An 8-year-old boy presents with recurrent infections including multiple episodes of pneumonia and diarrhea. He reports difficulty seeing in the dark. Physical examination reveals white patches on the sclera and conjunctival dryness. What is the most likely cause of these findings?
Q62
A 43-year-old man presents with the complaint of pain in the small joints of his left hand. The pain is intermittent and cramping in nature in his 2nd and 3rd metacarpophalangeal (MCP) joints. It has progressively worsened over the past few weeks. He also reports that he has felt thirsty more often and has urinated more frequently over the past few weeks. He denies any pain during micturition. His stools are pale in color. He also reports that his skin appears to be darker than usual even though he has not been outdoors much over the past few weeks. Physical exam is significant for tenderness in the 2nd and 3rd MCPs of both hands as well as tenderness in the right upper quadrant of his abdomen. Lab results show:
Aspartate aminotransferase (AST) 450 U/L
Alanine aminotransferase (ALT) 350 U/L
Serum ferritin 460 ng/mL
Inappropriately low levels of which of the following is the most likely cause of his symptoms?
Q63
A 6-month-old boy presents with decreased growth, pigmented retinopathy, hemolytic anemia, and peripheral neuropathy. You suspect that these signs are the result of a vitamin deficiency leading to increased oxidative damage to lipids. Which of the following is most likely responsible for this patient's symptoms?
Q64
A 17-year-old girl is brought to the physician by her mother because she has not had her menstrual period yet. At birth, she had ambiguous genitalia. The mother reports that during the pregnancy she had noticed abnormal hair growth on her chin. A year ago, the girl broke her distal radius after a minor trauma. She is at the 95th percentile for height and 50th percentile for weight. Physical examination shows nodulocystic acne on the face, chest, and upper back. Breast development is at Tanner stage I. Pelvic examination reveals normal pubic hair with clitoromegaly. A pelvic ultrasound shows ovaries with multiple cysts and a normal uterus. Which of the following is the most likely diagnosis?
Q65
Steroid hormone synthesis, lipid synthesis, and chemical detoxification are activities of which of the following?
Q66
A 13-year-old boy is brought to the physician by his parents, who are concerned about recurrent muscle cramps he experiences while playing soccer. The boy has always loved sports and has been playing in a soccer league for the past 3 years. He now complains of severe cramping pain in his legs after intense practice sessions. He has no significant medical history. His physical examination is unremarkable. A battery of laboratory tests is ordered and they are all normal. Imaging studies yield no abnormalities as well. Which of the following is most likely deficient in this patient?
Q67
A 57-year-old man presents the urgent care clinic with a one-week history of diffuse bone pain and generalized weakness. He was diagnosed with end-stage renal disease 6 months ago and is currently on dialysis. His wife, who is accompanying him today, adds that he is not compliant with his medicines. He has been diabetic for the last 10 years and hypertensive for the last 7 years. He has smoked 4–5 cigarettes per day for 30 years but does not drink alcohol. His family history is insignificant. On examination, the patient has a waddling gait. Hypotonia of all the limbs is evident on neurologic examination. Diffuse bone tenderness is remarkable. X-ray of his legs reveal osteopenia and osseous resorption. The final step of activation of the deficient vitamin in this patient occurs by which of the following enzymes?
Q68
An 11-year-old male is brought in by ambulance to the emergency department after being a restrained passenger in a motor vehicle accident. His father was driving him to soccer practice when they were hit by a wrong way driver. On presentation, his temperature is 101°F (38.3°C), blood pressure is 100/62 mmHg, pulse is 108/min, and respirations are 21/min. He is found to be agitated and complains of nausea, severe epigastric pain, and lower extremity pain. Physical exam reveals lacerations and ecchymosis on his left forehead, right flank, and lower extremities. Radiographs demonstrate an open book fracture of the pelvis as well as bilateral femur fractures. Despite multiple interventions, his condition deteriorates and he passes away from his injuries. Post-mortem pathologic examination of abdominal tissues reveals white deposits containing calcium. Abnormal activity of which of the following proteins is most likely responsible for these deposits?
Q69
A 67-year-old gentleman with severe COPD is found to have a respiratory quotient of 0.8. His physician would like to decrease the amount of CO2 produced by the patient's metabolism, thereby reducing the energy breathing expenditure required to eliminate the patient's CO2 respiratory burden. Which of the following dietary modifications would decrease this patient's respiratory quotient?
