Information on Canavan Disease

Canavan disease, one of the most common cerebral degenerative diseases of infancy, is a gene-linked, neurological birth disorder in which the white matter of the brain degenerates into spongy tissue riddled with microscopic fluid-filled spaces. Canavan disease is one of a group of genetic disorders known as the leukodystrophies.

These diseases cause imperfect growth or development of the myelin sheath, the fatty covering that acts as an insulator around nerve fibers in the brain. Myelin, which lends its color to the "white matter" of the brain, is a complex substance made up of at least ten different chemicals. Each of the leukodystrophies affects one (and only one) of these substances. Canavan disease is caused by mutations in the gene for an enzyme called aspartoacylase.

Canavan disease (CD) belongs to a group of conditions known as leukodystrophies, which result from defects in myelin. Myelin, a substance made up of proteins and lipids, is an integral component of the nervous system. It is commonly known as the "white matter" in the brain; its function is to protect nerves and allow messages to be sent to and from the brain. Children with Canavan disease cannot crawl, walk, sit or talk. Over time they may suffer seizures, become paralyzed, mentally retarded or blind and have trouble swallowing. Although hearing usually remains a functioning sense, deafness may also result. Most children do not live past age 10.

Canavan disease is inherited in an autosomal recessive manner. At conception, the sibs of an affected individual have a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Each pregnancy of a couple in which both partners are heterozygous for a disease-causing mutation in the ASPA gene has a 25% chance of resulting in a child with Canavan disease. Prenatal testing for pregnancies at 25% risk is possible when molecular genetic testing has determined the specific ASPA disease-causing allele in both parents.

The fight to give Max and other children battling Canavan disease, access to the most ambitious research and treatments that can be found, has given way to breakthroughs in gene therapy, which can potentially help millions suffering from neurodegenerative diseases.

Canavan disease demonstrates bilateral symmetric T2 white matter hyperintensity, including involvement of the subcortical arcuate fibers. This disease appears diffusely throughout the cerebral white matter, does not enhance at computed tomography (CT) or MR imaging, and demonstrates variable involvement of the basal ganglia and cerebellar white matter .

Patients with Alexander disease present with clinical and imaging findings similar to those of patients with Canavan disease; this condition often results in a clinical conundrum.

The gene for Canavan disease has been located. Research supported by the NINDS includes studies to understand how the brain and nervous system normally develop and function and how they are affected by genetic mutations. These studies contribute to a greater understanding of gene-linked disorders such as Canavan disease, and have the potential to open promising new avenues of treatment.

Genetic screening of Ashkenazi Jewish individuals for Canavan disease carriers can be done by checking for these two mutations. Screening for Canavan disease carriers requires molecular diagnostic methods. Simple enzyme tests, as commonly used in Tay-Sachs screening, cannot be used for Canavan disease because the activity of the deficient enzyme, aspartoacylase, is not detectable in blood.

Testing for the most common Canavan disease mutations -- there are actually three of them -- will identify about 97% of Ashkenazi Jewish carriers (and 40-50% of the non-Jewish carriers).

Information on Canavan Disease –