What Is Holoprosencephaly (HPE)? Understanding Brain Development in Babies

When you hold a newborn baby in your arms, the joy and love you feel are hard to put into words. Yet sometimes, unexpected health challenges can happen before your little one enters the world. Today, we will explore a complex yet important birth condition known as holoprosencephaly so you can feel informed and prepared.

Hearing about a rare medical condition can feel overwhelming for any parent or caregiver. Understanding the fundamentals of how this condition develops can help guide your conversations with doctors. Let us walk through what holoprosencephaly means, how doctors diagnose it, and what support is available for families.

What Is Holoprosencephaly (HPE)?

Simply put, holoprosencephaly, often called HPE, is a birth condition that happens while a baby is growing inside the womb. In this condition, the developing brain fails to divide into right and left halves properly. Normally, the brain splits into two distinct halves connected by a bundle of nerve fibers called the corpus callosum. Each half also divides into specialized regions like the frontal, parietal, occipital, and temporal lobes.

This normal division of the brain is essential for everyday functioning. It allows different parts of the brain to process multiple signals and manage complex body tasks at the same time. When this proper division does not happen during early pregnancy, it can lead to physical and neurological challenges for the child.

HPE develops very early in pregnancy, often before you might even know you are pregnant. There are different types of HPE with varying levels of severity. Every child experiences this condition in a unique way. This symptoms can look very different from one family to another.

What Are the Main Types of HPE?

Medical experts classify holoprosencephaly into several main types based on how much the brain failed to divide. Let us look at them in order from most severe to mildest:

Alobar Holoprosencephaly.

This is the most severe form of HPE. In alobar HPE, the baby's brain does not divide into left and right hemispheres at all. As a result, structures in the middle of the brain and face fail to form properly, and the brain cavities merge into a single large chamber. This severe form often comes with major facial differences. Many babies with alobar HPE are stillborn or pass away shortly after birth.

Semilobar Holoprosencephaly.

With this type of HPE, the baby's brain divides only halfway into two hemispheres. This happens because the right and left sides remain connected in the front and middle areas of the brain. The dividing line between the two hemispheres is visible mostly in the back part of the brain.

Lobar Holoprosencephaly.

In lobar HPE, the brain shows a much greater degree of separation between the two halves. Although the hemispheres are mostly separate, complete separation does not occur in certain frontal regions of the cerebral cortex. This represents the mildest form of classical holoprosencephaly.

Middle Interhemispheric (MIH) Variant.

Aside from the three main types, doctors also recognize a fourth variation known as the middle interhemispheric variant. In this specific type, the middle sections of the brain hemispheres fail to separate properly during early fetal development.

What Is the Difference Between Hydranencephaly and Holoprosencephaly?

You might hear these two terms and feel a bit confused about how they differ. Both hydranencephaly and holoprosencephaly are brain-related birth conditions, but they involve entirely different developmental processes.

Hydranencephaly is a rare condition where parts of the baby's brain tissue are missing and replaced by sacs filled with fluid. Babies born with hydranencephaly often have an enlarged head due to fluid buildup.

On the other hand, holoprosencephaly involves the failure of the embryonic brain to divide into right and left halves. Understanding this distinction helps clarify why doctors run specific imaging tests to identify exact brain structures.

Who Does This Condition Affect and How Common Is It?

Holoprosencephaly affects developing embryos inside the womb. It typically occurs during the second and third weeks of pregnancy, which is often before a parent knows they are pregnant.

Research suggests that during early embryonic stages, roughly 1 in 250 pregnancies may be affected by HPE. However, a significant majority of these pregnancies end in miscarriage or stillbirth.

Because of this, HPE is considered a rare condition among live births. It is estimated to occur in about 1 out of every 16,000 live births worldwide.

What Are the Symptoms of HPE?

Because holoprosencephaly has several different types and severity levels, the signs and symptoms vary widely. Every child will experience a distinct combination of challenges.

Common Symptoms.

