Julia von Schnurbein

A New Missense Mutation in the Leptin Gene Causes Mild Obesity and Hypogonadism without Affecting T Cell Responsiveness

OBJECTIVE Leptin, a protein product of adipocytes, plays a critical role in the regulation of body weight, immune function, pubertal development, and fertility. So far, only three homozygous mutations in the leptin gene in a total of 13 individuals have been found leading to a phenotype of extreme obesity with marked hyperphagia and impaired immune function. DESIGN Serum leptin was measured by ELISA. The leptin gene (OB) was sequenced in patient DNA. The effect of the identified novel mutation was assessed using HEK293 cells. RESULTS We describe a 14-yr-old child of nonobese Austrian parents without known consanguinity. She had a body mass index of 31.5 kg/m(2) (+2.46 SD score) and undetectable leptin serum levels. Sequencing of the leptin gene revealed a hitherto unknown homozygous transition (TTA to TCA) in exon 3 of the LEP gene resulting in a L72S replacement in the leptin protein. RT-PCR, Western blot, and immunohistochemical analysis indicated that the mutant leptin was expressed in the patients adipose tissue but retained within the cell. Using a heterologous cell system, we confirmed this finding and demonstrated that the side chain of Leu72 is crucial for intracellular leptin trafficking. Our patient showed signs of a hypogonadotropic hypogonadism. However, in contrast to the literature, she showed only mild obesity and a normal T cell responsiveness. CONCLUSIONS These findings shed a new light on the clinical consequences of leptin deficiency. Congenital leptin deficiency should be considered possible in pediatric patients with mild obesity even if parents are lean and unrelated.

Leptin Therapy in a Congenital Leptin-Deficient Patient Leads to Acute and Long-Term Changes in Homeostatic, Reward, and Food-Related Brain Areas

CONTEXT Mutations that lead to congenital leptin deficiency cause severe obesity, hyperphagia, and impaired satiety due to malfunctions of peripheral and brain-related mechanisms. DESIGN AND PATIENT In a leptin-deficient adolescent girl, we investigated brain-related changes before and at two time points after leptin therapy (3 d and 6 months). Functional magnetic resonance imaging was performed during visual stimulation with food (high and low caloric) and nonfood pictures. RESULTS Results show acute and long-term effects in the amygdala, the orbitofrontal cortex, and the substantia nigra/ventral tegmental area for the comparison of food and nonfood pictures. For the comparison of high and low caloric pictures, pure acute effects in the ventral striatum and the orbitofrontal cortex could be observed as well as acute and long-term effects in the hypothalamus. CONCLUSION This study gives additional insight in the influence of leptin therapy on brain functions in leptin deficiency.

Severe Early-Onset Obesity Due to Bioinactive Leptin Caused by a p.N103K Mutation in the Leptin Gene.

Context: Congenital leptin deficiency is a very rare cause of severe early-onset obesity. We recently characterized a mutation in the leptin gene (p.D100Y), which was associated with detectable leptin levels and bioinactivity of the hormone. Case Description: We now describe two siblings, a 9-year-old girl and a 6-year-old boy with severe early-onset obesity and hyperphagia, both homozygous for a c.309C>A substitution in the leptin gene leading to a p.N103K amino acid exchange in the protein and detectable circulating levels of leptin. In vitro experiments in a heterologous cell system demonstrated that the mutated protein was biologically inactive. Treatment with sc recombinant human leptin led to rapid improvement of eating behavior and weight loss. Conclusions: Sequencing of the leptin gene may need to be considered in hyperphagic, severely obese children with detectable levels of circulating leptin.

Monogenic forms of childhood obesity due to mutations in the leptin gene

Congenital leptin deficiency is a rare autosomal recessive monogenic obesity syndrome caused by mutations in the leptin gene. This review describes the molecular and cellular characteristics of the eight distinct mutations found so far in humans.

Long-term stabilization effects of leptin on brain functions in a leptin-deficient patient.

Context Congenital leptin deficiency, caused by a very rare mutation in the gene encoding leptin, leads to severe obesity, hyperphagia and impaired satiety. The only systemic treatment is the substitution with metreleptin leading to weight reduction based on hormonal changes. Several studies have also shown alterations in brain function after metreleptin therapy. In a previous study, we were able to show changes in homeostatic (hypothalamus) and reward-related brain areas (striatum, orbitofrontal cortex (OFC), substantia nigra/ventral tegmental area, amygdala) 3 days and 6 months after therapy start in a leptin-deficient adolescent girl. To further access the time course of functional brain activation changes, we followed the patient for 2 years after initiation of the therapy. Design, Patient Functional magnetic resonance imaging during visual stimulation with food (high- and low-caloric) and non-food pictures was performed 1 and 2 years after therapy start in the previously described patient. Results The comparison of ‘food vs. non-food’ pictures showed a stabilization of the long-term effects in the amygdala and in the OFC. Therefore, no significant differences were observed between 6 months compared to 12 and 24 months in these regions. Additionally, a reduction of the frontopolar cortex activity over the whole time span was observed. For the comparison of high- and low-caloric pictures, long-term effects in the hypothalamus showed an assimilating pattern for the response to the food categories whereas only acute effects after 3 months were observed in hedonic brain regions. Conclusion This follow-up study shows that the long lasting benefit of metreleptin therapy is also associated with activation changes in homeostatic, hedonic and frontal control regions in congenital leptin deficiency.

