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?

1. A

   Angelman syndrome

2. B

   Prader-Willi syndrome

3. C

   Rett syndrome

4. D

   Down syndrome

Appeared in: NORCET 1 - 2020

Explanation

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• Prader-Willi syndrome (PWS) is directly caused by the loss of function of paternally inherited genes on chromosome 15q11.2-q13.
• A hallmark of PWS is a switch from poor feeding in infancy to the development of hyperphagia (insatiable appetite) in early childhood.
• This uncontrolled eating leads to progressive and severe obesity, which is the most prominent feature in childhood and adulthood, as seen in the patient.
• The combination of hyperphagia, obesity, and a chromosome 15 deletion is the classic triad for diagnosing PWS.

Why Other Options Were Wrong

• Option A: Angelman syndrome is caused by a deletion on the maternal chromosome 15. Its phenotype is different, characterized by severe intellectual disability, ataxia, seizures, and a happy, excitable demeanor, not hyperphagia and obesity.
• Option C: Rett syndrome is an X-linked dominant disorder, primarily affecting girls, caused by mutations in the MECP2 gene. It involves developmental regression and stereotyped hand movements, not a chromosome 15 deletion or hyperphagia.
• Option D: Down syndrome is caused by Trisomy 21 (an extra copy of chromosome 21). While obesity can be a concern, it is not characterized by the specific insatiable hunger (hyperphagia) seen in PWS, and the genetic cause is completely different.

Related Visual

• Visual 1: Diagram - An illustration of genomic imprinting on chromosome 15, showing how a paternal deletion leads to Prader-Willi syndrome while a maternal deletion leads to Angelman syndrome.
• Visual 2: Chart - A comparison table highlighting the key differences in clinical features between Prader-Willi syndrome, Angelman syndrome, Rett syndrome, and Down syndrome.

Clinical Relevance

• Nursing practice connection: Use the key finding related to Diagnosis of genetic syndromes based on clinical and genetic findings to guide bedside assessment, documentation, and the next nursing action.
• Nurses play a crucial role in managing children with Prader-Willi syndrome by educating the family on the importance of strict dietary management and environmental controls (e.g., locking food cabinets) to prevent life-threatening obesity.
• Behavioral interventions and a structured routine are essential to manage the obsessive-compulsive behaviors and temper tantrums often associated with PWS.
• What if? - If the genetic test showed a deletion on the maternal chromosome 15 instead of just 'chromosome 15', the most likely diagnosis would shift to Angelman syndrome, and the nursing care plan would focus on seizure management, safety due to ataxia, and communication strategies instead of dietary restriction.

How to Approach the Question

• First, dissect the clinical vignette to identify the key pieces of information: the patient's age and sex (10-year-old boy), primary symptoms (hyperphagia, obesity), and the specific laboratory finding (deletion on chromosome 15).
• Next, evaluate each option based on this information.
• Recall or look up the genetic basis for each syndrome. Down syndrome is Trisomy 21 and Rett syndrome is X-linked, so they can be quickly eliminated as they do not involve chromosome 15.
• This leaves Prader-Willi and Angelman syndromes, both of which are linked to chromosome 15. The key is to differentiate them based on the clinical picture.
• Match the patient's symptoms of hyperphagia and obesity to the known characteristics of the remaining options. Prader-Willi syndrome is famously associated with an insatiable appetite, which confirms it as the correct diagnosis.

Concept Tested & Keywords

• Concept Tested: Diagnosis of genetic syndromes based on clinical and genetic findings
• Stem keywords: hyperphagia, obesity, deletion on chromosome 15, 10-year-old boy
• Lead-in keywords: most likely diagnosis
• Clinical cues: The combination of hyperphagia and a specific chromosomal deletion is a strong clue pointing to a particular syndromic cause of obesity.

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