Genetic counseling: Hypoplasia - Agenesis of the Corpus Callosum

Hypoplasia - Agenesis of the Corpus Callosum

Definition

 * underdevelopment (hypoplasia) complete absence (agenesis) of the CC

Corpus collosum

 * The area of the brain (large fiber tract) which permits the exchange of information between the left and right cerebral hemispheres.
 * "the seat of the soul". Used to be that the thickness of its body was related to the level of intelligence.
 * Function is uncertain because there is no consistent pattern when it is malformed or absent.
 * Embryology: forms between 9-16 weeks of development. anterior to posterior.

Indicence
rare; no specific numbers

Diagnosis

 * ACC is usually diagnosed between 0-2 years (by MRI or CT scan) but may never be dx.
 * May occur as severe syndrome, a milder condition, or an asymptomatic finding
 * Signs and Symptoms:
 * Seizures (infantile spasms)
 * Feeding problems
 * Delays in holding head erect, sitting, standing and walking
 * microcephaly

Possible clinical impairments

 * Deficit or delay in mental and physical development, hand-eye coordination and/or visual and auditory memory
 * Could also include: hydrocephaly, seizures, dyskinesia, repetitive speech, headaches

Etiology

 * Most are isolated/sporadic
 * Males and females equally affected
 * May be caused by a genetic syndrome such as:
 * Aicardi's syndrome: ACC, infantile spasms, severe mental retardation and chorioretinal lacunae
 * Grubben syndrome
 * Wolf-Hirschhorn syndrome: chromosome abnormality
 * Opitz-Frias syndrome
 * Joubert syndrome
 * X-linked syndromes: Bertini, Opitz-Kaveggia, Orofaciodigital, Proud, Pyruvatedehydrogenase
 * May be associated with other cerebral anomalies such as Arnold-Chiari malformation, Dandy-Walker syndrome, Andermann syndrome, schizencephaly, holoprosencephaly and migrational anomalies
 * Sometimes associated with complex multi-system anomalies and chromosomal abnormalities (trisomy 13 and 18).

Management

 * No specific treatment. May involve managing treatment of other conditions such as hydrocephaly and seizures if they occur

Prognosis

 * Excellent in most isolated cases
 * Does not cause death in vast majority
 * Many will lead normal lives and have average intelligence
 * Children w/ ACC and DD and/ or seizures should be screened for metabolic disorders.
 * Mental retardation is not progressive

Resources

 * NINDS Agenesis of the Corpus Callosum Information Page www.ninds.nih.gov/health_and _medical/disorders/agenesis_doc.htm
 * Agenesis of the Corpus Collosum. Mental Retardation and Congenital Malformations of the Central Nervous System. Warkany, J, Lemire, R, Cohen, M.
 * Human Embryology. Larsen, WJ.