A recent study released by researchers at the University of Wisconsin-Madison reveals male infants are more vulnerable to brain injury.
According to the study, each year, thousands of newborn babies suffer complications during pregnancy or birth that deprive their brains of oxygen and nutrient-rich blood and result in brain injury.
This deprivation results in hypoxic ischemic encephalopathy (HIE), which can lead to long-term neurological issues such as learning disabilities, cerebral palsy or even death. The newborn’s body can compensate for brief periods of depleted oxygen, but if the asphyxia lasts too long, brain tissue is destroyed. The timing and severity of asphyxia can affect the area of the brain that sustains the injury.
Birth asphyxia causes 840,000 or 23 percent of all neonatal deaths worldwide. Researchers have known for some time that male infants are more vulnerable to HIE, but why has remained a mystery.
Pelin Cengiz, associate professor in the Department of Pediatrics at the University of Wisconsin-Madison led the study, which was published this week in the journal eNeuro. Researchers discovered that a particular protein called estrogen receptor α, or ERα for short, found in the brains of both male and female mice is found in higher levels in females. The protein offers the female mice stronger protection against HIE.
When the researchers studied the brains of male and female mice that could make the ERα protein, they learned that levels of this protective protein were significantly higher in female compared to male brains following oxygen deprivation and reduced blood flow.
“Under normal circumstances the brains of male and female mice have similar amounts of ERα,” says Cengiz, who is now exploring why ERα levels increase in female but not male brains after HIE.
“Understanding the mechanism of how female brains are more resistant to damage from oxygen deprivation and reduced blood flow is a first step toward helping newborns of both sexes recover after suffering from HIE and live functional lives. It could also lead to more effective therapies and treatments for both genders,” Cengiz said.
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Signs and symptoms (click here for more information):
Mild hypoxic-ischemic encephalopathy
- Muscle tone may be slightly increased and deep tendon reflexes may be brisk during the first few days
- Transient behavioral abnormalities, such as poor feeding, irritability, or excessive crying or sleepiness (typically in an alternating pattern), may be observed
- Typically resolves in 24 hours
Moderately severe hypoxic-ischemic encephalopathy
- The infant is lethargic, with significant hypotonia and diminished deep tendon reflexes
- The grasping, Moro, and sucking reflexes may be sluggish or absent
- The infant may experience occasional periods of apnea
- Seizures typically occur early within the first 24 hours after birth
- Full recovery within 1-2 weeks is possible and is associated with a better long-term outcome
Severe hypoxic-ischemic encephalopathy
Seizures can be delayed and severe and may be initially resistant to conventional treatments. The seizures are usually generalized, and their frequency may increase during the 24-48 hours after onset, correlating with the phase of reperfusion injury.
As the injury progresses, seizures subside and the electroencephalogram becomes isoelectric or shows a burst suppression pattern. At that time, wakefulness may deteriorate further, and the fontanelle may bulge, suggesting increasing cerebral edema.
Other symptoms include the following:
- Stupor or coma is typical; the infant may not respond to any physical stimulus except the most noxious.
- Breathing may be irregular, and the infant often requires ventilatory support.
- Generalized hypotonia and depressed deep tendon reflexes are common.
- Neonatal reflexes (eg, sucking, swallowing, grasping, Moro) are absent.
- Disturbances of ocular motion, such as a skewed deviation of the eyes, nystagmus, bobbing, and loss of “doll’s eye” (ie, conjugate) movements may be revealed by cranial nerve examination.
- Pupils may be dilated, fixed, or poorly reactive to light.
- Irregularities of heart rate and blood pressure are common during the period of reperfusion injury, as is death from cardiorespiratory failure.