Genetics and Disease Practice Questions

Q: Wilson's disease is inherited in which pattern?

Autosomal recessive. **Explanation:** Wilson’s disease (Hepatolenticular degeneration) is an **Autosomal Recessive (AR)** disorder caused by mutations in the **ATP7B gene** located on **Chromosome 13**. This gene encodes a P-type ATPase responsible for transporting copper into the bile for excretion and incorporating it into ceruloplasmin. A defect in this protein leads to toxic copper accumulation in the liver, brain (basal ganglia), and cornea [1]. **Analysis of Options:** * **Autosomal Recessive (Correct):** Most inborn errors of metabolism, including Wilson’s disease, Hemochromatosis, and Cystic Fibrosis, follow an AR pattern. Both parents must be carriers for a child to be affected (25% risk). * **Autosomal Dominant:** These disorders usually involve structural proteins (e.g., Marfan syndrome) or receptors (e.g., Familial Hypercholesterolemia). * **X-linked Recessive:** These typically affect males (e.g., Hemophilia, G6PD deficiency). Menkes disease, another copper metabolism disorder, is X-linked, which is a common point of confusion with Wilson's. * **X-linked Dominant:** Rare patterns seen in conditions like Alport syndrome or Vitamin D-resistant rickets. **High-Yield Clinical Pearls for NEET-PG:** * **Kayser-Fleischer (KF) Rings:** Copper deposition in the **Descemet’s membrane** of the cornea (best seen on slit-lamp exam). * **Diagnosis:** Low serum ceruloplasmin (<20 mg/dL), increased 24-hour urinary copper excretion, and increased hepatic copper content (Gold Standard). * **Treatment:** Chelating agents like **D-Penicillamine** (first-line historically) or Trientine. Oral **Zinc** is used for maintenance as it interferes with intestinal copper absorption. * **Neurological sign:** "Giant Panda Face" appearance on MRI midbrain [1].

Q: Which of the following is NOT an acute porphyria?

Porphyria cutanea tarda. Porphyrias are metabolic disorders caused by deficiencies in enzymes of the heme biosynthetic pathway. They are clinically classified into **Acute Porphyrias** (presenting with neurovisceral crises) and **Cutaneous Porphyrias** (presenting with skin photosensitivity) [1]. ### **Why Porphyria Cutanea Tarda (PCT) is the Correct Answer** PCT is the most common type of porphyria worldwide [1]. It is classified as a **chronic cutaneous porphyria**, not an acute one. It results from a deficiency of **Uroporphyrinogen decarboxylase (UROD)**. Clinically, it presents with skin fragility, blistering, and hyperpigmentation on sun-exposed areas (hands and face), often triggered by alcohol, iron overload, or Hepatitis C [1]. It does **not** cause the acute abdominal pain or neurological symptoms characteristic of acute porphyrias. ### **Analysis of Incorrect Options (Acute Porphyrias)** The following are classified as acute porphyrias because they involve the accumulation of neurotoxic precursors (ALA and PBG): * **Acute Intermittent Porphyria (AIP):** The most common acute porphyria. It presents with the "5 Ps": Painful abdomen, Polyneuropathy, Psychosis, Pink urine, and Precipitation by drugs [1]. * **Variegate Porphyria (VP) & Hereditary Coproporphyria (HCP):** These are "mixed" porphyrias. They are classified as acute because they cause neurovisceral crises, but they can also present with cutaneous photosensitivity. ### **NEET-PG High-Yield Pearls** * **Enzyme Deficiencies:** * AIP: Porphobilinogen deaminase (PBGD). * PCT: Uroporphyrinogen decarboxylase (UROD). * **Diagnosis:** The first-line screening test during an acute attack is checking for elevated **urinary Porphobilinogen (PBG)**. * **Management:** Acute attacks are treated with **IV Hemin** (suppresses ALA synthase) and high-dose glucose. * **Key Trigger:** Barbiturates and sulfonamides are notorious for precipitating acute attacks [1].

Question 1

A 22-year-old man presents with sudden loss of vision in his right eye. Physical examination reveals subluxation of the right crystalline lens. Auscultation of the chest reveals a midsystolic click. Echocardiography shows a floppy mitral valve and a dilated aortic arch. The patient's brother and cousin have similar symptoms. He has been prescribed a beta-blocker. A genetic defect involving which of the following substances is most likely present in this patient?

Accepted Answer

Fibrillin-1

Answer

Collagen

Answer

Dystrophin

Answer

NF1 protein

Question 2

In X-linked recessive (XLR) diseases, a modified inheritance pattern called 'pseudodominance' occurs when?

Accepted Answer

One parent is an unaffected heterozygote and the other is an affected homozygote.

Answer

One parent is an affected homozygote and the other is an unaffected homozygote.

Answer

One parent is normal and the other is an unaffected heterozygote.

Answer

Both parents are unaffected.

Question 3

Wilson's disease is inherited in which pattern?

Accepted Answer

Autosomal recessive

Answer

Autosomal dominant

Answer

X-linked recessive

Answer

X-linked dominant

Question 4

Which of the following is NOT an acute porphyria?

Accepted Answer

Porphyria cutanea tarda

Answer

Acute intermittent porphyria

Answer

Variegate porphyria

Answer

Hereditary coproporphyria

Question 5

Which of the following statements is TRUE regarding Duchenne muscular dystrophy?

Accepted Answer

There is a universal increase in creatine kinase.

Answer

It is autosomal dominant.

Answer

It has an onset in the second decade of life.

Answer

Cardiac muscle fibers are normal.

Genetics and Disease — MCQs

Genetics and Disease — MCQs

On this page

Practice by Chapter

Want unlimited practice?