Q70
A 35-year-old pregnant woman gives birth to a baby at term. The antepartum course was uneventful. She was compliant with all prenatal examinations and was given a prophylactic tetanus vaccine. While performing the neonatal examination, the pediatrician reports Apgar scores of 9 and 10 at 1 and 5 min, respectively. The pediatrician notices that the baby has ambiguous genitalia and blood pressure that is high for a neonate. The notable laboratory results are as follows:
Renin 0.4 nmoL/L/h
Aldosterone 70 pmoL/L
Cortisol 190 nmoL/L
Serum creatinine 1.0 mg/dL
Sex hormones are higher than the normal values at this age. Which of the following is responsible for the neonate's hypertension?
Lipid metabolism US Medical PG Practice Questions and MCQs
Question 61: An 8-year-old boy presents with recurrent infections including multiple episodes of pneumonia and diarrhea. He reports difficulty seeing in the dark. Physical examination reveals white patches on the sclera and conjunctival dryness. What is the most likely cause of these findings?
A. Congenital rubella
B. Spinocerebellar ataxia (SCA) type 1
C. Deficiency of vitamin A (Correct Answer)
D. Autoimmune neutropenia
E. Vitamin B1 deficiency
Explanation: ***Deficiency of vitamin A***
- The combination of **recurrent infections** (pneumonia, diarrhea), **night blindness**, and **ocular signs** like white patches on the sclera (Bitot's spots due to keratinized epithelium) and conjunctival dryness (xerophthalmia) are classic manifestations of **vitamin A deficiency**.
- Vitamin A is crucial for **immune function**, **vision** (a component of rhodopsin), and the **maintenance of epithelial tissues**.
*Congenital rubella*
- This typically presents with a **triad of cataracts**, **heart defects** (e.g., patent ductus arteriosus), and **sensorineural hearing loss**, often detected earlier in infancy.
- It does not explain the recurrent infections, night blindness, or specific ocular epithelial changes described.
*Spinocerebellar ataxia (SCA) type 1*
- This is a **neurodegenerative disorder** primarily affecting coordination and balance, leading to progressive **ataxia**.
- It does not cause recurrent infections, night blindness, or xerophthalmia; its symptoms are distinct and neurological in nature.
*Autoimmune neutropenia*
- Primarily causes **recurrent bacterial infections** due to low neutrophil counts.
- It does not explain the night blindness, diarrhea, or the specific ocular findings of keratinization.
*Vitamin B1 deficiency*
- Also known as **thiamine deficiency**, it leads to **beriberi**, characterized by cardiac (wet beriberi) or neurological (dry beriberi) symptoms.
- Common symptoms include **peripheral neuropathy**, **heart failure**, and **Wernicke-Korsakoff syndrome**, none of which are descriptive of this patient's presentation.
Question 62: A 43-year-old man presents with the complaint of pain in the small joints of his left hand. The pain is intermittent and cramping in nature in his 2nd and 3rd metacarpophalangeal (MCP) joints. It has progressively worsened over the past few weeks. He also reports that he has felt thirsty more often and has urinated more frequently over the past few weeks. He denies any pain during micturition. His stools are pale in color. He also reports that his skin appears to be darker than usual even though he has not been outdoors much over the past few weeks. Physical exam is significant for tenderness in the 2nd and 3rd MCPs of both hands as well as tenderness in the right upper quadrant of his abdomen. Lab results show:
Aspartate aminotransferase (AST) 450 U/L
Alanine aminotransferase (ALT) 350 U/L
Serum ferritin 460 ng/mL
Inappropriately low levels of which of the following is the most likely cause of his symptoms?
A. Hepcidin (Correct Answer)
B. Ceruloplasmin
C. α1-antitrypsin
D. Transferrin
E. Pyridoxine
Explanation: ***Hepcidin***
- The constellation of **joint pain**, **darker skin (hyperpigmentation)**, **polydipsia/polyuria (diabetes mellitus)**, **pale stools (liver dysfunction/biliary obstruction)**, **elevated AST/ALT**, and **elevated ferritin** points to **hemochromatosis**.
