Energy metabolism in Bardet-Biedl syndrome

The overlapping of phenotypes in Wiedemann-Steiner, Kleefstra and Coffin-Siris syndromes: a study of eleven patients

BACKGROUND

Some chromatinopathies may present with common clinical findings (intellectual disability, brain and limb malformation, facial dysmorphism). Furthermore, one of their cardinal shared features is growth dysregulation.We aimed to assess and deepen this resemblance in three specific conditions, namely Wiedemann-Steiner (WDSTS), Kleefstra (KLEFS1) and Coffin-Siris syndrome (CSS1), with a particular focus on possible metabolic roots.

METHODS

Eleven patients were enrolled, three with WDSTS, five with KLEFS1 and three with CSS1, referring to Fondazione IRCCS Ca' Granda Ospedale Maggiore, Milan, Italy. We performed both a physical examination with detailed anthropometric measurements and an evaluation of the patients' REE (rest energy expenditure) by indirect calorimetry, comparing the results with age- and sex-matched healthy controls.

RESULTS

We observed new clinical features and overlap between these conditions suggesting that different disturbances of epigenetic machinery genes can converge on a common effect, leading to overlapping clinical phenotypes.
The REE was not distinguishable between the three conditions and healthy controls.

CONCLUSIONS

Epigenetic machinery plays an essential role both in growth regulation and in neurodevelopment; we recommend evaluating skeletal [craniovertebral junction abnormalities (CVJ) polydactyly], otolaryngological [obstructive sleep apnea syndrome (OSAs), recurrent otitis media], dental [tooth agenesis, talon cusps], and central nervous system (CNS) [olfactory bulbs and cerebellum anomalies] features. These features could be included in monitoring guidelines. Further studies are needed to deepen the knowledge about energy metabolism.

The olfactory bulb: A neuroendocrine spotlight on feeding and metabolism

Olfaction is the most ancient sense and is needed for food-seeking, danger protection, mating and survival. It is often the first sensory modality to perceive changes in the external environment, before sight, taste or sound. Odour molecules activate olfactory sensory neurons that reside on the olfactory epithelium in the nasal cavity, which transmits this odour-specific information to the olfactory bulb (OB), where it is relayed to higher brain regions involved in olfactory perception and behaviour. Besides odour processing, recent studies suggest that the OB extends its function into the regulation of food intake and energy balance. Furthermore, numerous hormone receptors associated with appetite and metabolism are expressed within the OB, suggesting a neuroendocrine role outside the hypothalamus. Olfactory cues are important to promote food preparatory behaviours and consumption, such as enhancing appetite and salivation. In addition, altered metabolism or energy state (fasting, satiety and overnutrition) can change olfactory processing and perception. Similarly, various animal models and human pathologies indicate a strong link between olfactory impairment and metabolic dysfunction. Therefore, understanding the nature of this reciprocal relationship is critical to understand how olfactory or metabolic disorders arise. This present review elaborates on the connection between olfaction, feeding behaviour and metabolism and will shed light on the neuroendocrine role of the OB as an interface between the external and internal environments. Elucidating the specific mechanisms by which olfactory signals are integrated and translated into metabolic responses holds promise for the development of targeted therapeutic strategies and interventions aimed at modulating appetite and promoting metabolic health.

Bardet-Biedl syndrome: A clinical overview focusing on diagnosis, outcomes and best-practice management

Bardet-Biedl syndrome (BBS) is a genetic disorder characterized by early-onset obesity, polydactyly, genital and kidney anomalies, developmental delay and vision loss due to rod-cone dystrophy. BBS is an autosomal recessive disorder with >20 implicated genes. The genotype-phenotype relationship in BBS is not clear, and there may be additional modifying factors. The underlying mechanism is dysfunction of primary cilia. In BBS, receptor trafficking in and out of the cilia is compromised, affecting multiple organ systems. Along with early-onset obesity, hyperphagia is a prominent symptom and contributes significantly to clinical morbidity and caregiver burden. While there is no cure for BBS, setmelanotide is a new pharmacotherapy approved for treatment of obesity in BBS. The differential diagnosis for BBS includes other ciliopathies, such as Alstrom syndrome, and other genetic obesity syndromes, such as Prader-Willi syndrome. Careful clinical history and genetic testing can help determine the diagnosis and a multidisciplinary team is necessary to guide clinical management.

