Question
A boy with karyotype 46 Xy del 15 q11-13 presents with obesity and increased ghrelin. What is the most likely diagnosis?
| A. |
Prader Willi syndrome
|
| B. |
Angelman syndrome
|
| C. |
Cri du chat syndrome
|
| D. |
Fragile X syndrome
|
Show Answer
|
Correct Answer � A
Explanation
|
|
Prader-Willi Syndrome
– Caused by loss of paternally expressed genes on 15q11–q13
Mechanisms:
– Paternal deletion (most common)
– Maternal uniparental disomy (both chromosome 15s from mother)
– Imprinting defects
Clinical features:
– Neonatal hypotonia
– Poor feeding in infancy → then hyperphagia & obesity in childhood
– Short stature, small hands & feet
– Hypogonadism, delayed puberty
– Intellectual disability & behavioral issues
– Elevated ghrelin drives hyperphagia
Why Other Options Are Incorrect:
B. Angelman Syndrome
– Also involves 15q11–q13 but loss of maternal UBE3A gene
– Features: severe intellectual disability, happy demeanor, frequent laughter, ataxia, seizures, microcephaly
– No hyperphagia or obesity
C. Cri-du-chat Syndrome
– Caused by 5p deletion
– Features: cat-like cry (laryngeal anomaly), microcephaly, severe intellectual disability
– No link to chromosome 15, obesity, or ghrelin
D. Fragile X Syndrome
– X-linked CGG repeat expansion in FMR1 gene
– Features: most common inherited intellectual disability, macroorchidism, large ears, long face, autism-like features
– Not associated with chromosome 15 or obesity
