Microcephaly is a condition caused by a defect in the generation of neurons during the development of the brain. It results in a smaller brain size with a reduction in the circumference of the head. Individuals with microcephaly present with a range of symptoms that include: learning disabilities, developmental delay, and seizures.

It is known to be caused by both environmental and genetic factors. Exposure during pregnancy to: infections (e.g. rubella); alcohol; toxic chemicals or nuclear radiation are all known to cause microcephaly. Genetic causes have been attributed to mutations in the following genes: CENPJ; CDK5RAP2; ASPM; microcephalin; TBR2 and STIL.