Lipid Metabolism Practice Questions

Q: A neonate presents with seizures and is found to have a cherry red spot on fundus examination. Enzyme assay reveals deficiency of hexosaminidase A. Which of the following substances is most likely to be accumulated in this patient?

GM2 ganglioside. ***GM2 ganglioside*** - Deficiency of **Hexosaminidase A** results in the accumulation of **GM2 ganglioside**, defining features of **Tay-Sachs disease**. - The accumulation of GM2 ganglioside in the retina's ganglion cells causes the characteristic **cherry red spot** on fundus examination. *GM1 ganglioside* - The accumulation of **GM1 ganglioside** occurs in **GM1 gangliosidosis**, due to a deficiency of **β-galactosidase**. - GM1 gangliosidosis typically presents with coarse facial features, hepatosplenomegaly, and skeletal deformities (**dysostosis multiplex**), features not always prominent in Tay-Sachs. *Sphingomyelin* - Accumulation of **Sphingomyelin** is the diagnostic feature of **Niemann-Pick disease** (especially Type A), caused by a deficiency of **sphingomyelinase**. - While Niemann-Pick Type A also causes a cherry red spot, it is classically associated with rapid neurodegeneration and marked **hepatosplenomegaly** and **foam cells** (lipid-laden macrophages). *Glucocerebroside* - This lipid accumulates in **Gaucher disease** because of deficient **glucocerebrosidase** activity. - Gaucher disease is characterized by bony involvement, pancytopenia, and massive **hepatosplenomegaly**, and does not typically feature the cherry red spot.

Q: A patient presents with orange-colored tonsils. Laboratory investigations reveal triglyceride level of 140 mg/dL and HDL cholesterol of 5 mg/dL. What is the most likely diagnosis?

Tangier disease. ***Tangier disease*** - This condition is a rare genetic disorder characterized by a mutation in the **ATP-binding cassette transporter A1 (ABCA1)** gene, leading to accelerated catabolism of HDL. - The clinical hallmarks are extremely low **HDL cholesterol** (often < 5 mg/dL) and the accumulation of cholesterol esters in macrophages, resulting in enlarged, characteristic **orange-colored tonsils** [1]. *Familial hypercholesterolemia* - Caused by defects in the **LDL receptor** or ApoB, resulting in severely elevated **LDL cholesterol** levels and premature atherosclerosis [1]. - It typically presents with tendon xanthomas and arcus senilis, but does not cause extremely low HDL or visible changes in the tonsils. *Type I hyperlipoproteinemia* - This type is characterized by functional deficiency of **lipoprotein lipase (LPL)** or its cofactor ApoC-II, leading to massive accumulation of **chylomicrons** in the plasma. - The primary finding is severe **hypertriglyceridemia** (often > 1000 mg/dL), leading to eruptive xanthomas and pancreatitis; HDL levels are not the primary diagnostic feature. *Abetalipoproteinemia* - Caused by a defect in the **microsomal triglyceride transfer protein (MTP)**, preventing the synthesis of ApoB-containing lipoproteins (chylomicrons, VLDL, LDL) [1]. - It presents with severe fat malabsorption, neurological deficits due to Vitamin E deficiency, and **acanthocytosis** (spiculated RBCs), rather than tonsillar changes.

Q: Which of the following is correct about the disease and its missing enzyme mentioned below?

X= Metachromatic leukodystrophy, Y= Arylsulfatase-A. ***Metachromatic leukodystrophy, Y= Arylsulfatase-A*** - **Metachromatic leukodystrophy (MLD)** is an autosomal recessive **leukodystrophy** caused by deficiency of **arylsulfatase A (cerebroside sulfatase)**. - This enzyme deficiency leads to accumulation of **sulfatides** (cerebroside sulfate) in the nervous system, particularly in **oligodendrocytes and Schwann cells**. - The pathway in the image shows the conversion of **sulfatide to galactocerebroside**, where enzyme Y represents arylsulfatase-A. - Clinical features include **progressive demyelination**, developmental regression, peripheral neuropathy, and metachromatic granules on nerve biopsy. - This is the correct answer as it accurately matches the **enzyme-disease relationship** and correlates with the biochemical pathway shown. *Canavan disease, Y= Aminoacylase* - While **Canavan disease** is a leukodystrophy, it is caused by deficiency of **aspartoacylase** (not simply "aminoacylase"), which metabolizes N-acetylaspartate (NAA). - This disease involves **spongy degeneration of white matter** and elevated NAA in urine and brain. - This enzyme and pathway are **not related to the sulfatide-galactocerebroside conversion** shown in the image. - The terminology "aminoacylase" is imprecise for this enzyme. *Gaucher disease, Y= Glucocerebrosidase* - **Gaucher disease** is caused by deficiency of **glucocerebrosidase (β-glucosidase)**. - This leads to accumulation of **glucocerebroside** in macrophages (Gaucher cells). - This enzyme acts on glucocerebroside, not on the **sulfatide pathway** shown in the image. *Niemann-Pick disease, Y= Sphingomyelinase* - **Niemann-Pick disease** (Types A and B) is caused by deficiency of **acid sphingomyelinase**. - This leads to accumulation of **sphingomyelin** in reticuloendothelial cells. - The pathway shown deals with **sulfatides and galactocerebrosides**, not sphingomyelin metabolism.