Body Fat Distribution Contributes to Defining the Relationship between Insulin Resistance and Obesity in Human Diseases

The risk for metabolic and cardiovascular complications of obesity is defined by body fat distribution rather than global adiposity. Unlike subcutaneous fat, visceral fat (including hepatic steatosis) reflects insulin resistance and predicts type 2 diabetes and cardiovascular disease. In humans, available evidence indicates that the ability to store triglycerides in the subcutaneous adipose tissue reflects enhanced insulin sensitivity. Prospective studies document an association between larger subcutaneous fat mass at baseline and reduced incidence of impaired glucose tolerance. Case-control studies reveal an association between genetic predisposition to insulin resistance and a lower amount of subcutaneous adipose tissue. Human peroxisome proliferator-activated receptorgamma (PPAR-γ) promotes subcutaneous adipocyte differentiation and subcutaneous fat deposition, improving insulin resistance and reducing visceral fat. Thiazolidinediones reproduce the effects of PPAR-γ activation and therefore increase the amount of subcutaneous fat while enhancing insulin sensitivity and reducing visceral fat. Partial or virtually complete lack of adipose tissue (lipodystrophy) is associated with insulin resistance and its clinical manifestations, including essential hypertension, hypertriglyceridemia, reduced HDL-c, type 2 diabetes, cardiovascular disease, and kidney disease. Patients with Prader Willi syndrome manifest severe subcutaneous obesity without insulin resistance. The impaired ability to accumulate fat in the subcutaneous adipose tissue may be due to deficient triglyceride synthesis, inadequate formation of lipid droplets, or defective adipocyte differentiation. Lean and obese humans develop insulin resistance when the capacity to store fat in the subcutaneous adipose tissue is exhausted and deposition of triglycerides is no longer attainable at that location. Existing adipocytes become large and reflect the presence of insulin resistance.

Neuronal primary cilia integrate peripheral signals with metabolic drives

Neuronal primary cilia have recently emerged as important contributors to the central regulation of energy homeostasis. As non-motile, microtubule-based organelles, primary cilia serve as signaling antennae for metabolic status. The impairment of ciliary structure or function can produce ciliopathies for which obesity is a hallmark phenotype and global ablation of cilia induces non-syndromic adiposity in mouse models. This organelle is not only a hub for metabolic signaling, but also for catecholamine neuromodulation that shapes neuronal circuitry in response to sensory input. The objective of this review is to highlight current research investigating the mechanisms of primary cilium-regulated metabolic drives for maintaining energy homeostasis.

Diabetes mellitus in Bardet Biedl syndrome

PURPOSE OF REVIEW

Bardet Biedl syndrome (BBS) is a rare disease characterized by obesity and hyperphagia. Despite the very high prevalence of paediatric and adult obesity in this population, the prevalence of diabetes mellitus is not well described.

RECENT FINDINGS

Studies in small and moderately large cohorts suggest a high prevalence of traditional risk factors for diabetes mellitus in people with BBS. People with BBS appear to have a high prevalence of insulin resistance and metabolic syndrome. Small cohort studies have identified high rates of sleep disordered breathing, including sleep apnoea syndrome. Recent research has characterized traditional behavioural risk factors such as sleep hygiene and physical inactivity in people with BBS. High rates of insufficient sleep and prolonged sedentary time suggest behavioural targets of interventions to treat or prevent diabetes mellitus. Hyperphagia, likely caused by defects in the hypothalamic melanocortin-4 receptor (MC4R) neuronal pathway, pose additional challenges to behavioural interventions to prevent diabetes mellitus.

SUMMARY

Understanding the prevalence of diabetes mellitus and other metabolic disorders in people with BBS and the impact of traditional risk factors on glucose regulation are important to developing effective treatments in this population.

Resting Energy Expenditure and Body Composition in Children and Adolescents With Genetic, Hypothalamic, Medication-Induced or Multifactorial Severe Obesity

Background

Pediatric obesity is a multifactorial disease which can be caused by underlying medical disorders arising from disruptions in the hypothalamic leptin-melanocortin pathway, which regulates satiety and energy expenditure.

