Zika Crisis: What is Microcephaly?

The term refers to a rare neurological condition in which children have unusually small heads. In many cases it also means a baby's brain is smaller and may not have developed properly. The condition can be caused by hundreds of factors, both genetic and environmental. Genetic disorders associated with microcephaly include Down's syndrome and other chromosomal disorders. Possible environmental factors include lack of oxygen to a baby’s brain in utero or during birth, drug/alcohol use during pregnancy, malnutrition, injury to the brain, exposure to radiation or toxins. Infections such as chicken pox or rubella have also been documented to lead to the condition.

[WHO declares global public health emergency, says causal link to brain defects ‘strongly suspected’]

What is the prognosis for a child with the condition?

The spectrum of ways in which microcephaly can affect a child is wide. About 10 percent of children are born with normal intelligence, and having a small head is mostly a superficial issue. At the other end are those who cannot talk or walk and need constant care. Then there are those in between who are high-functioning but have intellectual disabilities, difficulties with speech or coordination, or seizures. While there’s no treatment or way to reverse the condition, early intervention treatments — such as speech therapy, occupational therapy and other special needs therapy — have helped some children.

Ganeshwaran H. Mochida, a pediatric neurologist and researcher at Boston Children’s Hospital, explained in an interview that “microcephaly is not a single disease.” “It’s a physical sign diagnosed by measuring one’s head size by tape measure, and then you compare the size with the standard growth curve,” he said. Mochida said there is no consensus about where the cut-off is for head size, but it is typically two to three standard deviations smaller than the norm for the baby's gender and age.

Mochida said that the prognosis often depends on the cause of the microcephaly. In the cases of viruses, which may also apply to Zika, he said that babies with more severe effects may have been infected during the first trimester because that is when the brain is forming.

Early reports of cases in Brazil seem to indicate that many of the cases are on the more severe end, with some of the babies born with microcephaly having died as a result of miscarriage or shortly after birth.

"[We] are seeing babies who have severe microcephaly, much more than we would expect," Cynthia Moore, an expert in birth defects with the U.S. Centers for Disease Control and Prevention, said in a recent press briefing. "Close follow-up is needed for regular checkups to monitor and evaluate these affected babies."

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