Agenesis of the Corpus Callosum
Agenesis of the corpus callosum (ACC) is a rare neurological condition where the corpus callosum is underdeveloped. The corpus callosum is a bridge of white matter joining the two cerebral hemispheres (left and right sides) of the brain. White matter consists of nerve fibres surrounded by a type of fat called myelin, which gives the whitish appearance to the white matter. The corpus callosum forms during the brain development when a baby is in the womb. People usually only find out there is total or partial absence of the corpus callosum with brain imaging tests and these will usually only be performed if individuals have neurological problems that suggests something may be wrong with the nervous system or brain. So there may be people without symptoms that have partial or complete callosal agenesis (loss of white matter from the corpus callosum).
Medical text written November 1998 by Dr L Rosenbloom, Consultant Paediatric Neurologist, Alder Hey Children’s Hospital, Liverpool, UK. Last updated May 2012 by Dr KRE Pohl, Consultant Paediatric Neurologist, Evelina Children’s Hospital, Guy’s and St Thomas’ NHS Foundation Trust, London, UK.
The symptoms of ACC are best described under two headings: syndromic (those that are associated with a known syndrome), and nonsyndromic, agenesis of the corpus callosum that is not part of a known syndrome.
Non-syndromic ACC is common and affected patients usually have a large head, seizures and developmental delay. Hypertelorism (widely spaced eyes) also occur in many people with the condition. Seizures may be difficult to control. Hydrocephalus can also occur.
Many neurological syndromes also include ACC. All of these have additional brain malformations and affected individuals are usually severely affected often displaying typical facial features and global developmental delay. This is often associated with other midline cerebral and cranial abnormalities such as septo-optic dysplasia. ACC is sometimes associated with abnormal development of the pituitary gland. Because of this, fits are sometimes due to hypoglycaemia (low levels of growth hormone and cortisol) as well as due to structural brain abnormality.
ACC may be, and often is, associated with other developmental brain abnormalities and it is often these, rather than the callosal agenesis itself, which is the cause of subsequent difficulties with the neurological system.
In nonsyndromic ACC, genetic inheritance is rare. Genetic advice to affected individuals and their families can be helpful. More frequently, the non-syndromic form of callosal agenesis is an abnormality of brain development that is determined once a baby is conceived. In the syndromic form of ACC, referral for precise neurological diagnosis is required. The majority of these syndromes do occur sporadically but there are occasional groups reported with the condition occurring in families.
ACC is undetectable through routine prenatal tests, however, it may be detected with a scan at 18 weeks.
The Group is a Registered Charity in England and Wales No. 1086019. It provides information and support for children and adults with Agenesis of the Corpus Callosum or Aicardi Syndrome and their parents, families and carers.
Group details last updated December 2014.