Identify the disorder shown in this pedigree chart?

NORCET 2 -2021 (Shift-2)

Pathology & Genetics

Hard

Appeared in: NORCET 2 -2021 (Shift-2)

Explanation

The pedigree shows a vertical transmission pattern, with the disorder appearing in all three generations (I, II, and III), which is characteristic of dominant inheritance.
Both males and females are affected, indicating the gene is likely on an autosome rather than a sex chromosome.
There is clear male-to-male transmission from the father in Generation I to his son in Generation II. This definitively rules out any form of X-linked inheritance.
Affected individuals (genotype Aa) have a 50% chance of passing the trait to their children when mating with an unaffected partner (genotype aa), which is consistent with the offspring ratios seen in the chart.
Unaffected individuals (genotype aa) do not pass the trait to their offspring, as seen throughout the pedigree.

Option B: Autosomal recessive disorders typically skip generations, as affected individuals (aa) are often born to unaffected carrier parents (Aa). This pedigree shows the trait in every generation.
Option C: X-linked recessive inheritance is ruled out because there is male-to-male transmission (Generation I to II). Also, affected females are present, which is less common in X-linked recessive traits.
Option D: X-linked dominant inheritance is definitively ruled out by the presence of male-to-male transmission. A father passes his Y chromosome to his son, so he cannot pass an X-linked trait to him.

Visual 1: Diagram - A comparative flowchart showing the key decision points for analyzing a pedigree: 1. Does it skip generations? (Dominant vs. Recessive). 2. Are males/females affected differently? (Autosomal vs. X-linked). 3. Is there male-to-male transmission? (Rules out X-linked).
Visual 2: Infographic - Four mini-pedigree charts, each illustrating a classic example of Autosomal Dominant, Autosomal Recessive, X-linked Dominant, and X-linked Recessive inheritance for easy comparison.

Clinical Relevance

Nursing practice connection: Use the key finding related to Pedigree analysis and identification of Mendelian inheritance patterns to guide bedside assessment, documentation, and the next nursing action.
Understanding pedigree analysis is a fundamental skill for nurses in genetic counseling, risk assessment, and patient education.
By identifying the mode of inheritance, nurses can help families understand their risk of passing on a genetic condition and make informed decisions about family planning and genetic testing.
Examples of autosomal dominant disorders include Huntington's disease, Marfan syndrome, and neurofibromatosis type 1.

How to Approach the Question

Step 1: Examine the pedigree to see if the trait appears in every generation. If it does, it is likely a dominant trait. If it skips generations, it is likely recessive.
Step 2: Observe if both males and females are affected. If they are affected in roughly equal numbers, the trait is likely autosomal. If it affects one sex significantly more than the other, consider X-linked inheritance.
Step 3: Specifically look for male-to-male transmission (an affected father passing the trait to his son). If present, this definitively rules out X-linked inheritance and strongly suggests autosomal inheritance.
Step 4: Check if affected parents have unaffected children. In dominant inheritance, if an affected parent is heterozygous (like 'Aa' here), they can have unaffected ('aa') children.
Step 5: Synthesize these clues. The presence of the trait in every generation plus male-to-male transmission points directly to an autosomal dominant pattern.

Concept Tested & Keywords

Concept Tested: Pedigree analysis and identification of Mendelian inheritance patterns.
Stem keywords: pedigree chart, disorder, generation, inheritance
Lead-in keywords: Identify
Clinical cues: Trait appears in every generation
Clinical cues: Male-to-male transmission is present

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