Aim

To investigate and compare resting energy expenditure (REE) and body composition characteristics of children and adolescents with severe obesity with or without underlying medical causes.

Methods

This prospective observational study included pediatric patients who underwent an extensive diagnostic workup in our academic centre that evaluated endocrine, non-syndromic and syndromic genetic, hypothalamic, and medication-induced causes of obesity. REE was assessed by indirect calorimetry; body composition by air displacement plethysmography. The ratio between measured REE (mREE) and predicted REE (Schofield equations), REE%, was calculated, with decreased mREE defined as REE% ≤90% and elevated mREE ≥110%. Additionally, the influence of fat-free-mass (FFM) on mREE was evaluated using multiple linear regression.

Results

We included 292 patients (146 [50%] with body composition measurements), of which 218 (75%) patients had multifactorial obesity and 74 (25%) an underlying medical cause: non-syndromic and syndromic genetic (n= 29 and 28, respectively), hypothalamic (n= 10), and medication-induced (n= 7) obesity. Mean age was 10.8 ± 4.3 years, 59% were female, mean BMI SDS was 3.8 ± 1.1, indicating severe obesity. Mean REE% was higher in children with non-syndromic genetic obesity (107.4% ± 12.7) and lower in children with hypothalamic obesity (87.6% ± 14.2) compared to multifactorial obesity (100.5% ± 12.6, both p<0.01). In 9 children with pseudohypoparathyroidism type 1a, mean REE% was similar (100.4 ± 5.1). Across all patients, mREE was decreased in 60 (21%) patients and elevated in 69 (24%) patients. After adjustment for FFM, mREE did not differ between patients within each of the subgroups of underlying medical causes compared to multifactorial obesity (all p>0.05).

Conclusions

In this cohort of children with severe obesity due to various etiologies, large inter-individual differences in mREE were found. Consistent with previous studies, almost half of patients had decreased or elevated mREE. This knowledge is important for patient-tailored treatment, e.g. personalized dietary and physical activity interventions and consideration of pharmacotherapy affecting central energy expenditure regulation in children with decreased mREE.

Primary Cilia in Pancreatic β- and α-Cells: Time to Revisit the Role of Insulin-Degrading Enzyme

The primary cilium is a narrow organelle located at the surface of the cell in contact with the extracellular environment. Once underappreciated, now is thought to efficiently sense external environmental cues and mediate cell-to-cell communication, because many receptors, ion channels, and signaling molecules are highly or differentially expressed in primary cilium. Rare genetic disorders that affect cilia integrity and function, such as Bardet-Biedl syndrome and Alström syndrome, have awoken interest in studying the biology of cilium. In this review, we discuss recent evidence suggesting emerging roles of primary cilium and cilia-mediated signaling pathways in the regulation of pancreatic β- and α-cell functions, and its implications in regulating glucose homeostasis.

Primary Cilia Are Critical Regulators of White Adipose Tissue Expansion

The primary cilium is a microtubule-based cellular protrusion found on most mammalian cell types in diverse tissues. It functions as a cellular antenna to sense and transduce a broad range of signals, including odorants, light, mechanical stimuli, and chemical ligands. This diversity in signals requires cilia to display a context and cell type-specific repertoire of receptors. Recently, primary cilia have emerged as critical regulators of metabolism. The importance of primary cilia in metabolic disease is highlighted by the clinical features of human genetic disorders with dysfunctional ciliary signaling, which include obesity and diabetes. This review summarizes the current literature on the role of primary cilia in metabolic disease, focusing on the importance of primary cilia in directing white adipose tissue expansion during obesity.

Sleep and physical activity patterns in adults and children with Bardet-Biedl syndrome

Background

Overweight and obesity are common features of the rare disease Bardet–Biedl syndrome (BBS). Sleep and physical activity are behaviors that might impact overweight and obesity and thus may play a key role in the health and well-being of people with BBS. Objectively-measured sleep and physical activity patterns in people with BBS are not well known. We evaluated objectively-measured sleep and physical activity patterns in the largest cohort to date of people with BBS.

