An 18-month-old girl is brought to casualty drowsy after two days of vomiting and poor feeding. Blood glucose is 32 mg/dL, urine ketones are negative, plasma lactate and uric acid are normal, and ammonia is mildly raised. Urine shows dicarboxylic acids, and plasma acylcarnitines show raised octanoylcarnitine (C8). Deficiency of which enzyme is most likely?

Medium-chain acyl-CoA dehydrogenase

A 40-year-old miner is rescued after nine days trapped underground with water but no food. He is alert, his blood glucose is 58 mg/dL and urine ketones are strongly positive. Which adaptation most reduces the breakdown of his muscle protein during this prolonged fast?

Brain switching to ketone body oxidation

Muscle releasing glucose from its glycogen

Brain oxidising free fatty acids directly

Liver converting fatty acids into glucose

In June, several children aged 3-8 years from villages around Muzaffarpur, Bihar, are brought to the district hospital early in the morning with seizures and coma. Most had eaten lychees in the orchards the previous day and skipped the evening meal. Blood glucose on arrival is below 50 mg/dL. Toxins in unripe lychee (hypoglycin A and MCPG) cause hypoglycaemia mainly by which mechanism?

Blocking fatty acid beta-oxidation

Inhibiting hepatic glycogen synthesis

Blocking intestinal glucose absorption

Lipid metabolism and lipoproteins

21 NEET-PG practice questions on Lipid metabolism and lipoproteins, part of Biochemistry. The first 21 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
An 18-month-old girl is brought to casualty drowsy after two days of vomiting and poor feeding. Blood glucose is 32 mg/dL, urine ketones are negative, plasma lactate and uric acid are normal, and ammonia is mildly raised. Urine shows dicarboxylic acids, and plasma acylcarnitines show raised octanoylcarnitine (C8). Deficiency of which enzyme is most likely?
1. ALiver glycogen phosphorylase
2. BMedium-chain acyl-CoA dehydrogenase
3. CPyruvate carboxylase
4. DGlucose-6-phosphatase
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Answer: B · Medium-chain acyl-CoA dehydrogenase
Hypoglycaemia during fasting with no ketones means fat cannot be turned into ketone bodies, pointing to a fatty acid oxidation defect. Medium-chain acyl-CoA dehydrogenase deficiency, the commonest of these, blocks beta-oxidation of medium-chain fatty acids, so C8 acylcarnitine rises and fatty acids are diverted to omega-oxidation, giving dicarboxylic aciduria. Without acetyl-CoA from fat, gluconeogenesis is also impaired. Treatment is IV dextrose now and avoidance of prolonged fasting afterwards; newborn screening by tandem mass spectrometry detects it.
- A: Liver phosphorylase deficiency gives mild fasting hypoglycaemia with ketosis, not raised C8.
- C: Pyruvate carboxylase deficiency causes lactic acidosis, which is absent here.
- D: Glucose-6-phosphatase deficiency gives lactic acidosis and hyperuricaemia, which are absent here.
Question 2 · Medium
A 2-year-old boy born of a consanguineous marriage has had pale, bulky, foul-smelling stools since infancy and poor weight gain. He now walks unsteadily and his ankle jerks are absent. The smear shows many acanthocytes; total cholesterol is 38 mg/dL and triglycerides 12 mg/dL. Consider four statements: 1. The defect is in microsomal triglyceride transfer protein. 2. Chylomicrons, VLDL and LDL are almost absent from plasma. 3. The neurological damage is mainly due to vitamin E deficiency. 4. Long-chain fat in the diet should be increased to improve absorption. Which statements are correct?
1. A1, 3 and 4 only
2. B1, 2 and 3 only
3. C1, 2 and 4 only
4. D2 and 3 only
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Answer: B · 1, 2 and 3 only
Statements 1, 2 and 3 are correct. Abetalipoproteinaemia is an autosomal recessive defect of microsomal triglyceride transfer protein, which loads lipid onto apoB, so apoB-containing lipoproteins (chylomicrons, VLDL, LDL) are almost absent and fat stays trapped in enterocytes. Fat-soluble vitamins, especially vitamin E, are not carried, and vitamin E deficiency causes the spinocerebellar degeneration and retinopathy; acanthocytes reflect the abnormal membrane lipids. Statement 4 is wrong: long-chain fat is restricted, and high-dose vitamin E and A are given.
- A: Includes more long-chain fat, which worsens steatorrhoea, and omits the absent lipoproteins.
- C: Includes more long-chain fat and omits vitamin E deficiency, the cause of the neurological damage.
- D: Omits statement 1; the defect is in microsomal triglyceride transfer protein.
Question 3 · Medium
A 40-year-old miner is rescued after nine days trapped underground with water but no food. He is alert, his blood glucose is 58 mg/dL and urine ketones are strongly positive. Which adaptation most reduces the breakdown of his muscle protein during this prolonged fast?
1. AMuscle releasing glucose from its glycogen
2. BBrain oxidising free fatty acids directly
3. CLiver converting fatty acids into glucose
4. DBrain switching to ketone body oxidation
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Answer: D · Brain switching to ketone body oxidation
In early fasting the brain needs glucose, much of it made from amino acids taken from muscle protein. As fasting continues, the liver turns fatty acids into ketone bodies, and the brain increasingly oxidises acetoacetate and beta-hydroxybutyrate, so less glucose and therefore less protein breakdown is needed. This is why urinary nitrogen loss falls as starvation is prolonged. Refeeding such patients must be gradual, with phosphate, potassium and thiamine monitored, to avoid refeeding syndrome.
