KSR2 mutations are associated with obesity, insulin resistance, and impaired cellular fuel oxidation.

Kinase suppressor of Ras 2 (KSR2) is an intracellular scaffolding protein involved in multiple signaling pathways. Targeted deletion of Ksr2 leads to obesity in mice, suggesting a role in energy homeostasis. We explored the role of KSR2 in humans by sequencing 2,101 individuals with severe early-onset obesity and 1,536 controls. We identified multiple rare variants in KSR2 that disrupt signaling through the Raf-MEKERK pathway and impair cellular fatty acid oxidation and glucose oxidation in transfected cells; effects that can be ameliorated by the commonly prescribed antidiabetic drug, metformin. Mutation carriers exhibit hyperphagia in childhood, low heart rate, reduced basal metabolic rate and severe insulin resistance. These data establish KSR2 as an important regulator of energy intake, energy expenditure, and substrate utilization in humans. Modulation of KSR2-mediated effects may represent a novel therapeutic strategy for obesity and type 2 diabetes.

Clinical and molecular genetic spectrum of congenital deficiency of the leptin receptor.

BACKGROUND: A single family has been described in which obesity results from a mutation in the leptin-receptor gene (LEPR), but the prevalence of such mutations in severe, early-onset obesity has not been systematically examined. METHODS: We sequenced LEPR in 300 subjects with hyperphagia and severe early-onset obesity, including 90 probands from consanguineous families, and investigated the extent to which mutations cosegregated with obesity and affected receptor function. We evaluated metabolic, endocrine, and immune function in probands and affected relatives. RESULTS: Of the 300 subjects, 8 (3%) had nonsense or missense LEPR mutations--7 were homozygotes, and 1 was a compound heterozygote. All missense mutations resulted in impaired receptor signaling. Affected subjects were characterized by hyperphagia, severe obesity, alterations in immune function, and delayed puberty due to hypogonadotropic hypogonadism. Serum leptin levels were within the range predicted by the elevated fat mass in these subjects. Their clinical features were less severe than those of subjects with congenital leptin deficiency. CONCLUSIONS: The prevalence of pathogenic LEPR mutations in a cohort of subjects with severe, early-onset obesity was 3%. Circulating levels of leptin were not disproportionately elevated, suggesting that serum leptin cannot be used as a marker for leptin-receptor deficiency. Congenital leptin-receptor deficiency should be considered in the differential diagnosis in any child with hyperphagia and severe obesity in the absence of developmental delay or dysmorphism.

High throughput DNA sequence variant detection by conformation sensitive capillary electrophoresis and automated peak comparison.

We report the development of a heteroduplex-based mutation detection method using multicapillary automated sequencers, known as conformation-sensitive capillary electrophoresis (CSCE). Our optimized CSCE protocol detected 93 of 95 known base substitution sequence variants. Since the optimization of the method, we have analyzed 215 Mb of DNA and identified 3397 unique variants. An analysis of this data set indicates that the sensitivity of CSCE is above 95% in the central 56% of the average PCR product. To fully exploit the mutation detection capacity of this method, we have developed software, canplot, which automatically compares normal and test results to prioritize samples that are most likely to contain variants. Using multiple fluorescent dyes, CSCE has the capacity to screen over 2.2 Mb on one ABI3730 each day. Therefore this technique is suitable for projects where a rapid and sensitive DNA mutation detection system is required.