Alternate names

ISSD; Sialuria Infantile Form; Infantile Sialic Acid Storage Disorder; Free Sialic Acid Storage Disease; N-acetylneuraminic acid storage disease; NANA Storage Disease; Sialuria Finnish Type


Infantile Free Sialic Storage Disease (ISSD) is the most severe form of sialic acid storage disease, a rare inherited metabolic disorder. Affected children lack the ability to transport sialic acid out of the cell, leading to abnormal accumulations that primarily affect the nervous system. Affected infants have severe developmental delay, hypotonia, and failure to gain weight and grow at the expected rate (failure to thrive). They may have unusual facial features that are often described as ""coarse"", bone malformations, hepatosplenomegaly, and cardiomegaly. The abdomen may be swollen due to enlarged internal organs and ascites. Affected infants may also have hydrops fetalis at birth. Seizures are common.

Diagnostic testing, physical findings, and ICD-9-CM coding

Diagnostic testing:

  • Genetic testing for mutations in the SLC17A5 gene
  • Lab testing shows elevated sialic acid levels in cultured tissue cells, and increased free sialic acid in the urine

Physical findings: The diagnosis is suspected in infants with early multisystem involvement, including hydrops fetalis, failure to thrive, increasing coarse facial features, neurologic deterioration, and dysostosis (abnormal bone formation). These children also have ataxia and hypotonia at approximately age one year, along with developmental delay and growth retardation in early childhood, and severe cognitive and motor impairment.

Onset and progression 

Onset of this disorder is at or even before birth. Children usually live only into early childhood.


There is no current cure for this disorder. Treatment is supportive and may include physical, occupational and speech therapies; nutrition therapy; and anti-seizure treatment."

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