What is Sialidosis?
Sialidosis is a rare inherited pathological condition which is characterized by metabolic disorder and is caused by deficiency of neuraminidase enzyme. This enzyme is also known by the name of sialidase. As a result of deficiency of this enzyme, there is accumulation of excess fats and carbohydrates in the tissues of the body to include the brain, spinal cord, and other vital organs of the body.
It is basically a lysosomal storage disorder in which the lysosomes present in the cells are not able to break up the fats, carbohydrates, and sugars in the body and then they start to gradually accumulate within the body attaining toxic levels causing conditions like Sialidosis.
Sialidosis is basically of two types, namely type I and type II. Type I Sialidosis is a milder form of Sialidosis and the symptoms of this type of Sialidosis usually present themselves by the second decade of life of the affected individual. The type II of Sialidosis is the more severe form of this disorder with symptoms usually surfacing in early infancy or at maximum early childhood with characteristic red macules, distinct facial features, skeletal deformities, and in some cases cognitive impairment as well due to Sialidosis.
This condition is inherited as an autosomal recessive trait meaning that two copies of the faulty gene from each parent is required for the child to develop Sialidosis.
What are the Causes of Sialidosis?
The main cause of Sialidosis is mutation of gene NEU1. This gene is present in the short arm of chromosome 6. The NEU1 gene is responsible for production of an enzyme called neuraminidase. The function of this enzyme is to facilitate lysosomes to break down complex compounds like fats, carbohydrates, and sugars.
Due to this faulty gene, there is deficiency of the neuraminidase enzyme resulting in the lysosomes not being able to break down the complex fats and carbohydrates, which results in them being accumulated in the tissues of the body to include the brain, spinal cord, and other important organs of the body.
This abnormal accumulation reaches a level of being toxic resulting in condition like Sialidosis. As stated above, this is an autosomal recessive trait meaning that two copies of the faulty gene one from each parent is required for development of Sialidosis.
What are the Symptoms of Sialidosis?
There are two types of Sialidosis which are type I and type II.
Type I Sialidosis is milder form of the disorder and symptoms of this type of Sialidosis start to surface by the second decade of life of the affected individual. The characteristic presenting features of this type of Sialidosis are sudden involuntary muscle contractions, red colored macules in the eyes, and other neurological symptoms.
Type II of Sialidosis is the more severe form and the symptoms start to surface in early infancy or childhood and is again characterized by red colored macules in the eyes, distinct facial features, skeletal deformities, and in some cases cognitive impairment.
How is Sialidosis Diagnosed?
The diagnosis of Sialidosis can be made with the distinct features that this conditions presents with. If it is type I then the symptoms will appear much later in life whereas symptoms of type II Sialidosis will appear much earlier in infancy.
An enzyme assay may be done to confirm the diagnosis of Sialidosis as it will clearly show deficiency of the enzyme neuraminidase. A urinalysis may also be done which will show increased levels of oligosaccharides which is yet another indication of Sialidosis. Additionally, a genetic testing can be done which will clearly show mutation in gene NEU1 and confirm the diagnosis of Sialidosis.
What is the Treatment for Sialidosis?
There is no clear cut treatment for Sialidosis. The treatment is mainly symptomatic and supportive. For neurological symptoms like seizures medications can be used to control them. Antispasmodics can be given to control involuntary muscle spasms. Surgery may be required to treat some of the musculoskeletal deformities.
Additionally, speech and occupational therapy may be required to treat some of the cognitive impairments and make the patient as independent as possible despite suffering from Sialidosis. It is highly recommended that people who have a family history of Sialidosis or a family member suffering from Sialidosis go through genetic counseling as it is quite beneficial in determining their chances of having a baby with a condition like Sialidosis.