Question 1: A 3-month-old male infant presents with delayed motor development and orange, sand-like crystals in his diaper. His parents report he constantly chews on his fingers and lips, causing bleeding. Based on these symptoms, what is the most likely diagnosis?
A. Adenosine deaminase deficiency
B. Gouty arthritis
C. Lesch-Nyhan Syndrome
D. Orotic aciduria
E. Von Gierke’s disease
Correct Answer: C. Lesch-Nyhan Syndrome
Explanation: This scenario closely aligns with manifestations of Lesch-Nyhan Syndrome (LNS). The characteristic symptoms of LNS include hyperuricemia (evidenced by the orange crystals, which are uric acid), self-mutilation (finger and lip biting), and developmental delay.
Incorrect options:
A. Adenosine deaminase deficiency causes severe combined immunodeficiency (SCID) but does not present with the described symptoms.
B. Gouty arthritis typically occurs in adults and primarily affects joints, not causing self-mutilation or developmental delay.
D. Orotic aciduria presents with megaloblastic anemia and failure to thrive, and while excessive orotic acid excretion may cause crystalluria, it is not associated with self-mutilation or the described neurological symptoms.
E. Von Gierke’s disease is a glycogen storage disorder and is not related to purine metabolism or the described symptoms.
Question 2: A 55-year-old man experiences sudden, excruciating pain and swelling in his right big toe. The affected joint is red, warm, and tender to the touch. Analysis of synovial fluid reveals needle-shaped crystals under polarized light microscopy. Which metabolic pathway is most directly implicated in this patient’s condition?
A. De novo pyrimidine biosynthesis
B. Pyrimidine degradation
C. De novo purine biosynthesis
D. Purine salvage
E. Purine degradation
Correct Answer: E. Purine degradation.
Explanation: The symptoms, particularly the presence of monosodium urate (MSU) crystals in the synovial fluid, are classic for gouty arthritis. Gout results from the buildup of uric acid, the end product of purine degradation. When uric acid levels exceed the solubility limit in body fluids, MSU crystals precipitate in joints, triggering inflammation and the characteristic pain.
Incorrect options:
The other options are not directly involved in the pathogenesis of gout:
B. Pyrimidine metabolism is related to conditions like orotic aciduria, not gout.
C. De novo purine biosynthesis is not related to gouty arthritis unless it is uncontrolled or associated with increased cell turnover. It is mainly increased purine degradation that causes hyperuricemia.
D. Purine salvage is a pathway for reusing purines, and while its disruption in LNS leads to hyperuricemia, it is not the primary cause of gout in this scenario.
Question 3: A 1-year-old child is brought to the clinic with failure to thrive and megaloblastic anemia. Laboratory tests reveal elevated urinary orotic acid levels but normal serum vitamin B12 and folate levels. Which enzyme deficiency is the most likely cause of this child’s condition?
A. Adenosine deaminase
B. Aspartate transcarbamoylase
C. Glutamine PRPP amidotransferase
D. Hypoxanthine-guanine phosphoribosyl transferase (HGPRT)
E. Orotate phosphoribosyl transferase
Correct Answer: E. Orotate phosphoribosyl transferase.
Explanation:
The child’s symptoms, including failure to thrive, megaloblastic anemia, unresponsive to vitamin B12 or folate supplementation, and significantly elevated urinary orotic acid, point to orotic aciduria. This condition results from a deficiency in one or both enzymes involved in the conversion of orotic acid to UMP in pyrimidine synthesis:
1. Orotate phosphoribosyl transferase: Converts orotic acid to orotidine 5’-monophosphate (OMP).
2. Orotidine 5’-phosphate decarboxylase: Converts OMP to UMP.
A deficiency in either enzyme disrupts pyrimidine synthesis, leading to the accumulation of orotic acid and impaired DNA synthesis, causing megaloblastic anemia.
Incorrect Options:
A. Adenosine deaminase:
A deficiency in this enzyme causes severe combined immunodeficiency (SCID), which primarily affects the immune system, not pyrimidine synthesis.
B. Aspartate transcarbamoylase:
This enzyme catalyzes an earlier step in pyrimidine synthesis (the formation of carbamoyl aspartate) and is not directly responsible for orotic aciduria.
C. Glutamine PRPP amidotransferase:
This enzyme regulates de novo purine synthesis, not pyrimidine synthesis, and its dysfunction does not lead to orotic acid accumulation.
