Does Angelman Syndrome Cause Microcephaly (Small Head)?

Yes, a smaller-than-average head size—a medical term known as microcephaly—is a very common and expected feature of Angelman syndrome ^[1]. It is completely natural for parents to worry when they notice their baby’s head isn’t growing as fast as expected. However, in the context of Angelman syndrome, this is a well-documented part of how the condition develops ^[2].

How Head Growth Changes Over Time

When babies with Angelman syndrome are born, their head circumference (the distance around the largest part of the head) is typically within the normal range for their age and sex ^[2], though a small percentage may have a smaller head at birth.

As the child grows, the rate of their brain and head growth is slower than that of typically developing children ^[2]. This slower-than-normal head growth eventually leads to microcephaly. For most children with Angelman syndrome, this flattening growth curve becomes noticeable to pediatricians and parents by the time the child is between 1 and 2 years old ^[1]. A doctor may note microcephaly in the medical chart when the measurement drops below the 2nd or 3rd percentile on standard growth charts.

Importantly, your child’s head will not stop growing entirely; it will simply continue to grow at a slower pace, following a lower, parallel trajectory on their growth chart ^[1].

Why Does This Happen?

Angelman syndrome is typically caused by a loss of function in a specific gene in the brain, known as the UBE3A gene ^[2]. This gene plays a crucial role in typical brain development. Without enough of the protein it produces, the brain simply does not grow as rapidly or become as large ^[2].

Because the skull grows in response to the brain expanding, the smaller head size is simply a reflection of the brain’s slower growth rate. The skull bones themselves are not fusing too early (a condition called craniosynostosis), which means the brain is not being “squished” and surgery to expand the skull is not necessary ^[2]. The slower growth and smaller head size do not cause your child physical pain or headaches.

Research suggests that the specific genetic cause of your child’s Angelman syndrome can influence this feature. For example, children who have the condition due to a genetic deletion (where a small piece of the chromosome is missing) are more likely to develop microcephaly than those who have the condition due to other genetic mechanisms ^[3]. However, a smaller head size is primarily a physical trait of the syndrome, and having a smaller head does not necessarily mean your child will have more severe developmental delays than another child with Angelman syndrome ^[1].

Does Microcephaly Change Your Child’s Care Plan?

Knowing that your child has or is developing microcephaly does not fundamentally change their daily care plan. It is a known characteristic of the condition rather than a separate complication that requires its own specific medical treatment ^[1].

Your child’s medical team will continue to focus on managing the broader symptoms of Angelman syndrome ^[4]. This means continuing with physical, occupational, and speech therapies to support their overall development ^[5], as well as monitoring and managing other common features, such as seizures or sleep issues ^[3].

Your pediatrician will continue to measure your child’s head at well-child visits to monitor their growth ^[2]. It is important to remember that crossing percentiles on a growth chart for head size is an expected part of the journey for a child with Angelman syndrome, and simply means their body is following the typical pattern for this condition ^[1].