In familial β dyslipoproteinemia, which lipoprotein accumulates in the plasma?

In familial β dyslipoproteinemia, the accumulation of lipoproteins in the plasma primarily involves IDL, which is also known as Intermediate-Density Lipoprotein. This condition is characterized by a defect in the metabolism of lipoproteins, particularly due to a deficiency in the enzyme lipoprotein lipase, which is responsible for hydrolyzing triglycerides in chylomicrons and VLDL.

As a result, the clearance of IDL from circulation becomes impaired, leading to its accumulation. IDL is the transitional form in the metabolic pathway of lipoproteins, moving from VLDL to LDL as triglycerides are removed. The increased levels of IDL in the plasma can contribute to cardiovascular diseases due to its atherogenic potential.

While chylomicrons, VLDL, and LDL are also involved in lipid transport and metabolism, the specific accumulation seen in familial β dyslipoproteinemia is mainly related to IDL, making it the correct answer.