D. Hypoxanthine-guanine phosphoribosyl transferase (HGPRT):
A deficiency in HGPRT causes Lesch-Nyhan syndrome, characterized by hyperuricemia, gout, self-mutilation, and neurological symptoms. It is unrelated to pyrimidine metabolism or orotic aciduria.
Question 4: A 40-year-old woman with a history of recurrent kidney stones undergoes a metabolic evaluation. Her serum uric acid levels are consistently elevated. Which of the following dietary recommendations is most likely to help manage her condition?
A. Increase intake of purine-rich foods
B. Increase intake of pyrimidine-rich foods
C. Limit alcohol consumption
D. Consume a high-protein diet
E. Supplement with high doses of vitamin C
Correct Answer: C. Limit alcohol consumption.
Explanation:
While the exact cause of the patient’s hyperuricemia is not specified, limiting alcohol consumption is a key dietary recommendation for individuals with elevated uric acid levels. Alcohol metabolism (particularly beer and spirits) increases uric acid production by promoting purine breakdown and impairing renal uric acid excretion. This exacerbates hyperuricemia and increases the risk of gout and uric acid kidney stones.
Incorrect Options:
A. Increase intake of purine-rich foods:
Purine-rich foods (e.g., organ meats, shellfish, certain fish) contribute directly to uric acid production through purine breakdown. Consuming more purines would worsen hyperuricemia and should be avoided.
B. Increase intake of pyrimidine-rich foods:
Pyrimidine metabolism does not lead to uric acid production. Therefore, pyrimidine intake is not directly related to uric acid levels and has no role in managing hyperuricemia.
D. Consume a high-protein diet:
High-protein diets, particularly those rich in purine-containing animal proteins, can lead to increased uric acid production and are not advisable for hyperuricemia management.
E. Supplement with high doses of vitamin C:
Vitamin C has mild uricosuric effects, which may help reduce uric acid levels. However, it is not a primary strategy for managing hyperuricemia. Excessive vitamin C supplementation can lead to other side effects, such as oxalate stone formation, and should be used cautiously.
Question 5: Mycophenolate mofetil, an immunosuppressant drug used to prevent organ rejection, exerts its effects by inhibiting which enzyme involved in nucleotide metabolism?
A. Adenosine deaminase
B. Dihydrofolate reductase
C. Glutamine PRPP amidotransferase
D. Hypoxanthine-guanine phosphoribosyl transferase (HGPRT)
E. IMP dehydrogenase
Correct Answer: E. IMP dehydrogenase.
Explanation:
Mycophenolate mofetil is a prodrug that is converted to mycophenolic acid in the body. Mycophenolic acid specifically inhibits IMP dehydrogenase, an enzyme crucial for the de novo synthesis of guanine nucleotides. By blocking this pathway, the drug deprives rapidly dividing cells, particularly lymphocytes, of the guanine nucleotides needed for DNA replication. This suppression of lymphocyte proliferation helps reduce immune responses and prevents organ rejection.
Incorrect Options:
A. Adenosine deaminase:
This enzyme is involved in purine catabolism, and its deficiency causes severe combined immunodeficiency (SCID). It is not the target of mycophenolate mofetil.
B. Dihydrofolate reductase:
This enzyme is targeted by methotrexate, a different immunosuppressant and chemotherapeutic agent. Methotrexate inhibits folate metabolism, impairing the synthesis of both purines and thymidine.
C. Glutamine PRPP amidotransferase:
This enzyme catalyzes the committed step in de novo purine synthesis but is not inhibited by mycophenolate mofetil.
D. Hypoxanthine-guanine phosphoribosyl transferase (HGPRT):
This enzyme is part of the purine salvage pathway, and its deficiency leads to Lesch-Nyhan syndrome. It is not affected by mycophenolate mofetil.
Question 6: Which of the following statements accurately describes the role of 5-phosphoribosyl pyrophosphate (PRPP) in nucleotide metabolism?
A. PRPP is a product of purine degradation and contributes to hyperuricemia.
B. PRPP is a precursor for both purine and pyrimidine nucleotide biosynthesis.
C. PRPP is a competitive inhibitor of ribonucleotide reductase, limiting DNA synthesis.
D. PRPP is an allosteric activator of hypoxanthine-guanine phosphoribosyl transferase (HGPRT), promoting purine salvage.
Correct Answer: B. PRPP is a precursor for both purine and pyrimidine nucleotide biosynthesis.
