Alexander disease is a very rare
autosomal dominant
In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...
leukodystrophy
Leukodystrophies are a group of usually inherited disorders characterized by degeneration of the white matter in the brain. The word ''leukodystrophy'' comes from the Greek roots ''leuko'', "white", ''dys'', "abnormal" and ''troph'', "growth". ...
, which are neurological conditions caused by anomalies in the
myelin which protects nerve fibers in the brain. The most common type is the infantile form that usually begins during the first 2 years of life. Symptoms include mental and physical developmental delays, followed by the loss of developmental milestones, an abnormal
increase in head size and seizures. The juvenile form of Alexander disease has an onset between the ages of 2 and 13 years. These children may have excessive vomiting, difficulty swallowing and speaking, poor coordination, and loss of motor control. Adult-onset forms of Alexander disease are less common. The symptoms sometimes mimic those of
Parkinson’s disease or
multiple sclerosis
Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...
, or may present primarily as a
psychiatric disorder.
According to the
National Institute of Neurological Disorders and Stroke
The National Institute of Neurological Disorders and Stroke (NINDS) is a part of the U.S. National Institutes of Health (NIH). It conducts and funds research on brain and nervous system disorders and has a budget of just over US$2.03 billion. The ...
, the destruction of white matter is accompanied by the formation of
Rosenthal fibers—abnormal clumps of protein that accumulate in
astrocytes in the brain.
The disease occurs in both males and females, and no ethnic, racial, geographic or cultural/economic differences are seen in its distribution. Alexander disease is a progressive and often fatal disease.
Presentation
Delays in development of some physical, psychological and behavioral skills; progressive enlargement of the head (
macrocephaly),
seizures,
spasticity, and in some cases also
hydrocephalus,
idiopathic intracranial hypertension, and
dementia.
Cause
Alexander disease is a genetic disorder affecting the
midbrain and
cerebellum
The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebel ...
of the
central nervous system. It is caused by
mutations in the
gene for
glial fibrillary acidic protein (GFAP)
that maps to
chromosome 17q21. It is inherited in an
autosomal dominant
In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...
manner, such that the child of a parent with the disease has a 50% chance of inheriting the condition, if the parent is
heterozygotic
Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism.
Mo ...
. However, most cases arise ''de novo'' as the result of sporadic mutations.
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.
Rosenthal fibers appear not to be present in healthy people,
but occur in specific diseases, like some forms of
cancer, Alzheimer’s, Parkinson’s, Huntington’s, and ALS.
The Rosenthal fibers found in Alexander disease do not share the distribution or concentration of other diseases and disorders.
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 GFAP.
A
CT scan
A computed tomography scan (CT scan; formerly called computed axial tomography scan or CAT scan) is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers ...
shows:
* Decreased density of white matter
*
Frontal lobe predominance
* Dilated
lateral ventricles may present
Diagnosis
Detecting the signs of Alexander disease is possible with
magnetic resonance imaging
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...
(MRI), which looks for specific changes in the brain that may be tell-tale signs for the disease.
It is even possible to detect adult-onset Alexander disease with MRI.
Alexander disease may also be revealed by
genetic testing
Genetic testing, also known as DNA testing, is used to identify changes in DNA sequence or chromosome structure. Genetic testing can also include measuring the results of genetic changes, such as RNA analysis as an output of gene expression, or ...
for its known cause.
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.
Treatment
No cure or standard procedure for treatment is known, although a
University of Wisconsin study shows promise with gene editing of the astrocytes.
A phase III clinical trial of an
antisense therapy, sponsored by
Ionis Pharmaceuticals, began in 2021. A
bone marrow transplant has been attempted on a child, but it made no improvement.
Hydrocephalus may be seen in younger patients and can be relieved with surgery or by implanting a shunt to relieve pressure.
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 seven.
Usually, the later the disease occurs, the slower its course.
Prevalence
Its occurrence is very rare. The infantile form occurs from birth to 2 years of age.
The average duration of the infantile form is usually about 3 years. Onset of the juvenile form presents between 2 and 12 years of age.
Duration of this form is in most cases about 6 years. The adult form occurs after 12 years.
In younger patients,
seizures,
megalencephaly,
developmental delay, and
spasticity are usually present. Neonatal onset is also reported.
Onset in adults is least frequent. In older patients,
bulbar or
pseudobulbar
Pseudobulbar palsy is a medical condition characterized by the inability to control facial movements (such as chewing and speaking) and caused by a variety of neurological disorders. Patients experience difficulty chewing and swallowing, have in ...
symptoms and
spasticity predominate. Symptoms of the adult form may also resemble
multiple sclerosis
Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...
.
No more than 500 cases have been reported.
See also
*
The Myelin Project
*
The Stennis Foundation
References
External links
OMIM entries on Alexander diseaseInfantile-onset Alexander disease in a child with long-term follow-up by serial magnetic resonance imaging: a case reportAlexander Disease: New Insights From Genetics
{{Cytoskeletal defects
Disorders causing seizures
Leukodystrophies
Rare diseases
Demyelinating diseases of CNS
Neurological disorders in children
Cytoskeletal defects