Clinical Guidance

Free sialic acid storage disorder (FSASD) comprises a spectrum of neurodegenerative phenotypes resulting from increased lysosomal storage of free sialic acid . Historically, FSASD was divided into separate allelic disorders: Salla disease, intermediate severe Salla disease, and infantile free sialic acid storage disease (ISSD). Salla disease was named for a municipality in Finnish Lapland where a specific founder variant is relatively prevalent. However, the term "Salla" has been used in the literature to refer to less severe FSASD in general. Less severe FSASD is characterized by normal appearance and neurologic findings at birth followed by slowly progressive neurologic deterioration resulting in mild-to-moderate psychomotor delay, spasticity, athetosis, and epileptic seizures.

Diagnostic Criteria

There are no consensus clinical diagnostic criteria for free sialic acid storage disorder (FSASD).

Suggestive Findings

FSASD should be suspected in individuals with the following clinical, imaging, and laboratory findings [, , , ].

Less Severe FSASD (including Salla disease)

Clinical findings

• Truncal ataxia and hypotonia apparent at approximately age one year

Management Guidelines

No clinical practice guidelines for free sialic acid storage disorder (FSASD) have been published. In the absence of published guidelines, the following recommendations are based on the authors' personal experience managing individuals with this disorder.

Evaluations Following Initial Diagnosis

To establish the extent of disease and needs in an individual diagnosed with FSASD, the evaluations summarized (if not performed as part of the evaluation that led to the diagnosis) are recommended.

Surveillance Guidelines

To monitor existing manifestations, the individual's response to supportive care, and the emergence of new manifestations, the evaluations summarized in are recommended. Table 6. Free Sialic Acid Storage Disorder: Recommended Surveillance