Explanation:
PRPP (5-phosphoribosyl pyrophosphate) is a central molecule in nucleotide metabolism, serving as a precursor for the de novo synthesis of both purine and pyrimidine nucleotides. It provides the ribose-phosphate backbone onto which nucleotide bases are built, highlighting its critical role in nucleotide biosynthesis.
Incorrect Options:
A. PRPP is not a product of purine degradation. However, in conditions like Lesch-Nyhan syndrome (where HGPRT is deficient), unutilized PRPP can stimulate de novo purine nucleotide synthesis. The overproduction of purines leads to their eventual degradation, contributing to hyperuricemia.
C. PRPP is not a competitive inhibitor of ribonucleotide reductase. Ribonucleotide reductase regulates the conversion of ribonucleotides to deoxyribonucleotides (critical for DNA synthesis), but PRPP does not play a role in inhibiting this enzyme.
D. PRPP is not an allosteric activator of hypoxanthine-guanine phosphoribosyltransferase (HGPRT). While PRPP is a substrate for HGPRT in the salvage pathway of purines, it does not act as an allosteric activator for the enzyme.
Question 7: A 35-year-old man presents with recurrent episodes of painful, swollen joints. Laboratory tests reveal elevated serum uric acid levels. He denies alcohol use or diuretic therapy. Genetic testing identifies a partial deficiency in hypoxanthine-guanine phosphoribosyltransferase (HGPRT). Which metabolic consequence best explains his symptoms?
A. Increased salvage of purines and reduced uric acid production
B. Increased de novo purine synthesis and uric acid overproduction
C. Reduced PRPP levels and diminished purine synthesis
D. Accumulation of pyrimidines, leading to gouty arthritis
E. Impaired degradation of pyrimidines, contributing to uric acid buildup
Correct Answer: B. Increased de novo purine synthesis and uric acid overproduction.
Explanation: Partial HGPRT deficiency reduces purine salvage, leading to increased PRPP levels. Elevated PRPP drives de novo purine synthesis, resulting in excessive purine degradation and hyperuricemia.
Incorrect options:
A: Increased salvage of purines and reduced uric acid production: HGPRT deficiency decreases purine salvage, not increases it, leading to uric acid buildup rather than reduction.
C: Reduced PRPP levels and diminished purine synthesis: Reduced PRPP levels would inhibit purine synthesis, but PRPP is elevated in HGPRT deficiency.
D: Accumulation of pyrimidines, leading to gouty arthritis: Pyrimidines do not contribute to uric acid or gout.
E: Impaired degradation of pyrimidines, contributing to uric acid buildup: Pyrimidine metabolism does not produce uric acid; purines do.
Question 8: A 50-year-old woman is started on allopurinol to manage her arthritis. Which compound is likely to accumulate upstream due to this treatment?
A. PRPP
B. Hypoxanthine
C. UMP
D. Xanthosine
E. Guanine
Correct Answer: B. Hypoxanthine.
Explanation: Allopurinol inhibits xanthine oxidase, preventing the conversion of hypoxanthine and xanthine to uric acid. Hypoxanthine accumulates as a result.
Incorrect options
A: PRPP: PRPP is not directly affected by allopurinol; it is involved in nucleotide biosynthesis.
C: UMP: UMP is a pyrimidine nucleotide unrelated to this pathway.
D: Xanthosine: Xanthosine is not a major intermediate in the xanthine oxidase pathway.
E: Guanine: Guanine is salvaged, not degraded directly via xanthine oxidase.
Question 9: A 3-month-old boy presents with recurrent infections and failure to thrive. Genetic testing reveals a deficiency in adenosine deaminase (ADA). Which metabolic effect is most likely responsible for his symptoms?
A. Accumulation of ATP, impairing DNA synthesis
B. Accumulation of dATP, inhibiting ribonucleotide reductase
C. Deficient pyrimidine synthesis, impairing cell division
D. Increased purine salvage, causing immune suppression
E. Impaired PRPP synthesis, reducing nucleotide availability
Correct Answer: B. Accumulation of dATP, inhibiting ribonucleotide reductase.
Explanation: ADA deficiency causes dATP accumulation, which inhibits ribonucleotide reductase. This blocks DNA synthesis, impairing lymphocyte development and function, leading to SCID.