- A: Muscle lacks glucose-6-phosphatase, so its glycogen cannot supply blood glucose.
- B: Long-chain fatty acids cross the blood-brain barrier poorly and are not a major brain fuel.
- C: Even-chain fatty acids give acetyl-CoA, which cannot make net glucose.
Question 4 · Medium
In June, several children aged 3-8 years from villages around Muzaffarpur, Bihar, are brought to the district hospital early in the morning with seizures and coma. Most had eaten lychees in the orchards the previous day and skipped the evening meal. Blood glucose on arrival is below 50 mg/dL. Toxins in unripe lychee (hypoglycin A and MCPG) cause hypoglycaemia mainly by which mechanism?
1. ABlocking fatty acid beta-oxidation
2. BInhibiting hepatic glycogen synthesis
3. CStimulating insulin secretion
4. DBlocking intestinal glucose absorption
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Answer: A · Blocking fatty acid beta-oxidation
Investigations of the Muzaffarpur outbreaks linked this acute encephalopathy to hypoglycin A and methylenecyclopropylglycine (MCPG) in lychee. Their metabolites inhibit acyl-CoA dehydrogenases and so block beta-oxidation of fatty acids. Without fatty acid oxidation, the liver lacks the acetyl-CoA, ATP and NADH that drive gluconeogenesis, so an undernourished child who skipped dinner becomes severely hypoglycaemic overnight. Prompt correction of glucose, and advice that children eat an evening meal and limit lychees, are the key measures.
- B: Glycogen stores are already low from the missed meal; gluconeogenesis is the step that fails.
- C: Insulin is not raised; the hypoglycaemia is from failed glucose production.
- D: The toxins do not block intestinal glucose absorption.
Question 5 · Medium
A 24-year-old primigravida at 11 weeks has hyperemesis gravidarum and has kept almost nothing down for four days. Her urine shows 3+ ketones and her capillary glucose is 70 mg/dL. Her low insulin and high glucagon allow fatty acids to enter liver mitochondria freely for oxidation and ketogenesis, chiefly by lowering which molecule?
1. AAcetyl-CoA
2. BMalonyl-CoA
3. CCarnitine
4. DFructose-2,6-bisphosphate
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Answer: B · Malonyl-CoA
Malonyl-CoA, made by acetyl-CoA carboxylase in the first step of fatty acid synthesis, inhibits carnitine palmitoyltransferase I and so keeps newly made fatty acids out of mitochondria in the fed state. Glucagon, through protein kinase A, phosphorylates and inactivates acetyl-CoA carboxylase, and low insulin removes its stimulus, so malonyl-CoA falls. CPT I is released, fatty acids enter the mitochondria, and the acetyl-CoA formed beyond the TCA cycle's capacity is turned into ketone bodies. She needs IV fluids with dextrose and thiamine, and antiemetics.
- A: Acetyl-CoA rises in fasting liver mitochondria and is the substrate for ketone bodies.
- C: Carnitine is required for transport; lowering it would reduce fatty acid entry.
- D: Fructose-2,6-bisphosphate regulates glycolysis and gluconeogenesis, not CPT I.
Question 6 · Medium
A 28-year-old woman on a very low-carbohydrate diet for weight loss has ketones in her urine and asks her doctor whether this is harmful. Consider four statements about her ketone bodies: 1. They are made in liver mitochondria from acetyl-CoA. 2. Her liver oxidises them for its own energy. 3. Mitochondrial HMG-CoA synthase is the rate-limiting enzyme of their synthesis. 4. Her heart and skeletal muscle use them as fuel. Which statements are correct?
1. A1, 3 and 4 only
2. B2, 3 and 4 only
3. C1 and 3 only
4. D1, 2 and 4 only
Answer and explanation in LearnFree account
Question 7 · Hard
A 32-year-old primigravida at 35 weeks is admitted to the labour room with nausea, vomiting, abdominal pain and jaundice. Blood glucose is 52 mg/dL; bilirubin, transaminases, creatinine and uric acid are raised, PT is prolonged and the platelet count is normal. Ultrasound shows no biliary dilatation. After urgent delivery she recovers. At 4 months her baby develops hypoketotic hypoglycaemia and cardiomyopathy. A deficiency in the fetus of which enzyme is classically linked with this maternal illness?
1. ALong-chain 3-hydroxyacyl-CoA dehydrogenase
2. BCarnitine palmitoyltransferase II
3. CMedium-chain acyl-CoA dehydrogenase
4. DVery-long-chain acyl-CoA dehydrogenase
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Question 8 · Medium
A 23-year-old army recruit develops severe muscle pain and cola-coloured urine on the second day of a long route march during which meals were missed. CK is 48,000 U/L. Between episodes he is well and can sprint without cramps, and a forearm exercise test shows a normal rise in lactate. Plasma acylcarnitines show raised long-chain species (C16 and C18:1). Deficiency of which enzyme is most likely?
1. AMuscle phosphofructokinase
2. BMedium-chain acyl-CoA dehydrogenase
3. CMuscle glycogen phosphorylase
4. DCarnitine palmitoyltransferase II
Answer and explanation in LearnFree account
Question 9 · Medium
A 3-year-old boy is admitted with heart failure; echocardiography shows a dilated cardiomyopathy with an ejection fraction of 25%. Last year he had an episode of hypoglycaemia without ketosis during a febrile illness. Plasma free carnitine is very low and urinary carnitine loss is high. What is the most appropriate specific treatment?
1. AUncooked cornstarch at bedtime
2. BOral L-carnitine supplementation
3. CHigh-dose oral riboflavin
4. DIntravenous enzyme replacement
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Question 10 · Easy
A 19-year-old with type 1 diabetes is in casualty with pH 7.12, bicarbonate 7 mmol/L and an anion gap of 26 mmol/L. The nitroprusside urine dipstick shows only a trace of ketones. Which ketone body is the most abundant in his blood but is missed by this test?
