The fact that external microenvironment factors can modulate the phenotype of Neu1-deficient macrophages opens a therapeutic window for treating inflammatory and fibrotic conditions as well as genetic diseases such as sialidosis, an autosomal recessive disorder caused by mutations in the Neu1 gene (101) or galactosialidosis, a combined deficiency of Neu1 and cathepsin A (102). The gene discussed is NEU1; the disease is sialidosis.