Encyclopedia / M / Microcephaly



Microcephaly is a congenital anomaly characterized by abnormal smallness of the head in relation to the rest of the body and by underdevelopment of the brain, resulting in some degree of mental retardation.


Persons with Microcephaly have a head more than two standard deviations below the average circumference size for age, sex, race, and period of gestation, with a narrow, receding forehead.

A small head, often with a receding forehead, large ears and nose is often an associated feature of other disorders, rarely occurring in isolation. However, infants with true hereditary microcephaly, an autosomal recessive disorder, have only head and facial abnormalities as physical symptoms.


This defect may be caused by a number of factors - genetic, chromosome disorders, environment, and factors of unknown origin.

Environmental causes include prenatal radiation, infections (including rubella and toxoplasmosis), and drugs such as alcohol. Women with phenylketonuria (PKU) may also give birth to microcephalic children. A number of multiple anomaly syndromes have microcephaly as a feature.

Microcephaly may be inherited but the gene is considered to be extremely rare. In the general population, microcephaly due to genetic factors occurs in 1 in 30,000 to 50,000 live births, and in 1 per 10,000 births due to other causes. In some populations, frequency may be as high as 1 in 2,000 births.

True hereditary microcephalics live an average-length life span, yet some die early due to other congenital defects or infectious diseases.


Physical growth is generally retarded and children walk more slowly than their normal counterparts. There is a delay in speech and mental development. Some patients experience seizures and spasticity and may exhibit strabismus (cross eye). Personality and mood are variable and may vacillate to extremes.

Nearly 90 percent suffer from some form of brain damage. However, it is important to note that not all individuals with microcephaly will be retarded and have neurologic abnormalities. Some are entirely normal.


Microcephaly is sometimes visibly obvious in newborns by the characteristic forehead, flattened back of the head, and small or closed fontanels (the soft spots between the skull and the bones). It is most often diagnosed by measuring the infant's head circumference, though it may be diagnosed prenatally by ultrasound.


For those who are developmentally normal and asymptomatic, no treatment is required. In other children, treatment is supportive and depends on the child's symptoms and development. If there is evidence of speech or mental impairment, special education may be necessary.


What is the probable cause of the microcephaly?

Is it related to another disease or disorder?

To what extent is there delayed development?

Is there evidence of speech or mental impairment?

Is there mental retardation?

Can any of the symptoms be treated?

What is the future prognosis?