Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 21: Salt losing hydroxylase deficiency is characterized by?

A. Hyponatremia (Correct Answer)
B. Hyperkalemia
C. Hypoglycemia
D. Hypocalcemia

Explanation: **Explanation:** Salt-losing hydroxylase deficiency most commonly refers to **21-hydroxylase deficiency**, the most frequent cause of **Congenital Adrenal Hyperplasia (CAH)**. **1. Why Hyponatremia is the Correct Answer:** In this condition, a deficiency of the enzyme 21-hydroxylase leads to a failure in the synthesis of **Aldosterone** and **Cortisol**. Aldosterone is responsible for sodium reabsorption and potassium excretion in the distal renal tubules. Its absence results in "salt wasting"—the excessive loss of sodium in the urine—leading to profound **Hyponatremia**. This is the hallmark biochemical finding in the salt-wasting form of CAH. **2. Analysis of Other Options:** * **Hyperkalemia (Option B):** While hyperkalemia *is* a classic feature of salt-losing CAH (due to lack of aldosterone-mediated potassium excretion), the question asks for the primary characterization of "salt losing." In medical entrance exams, when both are present, hyponatremia is often prioritized as the defining "salt-losing" event, though both are clinically significant. * **Hypoglycemia (Option C):** Deficiency of Cortisol (a counter-regulatory hormone) can lead to hypoglycemia, especially during stress. However, it is a secondary metabolic consequence rather than the defining feature of the "salt-losing" state. * **Hypocalcemia (Option D):** Calcium metabolism is generally unaffected in CAH; this is not a feature of hydroxylase deficiencies. **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Enzyme:** 21-hydroxylase deficiency (>90% of cases). * **Biochemical Marker:** Elevated **17-hydroxyprogesterone (17-OHP)**. * **Clinical Presentation:** Ambiguous genitalia in females (virilization) and salt-wasting crisis (vomiting, dehydration, shock) in the second week of life. * **11-beta-hydroxylase deficiency:** Characterized by **hypertension** (due to 11-deoxycorticosterone buildup) rather than salt-wasting.

Question 22: True about Laron dwarfism is:

A. Growth hormone deficiency
B. Growth hormone insensitivity (Correct Answer)
C. Plasma IGF-1 is markedly increased
D. Plasma IGF-BP3 at normal levels

Explanation: **Explanation:** **Laron Syndrome (Laron Dwarfism)** is an autosomal recessive condition characterized by severe short stature due to **Growth Hormone (GH) insensitivity**. 1. **Why Option B is Correct:** The primary defect in Laron syndrome is a mutation in the **Growth Hormone Receptor (GHR)** gene. Although the pituitary gland secretes GH normally (or even in excess), the peripheral tissues cannot respond to it. This failure of GH to bind to its receptor leads to a failure in the production of **Insulin-like Growth Factor-1 (IGF-1)**, which is the mediator of GH's growth-promoting effects. 2. **Why Other Options are Incorrect:** * **Option A:** GH levels are typically **elevated or normal**, not deficient. The body attempts to compensate for the perceived lack of GH action by secreting more. * **Option C:** Plasma **IGF-1 is markedly decreased**, not increased. Since the GH receptor is defective, the liver cannot synthesize IGF-1. * **Option D:** Plasma **IGF-BP3 (and GHBP) levels are low**. IGF-BP3 is GH-dependent; without functional GH signaling, its levels fall significantly. **High-Yield Clinical Pearls for NEET-PG:** * **Phenotype:** Patients present with "doll-like" facies, prominent forehead, small chin, high-pitched voice, and truncal obesity. * **Biochemical Hallmark:** High GH + Low IGF-1. * **Metabolic Feature:** Recurrent **fasting hypoglycemia** (due to the lack of the counter-regulatory effects of IGF-1/GH). * **Treatment:** Recombinant human **IGF-1 (Mecasermin)**. Exogenous GH is ineffective because the receptors are non-functional. * **Unique Fact:** Interestingly, individuals with Laron syndrome show a striking **resistance to cancer and Type 2 diabetes**.

Question 23: Congenital adrenal hyperplasia is most likely a result of which of the following?