- **Hemochromatosis** is characterized by **excess iron accumulation** due to **hepcidin deficiency or dysfunction**, leading to increased intestinal iron absorption and deposition in organs like the liver, pancreas, heart, and joints.
*Ceruloplasmin*
- **Ceruloplasmin** deficiency causes **Wilson's disease**, characterized by copper overload, which can lead to liver disease, neurological symptoms, and Kayser-Fleischer rings.
- While liver involvement and elevated AST/ALT can be seen, the other symptoms like hyperpigmentation, high ferritin, and diabetes are not typical of Wilson's disease.
*α1-antitrypsin*
- **α1-antitrypsin** deficiency primarily affects the lungs (emphysema) and liver (cirrhosis), but it does not cause the specific combination of symptoms such as elevated ferritin, hyperpigmentation, diabetes, or joint involvement in the described pattern.
- Liver disease due to this deficiency is typically progressive and presents earlier in life, often with cholestasis in infancy or cirrhosis in adulthood.
*Transferrin*
- **Transferrin** is an iron-binding protein responsible for transporting iron in the blood; a deficiency would lead to **iron-deficiency anemia**, not iron overload.
- Patients with transferrin deficiency would exhibit low ferritin levels and not the signs of iron accumulation seen in this patient.
*Pyridoxine*
- **Pyridoxine (Vitamin B6)** deficiency can lead to microcytic anemia, peripheral neuropathy, and dermatitis.
- It is not associated with the severe liver dysfunction, iron overload, diabetes, or hyperpigmentation presented in this clinical case.
Question 63: A 6-month-old boy presents with decreased growth, pigmented retinopathy, hemolytic anemia, and peripheral neuropathy. You suspect that these signs are the result of a vitamin deficiency leading to increased oxidative damage to lipids. Which of the following is most likely responsible for this patient's symptoms?
A. Excessive boiling of formula
B. Goat milk ingestion
C. Abetalipoproteinemia (Correct Answer)
D. Pernicious anemia
E. Hartnup disease
Explanation: ***Abetalipoproteinemia***
- This condition is characterized by a defect in **microsomal triglyceride transfer protein (MTP)**, leading to an inability to synthesize ApoB-containing lipoproteins.
- The resulting **malabsorption of fat and fat-soluble vitamins (especially vitamin E)** leads to the neurological symptoms (retinopathy, neuropathy) and hemolytic anemia due to increased oxidative stress on red blood cell membranes.
*Excessive boiling of formula*
- Excessive boiling of formula could potentially degrade some **heat-sensitive vitamins**, such as vitamin C or thiamine (B1).
- However, this is unlikely to cause a severe, combined deficiency leading to the specific constellation of symptoms seen, particularly the ophthalmologic and neurological signs related to **fat-soluble vitamin malabsorption**.
*Goat milk ingestion*
- Goat milk is naturally low in **folate** and **vitamin D** and can cause **folate deficiency anemia** and rickets if it's the sole source of nutrition for an infant.
- However, it does not typically cause the entire spectrum of symptoms described, particularly **pigmented retinopathy** and **peripheral neuropathy**, which are more indicative of **vitamin E deficiency**.
*Pernicious anemia*
- Pernicious anemia is caused by a deficiency in **intrinsic factor**, leading to **vitamin B12 malabsorption**.
- Symptoms primarily include **megaloblastic anemia**, **glossitis**, and **neurological deficits** (subacute combined degeneration of the spinal cord), but not pigmented retinopathy or hemolytic anemia due to increased fatty acid oxidation via vitamin E malabsorption.
*Hartnup disease*
- Hartnup disease is an inherited disorder of **amino acid transport**, specifically affecting the absorption of **neutral amino acids** like tryptophan.
- It leads to **niacin deficiency** (pellagra-like symptoms) and can cause skin rashes, ataxia, and psychiatric symptoms, but not hemolytic anemia or pigmented retinopathy.
Question 64: A 17-year-old girl is brought to the physician by her mother because she has not had her menstrual period yet. At birth, she had ambiguous genitalia. The mother reports that during the pregnancy she had noticed abnormal hair growth on her chin. A year ago, the girl broke her distal radius after a minor trauma. She is at the 95th percentile for height and 50th percentile for weight. Physical examination shows nodulocystic acne on the face, chest, and upper back. Breast development is at Tanner stage I. Pelvic examination reveals normal pubic hair with clitoromegaly. A pelvic ultrasound shows ovaries with multiple cysts and a normal uterus. Which of the following is the most likely diagnosis?
