Leptin receptor gene mutations are a very rare cause of severe early-onset obesity. They are also associated with lack of pubertal development and intense hyperphagia. Presented here is a case of a 6-year-old Turkmenian girl with monogenic obesity due to a congenital deficiency of the leptin receptor. She was born from a consanguineous marriage of second cousins after 40 gestational weeks following an uncomplicated pregnancy. Her birth weight was 3500 g. However, rapid weight gain was observed after 6 months. On presentation she was 130 cm tall [> 97th percentile; standard deviation score (SDS): +2], with a weight of 90 kg (> 97th percentile; SDS: +5.3) and a body mass index (BMI) of 53.2 kg/m2 (SDS: +3.6). Results of genetic evaluation revealed the patient to be homozygous for two missense mutations in the leptin receptor gene (P316T;W646C) resulting in complete loss of leptin receptor function. Both parents were heterozygous for the same pair of missence mutations.
[Show abstract][Hide abstract] ABSTRACT: Obesity and diabetes mellitus are associated with low or elevated serum leptin and insulin levels (U-like relation). Mutations in LEP and INS are linked to decreases in leptin and insulin while mutations in LEPR and INSR are linked to their increase. Homozygous LEP mutations are associated with the early onset of severe obesity and the diverse impairment of physiological functions. The recessive LEPR mutations are associated with similar pathology in homozygous state. Missense mutations of INS are dominant and induce the synthesis of chimeric proinsulin, which may interfere with the folding and processing of active insulin molecules. In the heterozygous state, they cause insulin deficiency and PND. Recessive INS mutations do not induce the synthesis of anomalous proinsulin, and they are only associated with PND in the homozygous state. Mutations of INSR induce insulin resistance, lipodystrophy, other pathologies, and suggest the important role of insulin in glucose level regulation and in the stimulation of fat accumulation.
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