Results

Short sleep duration, assessed using wrist-worn accelerometers, was common in both children and adults with BBS. Only 7 (10%) of adults and 6 (8%) of children met age-specific sleep duration recommendations. Most adults 64 (90%) achieved recommended sleep efficiency. The majority of children 26 (67%) age 6–12 years achieved recommended sleep efficiency, but among children age 13–18, only 18 (47%). In both adults and children, sleep duration was significantly negatively correlated with duration of prolonged sedentary time. In children age 6–12 sleep duration was also significantly related to total activity score, children with lower sleep duration had lower total activity scores.

Conclusions

Insufficient sleep duration is very common in people with BBS. Prolonged sedentary time and short sleep duration are both potentially important health-related behaviors to target for intervention in people with BBS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01911-4.

Bardet-Biedl Syndrome Caused by Skipping of SCLT1 Complicated by Microvesicular Steatohepatitis

We treated the case of a 22-year-old male patient with liver dysfunction. At 1 year of age, hepatic fibrosis was suspected. In addition, due to the presence of retinitis pigmentosa, renal failure, obesity, mental retardation, and hypogonadism, he was diagnosed with Bardet-Biedl syndrome (BBS). Skipping of exons 14 and 17 in the sodium channel and clathrin linker 1 (SCLT1) gene was observed. At 22 years of age, the liver enzyme levels were further elevated and a diagnosis of microvesicular steatohepatitis was made. Insulin resistance, a reduction of muscle mass, an impairment of the fatty acid metabolism, and hyperleptinemia in this syndrome may cause steatohepatitis.

Clinical characteristics of individual organ system disease in non-motile ciliopathies

Non-motile ciliopathies (disorders of the primary cilia) include autosomal dominant and recessive polycystic kidney diseases, nephronophthisis, as well as multisystem disorders Joubert, Bardet-Biedl, Alström, Meckel-Gruber, oral-facial-digital syndromes, and Jeune chondrodysplasia and other skeletal ciliopathies. Chronic progressive disease of the kidneys, liver, and retina are common features in non-motile ciliopathies. Some ciliopathies also manifest neurological, skeletal, olfactory and auditory defects. Obesity and type 2 diabetes mellitus are characteristic features of Bardet-Biedl and Alström syndromes. Overlapping clinical features and molecular heterogeneity of these ciliopathies render their diagnoses challenging. In this review, we describe the clinical characteristics of individual organ disease for each ciliopathy and provide natural history data on kidney, liver, retinal disease progression and central nervous system function.

Revisiting the evolutionary origins of obesity: lazy versus peppy-thrifty genotype hypothesis

The recent global obesity epidemic is attributed to major societal and environmental changes, such as excessive energy intake and sedentary lifestyle. However, exposure to 'obesogenic' environments does not necessarily result in obesity at the individual level, as 40-75% of body mass index variation in population is attributed to genetic differences. The thrifty genotype theory posits that genetic variants promoting efficient food sequestering and optimal deposition of fat during periods of food abundance were evolutionarily advantageous for the early hunter-gatherer and were positively selected. However, the thrifty genotype is likely too simplistic and fails to provide a justification for the complex distribution of obesity predisposing gene variants and for the broad range of body mass index observed in diverse ethnic groups. This review proposes that gene pleiotropy may better account for the variability in the distribution of obesity susceptibility alleles across modern populations. We outline the lazy-thrifty versus peppy-thrifty genotype hypothesis and detail the body of evidence in the literature in support of this novel concept. Future population genetics and mathematical modelling studies that account for pleiotropy may further improve our understanding of the evolutionary origins of the current obesity epidemic.

The Endocrine and Metabolic Characteristics of a Large Bardet-Biedl Syndrome Clinic Population

CONTEXT

Bardet-Biedl syndrome (BBS) is a rare autosomal recessive disorder in which previous reports have described obesity and a metabolic syndrome.

OBJECTIVE

We describe the endocrine and metabolic characteristics of a large BBS population compared with matched control subjects.

DESIGN

We performed a case-control study.

SETTING

This study was performed at a hospital clinic.

PATIENTS

Study patients had a clinical or genetic diagnosis of BBS.

MAIN OUTCOME MEASUREMENTS

Our study determined the prevalence of a metabolic syndrome in our cohort.