Q: A patient has a family history positive for premature coronary artery disease. All are true about the disease shown in the image, except?

Defect on chromosome 1. ***Defect on chromosome 1*** - Familial hypercholesterolemia (FH) is primarily caused by **defects in the LDL receptor gene** which is located on **chromosome 19**, not chromosome 1. - Mutations in other genes like *APOB* (encoding apolipoprotein B) or *PCSK9* can also cause FH, but are not located on chromosome 1. *Familial hypercholesterolemia* - The image shows a **tendon xanthoma** (indicated by the arrow) which is a characteristic clinical manifestation of **familial hypercholesterolemia** (FH). - FH is an **autosomal dominant genetic disorder** characterized by very high levels of LDL cholesterol from birth, leading to premature cardiovascular disease. *Heterozygous familial hypercholesterolemia is seen in 1:500 population* - **Heterozygous familial hypercholesterolemia (HeFH)** is indeed one of the most common genetic disorders, affecting approximately **1 in 250 to 1 in 500 individuals** in the general population. - This high prevalence contributes to the significant burden of premature coronary artery disease. *Tendon xanthoma* - The arrow in the image points to a **clearly visible deposit on the Achilles tendon**, consistent with a **tendon xanthoma**. - Tendon xanthomas are pathognomonic for FH and are collections of **lipid-laden macrophages** (foam cells) in tendons, particularly the Achilles and extensor tendons of the hands.

Q: Consider the following statements with reference to 'trans fatty acids' : 1. They are geometrical isomers of cis-unsaturated fatty acids. 2. Though atherogenic, being unsaturated they are less so than saturated fatty acids. 3. It takes years for trans fatty acids to be flushed from the body. 4. They lower both LDL cholesterol and HDL cholesterol in the body. Which of the statements given above are correct ?

1 only. ***1 only*** - **Statement 1 is CORRECT**: Trans fatty acids are **geometrical isomers of cis-unsaturated fatty acids**, differing in the spatial arrangement of hydrogen atoms around the carbon-carbon double bond. This structural difference gives them physical and biological properties more similar to saturated fats. - **Statement 2 is INCORRECT**: Trans fatty acids are **MORE atherogenic** than saturated fatty acids, not less. They raise LDL cholesterol and lower HDL cholesterol more significantly than saturated fats. - **Statement 3 is INCORRECT**: Trans fatty acids are metabolized and eliminated from the body within **days to weeks**, not years. Long-term cardiovascular damage results from chronic dietary exposure, not slow elimination kinetics. - **Statement 4 is INCORRECT**: Trans fatty acids **raise LDL cholesterol** ("bad" cholesterol) and **lower HDL cholesterol** ("good" cholesterol). They do not lower both as stated. *1 and 3 only* - Statement 1 is correct, but statement 3 is **incorrect**. The body processes and eliminates trans fatty acids relatively quickly (days to weeks), not years. The detrimental cardiovascular effects accumulate due to chronic dietary exposure, not slow metabolism of individual molecules. *2, 3 and 4* - All three statements are **incorrect**. Statement 2 is wrong because trans fats are **more atherogenic** than saturated fats. Statement 3 is wrong because trans fats are metabolized within weeks, not years. Statement 4 is wrong because trans fats **raise LDL** (not lower it) while lowering HDL. *1, 3 and 4* - Only statement 1 is correct. Statement 3 is **incorrect** as trans fatty acids are metabolized within weeks, not years. Statement 4 is **incorrect** because trans fatty acids **increase LDL cholesterol** and **decrease HDL cholesterol** - they do not lower both.

Q: Which of the following are unsaturated fatty acids? 1. Lauric acid 2. Linoleic acid 3. Oleic acid 4. Palmitic acid Select the correct answer using the code given below.

