THE N-acetyl-β-D-glucosaminidase (hexosaminidase) activity in cultured human fibroblasts consists of at least three components (A, B and C) 1-3. At least two of these (designated Hex A and Hex B) seem to be closely related, for (1) antiserum against Hex A reacts against Hex B, and vice versa4,5 (2) in Tay-Sachs disease only Hex A activity is deficient, accompanied by an increase in Hex B activity in certain tissues1,6, and (3) both Hex A and Hex B activities are missing in Sandhoff disease, another autosomal recessive disorder7. But in spite of several theories 8-11, the precise relationship between these components remains unknown, as does the nature of the genetic and biochemical relationships between the two diseases. To investigate these questions we have fused Tay-Sachs with Sandhoff fibroblasts and obtained cultures containing heterokaryons which produce a hexosaminidase which is absent from the parent lines. It has the electrophoretic and heat lability characteristics of the Hex A found in normal fibroblasts.
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