A. Defects in adrenal steroidogenic enzymes (Correct Answer)
B. Addison's disease
C. Defects in ACTH secretion
D. Defects in corticosteroid-binding globulin

Explanation: **Explanation:** **Congenital Adrenal Hyperplasia (CAH)** is a group of autosomal recessive disorders characterized by a deficiency in one of the enzymes required for the synthesis of cortisol from cholesterol in the adrenal cortex. **1. Why Option A is Correct:** The primary pathology in CAH is a **defect in adrenal steroidogenic enzymes**. The most common deficiency (95% of cases) is **21-hydroxylase**. When cortisol synthesis is impaired, the lack of negative feedback leads to an overproduction of **Adrenocorticotropic Hormone (ACTH)** by the pituitary. Chronic ACTH stimulation causes **hyperplasia** of the adrenal cortex and shunts precursor steroids into the androgen pathway, leading to virilization. **2. Why Other Options are Incorrect:** * **Option B (Addison’s Disease):** This is primary adrenal insufficiency, usually due to autoimmune destruction or infection (TB). While it involves low cortisol, it is an acquired destruction of the gland, not a congenital enzymatic defect. * **Option C (Defects in ACTH secretion):** CAH actually features *increased* ACTH secretion. A defect/deficiency in ACTH would lead to secondary adrenal insufficiency and adrenal *atrophy*, not hyperplasia. * **Option D (Defects in CBG):** Corticosteroid-binding globulin (Transcortin) carries cortisol in the blood. Defects here affect total cortisol levels but do not cause the enzymatic block or androgen excess seen in CAH. **High-Yield Clinical Pearls for NEET-PG:** * **Most common enzyme deficiency:** 21-hydroxylase (leads to high 17-OH Progesterone). * **Classic Presentation:** Ambiguous genitalia in females, salt-wasting crisis (hyponatremia, hyperkalemia, hypotension) in males. * **11β-hydroxylase deficiency:** Differentiated by the presence of **hypertension** (due to 11-deoxycorticosterone buildup). * **Treatment:** Glucocorticoid replacement (to suppress ACTH) and mineralocorticoids if salt-wasting.

Question 24: What is the recommended screening time for neonatal hypothyroidism after birth?

A. 1-2 days after birth
B. 2-4 days after birth (Correct Answer)
C. 1-2 hours after birth
D. 2-4 hours after birth

Explanation: **Explanation:** The primary goal of screening for Congenital Hypothyroidism (CH) is to detect the condition early to prevent irreversible intellectual disability. **Why 2-4 days (48-96 hours) is the correct timing:** Immediately after birth, there is a physiological **"TSH surge"** caused by the cold stress of delivery. TSH levels peak within 30–60 minutes of birth and remain high for the first 24–48 hours. If screening is performed during this window, it leads to a high rate of **false-positive** results. Waiting until 48–96 hours allows TSH levels to stabilize, ensuring that an elevated TSH is truly indicative of hypothyroidism rather than a transient neonatal surge. **Analysis of Incorrect Options:** * **Options C & D (1-4 hours):** These are incorrect because they coincide with the peak of the physiological TSH surge, leading to inaccurate results. * **Option A (1-2 days):** While some programs screen after 24 hours to facilitate early discharge, the risk of false positives remains higher than the 2-4 day window. **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Cause:** Thyroid dysgenesis (Ectopy is the most common specific type). * **Clinical Presentation:** Most neonates are **asymptomatic** at birth due to maternal T4 crossing the placenta. Early signs include a large posterior fontanelle, prolonged jaundice, hoarse cry, and umbilical hernia. * **Treatment Goal:** Start Levothyroxine (10-15 μg/kg/day) within the first **2 weeks** of life to ensure normal neurodevelopment. * **Sample Collection:** Capillary blood via **heel prick** onto a Guthrie card (filter paper).

Question 25: A newborn with ambiguous genitalia and a 46,XY karyotype develops vomiting, low serum sodium concentration, and high serum potassium. Which of the following enzymes is most likely to be abnormal?

