Microcephaly Symptoms & Causes

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Q&A: Zika virus in mothers linked with microcephaly in babies in Brazil.

Learn more about Zika, the mosquito-transmitted virus that can affect how the brain forms before birth.

Microcephaly is a neurological condition that occurs because a child’s developing brain doesn’t grow properly. This causes the disease’s most obvious physical symptom: a head size that is much smaller than normal.

Because the brain does not grow at a normal pace, the skull doesn’t, either. Many (but not all) children with microcephaly also experience cognitive delays and neurological problems as a result.

  • Microcephaly is often (but not always) congenital, meaning it is already present at birth.
  • Other times, a child is born with a normal brain and skull, but then his brain fails to develop properly during his infancy.
  • A traumatic brain injury or infection can also lead to microcephaly.
  • Microcephaly is relatively rare, affecting about 25,000 children in the U.S. each year.

Some children with microcephaly have normal intelligence and experience no particular difficulty with schoolwork, physical activity, relationships or any other aspect of their lives. However, many children with the disease – especially those with more severe cases – face:

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

They can also have other medical problems, like:

Although it’s not possible to restore a child’s brain and skull to normal size and appearance, treatment for microcephaly can make a significant difference in helping him with any medical, neurological and emotional symptoms he might be facing. 

Here at Boston Children’s Hospital, our expert neurological and neurosurgical teams are fully equipped to assist your child – and each member of your family – at every step of the way.

Spotlight on: Neonatal & Congenital Anomaly Neurosurgery

Boston Children's Department of Neurosurgery specializes in complex procedures for newborns - and fetuses still in the womb - with disorders of the brain and nervous system.

Microcephaly Causes

What causes microcephaly?

There are a number of possible causes:

  • Most of the time, it happens because of an inherited defect in a gene that interferes with the brain’s maturing and growing.
  • There is evidence that, in some cases, microcephaly is caused by something that affects the mother during pregnancy. These factors can include:
  • substance abuse
  • inadequate nutrition
  • untreated phenylketonuria (PKU)
  • exposure to certain viruses – especially chickenpox, rubella (German measles) or cytomegalovirus
  • exposure to toxic chemicals
  • A baby can also be born healthy, but then acquire microcephaly because of:
  • a brain injury
  • lack of oxygen to the brain
  • an infection in the brain
  • Finally, microcephaly can be related to another disorder, such as:
  • Down syndrome and other chromosomal disorders
  • certain neurometabolic disorders 

Signs and Symptoms of Microcephaly


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. You should always seek a diagnosis from a qualified medical professional.

Frequently Asked Questions (FAQs) about Microcephaly 

Q: Will my child be OK?
Your child’s exact prognosis depends on her specific symptoms and circumstances. Your treating clinician is the best source of information about her long-term outlook.

However, it’s important to remember that – while microcephaly cannot be cured altogether – it is treatable. Not every child experiences neurological complications, and even in the most severe cases, there are treatment options that can help your child feel and function better.

Q: Is microcephaly always evident at birth?
No, not always. While many babies with microcephaly have a visibly small head size at birth, many others appear normal and don’t begin showing signs until their first few weeks or even first few months of life.

Q: Are there different types of microcephaly?
Microcephaly is classified according to its severity. The most seriously ill children will experience significant learning and memory problems. They may also have physical complications, such as seizures.

However, some children with microcephaly experience almost no noticeable symptoms: While their heads are smaller than average, and they may be shorter in stature than most children their age, they have normal intelligence and can do everything their peers can.

Q: Does microcephaly always cause complications?
No. Many children with the disorder have problems with learning, memory, speech or movement. However, others will never develop any complications beyond their noticeably small head size.

Q: Is there any way to prevent it?
A: When microcephaly is genetic – caused by a defect in an inherited gene – nothing can be done to prevent it.

If there is no genetic link to the disease, expectant mothers can lessen their chances of having a baby with microcephaly by avoiding the following during pregnancy:

Q: Can microcephaly be detected during pregnancy?
If your child has the congenital form of microcephaly – meaning it is caused by an inherited defect in his genes – it might be possible to detect the disorder with a prenatal ultrasound during the third trimester of pregnancy.

Q: If my child has microcephaly, do I need to be screened before any future pregnancies?
Whether you should be screened for microcephaly depends on the cause of your child’s disease: If his microcephaly is related to a type of brain injury, for example, genetic screening would not be useful.

If your child is believed to have congenital microcephaly (present at birth) that is caused by an inherited defect, genetic counseling is very advisable as you plan to add to your family.

Q: Besides medical treatment, what types of support might my child need as he grows?
The exact support your child will require depends on his specific symptoms and the severity of his disease. Your treatment team will advise you on the best resources to meet your child’s needs.

In general, children with microcephaly can benefit from:

Did you know?
In addition to diagnosing and treating brain disorders in babies, the experts in Boston Children's Fetal-Neonatal Neurology Program are also working hard to uncover new insights into these diseases.

Questions to ask your doctor

You and your family play an essential role in your child’s treatment for microcephaly. It’s important that you share your observations and ideas with your child’s treating physician, and that you have all the information you need to fully understand the treatment team’s explanations and recommendations.

You’ve probably thought of many questions to ask about your child’s symptoms and prognosis. It’s often very helpful to jot down your thoughts and questions ahead of time and bring them with you, along with a notebook, to your child’s appointment. That way, you will have all of your questions in front of you when you meet with your child’s treating clinician and can make notes to take home with you.
Initial questions to ask your doctor might include: 

  • How did you arrive at this diagnosis?
  • Are there any other conditions my child might have instead?
  • Are there any other related conditions my child could have?
  • Does my child require further testing or procedures?
  • How extensive is the damage to his neurological function?
  • What medications will you prescribe and what are the possible side effects?
  • What adjustments need to be made in his home and school routines?
  • How should I talk about my child’s condition with him as he gets older?
  • How should I explain my child’s condition to others?
  • Should I be screened as a carrier for this condition?
  • What other resources can you point me to for more information?
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