An infant presents with vomiting after feeding. Benedict's test was positive for a non-glucose reducing substance. What is the most likely diagnosis?
Q12
A 45-year-old patient presents with symptoms of anemia, depigmented hair, and myelopathy. Which of the following mineral deficiencies is most likely associated with this clinical presentation?
Q13
A young boy with a thin build and long fingers presents with diminished vision. On examination, subluxation of the lens is observed, and cystathionine synthase deficiency is detected. Which amino acid should the patient be supplemented with?
Q14
A farmer complains of a skin rash that worsens with sun exposure and redness of the tongue. Maize is the staple in his diet. Which vitamin deficiency is likely responsible for these symptoms?
Q15
A 5 year old child was brought to the physician with a history of black urine. There is no history of fever or any other complaints. There is no growth retardation and all the developmental milestones are normal. The child is suspected to have an enzyme defect for metabolism of an aromatic amino acid. What is the enzyme deficient
Q16
A patient had dinner at 8 PM at night and does his blood sugar test at 7 AM in the morning. What is the major source of glucose at this time?
Q17
Which amino acid needs to be supplemented through diet in patient with cystathionine beta synthase deficiency
Q18
A patient on a maize diet presented with diarrhea, dementia and dermatitis. Which vitamin deficiency is responsible for these features
Q19
A 25-year-old man comes to the office because of pain in his left shoulder. He says that this pain started 3 years ago and has progressively worsened. He denies joint trauma, fever, dysuria, or morning stiffness. He says that his urine turns black after it is exposed to air and has done so since childhood. He has one sexual partner and they regularly use condoms. His pulse is 72/min, respiratory rate is 18/min, temperature is 37.2°C (99.0°F), and blood pressure is 135/80 mm Hg. Physical examination shows bilateral scleral darkening and point tenderness upon palpation of his right elbow, left knee, and shoulder. Leukocyte count is 6,000/mm3. Which of the following enzymes is most likely deficient in this patient?
Q20
A 5-year-old boy with developmental delays presents to his pediatrician’s office with an ‘itchy rash’ on the flexor surfaces of his knees, elbows, and around his eyelids. The patient’s mother notes that the rashes have had a relapsing-remitting course since the child was an infant. Vital signs are within normal limits. Physical examination shows hypopigmentation of the patient’s skin and hair, as well as a musty odor in his sweat and urine. Based on the patient’s symptoms and history, which of the following is the most appropriate dietary recommendation?
Metabolism US Medical PG Practice Questions and MCQs
Question 11: An infant presents with vomiting after feeding. Benedict's test was positive for a non-glucose reducing substance. What is the most likely diagnosis?
A. Galactosemia due to GAL-1-P Uridyl Transferase enzyme deficiency (Correct Answer)
B. Fructosuria due to Fructokinase deficiency
C. Hereditary fructose intolerance due to Aldolase B deficiency
D. Primary lactose intolerance
E. Glycogen storage disease due to Glucose-6-phosphatase deficiency
Explanation: ***Galactosemia due to GAL-1-P Uridyl Transferase enzyme deficiency***
- Vomiting after feeding in an infant, coupled with a **positive Benedict's test** for a **non-glucose reducing substance**, is highly indicative of galactosemia. The accumulation of **galactose-1-phosphate** and **galactitol** leads to toxicity and symptoms.
- This enzyme deficiency, causing **classic galactosemia**, prevents the proper metabolism of **galactose**, leading to its buildup.
*Fructosuria due to Fructokinase deficiency*
- This condition is a **benign metabolic disorder** with no significant clinical symptoms.
- While it would lead to fructose in the urine, the infant would not typically present with **vomiting after feeding**.
*Hereditary fructose intolerance due to Aldolase B deficiency*
- Symptoms usually appear after the introduction of **fructose-containing foods** into the diet, causing severe hypoglycemia and vomiting.
- The positive Benedict's test in this scenario would typically indicate a reducing substance in the urine, while fructose intolerance is characterized by **hypoglycemia** and metabolic crises upon fructose ingestion.
*Glycogen storage disease due to Glucose-6-phosphatase deficiency*
- This disorder primarily causes **hypoglycemia** and liver enlargement, not primarily vomiting after feeding due to a **non-glucose reducing substance**.
- Glucose-6-phosphatase deficiency (Von Gierke's disease) leads to an inability to release **glucose from glycogen** and causes severe hypoglycemia, often requiring frequent feeding.