RESULTS

A total of 152 subjects were studied. Eighty-four (55.3%) were male. Mean (± standard deviation) age was 33.2 ± 1.0 years. Compared with age-, sex-, and body mass index-matched control subjects, fasting glucose and insulin levels were significantly higher in subjects with BBS (glucose: BBS, 5.2 ± 1.2 mmol/L vs control, 4.9 ± 0.9 mmol/L, P = 0.04; insulin: BBS, 24.2 ± 17.0 pmol/L vs control, 14.2 ± 14.8 pmol/L, P < 0.001). Serum triglycerides were significantly higher in subjects with BBS (2.0 ± 1.2 mmol/L) compared with control subjects (1.3 ± 0.8 mmol/L; P < 0.001), but total cholesterol, high-density lipoprotein, and low-density lipoprotein were similar in both groups. Systolic blood pressure was higher in the BBS group (BBS, 135 ± 18 mm Hg vs control subjects, 129 ± 16 mm Hg; P = 0.02). Alanine transaminase was raised in 34 (26.8%) subjects with BBS, compared with five (8.9%) control subjects (P = 0.01). The rate of metabolic syndrome, determined using International Diabetes Federation criteria, was significantly higher in the BBS group (54.3%) compared with control subjects (26% P < 0.001). Twenty-six (19.5%) of male subjects with BBS were hypogonadal (serum testosterone, 9.9 ± 5.3 mmol/L), but significant pituitary abnormalities were uncommon. Subclinical hypothyroidism was present in 24 of 125 (19.4%) patients with BBS, compared with 3 of 65 (4.6%) control subjects (P = 0.01).

CONCLUSIONS

Insulin resistance and the metabolic syndrome are increased in adult patients with BBS compared with matched control subjects. Increased subclinical hypothyroidism in the BBS cohort needs further investigation.

Physical Activity of Adults with Mental Retardation: Review and Research Needs

Objective

To characterize physical activity levels of adults with mental retardation and identify limitations in published research.

Data Sources

Key word searches for “mental retardation, ” “intellectual disability, ” “learning disability, ” or “developmental disability” combined with “physical activity” or “habitual exercise” identified articles from MEDLINE, Academic Search Elite, Psych Articles, Health Source, and SPORT Discus. This produced a total of 801 citations.

Study Inclusion and Exclusion Criteria

Published English-language literature that quantitatively measured physical activity levels of adults with mental retardation was included in this review. Fourteen articles met this criterion.

Data Extraction

Characteristics of participants, study design, outcome measures, methods of analyses, and findings in terms of percentages, step counts, and acceleromeler output were extracted.

Data Synthesis

Data were synthesized to identify the percentage of adults with mental retardation who met published health-related physical activity criteria and compare them with adults without mental retardation and to examine study limitations.

Results

The studies with the greatest rigor indicate that one-third of adults or fewer with mental retardation were sufficiently active to achieve health benefits. However, data are insufficient to determine whether adults with mental retardation are less active than the general community.

Conclusions

Future research would be enhanced by including appropriately powered representative samples, by including comparison groups, by validating physical activity questionnaires, and by determining the accuracy of proxy respondents.

Sleep disordered breathing in Bardet-Biedl Syndrome

INTRODUCTION

Bardet-Biedl Syndrome (BBS) is an autosomal recessive ciliopathy, and obesity is among its defining characteristics. Consequently, the incidence of sleep disordered breathing (SDB) in this population is expected to be high. Due to its relative rarity, the nature of SDB in this population is poorly described. The objective of this study was to review a single institutional experience in the assessment and management of SDB in patients with BBS.

METHODS

Retrospective chart review of tertiary care, academic pediatric hospital.

RESULTS

20 patients with BBS were evaluated over a 25-year period. Median age at initial consultation was 69 months; half of these patients were referred before the diagnosis of BBS was made. Eighteen of twenty patients had symptoms of sleep-disordered breathing. Median follow-up duration was 17.5 months. A wide range of polysomnographic outcomes was observed, including obstructive apnea-hypopnea indexes of 0-195 events/hour. Patients were managed with adenotonsillectomy and/or non-invasive positive pressure ventilation.