Incorrect options:
A: Accumulation of ATP, impairing DNA synthesis: ATP does not accumulate in ADA deficiency; dATP does.
C: Deficient pyrimidine synthesis, impairing cell division: Pyrimidine synthesis is unaffected in ADA deficiency.
D: Increased purine salvage, causing immune suppression: ADA deficiency does not increase purine salvage but disrupts purine catabolism.
E: Impaired PRPP synthesis, reducing nucleotide availability: PRPP synthesis is unrelated to ADA deficiency.
Question 10: A kidney transplant patient is prescribed mycophenolate mofetil as an immunosuppressant. The drug inhibits inosine monophosphate dehydrogenase (IMPDH). How does this inhibition suppress the immune response?
A. Increases AMP synthesis to suppress T-cell proliferation
B. Reduces GMP synthesis, impairing DNA and RNA production in lymphocytes
C. Enhances PRPP levels, reducing purine availability in immune cells
D. Blocks purine salvage pathways, impairing nucleotide recycling in lymphocytes
E. Inhibits xanthine oxidase, reducing uric acid levels in immune cells
Correct Answer: B. Reduces GMP synthesis, impairing DNA and RNA production in lymphocytes.
Explanation: IMPDH inhibition reduces GMP synthesis, essential for rapidly dividing lymphocytes. This suppression of DNA and RNA synthesis dampens immune activity.
Incorrect options:
A: Increases AMP synthesis to suppress T-cell proliferation: AMP synthesis is unaffected by IMPDH inhibition.
C: Enhances PRPP levels, reducing purine availability in immune cells: PRPP levels are not enhanced; the drug directly affects GMP production.
D: Blocks purine salvage pathways, impairing nucleotide recycling in lymphocytes: Purine salvage pathways are unaffected by mycophenolate.
E: Inhibits xanthine oxidase, reducing uric acid levels in immune cells: Xanthine oxidase is not targeted by mycophenolate.
Question 11: Which of the following explains why the hypoxanthine analog allopurinol, which effectively treats gout, has no effect on the severe neurological symptoms of Lesch-Nyhan Syndrome?
A. Decrease de novo purine synthesis
B. Decrease de novo pyrimidine biosynthesis
C. Decrease urate synthesis
D. Increase PRPP levels (phosphoribosyl pyrophosphate)
E. Inhibit xanthine oxidase
Correct Answer: A. Decrease de novo purine synthesis.
• Explanation: The neurological symptoms in Lesch-Nyhan Syndrome arise from the deficiency of HGPRT (hypoxanthine-guanine phosphoribosyltransferase), which leads to elevated PRPP levels and excessive de novo purine synthesis. Allopurinol inhibits xanthine oxidase, reducing urate formation, but it does not directly impact PRPP levels or de novo purine synthesis. Hence, it cannot alleviate the neurological symptoms associated with Lesch-Nyhan Syndrome.
Incorrect Options:
B. Decrease de novo pyrimidine biosynthesis
• Explanation: Pyrimidine biosynthesis is not affected in Lesch-Nyhan Syndrome, and it is unrelated to the disease’s pathology or symptoms. Allopurinol does not influence pyrimidine metabolism.
C. Decrease urate synthesis
• Explanation: Allopurinol effectively decreases urate synthesis by inhibiting xanthine oxidase and managing hyperuricemia and gout in Lesch-Nyhan patients. However, this mechanism does not address the neurological symptoms.
D. Increase PRPP levels (phosphoribosyl pyrophosphate)
• Explanation: Increased PRPP levels in Lesch-Nyhan Syndrome are due to the lack of HGPRT, which normally uses PRPP in the purine salvage pathway. Allopurinol does not directly alter PRPP levels, but this is not the reason it fails to address neurological symptoms.
E. Inhibit xanthine oxidase
• Explanation: Allopurinol effectively inhibits xanthine oxidase, which reduces urate production. This action helps control gout symptoms but has no impact on the neurological effects of Lesch-Nyhan Syndrome, as these are unrelated to urate levels.
Question 12: A 4-year-old presents to a pediatric clinic with megaloblastic anemia and failure to thrive. Blood biochemistry reveals “orotic aciduria.” Enzyme measurement of white blood cells reveals a deficiency of the pyrimidine biosynthesis enzyme orotate phosphoribosyl transferase and abnormally high activity of aspartate transcarbamoylase. Which of the following treatments will reverse all symptoms?