*Primary lactose intolerance*
- While lactose intolerance can cause vomiting and gastrointestinal symptoms, it is **extremely rare in infants** (primary lactose intolerance is a late-onset condition).
- Lactose would be a reducing sugar, but the key differentiator is that **galactose** (from galactosemia) is the non-glucose reducing substance detected in this case, along with the typical **toxic presentation** in neonates.
Question 12: A 45-year-old patient presents with symptoms of anemia, depigmented hair, and myelopathy. Which of the following mineral deficiencies is most likely associated with this clinical presentation?
A. Copper (Correct Answer)
B. Iron
C. Fluoride
D. Zinc
E. Selenium
Explanation: ***Copper***
- **Copper deficiency** can lead to anemia due to its role in iron metabolism, **depigmented hair** (achromotrichia) due to impaired melanin synthesis, and **myelopathy** due to its involvement in maintaining the myelin sheath.
- Symptoms often mimic those of **vitamin B12 deficiency**, including neurological manifestations like ataxia and spasticity.
*Iron*
- **Iron deficiency** is the most common cause of anemia but does not typically cause **depigmented hair** or **myelopathy**.
- Its neurological symptoms are usually limited to **restless legs syndrome** and **pica**, not demyelination.
*Fluoride*
- **Fluoride deficiency** is primarily associated with an increased risk of dental caries and does not cause anemia, hair depigmentation, or myelopathy.
- Excessive intake (fluorosis) can lead to **bone and tooth abnormalities**.
*Zinc*
- **Zinc deficiency** can cause immune dysfunction, **dermatitis**, impaired wound healing, and growth retardation.
- It may rarely cause anemia in severe cases but does not typically cause hair depigmentation or myelopathy as primary symptoms.
*Selenium*
- **Selenium deficiency** is associated with **Keshan disease** (cardiomyopathy) and **Kashin-Beck disease** (osteoarthropathy).
- While it can cause muscle weakness and fatigue, it does not typically present with the specific triad of anemia, hair depigmentation, and myelopathy seen in copper deficiency.
Question 13: A young boy with a thin build and long fingers presents with diminished vision. On examination, subluxation of the lens is observed, and cystathionine synthase deficiency is detected. Which amino acid should the patient be supplemented with?
A. Tyrosine
B. Serine
C. Cysteine (Correct Answer)
D. Methionine
E. Glycine
Explanation: ***Cysteine***
- In **cystathionine synthase deficiency** (homocystinuria), the body cannot convert **homocysteine to cystathionine**, and subsequently to **cysteine**.
- **Cysteine** therefore becomes an **essential amino acid** in these patients and must be supplemented.
*Tyrosine*
- **Tyrosine** is a non-essential amino acid synthesized from **phenylalanine**, and its deficiency is not directly related to cystathionine synthase deficiency.
- It is not involved in the **methionine or homocysteine metabolic pathway** that is disrupted in homocystinuria.
*Serine*
- **Serine** is a substrate for the **cystathionine synthase enzyme**, which combines with **homocysteine** to form **cystathionine**.
- Supplementation with serine alone would not bypass the enzyme deficiency or provide the essential product, **cysteine**.
*Methionine*
- **Methionine** is the precursor to **homocysteine**, and in cystathionine synthase deficiency, there's often an accumulation of methionine and homocysteine.
- Therefore, **methionine restriction** is typically part of the treatment, not supplementation.
*Glycine*
- **Glycine** is involved in one-carbon metabolism but is not directly involved in the **transsulfuration pathway** affected by cystathionine synthase deficiency.
- Glycine supplementation would not address the inability to synthesize **cysteine** from homocysteine.
Question 14: A farmer complains of a skin rash that worsens with sun exposure and redness of the tongue. Maize is the staple in his diet. Which vitamin deficiency is likely responsible for these symptoms?
A. Vitamin C deficiency
B. Vitamin K deficiency
C. Niacin deficiency (Correct Answer)
D. Folic acid deficiency
E. Riboflavin deficiency
Explanation: ***Niacin deficiency***
- The symptoms described (dermatitis that worsens with sun exposure, glossitis, and a diet high in maize) are characteristic of **pellagra**, which is caused by a **niacin (Vitamin B3) deficiency**.
- **Maize** is a poor source of niacin, and the niacin it contains is largely bound and unavailable, leading to higher rates of deficiency in populations relying on it as a staple.
