Alexander disease is one of a group of neurological conditions known as the leukodystrophies. Leukodystrophies are disorders that result from abnormalities in myelin, the “white matter” that protects nerve fibers in the brain.

In Alexander disease, the destruction of white matter is accompanied by the formation of Rosenthal fibers—abnormal clumps of protein that accumulate in non-nerve cells (astrocytes) in the brain and causes the nervous system to function abnormally.

Alexander disease can appear at any age, although most cases appear in infancy or early childhood. There is no known cure for the disease, but other symptoms may be treated. The disease is often fatal.

Alexander disease is a rare disorder of the nervous system. It is one of a group of disorders, called leukodystrophies, that involve the destruction of myelin. Myelin is the fatty covering that insulates nerve fibers and promotes the rapid transmission of nerve impulses. If myelin is not properly maintained, the transmission of nerve impulses could be disrupted. As myelin deteriorates in leukodystrophies such as Alexander disease, nervous system functions are impaired.

Most cases of Alexander disease begin before age 2 and are described as the infantile form. Signs and symptoms of the infantile form typically include an enlarged brain and head size (megalencephaly), seizures, stiffness in the arms and/or legs (spasticity), intellectual disability, and developmental delay. Less frequently, onset occurs later in childhood (the juvenile form) or in adulthood. Common problems in juvenile and adult forms of Alexander disease include speech abnormalities, swallowing difficulties, seizures, and poor coordination (ataxia). Rarely, a neonatal form of Alexander disease occurs within the first month of life and is associated with severe intellectual disability and developmental delay, a buildup of fluid in the brain (hydrocephalus), and seizures.

Alexander disease is also characterized by abnormal protein deposits known as Rosenthal fibers. These deposits are found in specialized cells called astroglial cells, which support and nourish other cells in the brain and spinal cord (central nervous system).

Mutations in the GFAP gene cause Alexander disease. The GFAP gene provides instructions for making a protein called glial fibrillary acidic protein. Several molecules of this protein bind together to form intermediate filaments, which provide support and strength to cells. Mutations in the GFAP gene lead to the production of a structurally altered glial fibrillary acidic protein. The altered protein is thought to impair the formation of normal intermediate filaments. As a result, the abnormal glial fibrillary acidic protein likely accumulates in astroglial cells, leading to the formation of Rosenthal fibers, which impair cell function. It is not well understood how impaired astroglial cells contribute to the abnormal formation or maintenance of myelin, leading to the signs and symptoms of Alexander disease.

Normal Function

The GFAP gene provides instructions for making a protein called glial fibrillary acidic protein. This protein is a member of the intermediate filament family of proteins. Intermediate filaments form networks that provide support and strength to cells. Several molecules of glial fibrillary acidic protein bind together to form the type of intermediate filament found in astroglial cells. Astroglial cells support and nourish cells in the brain and spinal cord. If brain or spinal cord cells are injured through trauma or disease, astroglial cells react by rapidly producing more glial fibrillary acidic protein.

Although its function is not fully understood, glial fibrillary acidic protein is probably involved in controlling the shape, movement, and function of astroglial cells. Some researchers have suggested that astroglial cells play an important role in the functioning of other cells, including specialized cells that surround nerves (oligodendrocytes) and are involved in the production and long-term maintenance of myelin. Myelin is the fatty substance that forms a protective coating around certain nerve cells and ensures the rapid transmission of nerve impulses. Additionally, astroglial cells may assist in maintaining the protective barrier that allows only certain substances to pass between blood vessels and the brain (the blood-brain barrier).

Health Conditions Related to Genetic Changes

Alexander disease

Researchers have identified more than 50 GFAP mutations that cause Alexander disease. Most of these mutations change one of the building blocks (amino acids) used to make glial fibrillary acidic protein. A few mutations add or remove two amino acids in the protein. All of these changes alter the structure of glial fibrillary acidic protein. The altered protein probably disturbs the formation of normal intermediate filaments. As a result, the abnormal glial fibrillary acidic protein may accumulate in astroglial cells, contributing to the formation of Rosenthal fibers, which impair cell function. It is not well understood how impaired astroglial cells contribute to the abnormal maintenance of myelin, causing the signs and symptoms of Alexander disease.

Other Names for This Gene

• FLJ45472
• GFAP_HUMAN
• Glial Intermediate Filament Protein

Genomic Location

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

Most cases result from new mutations in the gene. These cases occur in people with no history of the disorder in their family. Rarely, an affected person inherits the mutation from one affected parent.

The symptoms of Alexander disease vary depending on the form of the condition (neonatal, infantile, juvenile, and adult). Even within the different forms there may be huge differences in respect to symptoms and severity:

• Neonatal form - Leads to severe disability or death within two years. Characteristics include seizures, hydrocephalus, severe motor and intellectual disability.
• Infantile form - The most common type of Alexander disease. It has an onset during the first two years of life. Usually there are both mental and physical developmental delays, followed by the loss of developmental milestones, an abnormal increase in head size, and seizures.
• Juvenile form - Less common and has an onset between the ages of two and thirteen. These children may have excessive vomiting, difficulty swallowing and speaking, poor coordination, and loss of motor control.
• Adult form - Rare and is generally the most mild. Onset can be anywhere from the late teens to very late in life. In some cases the symptoms mimic those of Parkinson disease or multiple sclerosis.