A. Blood transfusion
B. Dietary supplementation of PRPP
C. Oral thymidine
D. Oral uridine
E. Plasmapheresis
Correct Answer: D. Oral uridine
Explanation:
The deficiency of orotate phosphoribosyl transferase in pyrimidine biosynthesis disrupts the conversion of orotic acid to UMP, leading to orotic aciduria and impaired pyrimidine nucleotide synthesis. Oral uridine bypasses this metabolic block, providing the necessary pyrimidines for RNA and DNA synthesis. This restores nucleotide balance, resolving both megaloblastic anemia and failure to thrive.
Incorrect Options:
A. Blood transfusion
• Explanation: While a transfusion might temporarily alleviate anemia, it does not address the underlying cause of the disease, which is a pyrimidine synthesis defect.
B. Dietary supplementation of PRPP
• Explanation: PRPP is a substrate in pyrimidine synthesis, but increasing PRPP levels will not overcome the enzymatic block caused by orotate phosphoribosyl transferase deficiency. Excess PRPP may exacerbate the accumulation of orotic acid.
C. Oral thymidine
• Explanation: Thymidine supplementation may help balance deoxynucleotide pools for DNA synthesis, but it does not provide a general source of pyrimidines, nor does it address the anemia caused by the pyrimidine synthesis defect.
E. Plasmapheresis
• Explanation: Plasmapheresis is used to remove pathological substances from the blood. It is not relevant in this condition, as orotic aciduria results from a metabolic defect, not a circulating toxin.
Question 13: Which of the following enzymes catalyzes the rate-limiting step of pyrimidine synthesis that exhibits allosteric inhibition by cytidine triphosphate (CTP)?
A. Aspartate transcarbamoylase
B. Hypoxanthine Guanine Phosphoribosyl Transferase
C. Thymidylate Synthase
D. Xanthine Oxidase
E. PRPP Synthetase
Correct Answer: A. Aspartate transcarbamoylase
Explanation:
Aspartate transcarbamoylase (ATCase) catalyzes the condensation of carbamoyl phosphate and aspartate to form carbamoyl aspartate, the first committed step in pyrimidine synthesis. This is the rate-limiting step of the pathway. ATCase is regulated by allosteric feedback inhibition from cytidine triphosphate (CTP), ensuring balanced pyrimidine nucleotide synthesis.
Incorrect Options:
B. Hypoxanthine Guanine Phosphoribosyl Transferase (HGPRT):
• Explanation: HGPRT is involved in the purine salvage pathway, not pyrimidine synthesis. Its deficiency causes Lesch-Nyhan syndrome.
C. Thymidylate Synthase:
• Explanation: Thymidylate synthase catalyzes the conversion of dUMP to dTMP, which is downstream of the pyrimidine synthesis pathway. It is not the rate-limiting step.
D. Xanthine Oxidase:
• Explanation: Xanthine oxidase is involved in purine degradation, converting hypoxanthine and xanthine to uric acid. It has no role in pyrimidine synthesis.
E. PRPP Synthetase:
• Explanation: PRPP synthetase generates PRPP, a precursor for both purine and pyrimidine synthesis, but it is not the rate-limiting step of pyrimidine synthesis specifically.
Question 14: A physician evaluates a 32-year-old patient for fatigue. The patient is found to have an elevated white blood cell count and an enlarged spleen. A referral to an oncologist results in a diagnosis of chronic myelogenous leukemia. Treatment with hydroxyurea, a ribonucleotide reductase inhibitor, is begun. The normal functioning of this enzyme is to do which of the following?
A. Converts xanthine to uric acid
B. Converts ribonucleotides to deoxyribonucleotides
C. Degrades guanine to xanthine
D. Degrades AMP to IMP
E. Converts PRPP to phosphoribosylamine
Correct Answer: B. Converts ribonucleotides to deoxyribonucleotides
Explanation:
Ribonucleotide reductase catalyzes the conversion of ribonucleotides (e.g., ADP, GDP) into their corresponding deoxyribonucleotides (e.g., dADP, dGDP). This step is crucial for DNA synthesis and repair, as deoxyribonucleotides are required for building the DNA backbone. Hydroxyurea inhibits ribonucleotide reductase, thereby reducing the supply of deoxyribonucleotides, limiting DNA synthesis, and suppressing the rapid proliferation of leukemic cells.
