More symptom information
Learn more about specific symptoms of this leukodystrophy in these pages.
Also known as: Infantile free sialic acid storage disorder (ISSD), Salla disease and intermediate severe Salla disease
Sialic acid storage disorders are a group of rare genetic metabolic disorders characterised by the accumulation of sialic acid-containing compounds in cells and tissues. These disorders result from mutations in the SLC17A5 gene involved in sialic acid metabolism. Symptoms vary widely but commonly include developmental delays, intellectual disabilities, coarse facial features, and skeletal abnormalities. Treatment aims to manage symptoms and may involve enzyme replacement therapy or supportive care. The severity and specific symptoms depend on the type of sialic acid storage disorder.
A new diagnosis can be overwhelming as it brings unique challenges and adjustments, but it is important to remember that you are not alone.
There are three forms of sialic acid storage disorder based on symptom severity, infantile free sialic acid storage disorder (ISSD), intermediate severe Salla disease, and Salla disease. All forms of Sialic acid storage disorder are caused by mutations in the SLC17A5 gene. This gene creates a protein called sialin, which moves free sialic acid around the cell – it may also have other functions which are not yet understood.
When the gene is mutated, sialin either is not produced or does not function normally. This creates a build up of free sialic acid, which is not being moved by the sialin. It is not yet known how this causes the described symptoms.
Autosomal recessive: In autosomal recessive conditions, two copies of the genetic mutation are needed to cause the condition. We all have two copies of every gene, one from our mother and one from our father. The parents of someone with an autosomal recessive condition both carry one copy of the gene with a genetic mutation. Therefore, someone with an autosomal recessive condition has two copies of the genetic mutation, one copy from each parent. Each child of parents that both carry the genetic mutation will have a 25% chance of having the condition, a 50% chance of carrying the genetic mutation (like the parent), and a 25% chance of not having the condition.
Genetic counselling is essential for affected families due to the inheritance pattern of the condition. This is available at hospitals and Regional Genetic Centres. Please contact your doctor if you have any questions.
Learn more about genetic testing and counselling here.
Infantile free sialic acid storage disorder is the most severe form. Infants with ISSD have severe developmental delay, coarse facial features and hypotonia. These distinctive facial features are a flat nasal bridge, anteverted (upturned) nostrils, micrognathism and median facial dysplasia; in which mid facial features are deficient and a cleft lip is present, with or without a cleft palate. They suffer from seizures and bone malformations as well as hepatosplenomegaly and cardiomegaly. Hydrops fetalis, accumulation of fluid in the body before birth, affects some with ISSD. Those with ISSD are not expected to survive past early childhood.
Salla disease is a less severe form of this. In the first year of life, those with Salla disease develop hypotonia and progressive neurological problems. Seizures, ataxia, spasticity, intellectual disability and athetosis are common. Those with Salla disease usually survive into adulthood.
Intermediate severe Salla disease falls between the conditions above in terms of severity.
Learn more about specific symptoms of this leukodystrophy in these pages.
Although there is currently no specific treatment for this leukodystrophy, there is condition management information that may be useful for you in managing your or your loved one’s leukodystrophy.
There may be a current clinical trial, natural history study or patient registry for your condition. Check our current research page and ask your specialist doctor for more information.
We understand that research is a significant priority and source of hope for the leukodystrophy community. There is more research in leukodystrophy now than ever before. Alex TLC actively promotes and supports research in a number of ways.
Every month we update our database of research summaries with the most recent research. This includes summaries of leukodystrophy articles, clinical trials and pharmaceutical press releases. Our summaries allow our community to read about relevant recent research developments in a format that is easily understood.
Learn about the ways in which we can help in the how we support you section. When you or a family member been diagnosed with a leukodystrophy it may be difficult to know where to go for more advice – this information could help.
Our services and equipment section is here to help leukodystrophy patients and their families manage their condition. All information is based on our knowledge of UK services, however, our team are happy to receive support requests from other countries – email us.
You may be introduced to many different medical professionals which you may find confusing. View our guide to the health and care professionals you may encounter, with short descriptions about what they do.
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