It is estimated that up to 40-70% of obesities is attributable to genetic factors.  Monogenic forms of obesity are uncommon.  We present the first such reported case in Iran. The patient presented with a history of severe hyperphagia, rapid weight gain and recurrent infections.  He was born after a normal pregnancy in a highly consanguineous marriage.  His birth weight had been normal.  At age of 18 months he weighted 28 kg.  Apart from obesity and syndactyly of second/third digits in both feet there were no other abnormalities on physical examination.    His fasting serum leptin was 45 ng/ml.  Genotyping revealed 66-bp deletion in codon 514 of leptin receptor gene.

Unfortunately he developed another respiratory infection which was unresponsive to intensive treatment and died following a cardiorespiratory arrest. Genetic assessment is recommended in morbid obese patients especially those with a childhood onset.  Leptin receptor mutations can be associated with immune system deficiency and recurrent infections.