A. Aromatase deficiency
B. Kallmann syndrome
C. Polycystic ovary syndrome
D. Mullerian agenesis
E. Congenital adrenal hyperplasia (Correct Answer)
Explanation: ***Congenital adrenal hyperplasia (CAH)***
- The patient's **ambiguous genitalia at birth**, maternal virilization during pregnancy, clitoromegaly, **primary amenorrhea**, and nodulocystic acne are all characteristic signs of **classic congenital adrenal hyperplasia**, specifically 21-hydroxylase deficiency.
- The tall stature (95th percentile for height) is consistent with **accelerated growth** due to excess androgens, while **lack of breast development** (Tanner stage I) and **cystic ovaries** suggest impaired estrogen production and anovulation.
*Aromatase deficiency*
- This condition presents with **ambiguous genitalia at birth** in females and leads to **primary amenorrhea** and **virilization** in adolescence due to the inability to convert androgens to estrogens.
- However, patients with aromatase deficiency often have **tall stature** with delayed epiphyseal fusion due to low estrogen levels, which doesn't fully align with the patient's current growth pattern and other findings.
*Kallmann syndrome*
- This syndrome is characterized by **hypogonadotropic hypogonadism** and **anosmia** (loss of smell), leading to **primary amenorrhea** and **absent/delayed puberty**; however, it does not cause androgen excess or ambiguous genitalia.
- Patients with Kallmann syndrome would typically present with **eunuchoid proportions** rather than tall stature, and would not have clitoromegaly or acne due to androgen excess.
*Polycystic ovary syndrome (PCOS)*
- While PCOS presents with **anovulation**, **hirsutism**, and **polycystic ovaries**, it typically manifests in adolescence or adulthood and does not cause **ambiguous genitalia at birth** or clitoromegaly to the extent described.
- The onset of symptoms in PCOS is usually insidious, and the patient's history of ambiguous genitalia points to a congenital adrenal issue.
*Mullerian agenesis*
- This condition, also known as Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome, causes **primary amenorrhea** due to **absent or underdeveloped uterus and vagina**.
- However, patients with Mullerian agenesis have **normal secondary sexual characteristics** (breast development, pubic hair pattern) and external female genitalia, and do not exhibit signs of androgen excess like ambiguous genitalia or clitoromegaly.
Question 65: Steroid hormone synthesis, lipid synthesis, and chemical detoxification are activities of which of the following?
A. Peroxisomes
B. Nucleolus
C. Rough Endoplasmic Reticulum
D. Smooth Endoplasmic Reticulum (Correct Answer)
E. Golgi bodies
Explanation: ***Smooth Endoplasmic Reticulum***
- The **smooth endoplasmic reticulum (SER)** is rich in enzymes that catalyze the synthesis of **lipids**, including steroid hormones, and is crucial for the detoxification of drugs and poisons, particularly in liver cells.
- Its tubular structure, devoid of ribosomes, differentiates its functions from the rough ER, focusing on metabolic processes like **calcium ion storage** and carbohydrate metabolism.
*Peroxisomes*
- Peroxisomes are primarily involved in the breakdown of **fatty acids** and amino acids, producing hydrogen peroxide as a byproduct.
- They also play a role in detoxification but are not the primary site for steroid hormone or general lipid synthesis.
*Nucleolus*
- The **nucleolus** is a dense structure within the nucleus responsible for synthesizing **ribosomal RNA (rRNA)** and assembling ribosomes.
- It has no direct role in steroid hormone synthesis, lipid metabolism, or chemical detoxification.
*Rough Endoplasmic Reticulum*
- The **rough endoplasmic reticulum (RER)** is studded with **ribosomes** and is primarily involved in the synthesis and modification of **proteins** destined for secretion or insertion into membranes.
- While it's part of the endomembrane system, it does not directly perform lipid synthesis or chemical detoxification as its main functions.
*Golgi bodies*
- **Golgi bodies (or Golgi apparatus)** are responsible for modifying, sorting, and packaging **proteins and lipids** synthesized in the ER into vesicles for secretion or delivery to other organelles.
