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Deletion of the MC4R gene in a 9-year-old obese boy
Lesley Turner1, Anne Gregory, Laurie Twells
11 Faculty of Medicine, Memorial University of Newfoundland , St. John's, Newfoundland, Canada .
Background:
The most common monogenic form of obesity is caused by mutations in the melanocortin 4 receptor (MC4R) gene. More than 150 mutations have been reported in the MC4R gene, the majority being point mutations. Most individuals with MC4R gene mutations have early-onset obesity, hyperphagia, and increased longitudinal growth.
Methods:
A 9-year-old Caucasian boy was referred to genetics for obesity, food-seeking behavior, and developmental delay. History and physical exam were not consistent with Prader Willi syndrome, but revealed several minor anomalies. Owing to significant obesity and hyperphagia, a Prader Willi syndrome methylation test and a microarray were requested.
Results:
Methlylation testing for Prader Willi syndrome was normal. Microarray analysis revealed two changes: (1) A 2.6-Mb deletion at chromosome 18q21.31 was identified and contained several OMIM genes, including the MC4R gene, and (2) an 0.87-Mb duplication at chromosome region 16p13.3 was found and contained one gene. Parental samples revealed that the boy's father had the same deletion and duplication. This case appears to be the first with a deletion of 18q21.31 encompassing the MC4R gene presenting with features of hyperphagia and obesity.
Conclusions:
Haploinsufficiency of the MC4R gene either through whole gene deletion or nonsense or missense mutations is associated with a significant risk of obesity. The case emphasizes both the role of the MC4R gene in obesity as well as the importance of looking for chromosomal microdeletions/duplications as a cause of obesity in children with minor anomalies or developmental delay.
Insights
A genetic deletion encompassing the MC4R gene caused obesity and hyperphagia in a child. This highlights the role of MC4R gene haploinsufficiency in obesity and the importance of genetic testing for microdeletions.
Area of Science:
- Genetics
- Pediatrics
- Endocrinology
Background:
- Monogenic obesity is frequently caused by mutations in the melanocortin 4 receptor (MC4R) gene.
- Over 150 MC4R gene mutations are known, primarily point mutations, leading to early-onset obesity, hyperphagia, and growth acceleration.
Observation:
- A 9-year-old boy presented with obesity, hyperphagia, and developmental delay, with minor anomalies noted.
- Prader Willi syndrome testing was negative, but microarray revealed a 2.6-Mb deletion at 18q21.31 including MC4R and a 0.87-Mb duplication at 16p13.3.
Findings:
- The deletion at 18q21.31 encompassed the MC4R gene, a known cause of obesity.
- The patient's father shared the same deletion and duplication, suggesting a familial inheritance pattern.
Implications:
- This case is the first reported instance of an 18q21.31 deletion including MC4R presenting with hyperphagia and obesity.
- MC4R gene haploinsufficiency, via deletion or mutation, significantly increases obesity risk.
- The study underscores the importance of considering chromosomal microdeletions/duplications in pediatric obesity cases with developmental delay or minor anomalies.
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