Canavan disease is a rare inherited disorder that damages the ability of nerve cells (neurons) in the brain to send and receive messages. This disease is one of a group of genetic disorders called leukodystrophies. Leukodystrophies disrupt the growth or maintenance of the myelin sheath, which is the covering that protects nerves and promotes the efficient transmission of nerve impulses.

Neonatal/infantile Canavan disease is the most common and most severe form of the condition. Affected infants appear normal for the first few months of life, but by age 3 to 5 months, problems with development become noticeable. These infants usually do not develop motor skills such as turning over, controlling head movement, and sitting without support. Other common features of this condition include weak muscle tone (hypotonia), an unusually large head size (macrocephaly), and irritability. Feeding and swallowing difficulties, seizures, and sleep disturbances may also develop.

The mild/juvenile form of Canavan disease is less common. Affected individuals have mildly delayed development of speech and motor skills starting in childhood. These delays may be so mild and nonspecific that they are never recognized as being caused by Canavan disease.

The life expectancy for people with Canavan disease varies. Most people with the neonatal/infantile form live only into childhood, although some survive into adolescence or beyond. People with the mild/juvenile form do not appear to have a shortened lifespan.

Canavan disease is a neurological disorder in which the brain degenerates into spongy tissue full of small fluid-filled spaces. It is caused by a mutation in the ASPA gene which makes an enzyme called aspartoacylase. This enzyme is primarily present in oligodendrocytes, contributes to the manufacture of myelin, and is responsible for breaking down (metabolizing) the brain chemical N-acetyl-L-aspartate or N-acetyl-L-aspartic acid. In Canavan disease, many oligodendrocytes do not mature and instead die, leaving nerve cell projections known as axons vulnerable and unable to properly function.  

Canavan disease causes progressive brain atrophy. There is no cure, nor is there a standard course of treatment. Treatment is symptomatic and supportive. The prognosis for Canavan disease is poor. Death usually occurs before age 10, although some children may survive into their teens and twenties.

While this condition occurs in people of all ethnic backgrounds, it is most common in people of Ashkenazi (eastern and central European) Jewish heritage. Studies suggest that this disorder affects 1 in 6,400 to 13,500 people in the Ashkenazi Jewish population. The incidence in other populations is unknown.

Mutations in the ASPA gene cause Canavan disease. The ASPA gene provides instructions for making an enzyme called aspartoacylase. This enzyme normally breaks down a compound called N-acetyl-L-aspartic acid (NAA), which is predominantly found in neurons in the brain. The function of NAA is unclear. Researchers had suspected that it played a role in the production of the myelin sheath, but recent studies suggest that NAA does not have this function. The enzyme may instead be involved in the transport of water molecules out of neurons.

Mutations in the ASPA gene reduce the function of aspartoacylase, which prevents the normal breakdown of NAA. The mutations that cause the neonatal/infantile form of Canavan disease severely impair the enzyme's activity, allowing NAA to build up to high levels in the brain. The mutations that cause the mild/juvenile form of the disorder have milder effects on the enzyme's activity, leading to less accumulation of NAA.

An excess of NAA in the brain is associated with the signs and symptoms of Canavan disease. Studies suggest that if NAA is not broken down properly, the resulting chemical imbalance interferes with the formation of the myelin sheath as the nervous system develops. A buildup of NAA also leads to the progressive destruction of existing myelin sheaths. Nerves without this protective covering malfunction, which disrupts normal brain development.

Normal Function

The ASPA gene provides instructions for making an enzyme called aspartoacylase. In the brain, this enzyme breaks down a compound called N-acetyl-L-aspartic acid (NAA) into aspartic acid (an amino acid that is a building block of many proteins) and another molecule called acetic acid.

The production and breakdown of NAA appears to be critical for maintaining the brain's white matter, which consists of nerve fibers surrounded by a myelin sheath. The myelin sheath is the covering that protects nerve fibers and promotes the efficient transmission of nerve impulses. The precise function of NAA is unclear. Researchers had suspected that it played a role in the production of the myelin sheath, but recent studies suggest that NAA does not have this function. The enzyme may instead be involved in the transport of water molecules out of nerve cells (neurons).

Health Conditions Related to Genetic Changes

Canavan disease

More than 80 mutations in the ASPA gene are known to cause Canavan disease, which is a rare inherited disorder that affects brain development. Researchers have described two major forms of this condition: neonatal/infantile Canavan disease, which is the most common and most severe form, and mild/juvenile Canavan disease. The ASPA gene mutations that cause the neonatal/infantile form severely impair the activity of aspartoacylase, preventing the breakdown of NAA and allowing this substance to build up to high levels in the brain. The mutations that cause the mild/juvenile form have milder effects on the enzyme's activity, leading to less accumulation of NAA.

An excess of NAA in the brain is associated with the signs and symptoms of Canavan disease. Studies suggest that if NAA is not broken down properly, the resulting chemical imbalance interferes with the formation of the myelin sheath as the nervous system develops. A buildup of NAA also leads to the progressive destruction of existing myelin sheaths. Nerves without this protective covering malfunction, which disrupts normal brain development.

While Canavan disease occurs in people of all ethnic backgrounds, it is most common in people of Ashkenazi (eastern and central European) Jewish heritage. Two specific ASPA gene mutations cause almost all cases of the disease in people of Ashkenazi Jewish descent. One of these mutations replaces the amino acid glutamic acid with the amino acid alanine at position 285 of the enzyme (written as Glu285Ala or E285A). This genetic change greatly reduces the amount of functional aspartoacylase. The other mutation, which is written as Tyr231Ter or Y231X, prematurely stops protein production and leads to an abnormally small, nonfunctional version of the enzyme.

A different ASPA gene mutation is most common in people who are not of Ashkenazi Jewish descent. This mutation substitutes the amino acid glutamic acid for the amino acid alanine at position 305 of aspartoacylase (written as Ala305Glu or A305E). This mutation also leads to the production of a nonfunctional version of the enzyme.

Other Names for This Gene

• ACY2
• ACY2_HUMAN
• aminoacylase 2
• aminoacylase II
• ASP
• N-acyl-L-aspartate amidohydrolase

Genomic Location

The following list includes the most common signs and symptoms in people with Canavan disease (CD). These features may be different from person to person. Some people may have more symptoms than others and symptoms can range from mild to severe. This list also does not include every symptom or feature that has been described in Canavan disease.

• Damage to the optic nerve (Optic atrophy)
• Blindness
• Deafness (Hearing loss)
• Increased head size (macrocephaly)
• Intellectual disability and developmental delay
• Low muscle tone (hypotonia)
• Gastroesophageal reflux
• Feeding difficulties in infancy
• Inability to straighten joints (Flexion contractures)
• Difficulty holding up head when pulled into a seated position (Head lag)
• Abnormal growth of white matter in the brain (leukodystrophy)
• Sleep disturbances

Infants with Canavan disease appear normal at birth and usually develop symptoms between two and six months of age. These include low muscle tone, poor head control, an increased head size, and poor motor development. Later symptoms include optic nerve damage, blindness, and seizures. Over time, stiffening of arms and legs combined with low muscle tone, lead to an inability to move and swallow voluntarily.

• Neurologist
• Ophthalmologist (eye doctor)
• Genetics specialist (genetic counselor and/or geneticist)
• Physical therapist
• Gastroenterologist