Agenesis Of The Corpus Callosum (ACC): Causes, Symptoms, Diagnosis, Treatment

Agenesis Of The Corpus Callosum (ACC): Causes, Symptoms, Diagnosis, Treatment

What is Agenesis Of The Corpus Callosum (ACC)?

Agenesis of the corpus callosum is a birth defect in which the structure that connects the two hemispheres of the brain (the corpus callosum) is partially or completely absent. Agenesis of the corpus callosum can occur as an isolated condition or in combination with other cerebral abnormalities, including Arnold-Chiari malformation, Dandy-Walker syndrome, Andermann syndrome, schizencephaly (clefts or deep divisions in brain tissue), and holoprosencephaly (failure of the forebrain to divide into lobes.) Girls may have a gender-specific condition called Aicardi's syndrome, which causes severe mental retardation, seizures, abnormalities in the vertebra of the spine, and lesions on the retina of the eye. Agenesis of the corpus callosum can also be associated with malformations in other parts of the body, such as midline facial defects. The effects of the disorder range from subtle or mild to severe, depending on associated brain abnormalities. Intelligence may be normal with mild compromise of skills requiring matching of visual patterns. But children with the most severe brain malformations may have intellectual retardation, seizures, hydrocephalus, and spasticity.

Agenesis of the corpus callosum occurs in approximately 30-70 of every 10,000 live births in the United States. In most cases, the exact cause of Agenesis of the corpus callosum is unknown, though it has been linked to certain genetic factors, prenatal infections, and chromosomal abnormalities.

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What types of callosal disorders can occur?

The types of callosal abnormality that occurs depends on the cause and timing of the disruption to prenatal brain development. If the corpus callosum does not form during the prenatal period, it will not develop later. Currently, there is some variation in how callosal conditions may be described in medical reports and by medical providers. Below is a list of the most common terms used to describe these conditions.

  • (ACC) Agenesis of the corpus callosum: All or a portion of the corpus callosum is absent; this includes both complete and partial Agenesis of the corpus callosum
  • (AgCC) Agenesis of the corpus callosum: All or a portion of the corpus callosum is absent. This acronym has appeared more recently in some research literature.
  • (c-ACC) Complete agenesis of the corpus callosum: The corpus callosum is completely absent
  • (p-ACC) Partial agenesis of the corpus callosum: A portion of the corpus callosum is absent; most often it is the posterior (back) portion that is missing
  • Hypogenesis of the corpus callosum: Another term sometimes used to describe partial Agenesis of the corpus callosum
  • Hypoplasia of the corpus callosum: The corpus callosum is present, but is abnormally thin
  • Dysgenesis of the corpus callosum: The corpus callosum is present but is malformed in some way; this includes p-Agenesis of the corpus callosum and Hypoplasia

How often do callosal disorders occur?

It is difficult to determine the precise incidence of Agenesis of the corpus callosum and other callosal disorders since a brain scan is required to diagnose the condition, and no one knows how many individuals may have Agenesis of the corpus callosum but not be aware of it.

The development and increased use of new and sophisticated imaging technologies (including prenatal technologies) are helping researchers and medical professionals identify this condition earlier in life as well as across the lifespan. Most sources estimate callosal disorders can occur in up to 4 individuals per 1,000 in the general population and occurs more frequently among persons with developmental disabilities (22-24 per 1,000). Recently, a group of researchers in the U.S. reported an incidence rate of 1 in 4,000 live births, based on a review of prenatal and neonatal imaging studies, but these researchers suggested this may be an underestimate of the true occurrence rate.

What causes Agenesis Of The Corpus Callosum (ACC) and other callosal conditions?

It is often difficult to determine the precise cause of the callosal abnormality, although medical testing, including genetic testing, can sometimes provide valuable information. Agenesis of the corpus callosum researchers, including geneticists, are working to gain a better understanding of the causes of callosal conditions.

Possible causes include:

  • Chromosome errors
  • Inherited genetic factors
  • Prenatal infections or injuries
  • Prenatal toxic exposures
  • Structural blockages, such as cysts
  • Metabolic disorders
  • Other unknown factors

Symptoms of Agenesis Of The Corpus Callosum (ACC)

If an individual has a specific diagnosis, such as Aicardi syndrome, then it may be more appropriate to look at the characteristics of other individuals with the same condition.

  • Delay in achieving motor, language, and cognitive milestones
  • Poor motor coordination (movement e.g. walking or throwing a ball)
  • Increased sensitivity to stimulation such as food textures and touch
  • High tolerance to pain
  • Difficulty with complex tasks, such as using language in social situations, complex reasoning, creativity, and problem solving

  • Limited sophistication of humour
  • Difficulty imagining the potential consequences of behaviour
  • Immature play for age
  • Problems in social situations such as making inappropriate comments
  • A lack of awareness of the thoughts and feelings of others
  • Difficulty starting conversations and keeping conversation flowing
  • Difficulty identifying what a speaker is feeling from their tone of voice or facial expressions
  • Difficulty distinguishing between lies and sarcasm
  • Difficulty in relationships with others, such as emotional give and take
  • Limited insight into their own behaviour
A number of children with corpus callosum abnormalities will have a diagnosis of autistic spectrum disorder or Asperger's syndrome. Some children who have problems with motor coordination may be diagnosed with dyspraxia.

