1. The relative amount of free neuraminic acid shows a marked fluctuation.

2. Further research showed that an optimal agglutination of erythrocytes by influenza virus requires a distinct amount of neuraminic acid at the receptor site, probably dependent on the nature of the agglutinating virus.

3. ‘The condition differs from the other forms of Amaurotic idiocy by virtue of lack of fundal changes and the presence of significant cerebellar dysfunction.’ ‘Klenk found no increase in the total amount of gangliosides; but Cumings reported an increase in the neuraminic acid level in the cortex in adult cases of Amaurotic family idiocy.’

4. The present invention relates to a method for preparing a sialic acid derivative, wherein the method is characterized in that a process of using N-acetyl-D-glucosamine to prepare CMP-M-acetylneuraminic acid and a process of combining sialic acid with galactose or a galactose derivative to prepare a sialic acid (neuraminic acid) derivative are performed together in one reactor.