A 10-year-old boy presents with excessive eating (hyperphagia) and obesity, with a BMI of 33. Genetic testing shows a deletion on chromosome 15. What is the most likely diagnosis?

Appeared in: INI-CET EXAM -2026

Explanation

Prader-Willi syndrome (PWS) is the correct diagnosis as it classically presents with hyperphagia (insatiable hunger) leading to obesity, which matches the patient's symptoms.
The genetic cause of PWS is a loss of function of genes on the paternal copy of chromosome 15 (specifically region 15q11-13), which aligns with the genetic testing result of a deletion on chromosome 15.
The hyperphagia in PWS is due to hypothalamic dysfunction, which disrupts the normal feelings of satiety or fullness.
Other features, though not all mentioned in the stem, include hypotonia in infancy, developmental delays, and hypogonadism.

Why Other Options Were Wrong

Option A: Angelman syndrome is caused by a deletion on the maternal copy of chromosome 15. Its clinical picture is very different, characterized by severe intellectual disability, seizures, ataxia, and a happy, excitable demeanor with frequent laughter, not hyperphagia and obesity.
Option C: Rett syndrome is an X-linked dominant disorder caused by mutations in the MECP2 gene. It almost exclusively affects females and is characterized by a period of normal development followed by regression, loss of purposeful hand skills (replaced by stereotyped wringing movements), and gait abnormalities.
Option D: Down syndrome is caused by trisomy 21 (an extra copy of chromosome 21), not a deletion on chromosome 15. While obesity can be a concern, it is not characterized by the insatiable hyperphagia seen in PWS. Down syndrome has its own distinct set of physical and developmental features.

Related Visual

Clinical Relevance

Nursing practice connection: Use the key finding related to Diagnosis of genetic disorders based on clinical features and cytogenetic analysis to guide bedside assessment, documentation, and the next nursing action.
A key nursing priority for a child with Prader-Willi syndrome is managing their diet and environment to control caloric intake and prevent life-threatening obesity and its complications (e.g., type 2 diabetes, sleep apnea, heart failure).
Nurses play a crucial role in educating and supporting the family. This includes strategies for securing food, implementing strict meal plans, and managing the significant behavioral challenges associated with the constant drive for food.
What if the question stated the deletion was on the maternal chromosome 15? In that case, the diagnosis would be Angelman syndrome, and the nursing priorities would shift to seizure management, safety due to ataxia, and communication strategies, rather than dietary control for hyperphagia.

How to Approach the Question

First, dissect the clinical scenario to identify the key pieces of information: a 10-year-old boy, excessive eating (hyperphagia), obesity, and a deletion on chromosome 15.
Focus on the most specific and unique combination of findings: hyperphagia and a chromosome 15 deletion.
Systematically evaluate each option against these key findings.
Recall or look up the genetic basis and hallmark features of each syndrome. For Angelman and Prader-Willi, remember that they are both linked to chromosome 15 but have opposite parental origins and distinct clinical presentations.
Eliminate options that do not match the genetic finding (e.g., Rett syndrome is X-linked, Down syndrome is Trisomy 21).
Differentiate between the remaining options (Prader-Willi and Angelman) based on the clinical phenotype. The patient's hyperphagia and obesity are classic for Prader-Willi, not Angelman syndrome.

Concept Tested & Keywords

Concept Tested: Diagnosis of genetic disorders based on clinical features and cytogenetic analysis.
Stem keywords: hyperphagia, obesity, deletion on chromosome 15
Lead-in keywords: most likely diagnosis
Clinical cues: The combination of a specific behavior (hyperphagia), a physical sign (obesity), and a precise genetic finding (chromosome 15 deletion) points directly to a specific syndromic diagnosis.

Question ID

Q97zIvihRUy7jnppZwkBiy

Reference Book

E6 Robert Boland, Marcia L. Verduin - Kaplan and Sadock's Comprehensive Text of Psychiatry-Wolters Kluwer Health (2024) (pp 1-16525 of 16525) p. 11786-11788

E6 Nelson Textbook of Pediatrics(2024) — Volume 1 p. 486-488

E6 Medicine Harrison 22e Part 2 p. 1088-1090

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