Sickle cell disease is characterized by which hemoglobin genotype?

AIIMS CRE, SNO-2024

Pathology & Genetics

Easy

Appeared in: AIIMS CRE, SNO-2024

Explanation

Sickle cell disease (specifically sickle cell anemia) is an autosomal recessive disorder caused by inheriting two abnormal hemoglobin S (HbS) genes.
The genotype is therefore homozygous for HbS, written as HbS + HbS or HbSS.
In this condition, all the hemoglobin produced is abnormal, leading to the full manifestation of the disease, including sickling of red blood cells under hypoxic conditions.
This is the most common and severe form of sickle cell disease.

Option A: This genotype represents sickle cell trait, not the disease itself. Individuals have one normal hemoglobin gene (HbA) and one sickle gene (HbS).
Option C: This combination represents normal adult hemoglobin (HbA) and fetal hemoglobin (HbF). It is not associated with sickle cell disease.
Option D: This genotype causes Hemoglobin SC disease, which is a variant, and often milder, form of sickle cell disease.

Visual 1: Diagram - An infographic illustrating the autosomal recessive inheritance pattern of sickle cell anemia, showing the chances of offspring having the disease (HbSS), the trait (HbAS), or being unaffected (HbAA) when both parents are carriers.
Visual 2: Microscopic Image - A comparison of a normal blood smear with one from a patient with sickle cell anemia, clearly showing the biconcave disc shape of normal red blood cells versus the elongated, crescent shape of sickled cells.

Clinical Relevance

Nursing practice connection: Knowing Genetic basis of Sickle Cell Disease helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Nurses must be able to differentiate between sickle cell disease and sickle cell trait for patient education, especially regarding genetic counseling and risks during extreme conditions like high altitude or dehydration for trait carriers.
Recognizing the signs of a vaso-occlusive crisis (severe pain, swelling, fever) is critical for prompt intervention to manage pain, improve hydration and oxygenation, and prevent complications like acute chest syndrome or stroke.
What if? If a patient with known sickle cell disease presents with shortness of breath and chest pain, the nurse should immediately suspect Acute Chest Syndrome, a life-threatening complication, and initiate rapid response protocols, including oxygen administration and notifying the physician urgently.

How to Approach the Question

First, identify the core of the question, which is asking for the specific genetic makeup (genotype) that defines sickle cell disease.
Recall the basics of hemoglobin genetics. Normal adult hemoglobin is HbA. The sickle cell mutation creates HbS.
Differentiate between the disease state and the carrier state (trait). A recessive disease like sickle cell anemia requires two copies of the abnormal gene (homozygous).
Evaluate the options: HbA + HbS is heterozygous (trait). HbS + HbS is homozygous (disease). HbA + HbF is a mix of normal hemoglobins. HbC + HbS is a different variant of the disease.
Select the option representing the homozygous state for the sickle cell gene, which corresponds to the classic and most severe form of the disease.

Concept Tested & Keywords

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