1. ABeta-hydroxybutyrate
2. BAcetone
3. CAcetoacetate
4. DAcetoacetyl-CoA
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Question 11 · Medium
A 52-year-old man with poorly treated hypothyroidism has yellow-orange creases on his palms and tuberous xanthomas over his elbows. Total cholesterol is 380 mg/dL and triglycerides 420 mg/dL, raised to a similar degree; lipoprotein electrophoresis shows a broad beta band. Which genotype is most likely?
1. AApolipoprotein E2/E2
2. BApolipoprotein E4/E4
3. CHeterozygous LDL receptor mutation
4. DApolipoprotein C-II deficiency
Answer and explanation in LearnFree account
Question 12 · Medium
A 30-year-old man has night blindness from retinitis pigmentosa, an unsteady gait, a loss of sense of smell, a peripheral neuropathy with thickened nerves, and dry, scaly skin. Plasma phytanic acid is markedly raised. Which pathway is defective?
1. APeroxisomal alpha-oxidation
2. BPeroxisomal VLCFA beta-oxidation
3. CMitochondrial beta-oxidation
4. DMicrosomal omega-oxidation
Answer and explanation in LearnFree account
Question 13 · Medium
A 34-year-old non-smoking software engineer has an anterior wall myocardial infarction. His blood pressure, glucose and BMI are normal. LDL is 102 mg/dL, HDL 48 mg/dL and triglycerides 130 mg/dL. His father had a heart attack at 44. Which lipoprotein, not part of the routine lipid profile, is most worth measuring?
1. AIntermediate-density lipoprotein
2. BVery-low-density lipoprotein
3. CChylomicron remnants
4. DLipoprotein(a)
Answer and explanation in LearnFree account
Question 14 · Easy
A 14-year-old boy is brought to the medicine OPD with firm, painless swellings over both Achilles tendons and over his knuckles. His father died of a heart attack at 41. Fasting lipids: total cholesterol 412 mg/dL, LDL 338 mg/dL, HDL 44 mg/dL, triglycerides 150 mg/dL. Which defect is most likely?
1. ALipoprotein lipase deficiency
2. BLDL receptor gene mutation
3. CApolipoprotein E2 homozygosity
4. DMicrosomal transfer protein deficiency
Answer and explanation in LearnFree account
Question 15 · Easy
A 52-year-old man with type 2 diabetes and an LDL of 168 mg/dL is started on atorvastatin 40 mg at night by his physician. Which enzyme does the drug inhibit?
1. AHMG-CoA synthase
2. BSqualene epoxidase
3. CHMG-CoA reductase
4. DAcyl-CoA cholesterol acyltransferase
Answer and explanation in LearnFree account
Question 16 · Medium
A 46-year-old schoolteacher attending a district hospital OPD has an LDL of 212 mg/dL on a routine check. She reports a year of tiredness, weight gain, constipation and feeling cold, and her ankle jerks relax slowly. Before a statin is started, which test should be done first?
1. ALDL receptor gene testing
2. BSerum TSH
3. CSerum apolipoprotein B
4. DSerum lipoprotein(a)
Answer and explanation in LearnFree account
Question 17 · Hard
A 48-year-old man with poorly controlled type 2 diabetes and heavy alcohol use has a fasting lipid profile: total cholesterol 286 mg/dL, HDL 32 mg/dL and triglycerides 940 mg/dL. The laboratory report calculates LDL as 66 mg/dL using the Friedewald formula. What is the best interpretation of the reported LDL?
1. AThe formula is invalid here; measure LDL directly
2. BLDL is 160 mg/dL once the formula is corrected
3. CLDL will be accurate if repeated after a 4-hour fast
4. DLDL is low at 66 mg/dL, so no statin is needed
Answer and explanation in LearnFree account
Question 18 · Medium
A 7-year-old boy who was doing well at school has, over the past year, become inattentive, with falling marks, clumsy handwriting and poor vision. His skin and gums have darkened, and his morning cortisol is low with a high ACTH. MRI shows symmetrical white matter changes in the parieto-occipital regions. Which blood test is most useful to confirm the diagnosis?
1. ASerum phytanic acid
2. BPlasma acylcarnitine profile
3. CUrine organic acids
4. DPlasma very-long-chain fatty acids
Answer and explanation in LearnFree account
Question 19 · Hard
A 9-year-old girl, the child of a first-cousin marriage, has yellow plaques on her eyelids, xanthomas over her tendons and in the finger webs, and an ejection systolic murmur from supravalvular aortic stenosis. Her LDL is 690 mg/dL, and both parents have LDL near 250 mg/dL. Fibroblast studies show almost no LDL receptor activity. On maximum-dose statin and ezetimibe her LDL falls only to 560 mg/dL. Which treatment is most appropriate to add?
1. ARegular LDL apheresis
2. BA bile acid sequestrant
3. CA PCSK9 inhibitor antibody
4. DA fibrate
Answer and explanation in LearnFree account
Question 20 · Easy
A 6-year-old girl is admitted with acute pancreatitis. She has crops of small yellow papules on her buttocks, and the retinal vessels look milky on fundoscopy. Her blood sample, left in the refrigerator overnight, forms a creamy top layer over a clear lower layer. Triglycerides are 2,400 mg/dL. Deficiency of which enzyme is most likely?
1. ALecithin-cholesterol acyltransferase
2. BHormone-sensitive lipase
3. CHepatic lipase
4. DLipoprotein lipase
Answer and explanation in LearnFree account
Question 21 · Medium
A 54-year-old man with type 2 diabetes taking dapagliflozin and metformin is admitted after two days of vomiting and poor intake following a laparoscopic cholecystectomy. Blood glucose is 196 mg/dL, pH 7.16, bicarbonate 9 mmol/L, anion gap 24 mmol/L and serum beta-hydroxybutyrate 5.4 mmol/L; lactate is 1.6 mmol/L. What is the most likely diagnosis?
1. AMetformin-associated lactic acidosis
2. BAlcoholic ketoacidosis
3. CSimple starvation ketosis
4. DEuglycaemic diabetic ketoacidosis
Answer and explanation in LearnFree account

