Microcephaly is a medical condition in which the brain does not develop properly resulting in a smaller than normal head. Microcephaly may be present at birth or it may develop in the first few years of life. Often people with this disorder have an intellectual disability, poor motor function, poor speech, abnormal facial features, seizures, and dwarfism.
The disorder may stem from a wide variety of conditions that cause abnormal growth of the brain, or from syndromes associated with chromosomal abnormalities. A homozygous mutation in one of the microcephalin genes causes primary microcephaly. It serves as an important neurological indication or warning sign, but no uniformity exists in its definition. It is usually defined as a head circumference (HC) more than two standard deviations below the mean for age and sex. Some academics advocate defining it as head circumference more than three standard deviations below the mean for the age and sex.
There is no specific treatment that returns the head size to normal. In general, life expectancy for individuals with microcephaly is reduced and the prognosis for normal brain function is poor. Occasional cases develop normal intelligence and grow normally (apart from persistently small head circumference). It is reported that in the United States microcephaly occurs in 2 to 12 babies per 10,000 births.