Homozygous null mutation of the melanocortin-4 receptor and severe early-onset obesity.

Objective: To describe the clinical and biological phenotype of a child who is severely obese and is homozygous for a new melanocortin-4 receptor (MC4R) gene mutation leading to a truncated receptor.

Study Design: Direct sequencing of the MC4R gene was performed in a child who was severely obese and his relatives. Phenotypic characterization included weight evolution, anthropometric parameters, and endocrine and metabolic complications.