Children with HPE often experience a range of neurological and physical signs:

• Delays in reaching key developmental milestones.
• Varying degrees of intellectual disability.
• Epilepsy and recurrent seizures.
• A smaller than average head size known as microcephaly.
• An enlarged head size caused by fluid buildup known as macrocephaly.
• Excess fluid accumulation inside the brain cavities called hydrocephalus.
• Distinctive facial structural variations.
• Dental irregularities such as a single central incisor tooth.
• Cleft lip and/or cleft palate.
• Difficulties regulating core body temperature, heart rate, and breathing.
• Challenges with feeding and swallowing.

Signs of Alobar HPE.

Because this is the most severe form, symptoms and facial differences are much more pronounced:

• Cyclopia, which involves a single fused eye in the center of the face.
• Ethmocephaly, where closely set eyes appear with a small proboscis structure above them.
• Anophthalmia, meaning the complete absence of one or both eyes.
• Microphthalmia, involving unusually small eyeballs paired with a tube-like nose structure.
• Orbital hypotelorism with a flat nose or a median or bilateral cleft lip.

Signs of Semilobar HPE.

Children with semilobar HPE may display specific physical characteristics:

• Close-set eyes, very small eyeballs, or missing eyes.
• A flat bridge and tip of the nose.
• A single nostril opening.
• Median or bilateral cleft lip.
• Cleft palate.

Signs of Lobar HPE.

As the mildest classic form of HPE, signs can be subtler:

• Bilateral cleft lip.
• Close-set eyes.
• A flattened or recessed nose bridge.

Sometimes, holoprosencephaly can also appear as part of larger genetic syndromes. Each of those syndromes carries its own unique set of medical features and symptoms.

What Causes Holoprosencephaly (HPE)?

Normally, the front part of the embryonic brain splits into right and left halves. Holoprosencephaly occurs when this division process does not happen properly. Instead of separating completely, the left and right sides remain abnormally connected.

Medical science shows that several factors can contribute to the development of HPE:

• Mutations occurring in at least 14 different genes.
• Abnormalities involving specific chromosomes.
• Certain underlying genetic syndromes.

Even with advanced medical testing, doctors are often unable to identify a single clear cause for every person case of HPE.

Genetic Mutations.

A genetic mutation is a change in your DNA sequence. DNA provides the instructions your body needs to build cells and perform vital tasks. If part of a DNA sequence is missing or damaged, it can lead to health conditions.

Babies can inherit gene mutations from one or both parents depending on how the gene passes down. However, many mutations happen entirely by chance with no previous family history.

Researchers have linked mutations in these specific genes to HPE:

• SHH .
• SIX3 .
• TGIF1 .
• ZIC2 .
• PTCH1 .
• FOXH1 .
• NODAL .
• CDON .
• FGF8 .
• GLI2 .

These gene mutations prevent the resulting proteins from working correctly, which disrupts normal brain development in the womb.

Chromosome Abnormalities.

Human cells normally contain 46 chromosomes organized into 23 pairs. These chromosomes carry our genetic instructions. We inherit one set of chromosomes from our mother and one set from our father.

About one-third of babies born with HPE have a chromosome abnormality. The most frequent abnormality linked to HPE is Trisomy 13, where a baby has three copies of chromosome 13 instead of two. Other conditions like Trisomy 18 and triploidy can also play a role.

Genetic Syndromes.

Sometimes holoprosencephaly occurs as part of specific multi-system genetic syndromes. Examples of syndromes linked to HPE include:

• Hartsfield syndrome .
• Kallman syndrome two .
• Steinfeld syndrome .
• Smith-Lemli-Opitz syndrome .
• Stromme syndrome .

How Is Holoprosencephaly Diagnosed?

Doctors can often identify holoprosencephaly—especially more severe forms—before birth using a routine prenatal ultrasound scan. A specialized fetal MRI scan can also reveal brain structure details prior to delivery.

While prenatal imaging can spot HPE, many mild cases are diagnosed only after the baby is born when facial differences or neurological signs become noticeable. Doctors then order head imaging tests to confirm the diagnosis.

Children with very mild forms of HPE might not receive a diagnosis until they are around one year old. Delays in developmental milestones often prompt doctors to check brain imaging scans.

Diagnostic Tests Used After Birth.

