Why Do Babies With Suspected HIE Need Genetic Testing?

It can be incredibly confusing to hear that your baby is undergoing genetic testing when their symptoms seem clearly linked to a difficult birth. When a baby has distress at birth, such as low Apgar scores (a measure of a newborn’s physical condition at birth) or abnormal umbilical cord blood gases, doctors often suspect Hypoxic-Ischemic Encephalopathy (HIE).

However, doctors order genetic and metabolic tests as a precaution to ensure no stone is left unturned. Testing helps doctors look for additional or alternative causes for a baby’s symptoms, ensuring the medical team is providing the safest and most effective care.

What Are HIE “Mimics”?

When a newborn shows signs of brain distress (known as encephalopathy) or has seizures, an oxygen issue like HIE is the most common cause ^[1]. However, other medical issues—such as infections, bleeding in the brain, strokes, or rare genetic and metabolic conditions—can cause the exact same symptoms ^{[2] [1]}. When a genetic or metabolic condition looks clinically identical to an oxygen injury, it is referred to as an HIE “mimic”.

Surprisingly, even if a baby had a very difficult delivery with clear signs of distress, a genetic or metabolic condition could still be the true cause, or at least a contributing factor, to their illness ^[3]. Birth complications do not rule out the possibility of a genetic condition ^[3].

Examples of Genetic and Metabolic Causes

While many babies tested will not have a genetic mimic, doctors typically look for a few specific types of conditions when symptoms are unusually severe or don’t perfectly match a typical HIE pattern:

• Rare Genetic Epilepsies: Some babies are born with genetic variations that cause severe, early-onset seizures. One example is a variation in the KCNQ2 gene ^[4]. These early seizures can easily be mistaken for a brain injury resulting from oxygen deprivation ^[5].
• Metabolic Disorders: These are conditions where a baby’s body cannot properly break down food or process certain chemicals, leading to stress on the brain ^[6]. Examples include urea-cycle disorders, maple syrup urine disease, and molybdenum cofactor deficiency ^[7].

While most babies receive standard newborn screening (a routine heel-prick blood test), the conditions covered vary by location, and this routine screen does not catch every metabolic or genetic disorder ^[8]. If doctors suspect a mimic, they will order more comprehensive testing.

Testing Does Not Delay Immediate Care

Do not worry that testing will pause your baby’s treatment. Doctors evaluate mimics and treat medical emergencies in parallel.

• Cooling Therapy Continues: If a baby meets the established medical criteria for HIE, the standard of care is therapeutic hypothermia (cooling the baby’s body temperature for 72 hours) ^[9]. Doctors will start this time-sensitive treatment immediately; they do not wait for genetic results to return.
• Targeted Seizure Medications: If a genetic test reveals a condition like KCNQ2, it can help the neurologist choose the most effective anti-seizure medication for that specific genetic profile ^[4].
• Urgent Metabolic Interventions: If doctors suspect a metabolic mimic, they may run rapid blood and urine tests. Certain metabolic disorders require immediate interventions like specialized diets, detoxifying medications, or specific vitamins under strict medical supervision ^{[6] [10]}. (Note: Never give your baby supplements or change their feeding plan without direct instruction from the medical team).

What to Expect from the Results

Genetic testing is not a simple “yes or no” process, and comprehensive results can take days or weeks depending on the specific test used ^[11].

Often, doctors will request blood samples from both parents as well as the baby. This is called “trio testing” and helps the lab determine if a genetic variation was inherited or if it is brand new to the baby.

When the results return, they might be:

• Positive: A clear genetic or metabolic cause is found.
• Negative: No genetic cause is found (though this does not absolutely guarantee a genetic condition does not exist).
• Variant of Uncertain Significance (VUS): A genetic change is found, but the medical community does not yet know if it causes health problems.

Finding a genetic condition does not mean you did anything wrong, and a lack of family history does not mean a genetic condition is impossible. A genetics counselor or specialist will sit down with you to explain the results, what they mean for your baby’s treatment, and what it might mean for your family moving forward.