A boy presents with developmental delay, obesity, hypotonia, normal neurological development, and hypogonadism. His karyotype shows 46 XY with a deletion of del(15)(q11-q13). What is the most likely diagnosis?

1. A

   Prader-Willi syndrome

2. B

   Angelman syndrome

3. C

   Patau syndrome

4. D

   Cri du chat syndrome

Appeared in: INI-CET EXAM -2025

Explanation

• Prader-Willi syndrome (PWS) is caused by the loss of function of genes on the paternal chromosome 15 in the 15q11-q13 region.
• The patient's karyotype, del(15)(q11-q13), directly corresponds to the genetic basis of PWS.
• The clinical triad of hypotonia (muscle weakness), hyperphagia leading to obesity, and hypogonadism (underdeveloped gonads) are hallmark features of PWS.
• While developmental delay is present, neurological development is often described as relatively normal compared to the severity seen in other syndromes like Angelman syndrome.

Why Other Options Were Wrong

• Option B: Angelman syndrome presents with a different set of clinical features, such as severe intellectual disability, ataxia, seizures, and a characteristically happy demeanor with frequent laughter. The patient's symptoms of obesity and hypogonadism are not typical of Angelman syndrome.
• Option C: Patau syndrome is caused by Trisomy 13 (an extra chromosome 13), not a deletion on chromosome 15. Its features include severe congenital malformations like holoprosencephaly, polydactyly, and cleft palate.
• Option D: Cri du chat syndrome results from a deletion on the short arm of chromosome 5 (5p-). The most characteristic feature is a high-pitched, cat-like cry in infancy, which is not mentioned in the patient's presentation.

Related Visual

• Visual 1: Karyotype Diagram - A diagram showing a human karyotype with a highlighted deletion on the long arm of chromosome 15 (15q11-q13) to illustrate the genetic defect.
• Visual 2: Genomic Imprinting Flowchart - A flowchart explaining the concept of genomic imprinting, showing how a deletion on the paternal chromosome 15 leads to Prader-Willi syndrome, while a deletion on the maternal chromosome 15 leads to Angelman syndrome.
• Visual 3: Clinical Features of PWS - An infographic illustrating the key clinical features of Prader-Willi syndrome, such as hypotonia in infancy, almond-shaped eyes, and the progression to obesity in childhood.

Clinical Relevance

• Nursing practice connection: Use the key finding related to Identification of genetic syndromes based on clinical features and karyotype analysis, specifically focusing on microdeletion syndromes and genomic imprinting to guide bedside assessment, documentation, and the next nursing action.
• Nurses play a crucial role in the multidisciplinary management of individuals with Prader-Willi syndrome, which includes strict dietary supervision to prevent life-threatening obesity, administering growth hormone and sex hormone treatments, and supporting families.
• Early diagnosis through genetic testing is vital. Nurses should be aware of the early signs, such as infantile hypotonia and feeding problems, to facilitate timely referral and intervention.
• Genetic counseling is essential for families, explaining the concept of genomic imprinting and the low recurrence risk in most cases (de novo deletion).

How to Approach the Question

• First, analyze the stem for the two main categories of clues: the clinical presentation and the laboratory findings.
• Focus on the specific karyotype provided: del(15)(q11-q13). This is a highly specific finding that points directly to a problem on chromosome 15.
• Recall or deduce that the 15q11-q13 region is associated with two major imprinting disorders: Prader-Willi syndrome (paternal deletion) and Angelman syndrome (maternal deletion). This allows you to immediately focus on these two options.
• Next, correlate the clinical features (developmental delay, obesity, hypotonia, hypogonadism) with the known phenotypes of Prader-Willi and Angelman syndromes.
• The combination of hypotonia, obesity, and hypogonadism is the classic presentation of Prader-Willi syndrome.
• Eliminate the other options based on their distinct genetic causes: Patau syndrome is Trisomy 13, and Cri du chat syndrome is a 5p deletion. These do not match the given karyotype.

Concept Tested & Keywords

• Concept Tested: Identification of genetic syndromes based on clinical features and karyotype analysis, specifically focusing on microdeletion syndromes and genomic imprinting.
• Stem keywords: developmental delay, obesity, hypotonia, hypogonadism, karyotype, del(15)(q11-q13)
• Lead-in keywords: most likely diagnosis
• Clinical cues: [object Object]
• Negative lead-in flag: false

Question ID

QEw5XXNAF133QR311MIhxV

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