**Question:** Which is Not true regarding Hypertrophic pyloric stenosis -

A. Hypertrophic pyloric stenosis is a congenital condition affecting infants
B. The condition is primarily caused by an autoimmune response
C. Symptoms typically appear within the first few days of life
D. Treatment involves medication to reduce gastric acidity

**Core Concept:**
Hypertrophic pyloric stenosis (HPS) is a pediatric gastrointestinal disorder characterized by the overgrowth and narrowing of the muscularis layer in the pyloric sphincter, leading to reduced stomach emptying and gastric outlet obstruction. This condition primarily affects infants and is often caused by developmental abnormalities rather than an autoimmune response.

**Why the Correct Answer is Right:**
Option B is incorrect because HPS is primarily caused by developmental abnormalities and not an autoimmune response. The exact etiology is not fully understood, but it is believed to involve abnormal development of the pyloric sphincter.

**Why Each Wrong Option is Incorrect:**
Option A is partially correct as HPS does occur in infants, but it is not exclusive to them. Although it is more common in infants, it can also affect older children and rarely adults. Option C is also partially correct as symptoms typically appear within the first few days of life, but it is not the only timeframe, and the condition can persist longer in some cases. Lastly, Option D is incorrect as the primary treatment for HPS does not involve medication to reduce gastric acidity. Instead, the gold standard treatment is surgery, specifically pyloromyotomy, which involves making a small incision in the pylorus to relieve the obstruction.

**Clinical Pearl:**
Hypertrophic pyloric stenosis is a common cause of vomiting in infants, particularly in the first few days of life. The diagnosis is often made after ruling out other causes of vomiting such as gastroesophageal reflux, viral illnesses, and congenital anomalies. Treatment of HPS focuses on relieving the obstruction via pyloromyotomy, as reducing gastric acidity is not the primary treatment. Understanding the underlying pathophysiology and appropriate management of this condition is crucial for pediatricians and gastroenterologists in accurately diagnosing and treating infants experiencing persistent vomiting.