- The classic **3 D's of pellagra** are: **Dermatitis** (photosensitive), **Diarrhea**, and **Dementia**.
*Riboflavin deficiency*
- **Riboflavin (Vitamin B2) deficiency** causes **angular stomatitis**, **cheilosis**, and **glossitis**, but the dermatitis is typically **seborrheic** (not photosensitive).
- The **photosensitive** nature of the rash in this case is the key differentiating feature pointing to niacin deficiency.
*Vitamin C deficiency*
- **Vitamin C deficiency** leads to **scurvy**, characterized by **gingival bleeding**, **poor wound healing**, and **petechiae**, none of which are mentioned here.
- While it can manifest with fatigue, it does not typically cause a photosensitive rash or glossitis as described.
*Vitamin K deficiency*
- **Vitamin K deficiency** primarily affects **blood clotting**, leading to **bleeding disorders** and **easy bruising**.
- It is not associated with skin rashes or glossitis.
*Folic acid deficiency*
- **Folic acid deficiency** causes **macrocytic anemia**, fatigue, and potentially **glossitis**, but it does not cause a photosensitive rash.
- The distinctive combination of photosensitive dermatitis and glossitis points away from folic acid deficiency.
Question 15: A 5 year old child was brought to the physician with a history of black urine. There is no history of fever or any other complaints. There is no growth retardation and all the developmental milestones are normal. The child is suspected to have an enzyme defect for metabolism of an aromatic amino acid. What is the enzyme deficient
A. Homogentisate dehydrogenase
B. Homogentistae oxidase (Correct Answer)
C. Tyrosine Transaminase
D. Tryptophan Hydroxylase
E. Phenylalanine Hydroxylase
Explanation: ***Homogentistae oxidase***
- The presentation of a child with **black urine** (alkaptonuria) in the absence of other symptoms is characteristic of a deficiency in **homogentisate oxidase**.
- This enzyme is crucial in the catabolism of **tyrosine**, and its deficiency leads to the accumulation of **homogentisic acid**, which oxidizes upon exposure to air, turning urine black.
*Homogentisate dehydrogenase*
- This enzyme is not a recognized component of the **tyrosine degradation pathway** in humans.
- The correct enzyme involved in the breakdown of **homogentisate** is an oxidase, not a dehydrogenase, in this context.
*Tyrosine Transaminase*
- A deficiency in **tyrosine transaminase** (tyrosinemia type II) would lead to elevated tyrosine levels and typically presents with symptoms affecting the eyes, skin, and intellectual disability, not primarily black urine.
- This condition is characterized by **ocular findings** (corneal ulcers), **skin lesions**, and **neurological symptoms**.
*Tryptophan Hydroxylase*
- This enzyme is involved in the synthesis of **serotonin** and **melatonin** from tryptophan, a different amino acid pathway.
- A deficiency or abnormality in **tryptophan hydroxylase** would not cause black urine but could lead to neurological or mood disorders.
*Phenylalanine Hydroxylase*
- A deficiency in **phenylalanine hydroxylase** causes **phenylketonuria (PKU)**, which affects phenylalanine metabolism, not tyrosine metabolism directly.
- PKU typically presents with **intellectual disability**, **musty odor**, **fair skin**, and **seizures** if untreated, not black urine.
Question 16: A patient had dinner at 8 PM at night and does his blood sugar test at 7 AM in the morning. What is the major source of glucose at this time?
A. Liver Glycogen (Correct Answer)
B. Muscle Glycogen
C. Gluconeogenesis
D. Dietary Carbohydrate
E. Ketone bodies
Explanation: ***Liver Glycogen***
- After an overnight fast (approximately 11 hours in this scenario), the primary mechanism for maintaining blood glucose levels is the breakdown of **liver glycogen** stores.
- The liver is crucial for glucose homeostasis as it can release glucose directly into the bloodstream, a function muscle glycogen cannot perform.
*Muscle Glycogen*
- **Muscle glycogen** serves as an energy reserve primarily for the muscle itself and cannot be directly released into the bloodstream to maintain blood glucose levels.
- It is utilized for physical activity and local energy demands within muscle cells.
*Gluconeogenesis*
- **Gluconeogenesis**, the synthesis of glucose from non-carbohydrate precursors, becomes increasingly important for glucose production after prolonged fasting (typically *after* liver glycogen stores are depleted).
