Microcephaly Symptoms & Causes

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What causes 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 associated 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 comes with vision and hearing problems.

Microcephaly is often (but not always) congenital, meaning it is already present at birth. In other cases, a baby may be born with an apparently normal head size, and doesn’t begin showing signs until his first few weeks or even first few months of life.

Causes of congenital microcephaly (microcephaly present at birth) include:

  • Prenatal infections: Exposure to Zika virus, especially in the first trimester of pregnancy, can damage nerve cells (neurons) in the brain, especially immature neurons. Other viruses can also cause microcephaly, including rubella (German measles), varicella (chickenpox), toxoplasmosis 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 maturation and growth. In some cases, microcephaly may be related to Down syndrome or certain neurometabolic disorders.
  • Other maternal factors: There is evidence that maternal substance abuse, inadequate nutrition, untreated phenylketonuria (PKU) or exposure to toxic chemicals can cause microcephaly in a baby.

Causes of microcephaly with onset during infancy include:

  • Traumatic brain injury 
  • lack of oxygen to the brain
  • an infection in the brain

What are the symptoms of microcephaly?

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

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

  • failure to thrive
  • poor appetite/feeding
  • unusually high-pitched crying
  • spasticity (involuntary muscle contractions)

Not every child with microcephaly will display noticeable symptoms beyond a small head size. Some children have normal intelligence and can do everything their peers can. However, many children with the condition experience:

  • mild to significant learning disabilities
  • impaired motor function
  • difficulty with movement and balance
  • speech delays

If the brain stem is affected, problems could be more serious, because the brain stem controls vital functions such as breathing. In addition, sometimes microcephaly is accompanied by other medical problems such as:

  • very short stature or dwarfism
  • facial deformities
  • seizures
  • vision and hearing problems (seen in some cases caused by infection)
  • joint deformities (seen in children with congenital Zika infection).
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