Studies of lysosomal sialic acid metabolism: retention of sialic acid by Salla disease lysosomes.

Purified rat liver lysosomes were incubated in 0.2 M sialic acid resulting in an increase in lysosomal free sialic acid of 3.8 +/- 1.5 nmol/unit beta hexosaminidase. Sialic acid loss by these lysosomes was stimulated 2-3 fold by 25 mM sodium phosphate. Loss of sialic acid by lysosomes from cultured human diploid fibroblasts was similar to that observed in rat liver lysosomes while loss of sialic acid by lysosomes from cultured fibroblasts from a patient with infantile Salla disease occurred much more slowly. Salla disease appears to be the consequence of defective lysosomal transport of sialic acid and is analogous to cystinosis, a disorder of lysosomal amino acid transport.