- While it contributes during an overnight fast, **liver glycogenolysis** is the dominant source initially.
*Dietary Carbohydrate*
- **Dietary carbohydrates** from the previous dinner (8 PM) would have been absorbed and utilized or stored as glycogen much earlier than 7 AM the next morning.
- By 7 AM, the direct impact of the previous night's meal on circulating glucose is negligible, having been processed hours before.
*Ketone Bodies*
- **Ketone bodies** are alternative fuel sources produced during prolonged fasting or starvation, but they are **not glucose**.
- While they can be used by tissues (brain, heart, muscle) for energy during extended fasting, they do not contribute to blood glucose levels and are metabolically distinct from glucose.
Question 17: Which amino acid needs to be supplemented through diet in patient with cystathionine beta synthase deficiency
A. Tryptophan
B. Serine
C. Methionine
D. Cysteine (Correct Answer)
E. Tyrosine
Explanation: ***Cysteine***
- In **cystathionine beta synthase (CBS) deficiency**, the conversion of **homocysteine** to **cystathionine** (and subsequently to cysteine) is impaired.
- This makes **cysteine** an **essential amino acid** for these patients, requiring dietary supplementation.
*Tryptophan*
- **Tryptophan** is an **essential amino acid** and a precursor for **serotonin** and **niacin**, but its metabolism is not directly affected by CBS deficiency.
- Its supplementation is not specifically indicated for this condition.
*Serine*
- **Serine** is a **non-essential amino acid** that provides the **carbon skeleton** for the synthesis of cysteine from homocysteine in the presence of CBS.
- While important in the pathway, CBS deficiency specifically disrupts the downstream conversion of homocysteine, making **cysteine** the deficient product, not serine.
*Methionine*
- **Methionine** is an **essential amino acid** that is a precursor to **homocysteine**; in CBS deficiency, homocysteine levels are already elevated due to impaired conversion to cystathionine.
- Restricting methionine intake is typically recommended in CBS deficiency to reduce homocysteine accumulation, not supplementing it.
*Tyrosine*
- **Tyrosine** is a **non-essential amino acid** derived from **phenylalanine** and serves as a precursor for catecholamines and thyroid hormones.
- Its metabolism is not affected by CBS deficiency, and supplementation is not indicated for this condition.
Question 18: A patient on a maize diet presented with diarrhea, dementia and dermatitis. Which vitamin deficiency is responsible for these features
A. Niacin (Correct Answer)
B. Riboflavin
C. Thiamine
D. Pyridoxine
E. Cobalamin
Explanation: ***Niacin***
- The classic presentation of **pellagra**, caused by a deficiency of **niacin (Vitamin B3)**, is characterized by the "**3 Ds**": **dermatitis**, **diarrhea**, and **dementia**. In severe cases, a fourth 'D' for death can also occur.
- A **maize (corn)** staple diet is a known risk factor for niacin deficiency because maize contains niacin in a bound, non-bioavailable form (niacytin) and is low in tryptophan, a precursor to niacin.
*Riboflavin*
- **Riboflavin (Vitamin B2)** deficiency leads to **ariboflavinosis**, which can cause **cheilosis**, **angular stomatitis**, **glossitis**, and **seborrheic dermatitis**, but not the constellation of diarrhea, dementia, and dermatitis seen in pellagra.
- It does not typically manifest with neurological or gastrointestinal symptoms as severe as those described in the question.
*Thiamine*
- **Thiamine (Vitamin B1)** deficiency causes **beriberi**, characterized by **neurological (dry beriberi)** or **cardiovascular (wet beriberi)** symptoms.
- It can lead to **Wernicke-Korsakoff syndrome** in severe cases, which includes neurological deficits, but not the specific "3 Ds" of pellagra.
*Pyridoxine*
- **Pyridoxine (Vitamin B6)** deficiency can cause **neurological symptoms** such as **peripheral neuropathy**, **seizures**, and **depression**, as well as **dermatitis** and **glossitis**.
- It does not present with the characteristic triad of dermatitis, diarrhea, and dementia seen in pellagra.
*Cobalamin*
- **Cobalamin (Vitamin B12)** deficiency causes **megaloblastic anemia** and **neurological symptoms** including **subacute combined degeneration** of the spinal cord, **peripheral neuropathy**, and **cognitive changes**.
- While it can cause neurological symptoms, it does not present with the classic dermatitis and diarrhea combination seen in pellagra.