Lipid metabolism and lipoproteins

A 40-year-old miner is rescued after nine days trapped underground with water but no food. He is alert, his blood glucose is 58 mg/dL and urine ketones are strongly positive. Which adaptation most reduces the breakdown of his muscle protein during this prolonged fast?

A 19-year-old with type 1 diabetes is in casualty with pH 7.12, bicarbonate 7 mmol/L and an anion gap of 26 mmol/L. The nitroprusside urine dipstick shows only a trace of ketones. Which ketone body is the most abundant in his blood but is missed by this test?

A 30-year-old man has night blindness from retinitis pigmentosa, an unsteady gait, a loss of sense of smell, a peripheral neuropathy with thickened nerves, and dry, scaly skin. Plasma phytanic acid is markedly raised. Which pathway is defective?

A 14-year-old boy is brought to the medicine OPD with firm, painless swellings over both Achilles tendons and over his knuckles. His father died of a heart attack at 41. Fasting lipids: total cholesterol 412 mg/dL, LDL 338 mg/dL, HDL 44 mg/dL, triglycerides 150 mg/dL. Which defect is most likely?

A 52-year-old man with type 2 diabetes and an LDL of 168 mg/dL is started on atorvastatin 40 mg at night by his physician. Which enzyme does the drug inhibit?

A 46-year-old schoolteacher attending a district hospital OPD has an LDL of 212 mg/dL on a routine check. She reports a year of tiredness, weight gain, constipation and feeling cold, and her ankle jerks relax slowly. Before a statin is started, which test should be done first?