Last updated: 2003-09-11
Canavan disease, also known as "spongy degeneration of the brain," was first described by Myrtelle M. Canavan in 1931.
This disease is characterized by the progressive loss of white matter, the regions of the brain through which nerve impulses are sent to other parts of the brain or to the spinal cord. Loss of white matter gives the brain a spongy, degenerative appearance. Affected infants appear normal after birth. Later they are found to be hypotonic (floppy), fail to achieve head control, and become developmentally delayed by five to eight months of life. Characteristic features include an enlarged head, mental retardation, seizures and feeding difficulties. The severity and life expectancy of children with Canavan disease vary. Some die in the first year of life, while others survive beyond their teens.
As no proven treatment is currently available for the underlying cause of Canavan disease, supportive care is essential. For example, insertion of a gastrostomy tube through an incision in the stomach may help maintain good nutrition and minimize the risk of aspiration (inhalation of food or liquids into the lungs). Medications to control seizures or other manifestations of Canavan disease are also important to consider.
Until 1988 the diagnosis of Canavan disease required brain biopsy to show spongy degeneration of the white matter. In 1987, it was discovered that children with Canavan disease excrete increased amounts of a substance known as N-acetylaspartic acid (NAA) in their urine. Following this discovery, many diagnoses of Canavan disease were made by demonstration of increased NAA in the urine.
Canavan disease is inherited in an autosomal recessive manner, which means that couples with an affected child have a 1 in 4 (25%) chance in each future pregnancy to have another child with Canavan disease. The parents of a child with Canavan disease are said to be "carriers," but are not themselves affected with the disease. Although Canavan disease may occur in families of many different ethnic backgrounds, it is significantly more common among Ashkenazi Jews. It is estimated that approximately 1 in 40 Ashkenazi Jews are carriers of Canavan disease. In the past, carrier testing for Canavan disease was performed by measurement of an enzyme called aspartoacylase, which is deficient in children with the disease. In 1993, the gene for aspartoacylase was identified on chromosome 17, and two specific gene mutations were found in Ashkenazi Jewish families. These findings now permit more accurate carrier testing and prenatal diagnosis of Canavan disease in the Ashkenazi Jewish population. In some instances, prenatal diagnosis by gene mutation analysis may not be possible. Under those circumstances, it is possible to perform prenatal diagnosis by measuring the amount of NAA in amniotic fluid.
In November of 1998, the American College of Obstetricians and Gynecologists adopted a position statement recommending that Ashkenazi Jewish couples be offered carrier screening for Canavan disease. Ideally the screening should be offered prior to pregnancy, and may be offered in conjunction with carrier screening for Tay-Sachs disease. Because of the increased frequency of the disease in Ashkenazi Jews, as well as the ability to identify a majority of a carriers with a high degree of accuracy, population based screening programs for Canavan disease are being implemented in many communities.