The function of NEU4 (neuraminidase 4, Ensembl gene identifier ENSG00000204099) is as follows. Exo-alpha-sialidase that catalyzes the hydrolytic cleavage of the terminal sialic acid (N-acetylneuraminic acid, Neu5Ac) of a glycan moiety in the catabolism of glycolipids, glycoproteins and oligosaccharides. Efficiently hydrolyzes gangliosides including alpha- (2->3)-sialylated GD1a and GM3 and alpha-(2->8)-sialylated GD3 (PubMed:15213228, PubMed:15847605, PubMed:21521691). Hydrolyzes poly- alpha-(2->8)-sialylated neural cell adhesion molecule NCAM1 likely at growth cones, suppressing neurite outgrowth in hippocampal neurons (By similarity). May desialylate sialyl Lewis A and X antigens at the cell surface, down-regulating these glycan epitopes recognized by SELE/E selectin in the initiation of cell adhesion and extravasation (PubMed:21521691). Has sialidase activity toward mucin, fetuin and sialyllactose (PubMed:15847605). {ECO:0000250|UniProtKB:Q8BZL1, ECO:0000269|PubMed:15213228, ECO:0000269|PubMed:15847605, ECO:0000269|PubMed:21521691}.