CONCLUSIONS

SDB is commonly seen in BBS. These patients should be routinely screened for OSA and if present, a polysomnogram should be obtained. Based on patient characteristics, the failure rate of primary surgical intervention, namely adenotonsillectomy, is expected to be high. Further investigation into the role of ancillary diagnostic testing is still needed.

Insulin regulates Bbs4 during adipogenesis

Bardet-Biedl syndrome (BBS) is a pleiotropic autosomal recessive disorder associated with marked obesity, increased susceptibility to insulin resistance and type 2 diabetes. However, it is unknown whether the link between BBS and diabetes is indirect or direct. Adipogenesis and adipocyte function are regulated by hormonal stimuli, with insulin and insulin growth factor (IGF) playing an important role both in normal and impaired conditions. We have previously shown augmented transcript levels of BBS genes upon induction of adipogenesis. The aim of this study was to investigate the role of insulin in BBS. Through in vitro studies in adipocytes in which Bbs4 expression was either silenced (SiBbs4) or overexpressed (OEBbs4), we showed that insulin and IGF dose- and time-dependently decrease transcription and protein expression of BBS genes during adipogenesis. Silencing of Bbs4 expression in adipocytes significantly impaired and reduced glucose uptake. This effect was reversed by Bbs4 overexpression. Inhibition of PI 3-kinase resulted in upregulation of Bbs transcripts, suggesting that the PI3K pathway is involved in the regulation of these genes. In conclusion, we showed that insulin is a direct regulator of Bbs1, 2, 4 and 6. This hormonal regulation might indicate a metabolic link of these genes to obesity and metabolic syndrome. © 2017 IUBMB Life, 69(7):489-499, 2017.

Beneficial Outcomes of Sleeve Gastrectomy in a Morbidly Obese Patient With Bardet-Biedl Syndrome

Context

Severe obesity is one of the major features of Bardet-Biedl syndrome (BBS) and causes reduced life expectancy. Bariatric surgery is an effective treatment of morbid obesity. Data on the effect of bariatric surgery for monogenic obesity is essentially lacking. We present the clinical and metabolic 3-year follow-up of sleeve gastrectomy in a BBS patient.

Case Description

A 37-year-old obese woman with BBS (body mass index, 40 kg/m²) was referred to our clinic for uncontrolled diabetes, dyslipidemia, hypertension, and nonalcoholic fatty liver disease (NAFLD). After sleeve gastrectomy, progressive weight loss was observed, with a 32% total weight loss at 3-year follow-up. Glycemic control and NAFLD improved significantly. Blood pressure normalized, and treatment was discontinued 3 months after surgery.

Conclusions

Laparoscopic sleeve gastrectomy can be a safe and effective treatment of morbid BBS-related obesity in adult patients. Significant and sustained weight loss leads to the improvement of several obesity-related comorbidities such as diabetes, hypertension, and NAFLD, as in polygenic obesity. Further data are needed to confirm the long-term efficacy and safety of bariatric surgery in BBS.

The cilium: a cellular antenna with an influence on obesity risk

Primary cilia are organelles that are present on many different cell types, either transiently or permanently. They play a crucial role in receiving signals from the environment and passing these signals to other parts of the cell. In that way, they are involved in diverse processes such as adipocyte differentiation and olfactory sensation. Mutations in genes coding for ciliary proteins often have pleiotropic effects and lead to clinical conditions, ciliopathies, with multiple symptoms. In this study, we reviewed observations from ciliopathies with obesity as one of the symptoms. It shows that variation in cilia-related genes is itself not a major cause of obesity in the population but may be a part of the multifactorial aetiology of this complex condition. Both common polymorphisms and rare deleterious variants may contribute to the obesity risk. Genotype-phenotype relationships have been noticed. Among the ciliary genes, obesity differs with regard to severity and age of onset, which may relate to the influence of each gene on the balance between pro- and anti-adipogenic processes. Analysis of the function and location of the proteins encoded by these ciliary genes suggests that obesity is more linked to activities at the basal area of the cilium, including initiation of the intraflagellar transport, but less to the intraflagellar transport itself. Regarding the role of cilia, three possible mechanistic processes underlying obesity are described: adipogenesis, neuronal food intake regulation and food odour perception.

