-activity cases.