Disorders of Hemoglobin Metabolism and MCQs for NEET, GPAT, NORCET, GATE, CSIR NET Exams

Disorders of Heme Synthesis

Porphyria

Porphyria is a group of disorders which are resulting from the deficiency of enzymes required for the biosynthesis of heme. This leads to the accumulation and increased excretion of porphyrins, ALA and PBG. Porphyria can be caused genetically or acquired.

The most common form of acquired porphyria is due to lead poisoning, delta-ALA dehydratase. Thus during lead poisoning, production of heme decreases and causes anemia.

Classification of porphyria

The porphyria are classified on the basis of the organ and cells which are most affected like bone marrow and liver. Thus porphyria are classified in two main classes

• Erythropoietic porphyria
• Hepatic porphyria

Six major types of porphyria fall in these two categories. These are described in the below given table.

Causes:- Exposure to sunlight, certain hormonal drugs, dieting or fasting, recreational drug, smocking, alcohol consumption, physical stress.

Treatment:-

• treatment is mainly symptomatic. Patients should avoid drugs that stimulate cytochrome P₄₅₀.
• Patients that exhibit photosensitivity may be helpful by the administration of beta-carotene.

Disorders of Heme Catabolism

hyperbilirubinemia

Diseases or condition that interfere the bilirubin metabolism causes a rise in serum concentration. When bilirubin in blood exceeds the value of 1mg/dl, then it causes hyperbilirubinemia .

In such situations, bilirubin tends to accumulate in the blood, and when its concentration reaches 2.2mg/dl to 5mg/dl then it diffuses into the tissues. The skin and sclera of the eye becomes yellow due to excessive bilirubin. This condition is known as jaundice or icterus .

Hyperbilirubinemia may be acquired or genetic:

Acquired hyperbilirubinemia includes:

• Pre-hepatic or hemolytic jaundice: in this disorder, there is increase breakdown of hemoglobin to bilirubin at a rate higher than its excretion.
• Hepato-cellular or hepatic jaundice: in this type of jaundice, there is disorder in the liver cells or the bile passages within the liver.
• Post-hepatic or obstructive jaundice: this occurs when there is obstruction in the passageway of the conjugated bilirubin from liver to intestine. This condition is also known as cholestasis.

Genetic hyperbilirubinemia includes:

• Gilbert’s syndrome: it is inherited disease characterized by mild benign unconjugated hyperbilirubinemia
• Crigler-Najjar syndrome: this is a rare disorder due to the deficiency of hepatic glucuronyl transferase enzyme.
• Dubin-Johnson syndrome: this is a rare disorder which is due to defective hepatic secretion of conjugated bilirubin into bile.

Causes:-

1. Increased bilirubin production
2. Decreased hepatic uptake
3. Decreased hepatic conjugation
4. Decreased excretion of bilirubin into bile.

Treatment:-

• Light therapy
• increasing the amount of iron in blood
• anti-viral or steroid medications,

Multiple Choice Questions (MCQs)

1. Which compound is accumulated during porphyrias?

A. ALA

B. PBG

C. Porphyrins

D. All of the above

2. What is the cause of porphyria?

A. Genetic cause

B. Acquired cause

C. Both

D. None

3. Which type of poisoning causes acquired porphyria?

A. Cyanide poisoning

B. Lead poisoning

C. Arsenic poisoning

D. Both A and C

4. In protoporphyria, which enzyme is defected?

A. Protoporphyrinogen oxidase

B. Heme synthase

C. Coproporphyrinogen oxidase

D. None of the above

5. Which of the following is the main symptom of porphyria?

A. Mental retardation

B. Photosensitivity

C. Jaundice

D. All of the above

6. Variegate porphyria comes under which class?

A. Hepatic

B. Erythropoiesis

C. Both

D. None

7. What is the saturation value after which hyperbilirubinemia is caused?

A. 0.1 mg/dl

B. 2mg/dl

C. 1mg/dl

D. 0.5mg/dl

8. What happens during jaundice?

A. Abdominal pain

B. Confusion

C. Yellowish skin and eye

D. All of the above

9. Match the following disorder and its cause-

a. Hepatic jaundice                    1. Defective enzyme for heme synthesis
b. Hemolytic jaundice               2. Blockage of bile duct
c. Obstructive jaundice             3. Incompatible blood transfusion
d. Porphyria                                4. Toxic chemicals

10. What happens during hemolytic jaundice?
A. Increased breakdown of hemoglobin

B. Defect in liver cell

C. Defective bile passage within liver

D. Obstruction in passage between liver and intestine

11. Which type of jaundice is caused due to cirrhosis?

A. Hemolytic jaundice

B. Hepatic jaundice

C. Obstructive jaundice

D. Rotor syndrome
 12. Absence of bilirubin in urine is the clinal feature of which type of jaundice?

A. Hemolytic jaundice

B. Hepatic jaundice

C. Obstructive jaundice

D. Rotor syndrome

13. Which of the following statement is NOT true?

A. Hepatic jaundice is caused due to drugs

B. Post hepatic jaundice is  also known as acholuric jaundice

C. The normal range of unconjugated bilirubin is 0.2 to 0.7 mg/dl

D. Crigler-Najjar syndrome is of 2 types

14. Which of the following comes under inherited hyperbilirubinemia?
A. Hemolytic jaundice

B. Hepatic jaundice

C. Obstructive jaundice

D. None of the above

15. After which value of blood-bilirubin, the bilirubin diffuses into the tissues from blood?
A. 0.1 mg/dl

B. 0.2mg/dl

C. 1mg/dl

D. 4mg/dl

ANSWERS-
1. All of the above
2. Both
3. Lead poisoning
4. Heme synthase
5. Photosensitivity
6. Hepatic
7. 1mg/dl
8. Yellowish skin and eye
9. a – 4 b – 3 c – 2 d – 1
10. Increased breakdown of hemoglobin
11. Hepatic jaundice
12. Hemolytic jaundice
13. Post hepatic jaundice is  also known as acholuric jaundice
14. None of the above
15. 4mg/dl

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REFERENCE:– 1. Pankaja Naik- Biochemistry; 4^th edition; page no:- 315, 316, 319, 320