2 and 3. ***2 and 3*** - **Linoleic acid** is an **omega-6 fatty acid** with two double bonds, making it polyunsaturated. - **Oleic acid** is an **omega-9 fatty acid** with one double bond, making it monounsaturated. *1 and 4* - **Lauric acid** is a **saturated fatty acid** with no double bonds. - **Palmitic acid** is also a **saturated fatty acid** with no double bonds. *1 and 2* - While **linoleic acid** (2) is unsaturated, **lauric acid** (1) is a saturated fatty acid. - This option incorrectly includes a saturated fatty acid. *3 and 4* - While **oleic acid** (3) is unsaturated, **palmitic acid** (4) is a saturated fatty acid. - This option incorrectly includes a saturated fatty acid.

Q: Which of the following fats has the highest concentration of saturated fatty acids ?

Coconut oil. ***Coconut oil*** - **Coconut oil** has the **highest concentration of saturated fatty acids** among common dietary fats, with approximately **82-92% of its total fatty acids being saturated**. - The predominant saturated fatty acid is **lauric acid (C12:0)**, which comprises roughly **45-50%** of its fatty acid profile. - This exceptionally high saturation contributes to its **solid consistency** at room temperature and its stability during cooking. *Butter* - **Butter** is a dairy product containing approximately **50-65% saturated fatty acids**, which is significantly less than coconut oil. - It contains a mix of short-chain, medium-chain, and long-chain saturated fats, along with **monounsaturated** and **polyunsaturated** fats, and **cholesterol**. *Margarine* - **Margarine** was traditionally made from **partially hydrogenated vegetable oils**, leading to high **trans fat** content and variable saturated fat levels. - Modern formulations use **non-hydrogenated or interesterified oils** to reduce trans fats, with saturated fat content varying widely (10-80%) depending on the source oils and processing methods. *Palm oil* - **Palm oil** contains approximately **49-52% saturated fatty acids**, primarily **palmitic acid (C16:0)**, which makes up about 44% of its total fat content. - While high in saturated fat compared to most vegetable oils, it contains substantially less saturated fat than **coconut oil**.

Q: Which one of the following is a polyunsaturated fatty acid ?

Linoleic acid. ***Linoleic acid*** - **Linoleic acid** contains **two double bonds** in its carbon chain making it a **polyunsaturated fatty acid (PUFA)**. - It is an **omega-6 fatty acid**, and an essential fatty acid, meaning it cannot be synthesized by the human body and must be obtained from the diet. *Stearic acid* - **Stearic acid** is a **saturated fatty acid** with no double bonds in its hydrocarbon chain. - Saturated fatty acids are typically solid at room temperature and primarily found in animal fats. *Oleic acid* - **Oleic acid** is a **monounsaturated fatty acid (MUFA)**, meaning it contains only **one double bond** in its carbon chain. - It is an **omega-9 fatty acid**, commonly found in olive oil. *Palmitic acid* - **Palmitic acid** is also a **saturated fatty acid**, similar to stearic acid, with no double bonds. - It is one of the most common saturated fatty acids in animals and plants and is a major component of palm oil.

Q: A patient presented with reduced levels of high-density lipoprotein, and ABCA1 mutation. On examination, tonsils appeared as shown in the image. What is the diagnosis?

Tangier disease. ***Tangier disease*** - This condition is characterized by **very low HDL levels** due to mutations in the **ABCA1 gene**, which impairs cholesterol efflux from cells. - The classic physical finding is **enlarged, orange-yellow tonsils** due to cholesterol ester deposition, seen in the provided image. *Fabry disease* - This is an **X-linked lysosomal storage disorder** caused by a deficiency of **alpha-galactosidase A**, leading to globotriaosylceramide accumulation. - Clinical features include **neuropathic pain**, **angiokeratomas**, **corneal opacities**, and early renal and cardiac disease, not orange-yellow tonsils. *Niemann-Pick disease* - This is a group of **autosomal recessive lysosomal storage disorders** caused by deficiencies in enzymes like acid sphingomyelinase or proteins involved in cholesterol processing. - It typically presents with **hepatosplenomegaly**, **neurodegeneration** (especially type A and B), and **lung involvement**, but not oral lesions as depicted. *Gaucher disease* - This is an **autosomal recessive lysosomal storage disease** resulting from a deficiency of the enzyme **beta-glucosidase**, leading to accumulation of glucocerebroside. - Characteristic features include **hepatosplenomegaly**, **bone pain** and crises, and **pancytopenia**, without any specific tonsillar findings.

