NEET-PG 2025 Practice Questions

Q: A patient has elevated phenylalanine levels (40 mg/dL), but phenylalanine hydroxylase enzyme levels are normal. Which cofactor deficiency is most likely responsible for this condition?

Tetrahydrobiopterin (BH4). ***Tetrahydrobiopterin (BH4)*** - The conversion of **phenylalanine to tyrosine** by phenylalanine hydroxylase (PAH) absolutely requires the cofactor **Tetrahydrobiopterin (BH4)**. - Normal PAH enzyme levels combined with high phenylalanine (hyperphenylalaninemia) strongly indicates a defect in the essential cofactor (BH4 deficiency), often leading to a potentially treatable condition known as **Malignant PKU**. *Tetrahydrofolate* - **Tetrahydrofolate (THF)** is primarily involved in **one-carbon metabolism** and the transfer of methyl groups, crucial for purine and pyrimidine synthesis. - Its deficiency typically leads to **megaloblastic anemia** and neurological symptoms but does not directly impair phenylalanine hydroxylase activity. *Thiamine* - The active form, **Thiamine Pyrophosphate (TPP)**, is an essential cofactor for **dehydrogenase enzymes**, such as pyruvate dehydrogenase and $\alpha$-ketoglutarate dehydrogenase. - Deficiency is classically associated with impaired carbohydrate metabolism and results in conditions like **Beriberi**. *Pyridoxine* - **Pyridoxal phosphate (PLP)**, derived from pyridoxine, is a cofactor for manifold reactions in amino acid metabolism, including **transaminases** and decarboxylases. - While vital for general amino acid handling, it is not the required cofactor for the specific hydroxylation reaction catalyzed by **phenylalanine hydroxylase**.

Q: A man is trapped in a tunnel for 5 consecutive days without access to food but survives. What is the primary source of energy for his brain during this period?

Ketone bodies. ***Ketone bodies*** - During prolonged fasting (beyond 48-72 hours, such as 5 days), the liver generates **ketone bodies** (β-hydroxybutyrate and acetoacetate) from fatty acid oxidation via **ketogenesis**. - These **ketone bodies** efficiently cross the **blood-brain barrier** and replace up to **60-70%** of the brain's energy needs during prolonged starvation, thus conserving essential muscle protein. - This metabolic adaptation (ketosis) is crucial for survival during extended fasting periods. *Gluconeogenesis* - **Gluconeogenesis** (synthesis of new glucose from non-carbohydrate precursors) remains active during starvation to provide glucose for obligate glucose users like **RBCs** and the renal medulla. - However, the brain minimizes its dependence on glucose and shifts primarily to ketone body utilization by day 5. - Primary substrates for gluconeogenesis are **amino acids** (from muscle protein) and **glycerol** (from lipolysis). *Glycogenolysis* - **Glycogenolysis** (breakdown of liver glycogen to glucose) is the first-line response during early fasting, typically lasting only **12-24 hours**. - By 5 consecutive days, liver glycogen stores are **completely depleted**, making this pathway inactive and unable to fuel the brain. *Lipolysis* - **Lipolysis** (breakdown of adipose triglycerides) releases **fatty acids** and **glycerol** into circulation. - Fatty acids fuel peripheral tissues (skeletal muscle, heart) but **cannot cross the blood-brain barrier** efficiently. - Lipolysis provides substrates for hepatic ketogenesis, but is not the direct energy source for the brain itself.

Q: A 16-year-old boy presents with jaundice and splenomegaly. His father had a similar illness during adolescence. MCHC : high? What is the most likely diagnosis?

B. Hereditary spherocytosis. ***Hereditary spherocytosis*** - The presentation of **jaundice**, **splenomegaly**, strong **family history** (autosomal dominant pattern), and an elevated **MCHC** is classic for Hereditary Spherocytosis. [1] - Elevated MCHC is a key diagnostic feature due to mild cellular dehydration in the characteristic **spherocytes**. [1] *IDA* - **Iron Deficiency Anemia (IDA)** is typically microcytic and hypochromic, leading to a **low MCHC**, not high. - Symptoms of IDA include fatigue and pallor, generally without marked jaundice or splenomegaly unless severe. *Thalassemia major* - **Thalassemia major** presents with severe microcytic, hypochromic anemia (low MCHC) usually evident in early infancy, requiring regular transfusions. - While it causes jaundice and hepatosplenomegaly, it is characterized by severe bone changes and a very low MCHC. *AIHA* - **Autoimmune Hemolytic Anemia (AIHA)** typically presents acutely or subacutely and often responds to immunosuppression (e.g., steroids). - Unlike Hereditary Spherocytosis, AIHA generally does not present with a positive **family history** and the primary lab finding is a positive **Direct Antiglobulin Test (DAT)**, not specifically high MCHC.

