DESCRIPTION
In the United States, about 1 in every 800–5,000 babies are born with microcephaly. There is a wide range due to different causes at different ages. It is also because of a range of severities (mild or borderline, moderate and severe).
Children with microcephaly have a head circumference (distance around the head) at or below the third percentile for head growth. In other words, they will have a smaller head than 97% or more of children of their age and sex.
A healthcare provider will measure the head circumference during the physical examination. This is compared to the standard charts provided by organizations like the CDC (Center for Disease Control). These measurements are also compared to the measurements for parents or siblings.
Symptoms can range from mild to severe. In general, the smaller the head size, the more severe the symptoms. There are a number of different causes, as described below:
- Lack of normal brain growth
- Poor brain development before or after birth
- Exposures to infections, toxins, drugs and alcohol
- Interruption to flow of oxygen and or blood supply to the brain during development
There may also be unknown reasons.
SIGNS AND SYMPTOMS
Signs
Diagnosis is made by measuring the head.
This may be done with:
Differences in how a child’s brain has developed can be seen with brain imaging.
Magnetic resonance imaging (MRI) is often used for this imaging.
Symptoms
The two symptoms present in about half of all patients are:
- Developmental delay
- Cognitive disability
These symptoms can range from mild to severe. It depends on the cause and severity of the microcephaly.
Other possible symptoms include issues with:
- Seizures
- Movement
- Balance
- High muscle tone
- Low muscle tone
- Feeding
- Growing or gaining weight
- Hearing
- Vision
Sometimes, microcephaly is part of an underlying genetic syndrome in which other organ systems have problems.
Sometimes, a small head is the only sign of microcephaly.
CAUSES
There are many possible causes.
Genetic Causes
Genetic causes can occur for different reasons. They may be:
- Inherited from parents
- Due to a new change in a gene in the child
Examples of genetic causes include:
Chromosome disorders
Isolated primary microcephaly
Metabolic disorders
Metabolic disorders may be inherited or due to new mutations. They cause an abnormality of proteins that control functions in the brain and body, resulting in either a build-up of toxic substances in the brain and other tissues or an absence of an important function in the brain.
Structural brain malformations
Sometimes, the brain structure is abnormal during the developmental process in the womb. It can be caused by many factors such as genetic, infectious, metabolic issues and exposures. These include abnormal structural developmental diagnoses such as: holoprosencephaly, polymicrogyria, schizencephaly, lissencephaly, neural tube defects and others.
Syndromic microcephaly
Acquired Causes
Acquired causes are causes not related to genetics.
During Pregnancy
Microcephaly can be caused by issues affecting a mother during pregnancy.
They include:
- High blood pressure
- Untreated diabetes
- Problems with the placenta
- Malnutrition
- Infections, such as: Toxoplasmosis, Syphilis, Varicella Zoster, Parvovirus B-19, Rubella, Cytomegalovirus (CMV), Herpes virus, Zika virus
- Heavy alcohol or drug use, other toxins
Other Acquired Causes
Some other causes that can arise include:
Hypoxic ischemic brain injury
Due to lack of oxygen or blood flow. Learn more about hypoxic ischemic brain injuries.
Other brain injury
Stroke is an example, or trauma to the developing brain.
Sometimes, the exact cause cannot be determined.
OUTLOOK
Prognosis varies greatly. It depends on:
- Severity
- Underlying cause
In general, the more severe the condition (the smaller the child’s head), the more severe the symptoms.
Severe Cases
In severe cases:
Lifespan
Disability
Milder Cases
In milder cases:
Disability
