Category 1
A patient comes to the clinic with severe vitamin B₆ deficiency. Which metabolic process involving amino acids will be most impaired?
Transamination, because all aminotransferases require pyridoxal phosphate (PLP)—the active form of vitamin B₆.
This leads to poor amino acid metabolism and mild neurological symptoms.
A patient with chronic gastritis is taking H2-blockers. Which biochemical molecule are these drugs targeting?
They block histamine (H₂ receptors) in the stomach, reducing gastric acid secretion.
A patient’s ALT level is much higher than AST. What does this suggest?
This pattern suggests liver cell injury, especially acute hepatitis, because ALT is more specific to the liver.
A patient experiences itching, redness, and swelling after eating seafood. Which amino acid derivative is responsible?
Histamine, a decarboxylation product of histidine, released by mast cells during allergic reactions.
A child with a genetic defect in aminotransferases shows poor growth and lethargy. What is the main biochemical problem?
Impaired transamination → amino acids cannot be converted into keto acids →
↓ energy production
↑ unused amino acids
↓ synthesis of non-essential amino acids
This leads to growth retardation and metabolic imbalance.
A patient on long-term isoniazid therapy develops peripheral neuropathy. Why does this drug cause amino acid metabolism problems?
Isoniazid causes vitamin B₆ (PLP) deficiency, leading to:
Impaired transamination
Impaired decarboxylation (reduced GABA synthesis)
Lack of GABA contributes to neurological symptoms.
A patient with liver failure has elevated blood ammonia. Which metabolic process is failing?
The indirect deamination (transdeamination) pathway:
Amino acids → glutamate (via transamination)
Glutamate → NH₃ (via oxidative deamination by GDH)
Liver failure prevents urea cycle, causing hyperammonemia → confusion, irritability.
A patient’s AST level is more than twice ALT. What diagnosis is most likely?
Alcoholic liver disease.
AST > ALT (often ratio > 2) because:
Mitochondrial AST increases
Alcohol causes vitamin B₆ deficiency → lowers ALT activity
A person experiences flushing, headache, and hypotension after eating spoiled fish (“scombroid poisoning”). What metabolic process explains this reaction?
Bacterial decarboxylation of histidine → histamine in spoiled fish.
Excess histamine acts like an allergic reaction.
A patient has a deficiency of glutamate dehydrogenase. What symptoms might appear due to impaired oxidative deamination?
Accumulation of glutamate
Reduced ammonia production, impairing the urea cycle
Possible encephalopathy due to altered glutamate/GABA balance
↓ TCA cycle intermediates (α-ketoglutarate)
A newborn has vomiting and irritability after feeding. Labs show high ammonia and low α-ketoglutarate. Which amino acid metabolic step is likely defective?
A defect in transamination leading to decreased formation of glutamate, the key amino group carrier. This disrupts ammonia detoxification → hyperammonemia.
A patient suffers from bronchospasm, hypotension, and urticaria after a bee sting. Which receptor type mediates most of these harmful effects?
H₁ receptors, responsible for:
Bronchoconstriction
Increased vascular permeability
Vasodilation
Itching
Thus, H₁ antihistamines are used.
A patient with severe malnutrition develops fatty liver. How could impaired amino acid metabolism contribute to this?
Low amino acid availability → decreased synthesis of apolipoproteins → fat cannot be exported as VLDL → fat accumulation in the liver. This occurs because amino acids normally supply the liver with essential proteins for lipid transport.
A patient with celiac disease has reduced amino acid absorption. What metabolic consequence is most likely?
Reduced amino acids reaching the liver → impaired protein synthesis and reduced substrate for transamination, causing muscle wasting and weakness.
A man with uncontrolled diabetes presents with high levels of alanine in the blood. What metabolic pathway explains this finding?
In diabetes, muscle proteolysis increases → alanine released → used for gluconeogenesis (glucose–alanine cycle). High alanine indicates increased amino acid catabolism.
A patient with liver cirrhosis shows confusion and tremors (hepatic encephalopathy). Which amino acid-derived product is mainly responsible?
Ammonia (NH₃) accumulates due to impaired deamination + urea cycle, crosses the blood–brain barrier → neurotoxicity → confusion, asterixis.
During an allergic asthma attack, histamine causes bronchoconstriction. Which enzyme normally breaks down histamine in tissues?
Diamine oxidase (DAO) and histamine-N-methyltransferase degrade histamine to inactive metabolites.
After strenuous exercise, a patient feels lightheaded. Labs show elevated glutamate levels. Which process is being overactivated?
Transamination of branched-chain amino acids in muscle → glutamate builds up before being converted to alanine or entering the TCA cycle
A patient with vitamin B6 deficiency shows decreased synthesis of dopamine. Which amino acid reaction is affected?
DOPA decarboxylation, which requires PLP. B₆ deficiency → ↓ dopamine → depression and neurological symptoms.
A patient with severe infection has very high levels of histidine in blood. What metabolic explanation fits best?
Inflammation increases demand for histamine production (decarboxylation of histidine). If decarboxylation enzymes or PLP are limited, histidine accumulates.