A. 21-hydroxylase (Correct Answer)
B. An enzyme involved in ovarian development
C. 5a-reductase
D. An androgen receptor

Explanation: **Explanation:** The clinical presentation of **hyponatremia, hyperkalemia, and vomiting** in a newborn indicates a **salt-wasting crisis** due to mineralocorticoid deficiency. In the context of ambiguous genitalia, this points toward **Congenital Adrenal Hyperplasia (CAH)**. **1. Why 21-hydroxylase is correct:** 21-hydroxylase deficiency is the most common cause of CAH (>90%). It impairs the conversion of precursors to cortisol and aldosterone. * **Aldosterone deficiency** leads to salt wasting (low Na+, high K+, dehydration/vomiting). * **Cortisol deficiency** leads to increased ACTH, shunting precursors toward the androgen pathway. * **Excess Androgens** cause virilization. In a **46,XY** individual, while the genitalia are male, severe enzyme defects can sometimes lead to undervirilization or ambiguous appearance depending on the specific block; however, the presence of a **salt-wasting crisis** is the pathognomonic "red flag" for 21-hydroxylase (or 3β-HSD) deficiency. **2. Why other options are incorrect:** * **An enzyme in ovarian development:** This would not cause electrolyte imbalances or adrenal crises. * **5α-reductase deficiency:** This results in 46,XY individuals with ambiguous genitalia (due to inability to convert Testosterone to DHT), but **electrolytes are normal** because the adrenal cortex is unaffected. * **Androgen receptor defect (AIS):** Complete AIS results in a female phenotype, while partial AIS results in ambiguous genitalia. However, like 5α-reductase deficiency, it **does not cause salt wasting.** **NEET-PG High-Yield Pearls:** * **21-hydroxylase deficiency:** Most common; Salt wasting + Virilization; High 17-OH Progesterone. * **11β-hydroxylase deficiency:** Virilization + **Hypertension** (due to 11-deoxycorticosterone buildup). * **17α-hydroxylase deficiency:** Hypertension + **Sexual infantilism** (no androgens). * **Mnemonic:** If the enzyme starts with **1** (11, 17), it causes HTN. If it ends with **1** (21, 11), it causes virilization.

Question 26: Mental retardation is not typically seen in which of the following conditions?

A. Down syndrome
B. Cretinism
C. Hypopituitarism (Correct Answer)
D. Birth asphyxia

Explanation: **Explanation:** The core concept tested here is the role of specific hormones and insults in neurodevelopment. **Hypopituitarism** (Option C) typically involves deficiencies in Growth Hormone (GH), ACTH, TSH, and Gonadotropins. While GH is essential for linear growth and metabolic functions, it is **not required for brain development** or cognitive function. Children with isolated GH deficiency or panhypopituitarism usually have normal intelligence, though they may experience delayed physical milestones and "doll-like" facial features. **Why the other options are incorrect:** * **Down Syndrome (Option A):** This is the most common chromosomal cause of intellectual disability (mental retardation). It is characterized by varying degrees of cognitive impairment due to trisomy 21. * **Cretinism (Option B):** Congenital hypothyroidism is a leading cause of *preventable* mental retardation. Thyroid hormones (T3/T4) are critical for neuronal migration, myelination, and synaptic connectivity during the first two years of life. * **Birth Asphyxia (Option D):** Hypoxic-Ischemic Encephalopathy (HIE) resulting from birth asphyxia leads to permanent neuronal damage. It is a major cause of cerebral palsy and associated intellectual disability. **High-Yield Clinical Pearls for NEET-PG:** 1. **GH vs. Thyroid:** GH deficiency causes "Short Stature with Normal IQ"; Thyroid deficiency causes "Short Stature with Low IQ." 2. **Laron Syndrome:** A type of GH insensitivity characterized by very short stature but normal intelligence. 3. **Bone Age:** In both Hypothyroidism and Hypopituitarism, bone age is significantly delayed compared to chronological age. 4. **Micropenis:** In a neonate, the triad of hypoglycemia, jaundice, and micropenis strongly suggests Congenital Hypopituitarism.

Question 27: A child presents with hypercalcemia and hyperphosphatemia. What is the most likely diagnosis?