Incorrect Options:
A. Converts xanthine to uric acid
• Explanation: This reaction is catalyzed by xanthine oxidase, an enzyme involved in purine catabolism, not ribonucleotide reductase.
C. Degrades guanine to xanthine
• Explanation: This reaction is part of purine catabolism and is catalyzed by guanine deaminase, not ribonucleotide reductase.
D. Degrades AMP to IMP
• Explanation: This reaction is catalyzed by AMP deaminase, which is unrelated to the function of ribonucleotide reductase.
E. Converts PRPP to phosphoribosylamine
• Explanation: This reaction is catalyzed by glutamine PRPP amidotransferase, the committed step of purine biosynthesis, not by ribonucleotide reductase
Question 15: A child is noted to have recurrent respiratory infections that necessitate hospitalization. His lab tests demonstrate a decrease in T cells, B cells, natural killer cells, and decreased antibodies. He is found to have severe combined immunodeficiency (SCID). The enzyme that is defective in this disorder is important in which of the following processes?
A. Conversion of ribonucleotides to deoxyribonucleotides
B. Formation of AMP
C. Synthesis of UMP
D. Conversion of dUMP to dTMP
E. Conversion of adenosine to inosine
Correct Answer: E. Conversion of adenosine to inosine.
Explanation:
The enzyme defective in this form of SCID is adenosine deaminase (ADA), which catalyzes the conversion of adenosine to inosine in the purine salvage pathway. ADA deficiency leads to the toxic accumulation of adenosine and deoxyadenosine, which inhibits ribonucleotide reductase and interferes with DNA synthesis. This results in the loss of T cells, B cells, and natural killer cells, causing severe combined immunodeficiency.
Incorrect Options:
A. Conversion of ribonucleotides to deoxyribonucleotides
• Explanation: This reaction is catalyzed by ribonucleotide reductase, not adenosine deaminase. While ADA deficiency indirectly affects this process by increasing dATP levels, it is not the primary enzymatic defect in SCID.
B. Formation of AMP
• Explanation: AMP is formed from IMP or adenylosuccinate in purine synthesis. This process does not involve adenosine deaminase and is unaffected in ADA deficiency.
C. Synthesis of UMP
• Explanation: UMP is synthesized during pyrimidine biosynthesis and is unrelated to adenosine deaminase function.
D. Conversion of dUMP to dTMP
• Explanation: This reaction is catalyzed by thymidylate synthase in pyrimidine metabolism and is unrelated to ADA deficiency.
Question 16: A 58-year-old man is awoken by a throbbing ache in his great toe. He had a similar attack previously following a rich meal. On examination, he is noted to have an inflamed great toe and several nodules on the antihelix of his ear. Inhibition of which of the following enzymes might prevent the occurrence of such symptoms?
A. Amido transferase
B. PRPP synthetase
C. Xanthine oxidase
D. Orotate phosphoribosyl transferase
E. Carbamoyl phosphate synthetase-II
Correct Answer: C. Xanthine oxidase
Explanation:
The symptoms described, including inflamed great toe (indicative of gout) and tophi on the ear, suggest gout, which is caused by the accumulation of uric acid crystals in joints and tissues. Xanthine oxidase catalyzes the conversion of hypoxanthine to xanthine and xanthine to uric acid in the purine degradation pathway. Inhibiting xanthine oxidase with drugs like allopurinol or febuxostat reduces uric acid production, preventing gout attacks and tophi formation.
Incorrect Options:
A. Amido transferase
• Explanation: Glutamine PRPP amidotransferase is the rate-limiting enzyme of de novo purine synthesis. While inhibiting it could theoretically reduce purine production and uric acid levels, it is not the target for managing acute gout.
B. PRPP synthetase
• Explanation: PRPP synthetase catalyzes the formation of PRPP, a precursor for nucleotide biosynthesis. Overactivity of PRPP synthetase could contribute to increased purine synthesis and uric acid production, but inhibiting it is not a common therapeutic approach for gout.
D. Orotate phosphoribosyl transferase
• Explanation: This enzyme is involved in pyrimidine biosynthesis and has no role in purine degradation or uric acid production.
E. Carbamoyl phosphate synthetase-II
• Explanation: CPS-II is a key enzyme in the de novo synthesis of pyrimidines, and its inhibition is unrelated to the treatment or prevention of gout.
