What is microcephaly and what causes it?

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.

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."

How common is microcephaly?

In the United States, officials estimate that 25,000 children are born with microcephaly each year, but experts say that not all of them suffer from a neurological condition (see above).

I’ve seen a lot of the heartbreaking pictures of the babies with the condition Brazil. Can you bring me up to date on what is going on there?

Brazilian doctors have reported 4,000 suspected cases of microcephaly versus 147 in 2014. The clusters of cases appear to coincide with the regions where Zika virus is most active. Health officials in the northern part of the country were the first to report their suspicions, and after Brazilian officials began tracking the condition more closely they found a staggering number of other cases. There has been some talk that the big jump in suspected cases in Brazil reflects a greater degree of awareness and that the numbers in the past may have reflected under-reporting. But most global public health officials agree that probably only explains some of the increase — and that there still appears to be a very real and worrisome issue.

What about the cases in French Polynesia?

The country had an outbreak of Zika virus that affected more than 30,000 people, and officials did not notice an increase in microcephaly cases at the time. But after the Brazilian data was out, officials went back and saw an increase in microcephaly cases in French Polynesia, as well. Officials have said the number of microcephaly cases was small and have not said whether any  had been confirmed to be associated with Zika through blood or other tests.

What kind of tests are scientists conducting to try to figure out whether there is a link?

Centers for Disease Control and Prevention scientists worked with Brazilian authorities to test samples from two pregnancies that ended in miscarriage and from two infants with diagnosed microcephaly who died shortly after birth. All four were positive for Zika virus infection, which appears to indicate they may have been exposed while their mothers were pregnant. Tests showed that the infants who died after birth also had Zika virus in the brain. Genetic sequencing of the virus shows it’s the same as the Zika virus found in Brazil.

I'm worried--I'm pregnant and recently traveled to a region on the CDC list. How soon will my physician be able to tell if something's wrong?

Here's what the CDC's Moore told The Washington Post in an email:

“We've been told by clinical experts in maternal-fetal medicine and it is our impression from the literature that it is very difficult to accurately determine microcephaly at the mid-pregnancy ultrasound that most women get as part of routine prenatal care at about 20 weeks. From reports by Brazilian physicians it appears that around 30 weeks is when the microcephaly is best detected along with the ‎abnormalities of the developing brain.
One of the challenges is that the timing of the damage to the brain and resultant small head ‎probably varies depending on when in pregnancy the infection occurred.  Other signs that may also be picked up such as brain calcifications are also variable in the time they are detected by ultrasound. This is the best information we have at this time but of course subject to change as we get more information.”


That sounds like some pretty strong evidence. Why are public health officials saying the association is still only suspected?

There's still a lot of work to be done. Scientists have only been able to confirm the simultaneous presence of the virus and microcephaly in a limited number of babies and are still working their way through other suspected cases to get more information. Brazil is a large country, and there are cases in far-flung states. Part of the reason for the delay is that diagnostic tools to tell whether someone has had Zika are still not readily available. The virus typically clears a person’s blood within a few days to a week, meaning that it’s tricky to detect a past infection. In some cases, tests are able to tell someone had some kind of Zika-like infection in the past but are unable to tell whether it was actually Zika or a similar virus known as dengue fever.

What's next?

Experts say more epidemiological evidence is needed that looks at groups of pregnant women with and without the Zika virus to rule out other factors such as fetal alcohol syndrome, environmental factors or other types of infections.

One important issue is that the mosquito that carries Zika is also known to carry a large number of other viruses like yellow fever, and researchers are investigating whether past infections with other viruses may play a role. World Health Organization officials have said that some of the women who have been tested showed evidence of prior infections with other viruses while others did not — adding to the mystery of what's happening in Brazil.

Finally, if there is a link, researchers must then figure out the biological mechanism of how Zika causes the condition — how it enters the placenta and how it disturbs brain development. Many of those types of experiments could take years to complete.

Mochida, from Boston Children's, said another issue that needs to be looked at is whether women who had babies with the microcephaly are at risk of having other children with the same condition, and to come up with a comprehensive plan for what could be large numbers of children suffering from the condition. He said that local providers should have hope that a better outcome for the child is possible.

A child's "brain is still very plastic," Mochida said. "Even if certain parts are damaged or underdeveloped, sometimes with enough intervention early on we are surprised how much they are capable of."

Staff writer Lena H. Sun contributed to this report.

This post has been updated.

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