Question 19: A 25-year-old man comes to the office because of pain in his left shoulder. He says that this pain started 3 years ago and has progressively worsened. He denies joint trauma, fever, dysuria, or morning stiffness. He says that his urine turns black after it is exposed to air and has done so since childhood. He has one sexual partner and they regularly use condoms. His pulse is 72/min, respiratory rate is 18/min, temperature is 37.2°C (99.0°F), and blood pressure is 135/80 mm Hg. Physical examination shows bilateral scleral darkening and point tenderness upon palpation of his right elbow, left knee, and shoulder. Leukocyte count is 6,000/mm3. Which of the following enzymes is most likely deficient in this patient?
A. Cystathionine synthase deficiency
B. Branched-chain alpha-ketoacid dehydrogenase
C. Homogentisic acid oxidase (Correct Answer)
D. Phenylalanine hydroxylase
E. Propionyl-CoA carboxylase
Explanation: ***Homogentisic acid oxidase***
- The patient's symptoms, including **black urine (alkaptonuria)**, **scleral darkening (ochronosis)**, and progressive **arthralgia** in multiple joints, are classic manifestations of **alkaptonuria**.
- **Alkaptonuria** is an autosomal recessive disorder caused by a deficiency of **homogentisic acid oxidase**, an enzyme important in the metabolism of **tyrosine**.
*Cystathionine synthase deficiency*
- This deficiency causes **homocystinuria**, characterized by Marfanoid habitus, mental retardation, and premature atherosclerosis.
- It does not present with black urine or joint pain in this manner.
*Branched-chain alpha-ketoacid dehydrogenase*
- A deficiency in this enzyme leads to **maple syrup urine disease**, an inborn error of metabolism affecting branched-chain amino acids.
- Symptoms include neurological deterioration, seizures, and a distinctive maple syrup odor in urine, not black urine or joint issues.
*Phenylalanine hydroxylase*
- This deficiency causes **phenylketonuria (PKU)**, characterized by intellectual disability, seizures, and fair skin/hair if untreated.
- Patients typically have a mousy odor to their urine, but it does not turn black upon exposure to air, nor do they develop ochronosis or specific arthralgia.
*Propionyl-CoA carboxylase*
- A deficiency in this enzyme leads to **propionyl-CoA carboxylase deficiency**, a type of organic acidemia.
- It presents with metabolic acidosis, hyperammonemia, and developmental delay, not with black urine or the specific musculoskeletal symptoms described.
Question 20: A 5-year-old boy with developmental delays presents to his pediatrician’s office with an ‘itchy rash’ on the flexor surfaces of his knees, elbows, and around his eyelids. The patient’s mother notes that the rashes have had a relapsing-remitting course since the child was an infant. Vital signs are within normal limits. Physical examination shows hypopigmentation of the patient’s skin and hair, as well as a musty odor in his sweat and urine. Based on the patient’s symptoms and history, which of the following is the most appropriate dietary recommendation?
A. Avoid fresh fruits
B. Increase intake of dairy products
C. Avoid meat (Correct Answer)
D. Increase intake of bread
E. Switch to diet soda
Explanation: ***Avoid meat***
- This patient's symptoms are highly suggestive of **Phenylketonuria (PKU)** a genetic disorder causing an inability to metabolize **phenylalanine**. Meat is a high source of phenylalanine and must be avoided.
- The distinctive **musty odor** is due to the accumulation of **phenylacetate** which is a metabolite of phenylalanine.
*Avoid fresh fruits*
- **Fresh fruits** are generally low in protein and phenylalanine, making them safe to consume for individuals with PKU.
- There is no medical basis for avoiding fresh fruits in the management of PKU or any related conditions.
*Increase intake of dairy products*
- **Dairy products** such as milk, cheese, and yogurt are rich in protein, and therefore high in phenylalanine.
- Increasing their intake would exacerbate the accumulation of **phenylalanine** in individuals with PKU.
*Increase intake of bread*
- While some breads might be lower in protein than meat or dairy, regular bread still contains a significant amount of **protein** and thus **phenylalanine**.
- A special **low-protein bread** might be used, but increasing intake of typical bread is not advised for PKU patients.
*Switch to diet soda*
- Many diet sodas contain the artificial sweetener **aspartame**, which is metabolized in the body into **phenylalanine**.
- Consumption of aspartame-containing products is specifically contraindicated in patients with PKU.
