biology

Salla disease

Salla disease is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Salla disease rather than just read about it. In short: Salla disease (SD) or mild Free Sialic Acid Storage Disease (FSASD) is an autosomal recessive lysosomal storage disease characterized by early physical impairment and intellectual disability. Salla disease (also referred to as Finnish-type sialuria, OMIM#604369) was first reported as a lysosomal storage disorder in a family from northern Finland.

Key takeaways

Salla disease belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Salla disease to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Salla disease from memory before moving on to harder problems.

Reference excerpt

Salla disease (SD) or mild Free Sialic Acid Storage Disease (FSASD) is an autosomal recessive lysosomal storage disease characterized by early physical impairment and intellectual disability. Salla disease (also referred to as Finnish-type sialuria, OMIM#604369) was first reported as a lysosomal storage disorder in a family from northern Finland. Salla refers to the area where the affected family resided. It was first described in 1979, after Salla, a municipality in Finnish Lapland and is one of 40 Finnish heritage diseases. The term Salla disease is now used in the literature not only for FSASD cases with the Finnish founder variant in SLC17A5, but also for any mild FSASD cases, independent of the mutation or region of origin. FSASD (Salla and Infantile Free Sialic Acid Storage Disease) affects males and females in equal numbers. The worldwide prevalence of FSASD is estimated at less than 1 per 1,000,000 individuals. Higher estimated prevalence rates occur in the Salla region of Finland and other Scandinavian countries.

Signs and symptoms Affected infants appear normal at birth but may develop symptoms during the first year of life. Individuals with Salla disease may present with nystagmus as well as hypotonia, and may have difficulty coordinating voluntary movements (ataxia), reduced muscle tone and strength, and cognitive impairment. The most severely impaired children do not walk or acquire language, but the typical patient learns to walk and speak and has normal life expectancy. The MRI shows arrested or delayed myelination. Approximately two-thirds of children with mild FSASD eventually learn to walk. Some degree of speech impairment is usually present. Affected infants may learn single words or small sentences, but this ability may be lost as they age. The ability to produce speech is affected more severely than the ability to understand speech. Affected children exhibit some degree of cognitive impairment as well. FSASD (Salla and Infantile Free Sialic Acid Storage Disease) affects males and females in equal numbers. The worldwide prevalence of FSASD is estimated at less than 1 per 1,000,000 individuals. Higher estimated prevalence rates occur in the Salla region of Finland and other Scandinavian countries. Approximately ~300 individuals with FSASD have been reported in the literature, of which the majority (> 160 cases) are of Finnish or Swedish ancestry. Individuals with FSASD may be misdiagnosed or undiagnosed, making it difficult to determine the true frequency of the disease in the general population.

Genetics

SD is caused by a mutation in the SLC17A5 gene, located at human chromosome 6q14-15. This gene codes for sialin, a lysosomal membrane protein that transports the charged sugar, N-acetylneuraminic acid (sialic acid), out of lysosomes. The mutation causes sialic acid to build up in the cells. The disease is inherited in an autosomal recessive manner. This means the defective gene responsible for the disorder is located on an autosome (chromosome 6 is an autosome), and two copies of the defective gene (one inherited from each parent) are required to be born with the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder.

Diagnosis A diagnosis of this disorder can be made by measuring urine to look for elevated levels of free sialic acid. Prenatal testing is also available for known carriers of this disorder. The diagnosis is ultimately confirmed by identifying genetic mutation(s) in the SLC17A5 gene by molecular genetic testing. This testing is available on a clinical basis.

Treatment There is no cure for Salla disease. Treatment is limited to controlling the symptoms of this disorder. Anti-convulsant medication may control seizure episodes. Physical therapists can assist an affected individual in building muscle strength and coordination. Genetic counseling is recommended for affected individuals and their families. All studies receiving U.S. Government funding, and some supported by private industry, are posted on this government website.

Prognosis Some individuals with mild FSASD may not develop symptoms until later in childhood when a variety of neurological findings become apparent. These include seizures, involuntary muscle spasms that result in slow, stiff movements of the legs (spasticity), and repetitive, involuntary, writhing movements of the arms and legs (athetosis). Some individuals who previously developed the ability to walk or talk may lose these skills (regression). Some individuals may experience a gradual coarsening of facial features.

See also Infantile free sialic acid storage disease (ISSD)

References

External links GeneReview/NIH/UW entry on Free Sialic Acid Storage Disorders

Illustrations

Worked examples

Example 1 — a first encounter with Salla disease

Start with the simplest possible case. Write down what Salla disease claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Salla disease before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Salla disease ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Salla disease

In research: Salla disease appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Salla disease in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Salla disease is common in secondary-school and first-year university syllabi. It links to neighbouring topics Autosomal recessive disorders, Finnish heritage disease, Glycoprotein metabolism disorders, so understanding it makes those chapters shorter.
In everyday life: Look for Salla disease outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Salla disease in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Salla disease means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Salla disease out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Salla disease in simple terms?

Why does Salla disease matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Salla disease?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Salla disease.