To evaluate a baby after birth, doctors rely on several imaging studies:

• Head Ultrasound: This painless test uses high-frequency sound waves to create live images of internal brain structures without radiation.
• Brain MRI Scan: An MRI uses a strong magnetic field and radio waves to generate detailed pictures of brain tissue and neural pathways.
• Head CT Scan: A computed tomography scan combines X-rays and computer processing to create cross-sectional 3D images of the head.

When possible, doctors also perform blood tests and genetic studies, such as chromosomal analysis, to pinpoint the underlying cause.

If genetic testing confirms a mutation or chromosome change, your doctor may recommend genetic counseling if you plan to grow your family in the future.

What Are the Treatments for HPE?

Unfortunately, there is currently no cure or primary treatment to reverse holoprosencephaly. Instead, medical care focuses on managing the specific symptoms each child experiences. Treatment plans are customized to meet person needs.

Managing HPE often requires a coordinated team of medical specialists working together, including:

• Pediatricians .
• Neurologists .
• Endocrinologists .
• Plastic surgeons .
• Occupational and physical therapists .
• Palliative care teams .
• Complex care specialists .

Common Treatment Approaches.

Medical teams use various strategies to support children with HPE:

• Anti-seizure medicines to prevent, reduce, or control epilepsy.
• Surgical placement of a ventriculoperitoneal (VP) shunt if excess fluid accumulates in the brain.
• Physical therapy and medicines to manage muscle stiffness or movement challenges.
• Plastic and reconstructive surgery to repair cleft lip, cleft palate, or facial features.
• Treatments for pituitary gland hormone imbalances.
• Specialized nutritional support, such as a gastrostomy tube (G-tube), for babies with feeding difficulties.

Every step of care aims to maximize comfort and support the child's overall quality of life.

Can Holoprosencephaly Be Prevented?

Sadly, most cases of holoprosencephaly cannot be prevented because they stem from hidden genetic factors. If you are planning a pregnancy, talking with your doctor about genetic screening can help you understand potential risks.

Medical researchers have identified certain risk factors that may increase the likelihood of HPE:

• Having Diabetes: Pre-existing Type 1 or Type 2 diabetes before pregnancy raises the risk of HPE. This is different from gestational diabetes that develops later in pregnancy.
• Folate Deficiency: Vitamin B9 (folate) is vital for healthy brain and spinal cord development in early pregnancy. Low folate levels can increase risks.
• Exposure to Teratogens: Substances like alcohol, retinoic acid, and certain food mycotoxins can disrupt normal embryonic development.

Maintaining a healthy lifestyle, eating a balanced diet with proper vitamins, and following medical advice before and during pregnancy are essential steps.

What Is the Prognosis for HPE?

The outlook or prognosis for holoprosencephaly depends greatly on the severity of the condition and its underlying cause.

Moderate to severe cases generally have a more guarded outlook. Only a small percentage of children with severe HPE survive into childhood or adolescence. Children with mild to moderate forms often live into adulthood, though they usually manage ongoing medical needs.

Many children with HPE require daily medicines and therapies to manage seizures and other health complications.

Life Expectancy.

Life expectancy varies depending on the specific type of HPE:

• Babies with alobar HPE typically pass away before birth, shortly after birth, or within the first six months of life.
• Children with semilobar or lobar HPE who do not have other major organ malformations often survive past their first year of life.
• Children with mild forms of HPE often live well into adulthood.

What Should You Expect If Your Baby Has HPE?

It is important to remember that no two children with holoprosencephaly are affected in the exact same way. Predicting the exact path ahead for your child can be difficult. Connecting with pediatric specialists who have experience with HPE is one of the best ways to get clear guidance.

How Can You Care for a Baby with HPE?

To help care for your child, your medical team will offer specific guidance. Follow these essential care steps:

• Give all prescribed medicines exactly as directed by your doctor.
• Attend all recommended developmental assessments and physical therapies.
• Keep all scheduled follow-up medical appointments.

HPE can affect cognitive, neurologic, and motor functions. Many children need ongoing support with daily activities as they grow.

Your child's medical team can answer your questions and connect you with local or online support groups. Remember that you are never alone on this journey.

When Should You Call the Doctor?

If your child has been diagnosed with holoprosencephaly, you will need to stay in regular contact with their medical team to track their progress and adjust care plans as needed.