A. Vitamin D dependent rickets
B. Vitamin D resistant rickets
C. Renal osteodystrophy (Correct Answer)
D. Hypophosphatasia

Explanation: **Explanation:** The hallmark of **Renal Osteodystrophy** (specifically in the context of Chronic Kidney Disease-Mineral and Bone Disorder) is the inability of the kidneys to excrete phosphate, leading to **hyperphosphatemia**. While early stages often show hypocalcemia, the development of **Tertiary Hyperparathyroidism** (autonomous PTH secretion) or the administration of calcium-based phosphate binders and Vitamin D analogs often results in **hypercalcemia**. The combination of high calcium and high phosphate is a classic laboratory finding in advanced renal bone disease. **Why the other options are incorrect:** * **Vitamin D Dependent Rickets (VDDR):** Caused by a defect in 1-alpha-hydroxylase (Type I) or Vitamin D receptors (Type II). Both types present with **hypocalcemia** and **hypophosphatemia** (due to secondary hyperparathyroidism). * **Vitamin D Resistant Rickets (X-linked Hypophosphatemic Rickets):** Characterized by renal phosphate wasting. It presents with **hypophosphatemia** and usually normal serum calcium levels. * **Hypophosphatasia:** A genetic deficiency of alkaline phosphatase. While it can cause hypercalcemia and hyperphosphatemia, it is characterized by a pathognomonic **very low Serum Alkaline Phosphatase (ALP)** level, which distinguishes it from other metabolic bone diseases. **NEET-PG High-Yield Pearls:** * **Calcium-Phosphate Product:** In Renal Osteodystrophy, if $Ca \times PO_4 > 55 \text{ mg}^2/\text{dL}^2$, there is a high risk of metastatic calcification (calciphylaxis). * **Rickets vs. Renal Osteodystrophy:** Most forms of Rickets present with *low* phosphate; Renal Osteodystrophy is the major pediatric bone pathology presenting with *high* phosphate. * **Radiology:** Look for "Rugger-jersey spine" (subperiosteal resorption) in renal osteodystrophy.

Question 28: What is the most common cause of peripheral precocious puberty in males?

A. Congenital adrenal hyperplasia (Correct Answer)
B. Constitutional
C. Klinefelter's syndrome
D. CNS pathology

Explanation: **Explanation:** Precocious puberty is defined as the onset of secondary sexual characteristics before age 9 in boys. It is divided into **Central (GnRH-dependent)** and **Peripheral (GnRH-independent)** types. **1. Why Congenital Adrenal Hyperplasia (CAH) is correct:** In males, peripheral precocious puberty is characterized by virilization (pubic hair, phallic enlargement) without a corresponding increase in testicular volume (testes remain prepubertal, <4ml). **Congenital Adrenal Hyperplasia (specifically 21-hydroxylase deficiency)** is the most common cause. It leads to an overproduction of adrenal androgens, which bypasses the Hypothalamic-Pituitary-Gonadal (HPG) axis, causing "isosexual" precocity. **2. Analysis of Incorrect Options:** * **Constitutional (Option B):** This refers to "Constitutional Delay," which is a variation of normal growth leading to *late* puberty, not precocious puberty. * **Klinefelter's syndrome (Option C):** This is a chromosomal anomaly (47, XXY) typically associated with *delayed* puberty and hypergonadotropic hypogonadism, not precocity. * **CNS Pathology (Option D):** CNS lesions (e.g., hypothalamic hamartomas) are the most common cause of **Central** (True) precocious puberty in males, where the HPG axis is activated early, leading to increased testicular volume. **High-Yield Clinical Pearls for NEET-PG:** * **Testicular Volume Rule:** In precocious puberty, if testes are **enlarged** (>4ml), think **Central** causes. If testes are **small/prepubertal**, think **Peripheral** (Adrenal) causes. * **Exception:** In CAH, if ectopic adrenal rests are present in the testes, they may appear enlarged, but this is rare. * **McCune-Albright Syndrome:** A classic cause of peripheral precocity in girls (triad of café-au-lait spots, polyostotic fibrous dysplasia, and autonomous endocrine function).

Question 29: Pseudohermaphroditism in a female child is most commonly due to which of the following enzymatic deficiencies?

