Neuraminidase treatment reveals sialic acid differences in certain genetic variants of the Gc system (vitamin-D-binding protein).

Common and rare Gc phenotypes were analyzed by agarose gel electrophoresis immunofixation and by isoelectric focusing immunofixation before and after neuraminidase treatment. There is a difference between Gc types with double-band and with single-band patterns. Neuraminidase affects only Gc types with a double-band pattern: The double-band pattern is reduced to a single-band pattern. The anodal band disappears after removal of sialic acid by enzymatic cleavage; the cathodal band remains unchanged in its position and becomes stronger. Single-band Gc phenotypes remain unaltered after neuraminidase treatment.