Q: A 60-year-old patient presents with pain in multiple bones and a history of increased hat size. On examination, some bones feel warm to touch. Biochemical investigations show normal serum calcium, phosphate, and parathyroid hormone (PTH) levels, but markedly elevated alkaline phosphatase (ALP). What is the most likely diagnosis

Paget's disease of bone. ***Paget's disease of bone*** - The presentation with pain in multiple bones, **increased hat size** (due to skull involvement), and markedly elevated **Alkaline Phosphatase (ALP)** with normal calcium and phosphate is the classic biochemical profile [1]. - The sensation of warmth over the bones is caused by increased bone turnover and subsequent **hypervascularity** (increased blood flow) in the affected areas [1]. *Osteosarcoma* - This is a highly malignant bone tumor, typically presenting as localized pain and a mass, especially in the **metaphysis of long bones** (e.g., around the knee). - It does not usually present with the widespread, multiple bone involvement or the classic sign of increased **hat size** seen in this older patient. Paget's disease accounts for most cases of osteosarcoma occurring in older populations [1]. *Multiple myeloma* - This plasma cell malignancy involves the axial skeleton, commonly presenting with **anemia**, **renal failure**, and **hypercalcemia** (due to lytic bone lesions), which is ruled out by the normal calcium level here [2]. - The hallmark is the presence of a serum or urine **M-protein** (paraprotein), and ALP elevation is usually mild or absent unless related to pathological fracture [2]. *Osteomalacia* - This condition is characterized by defective mineralization, leading to low or low-normal serum **calcium** and/or **phosphate** levels, which contradicts the normal biochemical profile presented [3]. - While ALP can be elevated due to secondary hyperparathyroidism or increased osteoblast activity, the findings of severe widespread thickening and increased hat size are not typical [3].

Q: A lymphoma characterized by the presence of centrocytes and centroblasts, along with BCL2 positivity and CD10 expression, is most commonly associated with which chromosomal translocation?

t(14 ; 18). ***t(14 ; 18)*** [1], [2] - This translocation is the genetic hallmark of **Follicular Lymphoma (FL)**, characterized by the presence of **centrocytes** and **centroblasts**, **BCL2 positivity**, and **CD10 expression** [1], [2]. - It results in the juxtaposition of the **BCL2 gene** (on chromosome 18) with the **IgH locus** (on chromosome 14), leading to constitutive overexpression of the anti-apoptotic BCL2 protein [1], [2]. *t(2 ; 5)* - This translocation is characteristic of **Anaplastic Large Cell Lymphoma (ALCL)**, leading to the activation of the **ALK gene**. - ALCL is typically **CD30 positive** and lacks the centrocytes/centroblasts morphology and germinal center markers (like CD10) seen in the described B-cell lymphoma. *t(11 ; 14)* - This translocation is associated with **Mantle Cell Lymphoma (MCL)**, causing the overexpression of **Cyclin D1**. - While MCL cells are often BCL2 positive, they typically lack **CD10 expression**, which is a key feature of the described germinal center lymphoma. *t(8 ; 14)* - This translocation is the hallmark of **Burkitt Lymphoma**, resulting in **MYC gene** overexpression. - Burkitt Lymphoma is typically **CD10 positive** but shows a high proliferation index (Ki-67 ~100%) and lacks BCL2 expression [3], unlike the described follicular lymphoma. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, pp. 602-604. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Diseases Of The Urinary And Male Genital Tracts, pp. 561-562. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, p. 606.

Q: A 30-year-old man presents with a painless testicular mass. An ultrasound shows a well-circumscribed, homogeneous, non-hemorrhagic testicular tumor. Which of the following is the most likely diagnosis?

