Mutations in transporter protein shed light on neurodegenerative disorders

Bethesda, MD Researchers at Stanford University have made new discoveries that shed light on two inherited neurodegenerative disorders that are caused by inability of the body to transport sialic acid out of cellular compartments. The findings focus on how different mutations in one transporter molecule can cause a wide spectrum of symptoms in Salla Disease and infantile sialic acid storage disease (ISSD).

The research appears as the "Paper of the Week" in the January 14 issue of the Journal of Biological Chemistry, an American Society for Biochemistry and Molecular Biology journal.

The free sialic acid storage diseases are a range of rare, autosomal recessive, neurodegenerative disorders that result from the accumulation of sialic acid within lysosomes. There are two forms of the disease--Salla Disease, the milder form, and the more severe infantile sialic acid storage disease (ISSD).

"Clinically, these diseases consist of a spectrum," notes Dr. Richard J. Reimer of Stanford University. "In the severe phenotype infants are born with dysmorphic features, enlarged internal organs and die within a few months. With the milder disease the affected individuals have physical and mental developmental delay, but can live to adulthood."

In Salla Disease and ISSD, the amino sugar sialic acid accumulates in lysosomes, the cellular compartments that are responsible for degrading macromolecules. "Sialic acid is part of a number of proteins and normally it is removed from proteins as they are degraded in lysosomes," explains Dr. Reimer. "The free sialic acid is then released into the cytoplasm of the cell so that it can be reincorporated in to newly synthesized proteins. In Salla Disease and ISSD, the sialic acid is removed from the protein, but it is not released from the lysosome."

Genetic studies have shown that mutations in a single gene encoding a protein called sialin are responsible for both diseases. "The mil

Contact: Nicole Kresge
American Society for Biochemistry and Molecular Biology

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