Which mode of inheritance is found in cystic fibrosis? & x20; - RRB Nsg. Superintendent-21 July 2019 (Shift-2nd)

RRB Nsg. Superintendent-21 July 2019 (Shift-2nd)

Pathology & Genetics

Easy

Appeared in: RRB Nsg. Superintendent-21 July 2019 (Shift-2nd)

Explanation

Cystic fibrosis (CF) is the most common lethal genetic disease in Caucasian populations and follows an autosomal recessive inheritance pattern.
This pattern requires an individual to inherit two copies of a mutated gene, one from each parent, to express the disease.
The gene responsible for CF is the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene, located on chromosome 7.
Individuals with only one copy of the mutated gene are carriers. They typically do not show symptoms but can pass the gene to their children.
When two carriers have a child, there is a 25% chance the child will be affected, a 50% chance the child will be a carrier, and a 25% chance the child will be unaffected.

Option B: This pattern requires only one mutated gene to cause the disease. In contrast, cystic fibrosis requires two mutated genes.
Option C: This involves a combination of multiple genes and environmental factors. Cystic fibrosis is a monogenic disorder, caused by mutations in the single CFTR gene.
Option D: This pattern involves genes on the X chromosome and affects males more frequently than females. Cystic fibrosis is autosomal, meaning the gene is on a non-sex chromosome and affects males and females equally.

Visual 1: Diagram - A Punnett square illustrating autosomal recessive inheritance, showing the 25% chance of an affected child, 50% chance of a carrier child, and 25% chance of an unaffected child when both parents are carriers.
Visual 2: Infographic - A chart comparing the key features of autosomal recessive, autosomal dominant, and X-linked recessive inheritance patterns, with examples for each.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Genetic Inheritance Patterns: Cystic Fibrosis as background academic context rather than a clinical decision trigger.
Understanding the inheritance pattern of cystic fibrosis is crucial for genetic counseling. It allows nurses to educate families about the risks of having an affected child and the availability of carrier screening.
Nurses play a key role in supporting families with a new diagnosis, explaining the genetic basis of the disease, and connecting them with resources for management and support.
What if? If a patient with cystic fibrosis plans to have children, their partner should be offered carrier testing. If the partner is a carrier, there is a 50% chance each child will be a carrier and a 50% chance each child will be affected. If the partner is not a carrier, all children will be carriers but none will be affected.

How to Approach the Question

First, identify the core question, which asks for the specific mode of inheritance for cystic fibrosis.
This is a factual recall question. Access your knowledge about common genetic disorders.
Recall that cystic fibrosis is a well-known single-gene disorder.
Evaluate the options: 'Autosomal' means the gene is on a non-sex chromosome, and 'recessive' means two copies of the mutated gene are needed. This matches the known genetics of cystic fibrosis.
Eliminate the other options by recalling their definitions: 'dominant' (one gene copy), 'X-linked' (on the X chromosome), and 'multifactorial' (multiple genes + environment).

Concept Tested & Keywords

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