Seminoma. Seminoma - The clinical presentation (painless mass in a 30-year-old) combined with ultrasound findings (well-circumscribed, homogeneous, non-hemorrhagic tumor) strongly favors seminoma, the most common testicular germ cell tumor [1]. - Histologically, seminomas consist of large, clear cells separated by delicate fibrovascular septa infiltrated with lymphocytes, confirming this diagnosis [1]. Yolk sac tumor - This tumor is primarily the most common germ cell malignancy in infants and young children (under 3 years old) [1]. - It is classically associated with significantly elevated serum marker Alpha-fetoprotein (AFP). Choriocarcinoma - This highly aggressive tumor is characterized by significant hemorrhage, necrosis, and cavitation due to vascular invasion, which contradicts the 'non-hemorrhagic' description [2]. - It produces high levels of Human Chorionic Gonadotropin (hCG) due to the presence of syncytiotrophoblasts [1]. Teratoma - Teratomas are typically seen as heterogeneous or complex cystic masses on ultrasound due to the presence of various differentiated tissue elements (e.g., cartilage, bone, fat) [3]. - Pure teratomas are rare in adults; they usually form part of a mixed germ cell tumor [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lower Urinary Tract and Male Genital System, pp. 979-982. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Diseases Of The Urinary And Male Genital Tracts, pp. 512-513. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lower Urinary Tract and Male Genital System, pp. 982-983.

Q: Benralizumab acts on which receptor?

IL 5. ***IL 5***- Benralizumab is a monoclonal antibody that specifically targets the **alpha subunit (IL-5Rα) of the Interleukin-5 Receptor** [1].- By blocking this receptor, it facilitates the depletion of **eosinophils** via **antibody-dependent cell-mediated cytotoxicity (ADCC)**, crucial for treating severe eosinophilic asthma [1].*IL4*- IL-4 is a key mediator of **Type 2 inflammation** often targeted by drugs like **Dupilumab**, which inhibits both IL-4 and **IL-13 signaling**.- Targeting IL-4 is generally aimed at reducing IgE production and overall Th2 response, a different mechanism than the eosinophil depletion mechanism of Benralizumab.*IL1*- IL-1 is a potent **pro-inflammatory cytokine** primarily associated with **autoinflammatory diseases** and targeted by agents like **Anakinra** (IL-1 receptor antagonist).- It is not the primary or specific therapeutic target in severe eosinophilic asthma, which involves Th2 mechanisms and eosinophil recruitment.*TNF alpha*- **TNF-alpha** is a major systemic inflammatory cytokine targeted by biological agents like **Infliximab** and **Etanercept** used in conditions such as **Rheumatoid Arthritis** and **Crohn’s disease**.- While inflammation is involved in asthma, TNF-alpha antagonists are not the standard specific treatment for severe eosinophilic asthma.

Q: A female patient presents with flashbacks and a history of forgetting about her father's death in a road traffic accident 2 weeks ago. What is the most likely diagnosis?

Acute Stress Disorder (ASD). ***Acute Stress Disorder (ASD)*** - This diagnosis is defined by the presence of severe dissociative, intrusive (**flashbacks**), negative mood, and arousal symptoms occurring between **3 days and 1 month** after exposure to a traumatic event (2 weeks in this case). - The combination of **flashbacks** (intrusion symptom) and forgetting/amnesia (dissociative symptom) is characteristic of the acute reaction to trauma seen in ASD. *Post-Traumatic Stress Disorder (PTSD)* - PTSD requires similar symptoms (intrusion, avoidance, negative alterations in cognition/mood) to persist for **more than 1 month** following the traumatic event. - Since the event occurred only 2 weeks ago, the required duration criterion for a PTSD diagnosis has not been fulfilled yet. *Dissociative Amnesia* - While the patient exhibits amnesia, this diagnosis is generally reserved for extensive memory loss concerning important **autobiographical information**, not better explained by another mental disorder. - The presence of accompanying **flashbacks** and the acute time frame following the trauma better support the diagnosis of ASD. *Adjustment Disorder* - Adjustment disorder involves emotional or behavioral symptoms developed within 3 months of an identifiable stressor, but the symptoms are not severe enough to meet criteria for ASD or PTSD. - The presence of severe clinical features like **flashbacks** and **dissociative amnesia** excludes an Adjustment Disorder diagnosis, as it meets the criteria for the more specific and severe ASD.

Q: A person was found in a bizarre location, appearing confused. The caretaker reports he had no memory of how he got there, and the patient is unaware of his travel to the location. What is the most likely diagnosis?

