Which of the following is the genetic cause of Intellectual Disability (formerly termed as Mental Retardation)?

Appeared in: RUHS, Jaipur, PB B.Sc Nursing Entrance-2019

Explanation

Phenylketonuria (PKU) is the correct answer as it is a genetic disorder.
It is an inborn error of metabolism transmitted as an autosomal recessive trait.
The condition results from the absence or inactivity of the liver enzyme phenylalanine hydroxylase.
This enzyme deficiency leads to the accumulation of phenylalanine, an amino acid that is toxic to the brain and causes intellectual disability if untreated.
Early dietary intervention can prevent the development of intellectual disability.

Option A: Poor housing is a socioeconomic and environmental factor, not a genetic one. It can affect development through malnutrition or lack of stimulation but does not alter genetic makeup.
Option B: Birth asphyxia is an acquired injury that occurs around the time of birth (perinatal period) due to oxygen deprivation. It is not an inherited genetic condition.
Option D: Maternal rubella is a prenatal infection. The virus crosses the placenta and can cause congenital defects, including intellectual disability. This is an environmental/infectious cause, not a genetic one.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Causes of Intellectual Disability as background academic context rather than a clinical decision trigger.
Understanding the different causes of intellectual disability is crucial for nurses in providing accurate information, counseling, and support to families.
Nurses play a key role in newborn screening programs, ensuring that tests like the one for PKU are performed correctly and that families of affected infants receive timely education on dietary management.
Genetic counseling is essential for parents who have a child with a genetic disorder like PKU to understand the risk of recurrence in future pregnancies (25% for autosomal recessive conditions).

How to Approach the Question

First, identify the key term in the question stem: 'genetic cause'. This directs you to look for an option that is inherited through genes.
Evaluate each option based on its nature:
Is 'Poor housing' a genetic factor? No, it's environmental.
Is 'Birth asphyxia' genetic? No, it's an injury that happens at birth (perinatal).
Is 'Phenylketonuria' genetic? Yes, it's a well-known inherited metabolic disorder.
Is 'Maternal Rubella' genetic? No, it's an infection during pregnancy (prenatal).

Concept Tested & Keywords

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E6 Kaplan Sadock's Synopsis of Psychiatry-2022 (pp 1-3768 of 3768) pp. 333-335, 328-330

E6 Pathology-Vandana Puri & Kavita Gaur Textbook of Pathology and Genetics p. 499-501

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Attempt every question from this paper in a timed mock, then review the full solution for each one.