Measurement of immunofunctional leptin to detect and monitor patients with functional leptin deficiency

Context and aims Functional leptin deficiency is characterized by high levels of circulating immunoreactive leptin (irLep), but a reduced bioactivity of the hormone due to defective receptor binding. As a result of the fact that affected patients can be successfully treated with metreleptin, it was aimed to develop and validate a diagnostic tool to detect functional leptin deficiency. Methods An immunoassay capable of recognizing the functionally relevant receptor-binding complex with leptin was developed (bioLep). The analytical quality of bioLep was validated and compared to a conventional assay for immune-reactive leptin (irLep). Its clinical relevance was evaluated in a cohort of lean and obese children and adults as well as in children diagnosed with functional leptin deficiency and their parents. Results In the clinical cohort, a bioLep/irLep ratio of 1.07 (range: 0.80–1.41) was observed. Serum of patients with non-functional leptin due to homozygous amino acid exchanges (D100Y or N103K) revealed high irLep but non-detectable bioLep levels. Upon treatment of these patients with metreleptin, irLep levels decreased, whereas levels of bioLep increased continuously. In patient relatives with heterozygous amino acid exchanges, a bioLep/irLep ratio of 0.52 (range: 0.48–0.55) being distinct from normal was observed. Conclusions The new bioLep assay is able to diagnose impaired leptin bioactivity in severely obese patients with a homozygous gene defect and in heterozygous carriers of such mutations. The assay serves as a diagnostic tool to monitor leptin bioactivity during treatment of these patients.

Sleep and glycemic control in adolescents with type 1 diabetes

Increasing evidence link sleep curtailment and circadian misalignment with adverse metabolic outcome. Adolescents might be most affected, given their late sleep timing and early school and work start times.

Leptin Replacement Reestablishes Brain Insulin Action in the Hypothalamus in Congenital Leptin Deficiency

OBJECTIVE Human obesity is associated with impaired central insulin signaling, and in very rare cases, severe obesity can be caused by congenital leptin deficiency. In such patients, leptin replacement results in substantial weight loss and improvement in peripheral metabolism. RESEARCH DESIGN AND METHODS In a leptin-deficient patient, we investigated the impact of leptin substitution on central insulin action, as quantified by changes in neuronal activity after intranasal insulin application. This was assessed before and during the first year of metreleptin substitution. RESULTS After only 1 year, treatment with metreleptin reestablishes brain insulin sensitivity, particularly in the hypothalamus and, to a lesser degree, in the prefrontal cortex. Results are depicted in comparison with a control group. In our patient, brain activation changes were accompanied by substantial weight loss, reduced visceral adipose tissue, reduced intrahepatic lipid content, and improved whole-body insulin sensitivity. CONCLUSIONS Leptin replacement and weight loss improved homeostatic insulin action in the patient in question.

Obesity and Weight Regulation

The last 12 months have shown once more that obesity and weight regulation are among the most interesting biomedical fields of science. The number of high-quality papers reflects the multiple research activities which now can be documented at many places around the world. The last 12 months have also demonstrated that different governments in Europe have taken over some responsibility of the obesity epidemic as demonstrated by the European Charter on counteracting obesity (www.iotf.org). The aim of the Charter is to address the growing challenge posed by the epidemic of obesity on health, economies and development. The Charter has been established by the WHO European Ministerial Conference on Counteracting Obesity (Istanbul, Turkey, November 15–17, 2006). It acknowledges that the prevalence of obesity has risen up to threefold in the last two decades. Half of all adults and 1 in 5 children in the WHO European Region are overweight. Of these, one third is already obese, and numbers are increasing fast. Overweight and obesity contribute to a large proportion of non-communicable diseases, shortening life expectancy and adversely affecting the quality of life. More than 1 million deaths in the Region annually are due to diseases related to excess body weight. The trend is particularly alarming in children and adolescents, thus passing the epidemic into adulthood and creating a growing health burden for the next generation. The annual rate of increase in the prevalence of childhood obesity has been rising steadily and is currently up to ten times higher than it was in 1970. This Charter will also help scientists and physicians to stimulate experimental and clinical studies as well as preventive activities in their countries. This Charter should be known by every ESPE member. For the yearbook selection this year, only articles published in journals with an impact factor of more than 4 were considered, assuming that relevant findings were published in these journals. The top findings of the last year lay within the areas of endocrinology of body weight regulation and endocrinology of the adipocyte. Two well-written reviews which are not included as an extensive summary are mentioned here:

Functional and phenotypic characteristics of human leptin receptor mutations

Abstract Several case series of extreme early-onset obesity due to mutations in the human leptin receptor (LEPR) gene have been reported. In this review we summarize published functional and phenotypic data on mutations in the human LEPR gene causing severe early-onset obesity. Additionally, we included data on six new cases from our obesity center. Literature research was performed using PubMed and OMIM. Functional relevance of mutations was estimated based on reported functional analysis, mutation size, and location, as well as phenotypic characteristics of affected patients. We identified 57 cases with 38 distinct LEPR mutations. We found severe early-onset obesity, hyperphagia, and hypogonadotropic hypogonadism as cardinal features of a complete loss of LEPR function. Other features, for example, metabolic disorders and recurring infections, were variable in manifestation. Obesity degree or other manifestations did not aggregate by genotype. Few patients underwent bariatric surgery with variable success. Most mutations occurred in the fibronectin III and cytokine receptor homology II domains, whereas none was found in cytoplasmic domain. In silico data were available for 25 mutations and in vitro data were available for four mutations, revealing residual activity in one case. By assessing provided information on the clinical phenotype, functional analysis, and character of the 38 mutations, we assume residual LEPR activity for five additional mutations. Functional in vitro analysis is necessary to confirm this assumption.