A. 21-hydroxylase deficiency (Correct Answer)
B. 17-hydroxylase deficiency
C. 11-hydroxylase deficiency
D. 3-hydroxylase deficiency

Explanation: **Explanation:** The most common cause of female pseudohermaphroditism (virilization of a 46,XX individual) is **Congenital Adrenal Hyperplasia (CAH)**, and **21-hydroxylase deficiency** accounts for approximately 90-95% of these cases. **1. Why 21-hydroxylase deficiency is correct:** In this condition, a block in the 21-hydroxylase enzyme prevents the conversion of progesterone to deoxycorticosterone (mineralocorticoid pathway) and 17-OH progesterone to 11-deoxycortisol (glucocorticoid pathway). This leads to a "shunting" of steroid precursors into the **androgen pathway**. The resulting excess of adrenal androgens causes virilization of the female fetus (ambiguous genitalia/clitoromegaly) while the internal female organs (uterus, ovaries) remain intact. **2. Analysis of incorrect options:** * **11-hydroxylase deficiency:** This is the second most common cause. While it also causes virilization, it is distinguished by the accumulation of 11-deoxycorticosterone, which leads to **hypertension** and hypokalemia (unlike the salt-wasting seen in 21-hydroxylase deficiency). * **17-hydroxylase deficiency:** This leads to a decrease in both androgens and cortisol. In females, it results in delayed puberty and primary amenorrhea, but **not** virilization. In males, it causes pseudohermaphroditism (undervirilization). * **3-beta-hydroxysteroid dehydrogenase deficiency:** A rare form that affects all classes of adrenal and gonadal steroids. It causes mild virilization in females but incomplete masculinization in males. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Marker:** Elevated **17-hydroxyprogesterone (17-OHP)** is the gold standard for diagnosing 21-hydroxylase deficiency. * **Salt-Wasting:** About 75% of 21-hydroxylase deficiency cases present with salt-wasting (hyponatremia, hyperkalemia, and hypotension) due to aldosterone deficiency. * **Karyotype:** Patients with female pseudohermaphroditism have a normal **46,XX** karyotype.

Question 30: Which endocrine disorder is associated with epiphyseal dysgenesis?

A. Hypothyroidism (Correct Answer)
B. Cushing's syndrome
C. Addison's disease
D. Hypoparathyroidism

Explanation: **Explanation:** **Hypothyroidism** is the correct answer because thyroid hormones are essential for normal linear growth and skeletal maturation. In congenital or juvenile hypothyroidism, there is a significant delay in the appearance of ossification centers. When these centers finally appear, they do so from multiple small foci rather than a single center. These foci fail to coalesce normally, resulting in a fragmented, stippled, or "moth-eaten" appearance on X-ray, known as **epiphyseal dysgenesis**. This is most commonly seen in the femoral head and is a hallmark radiological sign of the condition. **Why other options are incorrect:** * **Cushing’s Syndrome:** Excess glucocorticoids lead to growth failure and osteoporosis (decreased bone density), but they do not cause the specific fragmented pattern of dysgenesis seen in hypothyroidism. * **Addison’s Disease:** Chronic adrenocortical insufficiency primarily affects electrolyte balance and blood pressure; it does not typically manifest with specific epiphyseal maturation defects. * **Hypoparathyroidism:** This condition leads to hypocalcemia and hyperphosphatemia. While it may cause basal ganglia calcification or dental enamel hypoplasia, it is not associated with epiphyseal dysgenesis. **High-Yield Clinical Pearls for NEET-PG:** * **Bone Age:** In hypothyroidism, bone age is significantly delayed compared to chronological age. * **Most Common Cause:** Worldwide, iodine deficiency is the most common cause of congenital hypothyroidism; in iodine-sufficient areas, it is thyroid dysgenesis. * **Other Skeletal Findings:** Look for a "double-contoured" appearance of vertebrae or a "bullet-shaped" vertebra (T12/L1) in hypothyroid patients. * **Screening:** The best time to screen for congenital hypothyroidism is between 48–72 hours of life to avoid the physiological TSH surge.

Practice by Chapter

Disorders of Growth

Practice Questions

Thyroid Disorders

Practice Questions

Disorders of Puberty

Practice Questions

Adrenal Disorders

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Diabetes Mellitus in Children

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Disorders of Calcium and Phosphate Metabolism

Practice Questions

Disorders of Sexual Development

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Hypoglycemia

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Obesity and Metabolic Syndrome

Practice Questions

Pituitary Disorders

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Multiple Endocrine Neoplasia Syndromes

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Endocrine Emergencies

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