Inborn errors of metabolism are the following, EXCEPT

ESIC Nursing Officer - 2019 (Shift-2)

Pathology & Genetics

Medium

Appeared in: ESIC Nursing Officer - 2019 (Shift-2)

Explanation

Turner's syndrome is the correct exception because it is a chromosomal disorder, not an inborn error of metabolism (IEM).
It is characterized by the presence of only one X chromosome (45,X) in females, which is an abnormality in chromosome number (aneuploidy).
In contrast, IEMs are caused by single-gene mutations that affect specific enzymes in metabolic pathways.

Option A: Phenylketonuria (PKU) is a classic example of an inborn error of metabolism. It is caused by a deficiency of the enzyme phenylalanine hydroxylase.
Option B: Tay-Sachs disease is an inborn error of metabolism, specifically a lysosomal storage disease, caused by a deficiency of the hexosaminidase A enzyme.
Option C: Cystic fibrosis is a single-gene disorder affecting an ion channel (CFTR protein). While not a classic enzyme-based IEM, it is a genetic metabolic disease and fundamentally different from a large-scale chromosomal abnormality like Turner's syndrome.

Visual 1: Diagram: Comparison of a normal karyotype (46,XX) and a Turner's syndrome karyotype (45,X) to visually demonstrate the missing chromosome.
Visual 2: Flowchart: Illustrating the metabolic pathway blocked in Phenylketonuria, showing the buildup of phenylalanine and deficiency of tyrosine.
Visual 3: Infographic: A table summarizing the key differences between inborn errors of metabolism, other single-gene disorders, and chromosomal disorders, with examples for each.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Differentiation between inborn errors of metabolism and chromosomal disorders as background academic context rather than a clinical decision trigger.
Nurses play a crucial role in newborn screening programs, which test for many IEMs like PKU and galactosemia. Early detection and intervention (e.g., dietary changes) can prevent severe outcomes like intellectual disability.
Recognizing the signs of different genetic disorders is important. While IEMs often present with metabolic crises (e.g., vomiting, lethargy, unusual odor), chromosomal disorders like Turner's syndrome are associated with specific physical features (dysmorphisms) like a webbed neck and short stature.
What if? If a newborn's screening test is positive for PKU, the nurse's immediate priority is to ensure the infant is placed on a low-phenylalanine formula and to educate the parents about the critical importance of lifelong dietary management to prevent brain damage.

How to Approach the Question

First, identify the negative framing of the question indicated by the word 'EXCEPT'. This means you are looking for the option that does not belong to the specified category.
Next, define the key term in the question: 'Inborn errors of metabolism'. Understand that this refers to genetic disorders caused by defects in specific enzymes, disrupting metabolic processes.
Evaluate each option against this definition.
Phenylketonuria and Tay-Sachs disease are classic enzyme deficiency disorders, so they are IEMs.
Cystic fibrosis is a single-gene disorder, but not a chromosomal one.
Turner's syndrome involves a missing chromosome, which is a large-scale genetic error, not a specific metabolic pathway defect. This makes it the outlier and the correct answer.

Concept Tested & Keywords

Concept Tested: Differentiation between inborn errors of metabolism and chromosomal disorders.
Stem keywords: Inborn errors of metabolism
Lead-in keywords: EXCEPT
Negative lead-in flag: The question asks for the option that does NOT fit the category of 'inborn errors of metabolism'.

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