Dissociative fugue. ***Dissociative fugue*** - This diagnosis is defined by **sudden, unexpected travel** away from home or the known environment, coupled with the inability to recall one's past or identity details (generalized **amnesia** for the journey). - The patient being found in a **bizarre location** and having no memory of the travel perfectly encapsulates the clinical definition of a dissociative fugue (a specifier of Dissociative Amnesia in DSM-5). *Dissociative identity disorder* - The hallmark feature is the presence of **two or more distinct personality states** or alters, which recurrently take control of the person's behavior. - While amnesia is present, it involves gaps in the recall of everyday events, not just isolated memory loss related specifically to an unexpected journey. *Dissociative amnesia* - This involves the inability to recall important personal information, usually of a **stressful or traumatic nature**, that is too extensive to be explained by ordinary forgetting. - Simple dissociative amnesia lacks the specific component of **purposeful, unplanned travel** away from home that characterizes a fugue state. *Psychotic episode* - Psychotic disorders are characterized by **positive symptoms** like **delusions** (fixed false beliefs) and **hallucinations** (perceptual disturbances). - The patient's confusion stems from a lack of memory regarding the journey (**dissociation**), not from a primary break with reality or thought disorder.

Question 1

A patient has elevated phenylalanine levels (40 mg/dL), but phenylalanine hydroxylase enzyme levels are normal. Which cofactor deficiency is most likely responsible for this condition?

Accepted Answer

Tetrahydrobiopterin (BH4)

Answer

Tetrahydrofolate

Answer

Pyridoxine

Answer

Thiamine

Question 2

A man is trapped in a tunnel for 5 consecutive days without access to food but survives. What is the primary source of energy for his brain during this period?

Accepted Answer

Ketone bodies

Answer

Glycogenolysis

Answer

Lipolysis

Answer

Gluconeogenesis

Question 3

A 16-year-old boy presents with jaundice and splenomegaly. His father had a similar illness during adolescence. MCHC : high? What is the most likely diagnosis?

Accepted Answer

B. Hereditary spherocytosis

Answer

D. AIHA

Answer

C. Thalassemia major

Answer

A. IDA

Question 4

A 60-year-old patient presents with pain in multiple bones and a history of increased hat size. On examination, some bones feel warm to touch. Biochemical investigations show normal serum calcium, phosphate, and parathyroid hormone (PTH) levels, but markedly elevated alkaline phosphatase (ALP). What is the most likely diagnosis

Accepted Answer

Paget's disease of bone

Answer

Multiple myeloma

Answer

Osteosarcoma

Answer

Osteomalacia

Question 5

A lymphoma characterized by the presence of centrocytes and centroblasts, along with BCL2 positivity and CD10 expression, is most commonly associated with which chromosomal translocation?

Accepted Answer

t(14 ; 18)

Answer

t(2 ; 5)

Answer

t(11 ; 14)

Answer

t(8 ; 14)

Question 6

A 30-year-old man presents with a painless testicular mass. An ultrasound shows a well-circumscribed, homogeneous, non-hemorrhagic testicular tumor. Which of the following is the most likely diagnosis?

Accepted Answer

Seminoma

Answer

Yolk sac tumor

Answer

Choriocarcinoma

Answer

Teratoma

Question 7

Which of the following laboratory techniques is most commonly used to compare and quantify CD markers on cells?

Accepted Answer

Flow cytometry

Answer

Western blot

Answer

ELISA

Answer

Immunohistochemistry

Question 8

Benralizumab acts on which receptor?

Accepted Answer

IL 5

Answer

IL1

Answer

IL4

Answer

TNF alpha

Question 9

A female patient presents with flashbacks and a history of forgetting about her father's death in a road traffic accident 2 weeks ago. What is the most likely diagnosis?

Accepted Answer

Acute Stress Disorder (ASD)

Answer

Dissociative Amnesia

Answer

Post-Traumatic Stress Disorder (PTSD)

Answer

Adjustment Disorder

Question 10

A person was found in a bizarre location, appearing confused. The caretaker reports he had no memory of how he got there, and the patient is unaware of his travel to the location. What is the most likely diagnosis?

Accepted Answer

Dissociative fugue

Answer

Dissociative amnesia

Answer

Dissociative identity disorder

Answer

Psychotic episode

NEET-PG 2025

Biochemistry

Internal Medicine

Pathology

Pharmacology

Psychiatry