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Infantile Free Sialic Acid Storage Disease (ISSD) is caused by a defective sialic acid transporter (called sialin) in the lysosome membrane normally ensuring the efflux of free sialic acid (or N-acetylneuraminic acid) outside the lysosome. The condition is autosomal recessive and very rare (except in Northern Finland where an estimated 1/40 people are carriers). The disease presents in utero with fetal hydrops and ascites (fluid accumulations) or at birth with hypotonia (lack of muscle tone), hepatosplenomegaly (enlargement of the organs), coarse facial features, bone malformations, severe motor disorders, mental retardation, and seizures. Death usually occurs in early childhood. |