Alexander disease

Alexander disease, also known as fibrinoid leukodystrophy, is a progressive and fatal neurodegenerative disease. It is a rare genetic disorder and mostly affects infants and children, causing developmental delay and changes in physical characteristics.^[1][2][3]

Presentation

Delays in development of some physical, psychological and behavioral skills; progressive enlargement of the head (macrocephaly), seizures, spasticity, in some cases also hydrocephalus, idiopathic intracranial hypertension, dementia.^[2]

Cause

Alexander disease is a genetic disorder affecting the midbrain and cerebellum of the central nervous system. It is caused by mutations in the gene for glial fibrillary acidic protein (GFAP)^[4][5][6] that maps to chromosome 17q21. It is inherited in an autosomal dominant manner, such that the child of a parent with the disease has a 50% chance of inheriting the condition, if the parent is heterozygotic. However, most cases arise de novo as the result of sporadic mutations.^[2]

Alexander disease belongs to leukodystrophies, a group of diseases that affect the growth or development of the myelin sheath. The destruction of white matter in the brain is accompanied by the formation of fibrous, eosinophilic deposits known as Rosenthal fibers.^[2][3][7] Rosenthal fibers appear not to be present in healthy people,^[3][8] but occur in specific diseases, like some forms of cancer.^[3][8] The Rosenthal fibers found in Alexander disease do not share the distribution or concentration of other diseases and disorders.^[3]

Pathology

Alexander disease causes the gradual loss of bodily functions and the ability to talk. It also causes an overload of long chain fatty acids in the brain which destroy the myelin sheath. The cause of Alexander disease is a mutation in the gene encoding glial fibrillary acidic protein (GFAP).^{[2][3][4][5][9]}

A CT scan shows:

• decreased density of white matter
• frontal lobe predominance
• +/- dilated lateral ventricles

Diagnosis

It is possible to detect the signs of Alexander disease with magnetic resonance imaging (MRI), which looks for specific changes in the brain that may be tell-tale signs for the disease.^[10][11] It is even possible to detect adult-onset Alexander disease with MRI.^[9] Alexander disease may also be revealed by genetic testing for the known cause of Alexander disease.^[12][13] A rough diagnosis may also be made through revealing of clinical symptoms including, enlarged head size, along with radiological studies, and negative tests for other leukodystrophies.^[8]

Treatment

There is currently no cure, or standard procedure taken for treatment.^[2][3] A bone marrow transplant has been attempted on a child, but did not cause the patient's condition to improve.^[14][15] Hydrocephaly may been seen in younger patients and can be relieved with surgery or implanting a shunt to relieve pressure^[16]

Prognosis

The prognosis is generally poor. With early onset, death usually occurs within 10 years from the onset of symptoms. Individuals with the infantile form usually die before the age of 7.^[17] Usually, the later the disease occurs, the slower its course is.^[2][3]

Prevalence

Its occurrence is very rare. The infantile form from birth to 2 years of age.^[6] The average duration of the infantile form of the illness is usually about 3 years. Onset of the juvenile form presents between two and twelve years of age.^[6] Duration of this form is in most cases about 6 years. The adult form from twelve years and older.^[6] In younger patients, seizures, megalencephaly, developmental delay, and spasticity are usually present. Neonatal onset is also reported.^[18] Onset in adults is least frequent. In older patients, bulbar or pseudobulbar symptoms and spasticity predominate. Symptoms of the adult form may also resemble multiple sclerosis.^[2]

There are no more than 500 reported cases.^[2]

See also

• The Myelin Project
• The Stennis Foundation

References

External links

• OMIM entries on Alexander disease