What is microcephaly?

When a child has microcephaly, the brain develops abnormally, causing the head to be much smaller than expected for the child's age. ("Micro" means "small," while "cephaly" comes from the Greek word for "head.") Some children with microcephaly have developmental problems or learning disabilities because of a smaller brain size. Microcephaly is relatively rare, though it is estimated that — about 25,000 children in the U.S. are born with microcephaly each year.

Microcephaly is often congenital — meaning present at birth — but can also occur later during infancy. It can have several causes, from genetic problems to prenatal exposure to viruses such as Zika. For more information about the connection between the Zika virus and microcephaly, download 5 Things to Know About Microcephaly.

While there is no specific treatment for microcephaly, early intervention (such as physical, speech, and occupational therapy) can help brain connections grow.

What are the signs and symptoms of microcephaly?

The main feature of microcephaly is a head size that is much smaller than normal for the child’s age and gender.

Other signs and symptoms can vary widely from child to child. They can include:

  • poor weight gain and growth
  • poor appetite/feeding
  • difficulty with movement and balance
  • abnormal muscle tone (too loose, too tight)
  • speech delays
  • mild to severe learning disabilities

Some children with microcephaly also have other medical problems such as:

  • very short stature or dwarfism
  • facial deformities
  • seizures
  • vision and hearing problems
  • joint deformities (for example, in children with Zika infection)

What are the causes of microcephaly?

Microcephaly has a variety of causes. Knowing the cause is important in predicting what symptoms a child with microcephaly will have. For example, some forms of microcephaly are linked with severe developmental delay or a high risk for seizures, while others are not. Some forms can impair motor function or affect other organs in the body. Microcephaly linked to prenatal infections such as Zika sometimes causes with vision and hearing problems.

Microcephaly is often congenital, meaning a baby is born with the condition. In other cases, a baby can develop microcephaly after birth.

Causes of congenital microcephaly include:

  • Prenatal infections: Exposure to the Zika virus, especially in the first trimester of pregnancy, can damage nerve cells in the brain. Other infectious agents can also cause microcephaly, including rubella (German measles), chickenpox, toxoplasma, and cytomegalovirus.
  • Genetic mutations: Several hundred genes have been linked with microcephaly, and more are still being discovered. Defects in these genes can interfere with the brain’s growth. In some cases, microcephaly may be related to Down syndrome or certain neurometabolic disorders.
  • Other causes during pregnancy: There is evidence that alcohol and substance abuse, inadequate nutrition, untreated phenylketonuria (PKU) or exposure to toxic chemicals and certain prescription drugs during pregnancy can cause microcephaly in a baby.

Causes of microcephaly during infancy include:

  • genetic mutations
  • traumatic brain injury
  • lack of oxygen to the brain
  • an infection in the brain

How we care for microcephaly

Boston Children’s Hospital has a long history of caring for children with brain and nervous system disorders. Clinicians in our Department of Neurology, Department of Neurosurgery, and Division of Genetics and Genomics are international leaders in understanding and treating rare conditions like microcephaly. Our Fetal-Neonatal Neurology Program and Brain Development and Genetics Clinic also specializes in diagnosing, studying, and managing microcephaly.

Our care also has a research component. Physicians and scientists in our Brain Development and Genetics Clinic are working hard to understand how and why microcephaly develops, in hopes of one day introducing new therapies. The clinic is actively enrolling patients to understand the effects of different genetic mutations that cause microcephaly.

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