How is Agenesis Of The Corpus Callosum (ACC) diagnosed?

Agenesis of the corpus callosum is diagnosed by performing a scan of the brain. For many individuals a scan will be done during childhood because of problems identified with their development, seizures or other problems. One or more of three methods are commonly used (see glossary of terms section for details). At the moment there is no other test that can reliably diagnose the presence of Agenesis of the corpus callosum in an individual.

How (and when) does Agenesis Of The Corpus Callosum (ACC) occur in more than one member of a family?

Detailed investigation of a person with Agenesis of the corpus callosum may find a known cause for the disorder. Where Agenesis of the corpus callosum is thought to have occurred as the result of an infection or exposure to a medication, drug or excess alcohol, the risks of it recurring is reduced if the same exposure does not occur in the next pregnancy.

Sometimes a known syndrome is suspected by the presence of other problems such as a cleft lip or differences in how fingers have developed. Syndromes including Agenesis of the corpus callosum as a feature can be inherited through families or occur for the first time in an affected person. For individuals in whom a genetic or chromosomal cause is suspected there are a growing number of tests to look for changes in their genes or chromosomes. These are not currently available for all conditions. Your paediatrician or geneticist will be able to advise you further on this.

For the majority of families we are currently unable to say for certain how Agenesis of the corpus callosum has happened in an individual and how likely it is to happen again. For Aicardi syndrome the change is thought to occur in a gene on the X chromosome. Studies of many families with Aicardi syndrome indicate that the recurrence risk is very low.

What will happen during pregnancy?

If Agenesis of the corpus callosum is suspected, a series of additional tests will be conducted to confirm the diagnosis and identify any associated problems. These tests can include a fetal brain MRI and amniocentesis for chromosomal analysis.

Based on the results of these tests, your team of doctors will help you prepare for the care of your child after birth, including identifying specialists, such as a pediatric neurologist or neurosurgeon, to help treat and manage anticipated health problems.

Is there any treatment for Agenesis Of The Corpus Callosum (ACC)?

There is no standard course of treatment for Agenesis of the corpus callosum. Treatment usually involves management of symptoms and seizures if they occur.

Agenesis Of The Corpus Callosum for Children

Changes in the corpus callosum are often diagnosed during childhood because of concerns about development, speech, or other problems such as seizures. It is likely that your child will have had a number of investigations as well as the brain scan such as blood and urine samples. This is often a time where there are a number of appointments with different professionals, including an ophthalmologist (eye specialist), endocrinologist (hormone specialist) and clinical geneticist for their opinions. This can be a frustrating time as it can feel that no-one knows what is wrong with your child.

The majority of children will have a paediatrician (often a community paediatrician) who will be able to assess their development, coordinate their care and put you in touch with other professionals and therapists, such as social workers, occupational therapists, physiotherapist and speech and language therapists. The involvement of health professionals will depend on the level of difficulties your child has. Numerous hospital appointments can be difficult for families to organise and keep track of. This may change as your child grows and you may find it useful to keep a record of the people involved in his/her care.

Do not be afraid to ask questions and find out as much as you can about your child's individual problems. The answers may be helpful in making decisions about your child's current and future needs. Every child is an individual and although he/she is likely to share some of the features of Agenesis of the corpus callosum with other affected children he/she will still have their own unique personality and developmental path. It is not possible to predict exactly what will happen to a child as they grow up or what level of care they will require, although the health professionals involved in your child's care will be able to give you more advice and support about this issue.

Agenesis Of The Corpus Callosum for Adults

Occasionally a callosal abnormality can be found as an incidental finding on a scan done for another reason, such as a head injury. In others, development of other problems such as seizures may prompt further investigations like a brain scan. For a person diagnosed in late adolescence or adulthood the diagnosis can come as a considerable shock as they are often unaware that there has been any change in the way their brain has formed. For some individuals it can feel like an explanation for difficulties they have experienced throughout their life.

It may be useful to talk to a neurologist about the changes on a scan in more detail. If this has been an incidental finding and you are otherwise well there are often no regular medical checks that need to be arranged. As the findings on the brain scan will not change it is unlikely that this will affect your health in new or unexpected ways. You may find it useful to talk to a clinical geneticist if there have been any other unexplained developmental problems or there are concerns about other members of your family.

What is the prognosis?

Prognosis depends on the extent and severity of malformations. Agenesis of the corpus callosum does not cause death in the majority of children. Mental retardation does not worsen. Although many children with the disorder have average intelligence and lead normal lives, neuropsychological testing reveals subtle differences in higher cortical function compared to individuals of the same age and education without Agenesis of the corpus callosum.