- They do not perform the initial synthesis of steroid hormones or lipids, nor are they the primary site for chemical detoxification.
Question 66: A 13-year-old boy is brought to the physician by his parents, who are concerned about recurrent muscle cramps he experiences while playing soccer. The boy has always loved sports and has been playing in a soccer league for the past 3 years. He now complains of severe cramping pain in his legs after intense practice sessions. He has no significant medical history. His physical examination is unremarkable. A battery of laboratory tests is ordered and they are all normal. Imaging studies yield no abnormalities as well. Which of the following is most likely deficient in this patient?
A. Carnitine palmitoyltransferase I
B. Medium-chain acyl-coenzyme A dehydrogenase
C. Carnitine palmitoyltransferase II
D. Phosphofructokinase
E. Myophosphorylase (Correct Answer)
Explanation: ***Myophosphorylase***
- The patient's symptoms of **exercise-induced muscle cramps** and pain, specifically after intense activity, and normal lab findings, are classic for **McArdle disease** (glycogen storage disease type V).
- McArdle disease is caused by a deficiency in **myophosphorylase**, preventing the breakdown of glycogen for energy in muscles during exercise.
*Carnitine palmitoyltransferase I*
- Deficiency in CPT I primarily affects the liver and causes a hypoketotic hypoglycemia, not isolated exercise-induced muscle cramps.
- This enzyme is crucial for the transport of long-chain fatty acids into the mitochondria for beta-oxidation.
*Medium-chain acyl-coenzyme A dehydrogenase*
- MCAD deficiency is characterized by **hypoketotic hypoglycemia** and liver dysfunction, especially during fasting or illness, due to impaired fatty acid oxidation.
- It does not typically present with isolated exercise-induced muscle cramps in an otherwise healthy active adolescent.
*Carnitine palmitoyltransferase II*
- CPT II deficiency can cause **recurrent myoglobinuria** and acute muscle pain precipitated by prolonged exercise, fasting, or cold exposure, which might resemble the patient's symptoms.
- However, the presentation of "severe cramping pain in his legs after intense practice sessions" with normal lab tests points more directly to an issue with carbohydrate metabolism in muscle, making myophosphorylase deficiency a more likely primary diagnosis given the typical onset with intense, high-energy demand activities rather than prolonged exercise or fasting.
*Phosphofructokinase*
- PFK deficiency (Tarui disease) also presents with exercise intolerance, muscle pain, and cramps, and is a type of glycogen storage disease.
- It would typically result in **hemolytic anemia** and elevated bilirubin, which are not mentioned in this patient, and would also lead to an accumulation of glycolytic intermediates, which is not indicated by the normal lab results.
Question 67: A 57-year-old man presents the urgent care clinic with a one-week history of diffuse bone pain and generalized weakness. He was diagnosed with end-stage renal disease 6 months ago and is currently on dialysis. His wife, who is accompanying him today, adds that he is not compliant with his medicines. He has been diabetic for the last 10 years and hypertensive for the last 7 years. He has smoked 4–5 cigarettes per day for 30 years but does not drink alcohol. His family history is insignificant. On examination, the patient has a waddling gait. Hypotonia of all the limbs is evident on neurologic examination. Diffuse bone tenderness is remarkable. X-ray of his legs reveal osteopenia and osseous resorption. The final step of activation of the deficient vitamin in this patient occurs by which of the following enzymes?
A. α-1-antitrypsin
B. 24,25 hydroxylase
C. α-Glucosidase
D. 7-α-hydroxylase
E. 1-α-hydroxylase (Correct Answer)
Explanation: ***1-α-hydroxylase***
- The patient's symptoms (diffuse bone pain, generalized weakness, waddling gait, hypotonia, osteopenia, and osseous resorption) in the context of **end-stage renal disease (ESRD)** and non-compliance strongly suggest **renal osteodystrophy**, specifically **osteomalacia** due to impaired vitamin D activation.
- In ESRD, the kidneys are unable to produce sufficient amounts of **calcitriol (1,25-dihydroxyvitamin D)**, which is the active form of vitamin D. The enzyme responsible for the final activation step, converting 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D, is **1-α-hydroxylase**, primarily located in the renal proximal tubules.
*α-1-antitrypsin*
- This enzyme is a **serine protease inhibitor** primarily involved in protecting tissues from damage by proteases, especially in the lungs.
