Infantile sialidosis: natural history in a preterm infant with two new pathogenic mutations and new ocular findings.

Sialidosis is a rare lysosomal storage disease caused by an α-N-acetyl neuraminidase-1 deficiency due to mutations of the NEU1 gene (6p21). Disease severity varies among patients and is linked to the level of residual neuraminidase activity in vivo. At least 40 disease-causing mutations in the NEU1 gene have been reported. Sialidosis occurs in two main clinical variants: type I, the milder form of the disease, and type II, which is subdivided into congenital, infantile, and juvenile forms. We report the clinical, biochemical, and molecular characterization of a patient with infantile sialidosis type II. The abnormal urinary oligosaccharide profile is described for the first time. The genetic characterization of the patient showed two previously unreported missense mutations in the NEU1 gene: p.R78C (c.232C>T) and p.R290Q (c.869G>A).