Q: Cyclooxygenase plays a role in which pathway?

Prostaglandin. ***Prostaglandin*** - **Cyclooxygenase (COX)** enzymes specifically catalyze the conversion of **arachidonic acid** into **prostaglandins**, **prostacyclins**, and **thromboxanes**. - This pathway is crucial for mediating **inflammation**, **fever**, and **pain** responses in the body. *Leukotriene* - **Leukotrienes** are synthesized via the **lipoxygenase** pathway, not the cyclooxygenase pathway. - They are primarily involved in **allergic reactions** and **asthma**, causing bronchoconstriction and increased vascular permeability. *Vitamin K* - **Vitamin K** is a fat-soluble vitamin essential for the synthesis of **blood clotting factors** and does not involve cyclooxygenase enzymes. - It acts as a cofactor for the enzyme **gamma-glutamyl carboxylase**. *Krebs cycle* - The **Krebs cycle (citric acid cycle)** is a central metabolic pathway for **cellular respiration**, producing ATP, NADH, and FADH2. - It takes place in the **mitochondria** and is involved in the breakdown of carbohydrates, fats, and proteins for energy, unrelated to cyclooxygenase.

Question 1

A neonate presents with seizures and is found to have a cherry red spot on fundus examination. Enzyme assay reveals deficiency of hexosaminidase A. Which of the following substances is most likely to be accumulated in this patient?

Accepted Answer

GM2 ganglioside

Answer

GM1 ganglioside

Answer

Sphingomyelin

Answer

Glucocerebroside

Question 2

A patient presents with orange-colored tonsils. Laboratory investigations reveal triglyceride level of 140 mg/dL and HDL cholesterol of 5 mg/dL. What is the most likely diagnosis?

Accepted Answer

Tangier disease

Answer

Abetalipoproteinemia

Answer

Type I hyperlipoproteinemia

Answer

Familial hypercholesterolemia

Question 3

Which of the following is correct about the disease and its missing enzyme mentioned below?

Accepted Answer

X= Metachromatic leukodystrophy, Y= Arylsulfatase-A

Answer

X= Gaucher disease, Y= Glucocerebrosidase

Answer

X= Niemann Pick, Y= Sphingomyelinase

Answer

X= Canavan disease, Y= Aminoacylase

Question 4

A patient has a family history positive for premature coronary artery disease. All are true about the disease shown in the image, except?

Accepted Answer

Defect on chromosome 1

Answer

Familial hypercholesterolemia

Answer

Heterozygous familial hypercholesterolemia is seen in 1:500 population

Answer

Tendon xanthoma

Question 5

Consider the following statements with reference to 'trans fatty acids' :

1. They are geometrical isomers of cis-unsaturated fatty acids.

2. Though atherogenic, being unsaturated they are less so than saturated fatty acids.

3. It takes years for trans fatty acids to be flushed from the body.

4. They lower both LDL cholesterol and HDL cholesterol in the body. Which of the statements given above are correct ?

Accepted Answer

1 only

Answer

1 and 3 only

Answer

2, 3 and 4

Answer

1, 3 and 4

Question 6

Which of the following are unsaturated fatty acids?

1. Lauric acid
2. Linoleic acid
3. Oleic acid
4. Palmitic acid
Select the correct answer using the code given below.

Accepted Answer

2 and 3

Answer

1 and 4

Answer

1 and 2

Answer

3 and 4

Question 7

Which of the following fats has the highest concentration of saturated fatty acids ?

Accepted Answer

Coconut oil

Answer

Butter

Answer

Margarine

Answer

Palm oil

Question 8

Which one of the following is a polyunsaturated fatty acid ?

Accepted Answer

Linoleic acid

Answer

Stearic acid

Answer

Oleic acid

Answer

Palmitic acid

Question 9

A patient presented with reduced levels of high-density lipoprotein, and ABCA1 mutation. On examination, tonsils appeared as shown in the image. What is the diagnosis?

Accepted Answer

Tangier disease

Answer

Fabry disease

Answer

Niemann-Pick disease

Answer

Gaucher disease

Question 10

Cyclooxygenase plays a role in which pathway?

Accepted Answer

Prostaglandin

Answer

Leukotriene

Answer

Vitamin K

Answer

Krebs cycle

Lipid Metabolism — MCQs

Lipid Metabolism — MCQs

On this page

Practice by Chapter

Want unlimited practice?