Summary about Disease
Sialic acid storage disease (SASD) is a rare, inherited metabolic disorder caused by a deficiency in the sialin protein, which is responsible for transporting sialic acid (a sugar molecule) across the lysosomal membrane. This deficiency leads to the accumulation of free sialic acid within the lysosomes of cells throughout the body, leading to cellular dysfunction and a range of symptoms affecting multiple organ systems. SASD presents in a spectrum of severity ranging from a severe, infantile form (ISSD) to a milder, later-onset form (Salla disease).
Symptoms
Symptoms vary widely depending on the severity of the sialin deficiency and the specific form of SASD. Common symptoms include:
Infantile Free Sialic Acid Storage Disease (ISSD):
Severe developmental delays
Coarse facial features
Enlarged liver and spleen (hepatosplenomegaly)
Kidney problems (nephropathy)
Heart problems (cardiomyopathy)
Skeletal abnormalities
Hypotonia (decreased muscle tone)
Cataracts
Salla Disease:
Intellectual disability
Ataxia (lack of coordination)
Seizures
Muscle spasticity
Nystagmus (involuntary eye movements)
Delayed motor development
Causes
SASD is caused by mutations in the SLC17A5 gene. This gene provides instructions for making the sialin protein. Mutations in the *SLC17A5* gene disrupt the normal function of sialin, impairing the transport of sialic acid out of lysosomes and leading to its accumulation. SASD is inherited in an autosomal recessive pattern, meaning that an affected individual must inherit two copies of the mutated gene (one from each parent) to develop the disorder.
Medicine Used
There is currently no cure for SASD, and treatment is primarily supportive, focusing on managing the symptoms and complications of the disease.
Symptom Management:
Medications to control seizures
Physical and occupational therapy to improve motor skills and mobility
Speech therapy to improve communication skills
Nutritional support to ensure adequate growth and development
Treatment for specific organ involvement (e.g., kidney problems, heart problems)
Potential Therapies:
Research is ongoing to explore potential therapies for SASD, including enzyme replacement therapy and gene therapy.
Is Communicable
No, SASD is not communicable. It is a genetic disorder caused by a gene mutation and cannot be spread from person to person.
Precautions
Since SASD is a genetic disorder, precautions primarily involve genetic counseling for families with a history of the condition.
Genetic Counseling:
Families with a history of SASD should seek genetic counseling to understand the risk of having a child with the disorder.
Genetic testing can be performed to identify carriers of the mutated SLC17A5 gene.
Prenatal testing may be available to determine if a fetus is affected with SASD.
How long does an outbreak last?
SASD is not an infectious disease and therefore does not have outbreaks. It is a chronic condition that is present from birth, although the severity and progression of symptoms can vary.
How is it diagnosed?
Diagnosis of SASD typically involves a combination of clinical evaluation, biochemical testing, and genetic testing.
Clinical Evaluation: A thorough physical examination and evaluation of the individual's symptoms and medical history.
Biochemical Testing: Measuring the levels of free sialic acid in urine, fibroblasts, or other tissues. Elevated levels of free sialic acid are suggestive of SASD.
Enzyme Assay: Measuring sialin enzyme activity in cultured fibroblasts or leukocytes.
Genetic Testing: Sequence analysis of the SLC17A5 gene to identify mutations.
Brain Imaging: MRI can show characteristic changes in the brain.
Timeline of Symptoms
The timeline of symptoms varies significantly depending on the form of SASD.
Infantile Free Sialic Acid Storage Disease (ISSD): Symptoms typically manifest in infancy or early childhood. Severe symptoms such as developmental delays, coarse facial features, and organomegaly are present soon after birth.
Salla Disease: Symptoms may be more subtle and develop later in childhood. Motor delays, ataxia, and intellectual disability may become apparent in early to mid-childhood. Seizures may develop later. The progression is slow, but symptoms are present for life.
Important Considerations
SASD is a rare and complex disorder, and management requires a multidisciplinary approach involving specialists in genetics, neurology, nephrology, cardiology, and other areas.
Early diagnosis and intervention are important to optimize outcomes and improve quality of life for affected individuals.
Genetic counseling is essential for families with a history of SASD to understand the risks of recurrence and make informed reproductive decisions.
Support groups and patient advocacy organizations can provide valuable resources and support for individuals and families affected by SASD.
Research is ongoing to develop new treatments and therapies for SASD.