- Deficiency is associated with conditions like **emphysema** and **liver disease**, not directly with bone metabolism or vitamin D activation.
*24,25 hydroxylase*
- The enzyme **24-hydroxylase** inactivates calcitriol and its precursor by converting them into inert forms.
- Its activity would lead to reduced active vitamin D, mimicking a deficiency, but it is not the enzyme responsible for the **final activation step** of vitamin D.
*α-Glucosidase*
- This enzyme is crucial for the digestion of **carbohydrates** in the small intestine, breaking down complex sugars into glucose.
- Deficiencies are associated with conditions like **Pompe disease (glycogen storage disease type II)**, which primarily affects muscle and liver, not vitamin D metabolism.
*7-α-hydroxylase*
- **Cholesterol 7-α-hydroxylase (CYP7A1)** is a rate-limiting enzyme in the **bile acid synthesis pathway** in the liver.
- It plays no direct role in the activation of vitamin D; its function is related to cholesterol metabolism and bile production.
Question 68: An 11-year-old male is brought in by ambulance to the emergency department after being a restrained passenger in a motor vehicle accident. His father was driving him to soccer practice when they were hit by a wrong way driver. On presentation, his temperature is 101°F (38.3°C), blood pressure is 100/62 mmHg, pulse is 108/min, and respirations are 21/min. He is found to be agitated and complains of nausea, severe epigastric pain, and lower extremity pain. Physical exam reveals lacerations and ecchymosis on his left forehead, right flank, and lower extremities. Radiographs demonstrate an open book fracture of the pelvis as well as bilateral femur fractures. Despite multiple interventions, his condition deteriorates and he passes away from his injuries. Post-mortem pathologic examination of abdominal tissues reveals white deposits containing calcium. Abnormal activity of which of the following proteins is most likely responsible for these deposits?
A. Proteases
B. Plasmin
C. Thrombin
D. Lipases (Correct Answer)
E. Immunoglobulin
Explanation: ***Lipases***
- The patient's presentation with **severe epigastric pain**, **agitation**, and **fever** following massive trauma suggests **acute pancreatitis**, which can result from blunt abdominal injury.
- In acute pancreatitis, activated **lipases** degrade adipocytes, leading to the release of fatty acids that combine with calcium to form **calcium soaps**, appearing as white, chalky deposits in the abdominal tissues.
*Proteases*
- While proteases are also involved in the pathogenesis of acute pancreatitis, their primary role is the **breakdown of proteins** and cell membranes, contributing to tissue destruction.
- They do not directly cause the characteristic **white, calcium-containing deposits** observed in fat necrosis.
*Plasmin*
- **Plasmin** is a key enzyme in the **fibrinolytic system**, responsible for dissolving blood clots.
- While trauma can activate coagulation and fibrinolysis, plasmin's activity is not directly linked to the formation of **calcium deposits** in fat necrosis.
*Thrombin*
- **Thrombin** is a central enzyme in the **coagulation cascade**, converting fibrinogen to fibrin, leading to clot formation.
- Its primary role is in **hemostasis**, and it is not directly responsible for the development of **calcium soaps** in adipose tissue necrosis.
*Immunoglobulin*
- **Immunoglobulins** (antibodies) are part of the immune system, involved in recognizing and neutralizing pathogens or foreign substances.
- They are not directly involved in the enzymatic processes that lead to **fat necrosis** and **calcium deposition** in the context of acute pancreatitis.
Question 69: A 67-year-old gentleman with severe COPD is found to have a respiratory quotient of 0.8. His physician would like to decrease the amount of CO2 produced by the patient's metabolism, thereby reducing the energy breathing expenditure required to eliminate the patient's CO2 respiratory burden. Which of the following dietary modifications would decrease this patient's respiratory quotient?
A. Decreasing carbohydrate intake, increasing protein intake
B. Decreasing carbohydrate intake, increasing fat intake (Correct Answer)
C. Increasing carbohydrate intake, decreasing protein intake
D. Decreasing fat intake, increasing protein intake
E. Increasing carbohydrate intake, decreasing fat intake
Explanation: ***Decreasing carbohydrate intake, increasing fat intake***
- **Carbohydrates** have the highest respiratory quotient (RQ=1.0), meaning their metabolism produces the most CO₂ per unit of oxygen consumed. Decreasing carbohydrate intake directly reduces CO₂ production.
