Canavandisease is also known in the literature as spongiform degeneration of the nervous system, spongiform leukodystrophy or Canavan-van Bogaert-Bertrand. The disease was first described in the 1930s by Myrtelle Canavan, an American physician and neurologist.

Causes of the disease

The cause of the disease is a mutation in the ASPA gene, located on chromosome 17. The ASPA gene encodes an enzyme, N-acetylaparase, which is responsible for breaking down N-acetyl-L-aspartic acid (NAA). NAA is found primarily in the brain and its role is not fully explored. Scientists speculate that NAA may be involved in the production of myelin sheaths on neurons and may be involved in water transport in cells of the nervous system. In Canavan disease, a mutation in the ASPA gene causes impaired synthesis of the enzyme, resulting in the deposition of N-acetyl-L-aspartic acid in the brain, which damages the white matter. In addition, NAA degrades myelin sheaths, thereby impairing normal neuronal function. The result of such widespread changes is problems in the functioning of the brain, spinal cord and peripheral nerves.

Inheritance

The disease is inherited in an autosomal recessive manner, meaning that both parents must have the 'defective' gene and pass it on to their offspring. The disease is very rare, with an incidence of about 1 in 100,000 healthy born children, and affects boys more often than girls.

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Symptoms of the disease

The disease can present in several forms - congenital, childhood, adolescent or occasionally late-onset. The first symptoms of the disease occur around the age of 4-5 months and manifest themselves in the form of motor disturbances. The child has problems with motor control, rolling to the side, sitting. Children affected by Canavan's disease show weakened muscle tone, spastic paresis and sometimes polycephalus. Associated symptoms include epileptic episodes, gastro-oesophageal reflux, lack of weight gain, vomiting and sleep problems. As the disease progresses, blindness may occur, associated with optic nerve atrophy. In the juvenile and late forms, symptoms to be concerned about are sudden paresis, visual problems leading to blindness, memory loss and dementia.

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How to diagnose the disease?

When a parent observes worrying symptoms in a child, the first step is to report them to a doctor. The doctor may order a determination of N-acetyl-L-aspartic acid in urine, blood, PMR (cerebrospinal fluid) and brain tissue. Confirmation of the disease is also provided by a genetic test, which allows the disease to be diagnosed unequivocally, indicating a mutation in a gene. If there is a family history of Canavan disease, prenatal testing can be carried out by analysing the amniotic fluid or by performing trophoblast tests.

Treatment options

Treatment of genetic diseases with the current state of knowledge is based on minimising the effects of the disease. Unfortunately, at the moment, treatment does not allow the defective gene to be 'repaired' and thus improve the functioning of the nervous system. In the treatment of Canavan's disease, symptoms are primarily alleviated - rehabilitation is introduced, anticonvulsants are used, and vision loss is supported by the use of appropriate corrective glasses. In 2017, the US Food and Drug Administration (FDA) approved a treatment for Canavan disease based on the use of genetic engineering. The cost of the therapy reaches more than $1.5 million. More drug candidates are in clinical trials.

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Canavan's disease - spongiform degeneration of the nervous system

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