A female infant is born prematurely at 28 weeks’ gestation. Sholy after bih, she shows signs of dyspnea, cyanosis, and tachypnea. She is placed on a ventilator for assisted breathing, and a diagnosis of neonatal respiratory distress syndrome (hyaline membrane disease) is made. Which of the following is the cause of this syndrome?
**Core Concept**
The underlying cause of neonatal respiratory distress syndrome (hyaline membrane disease) is related to the immaturity of the fetal lung surfactant system. Surfactant is a complex mixture of phospholipids and proteins that reduces surface tension within the alveoli, facilitating lung expansion and preventing alveolar collapse during expiration.
**Why the Correct Answer is Right**
The correct answer is related to the deficiency of surfactant protein B (SP-B). Surfactant protein B is a crucial component of pulmonary surfactant, which plays a vital role in maintaining lung function. Premature infants often have a deficiency of surfactant protein B, leading to an inability to reduce surface tension within the alveoli. This results in alveolar collapse, increased airway resistance, and the clinical presentation of respiratory distress syndrome. The absence of surfactant protein B disrupts the normal function of surfactant, leading to the characteristic symptoms of hyaline membrane disease.
**Why Each Wrong Option is Incorrect**
**Option A:** While surfactant protein A (SP-A) is an important component of pulmonary surfactant, its deficiency is not the primary cause of neonatal respiratory distress syndrome. SP-A plays a role in surfactant function and immune defense, but its absence does not lead to the characteristic symptoms of hyaline membrane disease.
**Option B:** Surfactant phospholipids, specifically phosphatidylcholine, are essential for reducing surface tension within the alveoli. However, the primary cause of neonatal respiratory distress syndrome is not the deficiency of surfactant phospholipids, but rather the absence of surfactant protein B, which disrupts the normal function of surfactant.
**Option C:** Surfactant protein C (SP-C) is a minor component of pulmonary surfactant, and its deficiency is not associated with neonatal respiratory distress syndrome. SP-C plays a role in surfactant function, but its absence does not lead to the characteristic symptoms of hyaline membrane disease.
**Option D:** While genetic mutations in the SFTPB gene, which encodes surfactant protein B, can lead to surfactant deficiency and neonatal respiratory distress syndrome, this option is too specific and does not address the underlying cause of the syndrome.
**Clinical Pearl / High-Yield Fact**
Premature infants with respiratory distress syndrome often require surfactant replacement therapy, which can significantly improve lung function and reduce the risk of complications. Early administration of surfactant can lead to improved outcomes and reduced mortality in these patients.
**Correct Answer:** C. Surfactant protein B deficiency.