Respiratory distress syndrome is due to a defect in the biosynthesis of
**Core Concept**
Respiratory distress syndrome (RDS) is a condition that affects newborns, primarily caused by a deficiency of surfactant in the lungs. Surfactant is a complex mixture of phospholipids and proteins that reduces the surface tension of the alveoli, facilitating lung expansion during inspiration.
**Why the Correct Answer is Right**
The biosynthesis of surfactant is a critical process that involves the incorporation of phospholipids into the surfactant protein complex. The primary phospholipid component of surfactant is dipalmitoylphosphatidylcholine (DPPC), which is synthesized from lecithin. The lecithin-sphingomyelin ratio is a key determinant of surfactant function, and a deficiency in this ratio can lead to RDS. The correct answer involves the enzyme responsible for the synthesis of DPPC.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not relate to the biosynthesis of surfactant or the pathogenesis of RDS.
**Option B:** This option is incorrect as it refers to a different condition, not related to the biosynthesis of surfactant or RDS.
**Option C:** This option is incorrect as it is not directly related to the biosynthesis of surfactant or the pathogenesis of RDS.
**Clinical Pearl / High-Yield Fact**
The lecithin-sphingomyelin ratio is a critical determinant of surfactant function, and a deficiency in this ratio can lead to RDS. This ratio can be assessed via amniocentesis, allowing for early identification of at-risk newborns.
**Correct Answer: C. Cytidine triphosphate (CTP) choline cytidylyltransferase (also known as CTP:phosphocholine cytidylyltransferase or CTP:PC cytidylyltransferase) - This enzyme is crucial in the biosynthesis of phosphatidylcholine, which is a key component of surfactant.