What causes agenesis of the corpus callosum? 1 possible condition
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The corpus callosum is a structure in the brain that connects the right and left sides of your brain. “Agenesis” is a word that means “not formed” or “absence of an organ.” Corpus callosum agenesis is a birth defect where the connection between the right and left hemispheres of the brain is not formed or is incompletely formed.
The corpus callosum is a curved structure inside the brain that connects the right and left sides of the brain. In the corpus callosum, 200 million nerve fibers pass information back and forth between the hemispheres of the brain.
The complete or partial absence of the corpus callosum occurs as a birth defect. Agenesis of the corpus callosum (ACC) occurs when the nerve fibers that make up the corpus callosum do not form, or form incorrectly (corpus callosum dysgenesis). You can actually survive if the left and right sides of the brain are not connected, but you may have various problems over your lifetime.
Other terms used to refer to some form of ACC include:
- Partial corpus callosum agenesis
- Hypogenesis of the corpus callosum
- Hypoplasia of the corpus callosum
- Dysgenesis of the corpus callosum
It is estimated that four out of every 1,000 people have some disorder of the corpus callosum. ACC is the most common cerebral malformation.
No formation of the corpus callosum, or a partial or malformation of this structure, is a congenital birth defect. The corpus callosum forms late in the first trimester of pregnancy. Exposure to certain medications (including valproate, an epilepsy medication) or toxins (drugs or alcohol) during this period is one risk factor for the condition. Viral infections like rubella during pregnancy may result in this condition. Another risk factor is chromosomal damage and abnormalities like trisomy (having three copies of chromosome 8, 13 or 18). Cysts inside the brain that block the growth of the corpus callosum can also cause this condition.
Most cases of ACC actually occur along with other brain abnormalities. Some of these are genetic disorders. These usually have a larger impact on brain formation. These disorders include:
- Arnold-Chiari malformation
- Dandy-Walker syndrome
- Schizencephaly (deep clefts in brain tissue)
- Holoprosencephaly (failure to divide into lobes)
- Hydrocephalus (fluid in the brain)
- Aicardi syndrome
- Andermann syndrome
- Acrocallosal syndrome
Isolated ACC cases, where there is not significant other brain damage, may not have dramatic symptoms. Mental retardation is possible, but many individuals have normal intelligence. Seizures are a common problem in people with ACC.
Often, developmental delays do occur, but may be mild. Developmental delays seen with ACC include delay in motor skills like sitting, walking, or riding a bike. Poor coordination is common. Feeding problems and swallowing difficulties may exist. Some language and speech delays in expressive communication may be noted.
Other symptoms as a child gets older include:
- vision problems
- hearing impairment
- low muscle tone
- high pain tolerance
- sleep difficulties
- chronic constipation
- social immaturity
- inability to see another’s point of view
- poor understanding of social cues
- attention deficit
- obsessive behaviors
- inability to interpret facial expression
- difficulty with abstract reasoning
- no understanding of slang or idiom
- difficulty separating truth and untruth
ACC can be found during prenatal scans during an ultrasound. A magnetic resonance imaging scan (MRI) of the brain may be done on the pregnant mother to confirm diagnosis. If suspected in an older child, an MRI or computed tomography scan (CT scan) is performed.
There is no cure for ACC. However, the symptoms can be treated successfully. Depending on the severity of other brain malformations, patients can lead long healthy lives. Support with medications to control seizures, and physical, speech and occupational therapy can help.
- ACC- What is agenesis of the corpus callosum? (2013). University of Maine, Education and Human Development. Retrieved from http://umaine.edu/edhd/about/research/acc/what-is-agenesis-of-the-corpus-callosum-acc/
- Corpus Callosum of the brain. (August 2012). Medline Plus. Retrieved from http://www.nlm.nih.gov/medlineplus/ency/imagepages/8753.htm
- Corpus Callosum Disorders. (2009). National Organization for Disorders of the Corpus Callosum. Retrieved from http://www.nodcc.org/index.php?option=com_content&task=view&id=12&Itemid=27
- Isolated Corpus Callosum Agenesis. (June 2007). Orphanet. Retrieved from http://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN&Expert=200
- NINDS Agenesis of the Corpus Callosum Information Page. (February 2011). National Institute of Neurological Disorders and Stroke. Retrieved from http://www.ninds.nih.gov/disorders/agenesis/agenesis.htm
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