Which of the following statements is true about causes of congenital malformation?

UPUMS Nsg officer-2023

Pathology & Genetics

Easy

Appeared in: UPUMS Nsg officer-2023

Explanation

Most congenital malformations result from a complex interaction of multiple genes and environmental factors, which is known as multifactorial inheritance.
A large percentage of birth defects have no single identifiable cause and are classified as having an unknown etiology.
Medical literature indicates that combined, multifactorial and unknown causes account for the vast majority (60-85%) of congenital anomalies.
Common examples of multifactorial defects include neural tube defects, congenital heart disease, and cleft lip/palate.

Option A: Monosomy (missing a chromosome) and polysomy (having extra chromosomes) are classified as numerical chromosomal abnormalities, which relate to the number of chromosomes, not defects in their physical structure.
Option B: Single-gene defects are fundamentally caused by mutations in a single gene. The statement that they are not caused by mutations is factually incorrect and contradicts the definition of the disorder.
Option C: Trisomy 21 (Down syndrome) is the most well-known example of a numerical chromosomal abnormality, specifically an aneuploidy, characterized by an extra copy of chromosome 21.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Etiology of Congenital Malformations as background academic context rather than a clinical decision trigger.
Nurses use this knowledge to provide accurate genetic counseling and support to families, explaining that in most cases, no single cause or 'fault' can be identified, which can alleviate parental guilt.
Understanding the multifactorial nature of many defects, like neural tube defects, reinforces the importance of public health nursing interventions such as promoting folic acid supplementation before and during pregnancy.
What if? If a newborn presents with features of a known single-gene syndrome (like Marfan syndrome), the nurse's focus would shift from general possibilities to specific assessments (e.g., cardiac, skeletal, ocular) and counseling related to a dominant inheritance pattern, which has a 50% recurrence risk for future children.

How to Approach the Question

The question asks for a 'true' statement about the causes of congenital malformations. This requires evaluating the factual accuracy of each option.
First, analyze the options related to chromosomal defects (A and C). Differentiate between 'numerical' (an incorrect number of chromosomes) and 'structural' (physical changes to a chromosome's structure). Monosomy, polysomy, and Trisomy 21 are all numerical abnormalities.
Next, evaluate the option on single-gene defects (B). Recall that genetic disorders are fundamentally caused by mutations.
Finally, assess the option about the overall distribution of causes (D). Consider whether most birth defects have a simple, single cause or a more complex and often unknown origin.
By systematically eliminating the factually incorrect statements in A, B, and C, you can confidently identify D as the only true statement.

Concept Tested & Keywords

Qh6mlWr88q4fgVUOqkCHX6

E6 Pathology- ROBBINS & COTRAN PATHOLOGIC BASIS OF DISEASE 10TH Ed p. 460-462

E6 Nelson Textbook of Pediatrics(2024) — Volume 1 p. 822-824