Agenesis of the Corpus Callosum (ACC)

What the corpus callosum does

The corpus callosum contains around 200 million nerve fibers and lets the two halves of the brain share information. It helps coordinate movements that need both sides of the body, combine sensory information, and support processing speed, problem solving and social understanding. It forms between about 12 and 20 weeks of pregnancy.

Types of corpus callosum differences

Doctors also describe ACC as isolated (no other brain or body differences) or complex (with other brain malformations, a genetic syndrome or other birth differences). This distinction is the strongest predictor of outcome.

Signs and symptoms

Some people with isolated ACC are only diagnosed as adults, during a scan for an unrelated reason. When symptoms occur, they may include:

In babies and young children

• seizures, including infantile spasms
• feeding and swallowing difficulties
• low muscle tone (hypotonia)
• delays in sitting, crawling and walking
• delayed speech and language
• vision problems and poor eye tracking
• an unusually large or small head

In older children and adults

• clumsiness and poor coordination of tasks that need both hands
• slower processing speed and difficulty with complex reasoning
• difficulty understanding humor, sarcasm and social cues
• reduced sensitivity to pain or temperature in some people
• learning difficulties or intellectual disability
• autistic traits or ADHD-like symptoms in some

Causes

The corpus callosum can fail to form or develop properly because of:

• Chromosome differences: trisomy 8, 13 and 18, and various deletions and duplications.
• Single-gene conditions: more than 200 genetic syndromes include ACC, such as Aicardi syndrome (girls, with seizures and eye abnormalities), Andermann syndrome, Mowat-Wilson syndrome and some metabolic disorders.
• Other brain malformations: Dandy-Walker malformation, Chiari II malformation, schizencephaly and holoprosencephaly.
• Prenatal exposures: alcohol (fetal alcohol spectrum disorders), some medicines, and infections such as rubella and cytomegalovirus.
• Unknown causes in many cases.

Diagnosis

• Prenatal ultrasound: ACC is often suspected on the routine anatomy scan at about 18 to 22 weeks, from indirect signs such as an absent cavum septi pellucidi or enlarged, teardrop-shaped lateral ventricles (colpocephaly).
• Fetal MRI: confirms the diagnosis and looks for other brain differences, which helps estimate outcome.
• Genetic testing: chromosomal microarray and, often, exome sequencing, prenatally through amniocentesis or after birth.
• Brain MRI after birth for children with seizures, delays or a large or small head.
• Assessments: developmental, eye, hearing and neuropsychological testing.

Treatment

There is no treatment that replaces the corpus callosum. Care focuses on the child's specific needs:

• Seizure control with anti-seizure medicines. See epilepsy.
• Early intervention: physical, occupational and speech therapy.
• Feeding support from a feeding therapist or dietitian.
• Educational support with an individualized education program (IEP), focusing on concrete teaching, repetition and social skills.
• Management of associated problems, such as a shunt for hydrocephalus, vision correction and treatment of attention or behavior difficulties.
• Genetic counseling for families, because the chance of recurrence in future pregnancies depends on the cause.

Outlook

Outcomes vary greatly. In isolated ACC, studies suggest most children develop normally or have mild to moderate learning or coordination differences, though subtle social and reasoning differences are common and may only become apparent later in childhood. When ACC occurs with other brain malformations or a genetic syndrome, significant developmental disability and epilepsy are more likely. Many adults with ACC live independently, work and have families. Support groups such as the National Organization for Disorders of the Corpus Callosum connect families and adults with ACC.

Frequently asked questions

What is agenesis of the corpus callosum?

It is a birth difference in which the corpus callosum, the band of nerve fibers that links the two halves of the brain, is completely or partly missing. The brain develops other pathways to share information, which is why effects can range from mild to severe.

Can you live a normal life without a corpus callosum?

Many people with isolated ACC live full, independent lives, sometimes without knowing they have it. Others have learning, coordination or social difficulties, or more significant disability, especially when ACC occurs with other brain or genetic conditions.

What causes agenesis of the corpus callosum?

Causes include chromosome differences, single-gene syndromes, other brain malformations, and prenatal exposures such as alcohol or certain infections. In many children, no specific cause is found despite testing.

Is agenesis of the corpus callosum detected before birth?

Often, yes. It may be suspected on the routine mid-pregnancy ultrasound and confirmed by fetal MRI, which also checks for other brain differences. Genetic testing through amniocentesis can help identify a cause and guide counseling about the likely outcome.

Is ACC hereditary?

Sometimes. If ACC is caused by an inherited gene change, it can recur in future pregnancies. If it results from a new chromosome change or a non-genetic factor, the recurrence risk is usually low. Genetic counseling can give a family a personal estimate.