A 20 year old male patient presents with the chief complaint of pain in abdomen. General examination reveals xanthomas present (in clusters on back, buttocks and arms, legs). On percussion, hepatomegaly and splenomegaly can be appreciated. On blood investigations, LDL level decreased and HDL normal.Which is the most probable diagnosis?

**Core Concept**
Familial chylomicronemia syndrome (FCS) is a rare genetic disorder characterized by the deficiency of lipoprotein lipase (LPL), a key enzyme involved in the breakdown of triglycerides in the bloodstream. This leads to an accumulation of chylomicrons, large lipoprotein particles that transport dietary lipids.

**Why the Correct Answer is Right**
The clinical presentation of xanthomas, hepatomegaly, and splenomegaly in the context of decreased LDL and normal HDL levels is suggestive of a disorder affecting lipid metabolism. The absence of LDL elevation and normal HDL levels points towards a problem with chylomicron metabolism rather than LDL or VLDL metabolism. The enzyme deficiency in FCS leads to the accumulation of chylomicrons, which are then broken down into smaller particles, including triglyceride-rich VLDL particles and LDL particles. However, the primary issue lies with the breakdown of chylomicrons, resulting in the accumulation of triglycerides in the liver and spleen, causing hepatomegaly and splenomegaly.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided.
**Option B:** Not applicable.
**Option C:** Not applicable.
**Option D:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
Familial chylomicronemia syndrome is a rare but important diagnosis to consider in patients with lipodystrophy or lipid disorders. It is essential to investigate for LPL deficiency in patients with recurrent pancreatitis, xanthomas, and abnormal lipid profiles.

**Correct Answer:** A. Familial chylomicronemia syndrome (FCS) is characterized by the deficiency of lipoprotein lipase (LPL), leading to the accumulation of chylomicrons, xanthomas, hepatomegaly, and splenomegaly.

✓ Correct Answer: B. Familial Dysbeta lipoproteinemia (FDBL)- Type III