A newborn’s first breath is an emotional moment that is critical for survival. Researchers have highlighted the involvement of a gene that controls autonomic breathing, which is expressed just as the baby makes its first cry.
The first breath
We breathe in all circumstances, consciously or unconsciously. It is impossible to remember the first breath, only parents who hear their baby’s cry for the first time remember it. However, it is a crucial moment in life when the lungs receive air for the first time after intrauterine life.
This breathing reflex is controlled by several types of respiratory neurons. Among them is a group of neurons located in the retrotrapezoid nucleus (RTN) of the brainstem that controls the blood partial pressure of CO2 and hydrogen through a mechanism called the central CO2 respiratory chemoreflex, and also regulates the respiratory rhythm.
An abnormality in autonomic respiration is the cause of a rare genetic disorder, Ondine’s curse, in which a mutation in the phox2B gene, expressed in neurons of the retrotrapezoid nucleus, causes insufficient ventilation of the alveoli.
In a paper published in Nature, researchers conducted several experiments in mice to investigate the involvement of another gene expressed in neurons of the retrotrapezoid nucleus, PACAP, which encodes a neurotransmitter released when a newborn takes the first breath. Without it, breathing is impaired, and the mice show the symptoms of sudden death syndrome.
A gene involved in sudden death syndrome
The PACAP gene (Pituitary adenylate cyclase-activating polypeptide) encodes a neuropeptide, consisting of 176 amino acids and found on chromosome 18. When the researchers altered this gene, they found that newborn mice were four times more likely to develop apnea than others. These pauses in breathing are potentially dangerous for newborns. The researchers also found that these disorders are exacerbated by temperature. At 30°C, apneas are three times more common in mice without the PACAP gene than in normal mice.
Their central respiratory CO2 chemoreflex was also significantly reduced, by 50% compared to mice without the genetic alteration. The scientists observed that the respiratory abnormalities were not due to the absence of the neuropeptide PACAP, but to the decreased expression of its receptor, PAC1. When PACAP is dysfunctional, only 5% of neurons in the retrotrapezoid nucleus express PAC1.
A dysfunctional PACAP gene is not lethal to mice but increases their risk of sudden death. Indeed, in neonates, alteration of this gene has been observed to be associated with an increased risk of sudden death syndrome. When combined with environmental factors, abnormal respiratory chemoreflex can be fatal. But with medical management, babies with Ondine’s curse can lead near-normal lives.