- **Fats** have the lowest respiratory quotient (RQ=0.7), producing the least CO₂ per unit of oxygen consumed. Increasing fat intake as a primary energy source will therefore lower the overall RQ.
*Decreasing carbohydrate intake, increasing protein intake*
- While decreasing carbohydrate intake helps lower CO₂ production, **protein** has an intermediate respiratory quotient (RQ=0.8-0.9), higher than fat.
- Increasing protein intake instead of fat would not be as effective in minimizing CO₂ production and the respiratory burden.
*Increasing carbohydrate intake, decreasing protein intake*
- **Increasing carbohydrate intake** would raise the respiratory quotient (RQ=1.0), leading to increased CO₂ production and higher respiratory burden, which is the opposite of the desired outcome.
- Decreasing protein intake by itself would not offset the increased CO₂ from carbohydrates.
*Decreasing fat intake, increasing protein intake*
- Decreasing fat intake would replace a fuel source with a low RQ (fat, RQ=0.7) with one of a higher RQ (protein, RQ=0.8-0.9), leading to increased CO₂ production.
- This dietary change would increase the respiratory quotient and CO₂ burden, contrary to the goal.
*Increasing carbohydrate intake, decreasing fat intake*
- **Increasing carbohydrate intake** significantly raises the respiratory quotient (RQ=1.0), which would increase CO₂ production and the patient's respiratory burden, making breathing more difficult.
- Decreasing fat intake would further exacerbate this issue by removing the lowest RQ energy source.
Question 70: A 35-year-old pregnant woman gives birth to a baby at term. The antepartum course was uneventful. She was compliant with all prenatal examinations and was given a prophylactic tetanus vaccine. While performing the neonatal examination, the pediatrician reports Apgar scores of 9 and 10 at 1 and 5 min, respectively. The pediatrician notices that the baby has ambiguous genitalia and blood pressure that is high for a neonate. The notable laboratory results are as follows:
Renin 0.4 nmoL/L/h
Aldosterone 70 pmoL/L
Cortisol 190 nmoL/L
Serum creatinine 1.0 mg/dL
Sex hormones are higher than the normal values at this age. Which of the following is responsible for the neonate's hypertension?
A. Decreased amount of cortisol
B. Decreased angiotensin response
C. Increased amount of 11-deoxycorticosterone (Correct Answer)
D. Decreased amount of aldosterone
E. Increased concentration of sex hormones
Explanation: ***Increased amount of 11-deoxycorticosterone***
- The presented symptoms of **ambiguous genitalia**, **hypertension**, and **elevated sex hormones** alongside normal cortisol point to **11β-hydroxylase deficiency (CYP11B1)**.
- In this condition, **11-deoxycorticosterone (DOC)**, a potent mineralocorticoid, accumulates, leading to **volume expansion** and **hypertension**.
- The **low renin** (0.4 nmol/L/h) confirms volume expansion from DOC's mineralocorticoid activity.
*Decreased amount of cortisol*
- While adrenal enzyme deficiencies can lead to decreased cortisol, a normal cortisol level of **190 nmoL/L** makes this option unlikely.
- Decreased cortisol typically causes **adrenal crisis symptoms** (e.g., hypotension, hypoglycemia) rather than hypertension directly.
*Decreased angiotensin response*
- A decreased angiotensin response would likely contribute to **hypotension**, not hypertension, as angiotensin II is a potent vasoconstrictor.
- The high blood pressure in this case indicates an overactive pressor system.
*Decreased amount of aldosterone*
- While aldosterone is **secondarily suppressed** in 11β-hydroxylase deficiency due to low renin (from DOC-mediated volume expansion), this is not the **primary mechanism** of hypertension.
- The hypertension is caused by **DOC accumulation**, not by aldosterone deficiency.
- Decreased aldosterone alone would typically lead to **salt wasting** and **hypotension**, but DOC's mineralocorticoid effects override this.
*Increased concentration of sex hormones*
- While **elevated sex hormones** contribute to the **ambiguous genitalia**, they are not the direct cause of the hypertension.
- The hypertension in this context is primarily mediated by the **mineralocorticoid effects** of accumulated adrenal precursors.