Differential effects on β-cell mass by disruption of Bardet-Biedl syndrome or Alstrom syndrome genes

Rare genetic syndromes characterized by early-onset type 2 diabetes have revealed the importance of pancreatic β-cells in genetic susceptibility to diabetes. However, the role of genetic regulation of β-cells in disorders that are also characterized by highly penetrant obesity, a major additional risk factor, is unclear. In this study, we investigated the contribution of genes associated with two obesity ciliopathies, Bardet-Biedl Syndrome and Alstrom Syndrome, to the production and maintenance of pancreatic β-cells. Using zebrafish models of these syndromes, we identified opposing effects on production of β-cells. Loss of the Alstrom gene, alms1, resulted in a significant decrease in β-cell production whereas loss of BBS genes, bbs1 or bbs4, resulted in a significant increase. Examination of the regulatory program underlying β-cell production suggested that these effects were specific to β-cells. In addition to the initial production of β-cells, we observed significant differences in their continued maintenance. Under prolonged exposure to high glucose conditions, alms1-deficient β-cells were unable to continually expand as a result of decreased proliferation and increased cell death. Although bbs1-deficient β-cells were similarly susceptible to apoptosis, the overall maintenance of β-cell number in those animals was sustained likely due to increased proliferation. Taken together, these findings implicate discrepant production and maintenance of β-cells in the differential susceptibility to diabetes found between these two genetic syndromes.

Regulation of Insulin Receptor Trafficking by Bardet Biedl Syndrome Proteins

Insulin and its receptor are critical for the regulation of metabolic functions, but the mechanisms underlying insulin receptor (IR) trafficking to the plasma membrane are not well understood. Here, we show that Bardet Biedl Syndrome (BBS) proteins are necessary for IR localization to the cell surface. We demonstrate that the IR interacts physically with BBS proteins, and reducing the expression of BBS proteins perturbs IR expression in the cell surface. We show the consequence of disrupting BBS proteins for whole body insulin action and glucose metabolism using mice lacking different BBS genes. These findings demonstrate the importance of BBS proteins in underlying IR cell surface expression. Our data identify defects in trafficking and localization of the IR as a novel mechanism accounting for the insulin resistance commonly associated with human BBS. This is supported by the reduced surface expression of the IR in fibroblasts derived from patients bearing the M390R mutation in the BBS1 gene.

A main function of the hormone insulin in the body is to regulate metabolism of glucose. The hormone causes body cells in different organs and tissues to utilize glucose from the bloodstream, storing the excess amount. Insulin resistance which reflects the inability of insulin to properly regulate glucose metabolism is common in people with obesity and/or type 2 diabetes. This insulin resistance is strongly associated with cardiovascular disease and increases the risk of death. However, the reasons that account for this insulin resistance phenomenon are currently not well understood. Here, we show that Bardet Biedl Syndrome proteins are required for proper action of insulin. We found that cells or animals that are deficient in Bardet Biedl Syndrome proteins are unable to respond to insulin. These results provide an explanation why patients that carry mutations in the Bardet Biedl Syndrome genes are insulin resistant, and will potentially contribute to understand common human forms of insulin resistance.

Primary cilia in pancreatic development and disease

Primary cilia and their anchoring basal bodies are important regulators of a growing list of signaling pathways. Consequently, dysfunction in proteins associated with these structures results in perturbation of the development and function of a spectrum of tissue and cell types. Here, we review the role of cilia in mediating the development and function of the pancreas. We focus on ciliary regulation of major pathways involved in pancreatic development, including Shh, Wnt, TGF-β, Notch, and fibroblast growth factor. We also discuss pancreatic phenotypes associated with ciliary dysfunction, including pancreatic cysts and defects in glucose homeostasis, and explore the potential role of cilia in such defects.

A novel form of ciliopathy underlies hyperphagia and obesity in Ankrd26 knockout mice

Human ciliopathies are genetic disorders caused by mutations in genes responsible for the formation and function of primary cilia. Some are associated with hyperphagia and obesity (e.g., Bardet-Biedl Syndrome, Alström Syndrome), but the mechanisms underlying these problems are not fully understood. The human gene ANKRD26 is located on 10p12, a locus that is associated with some forms of hereditary obesity. Previously, we reported that disruption of this gene causes hyperphagia, obesity and gigantism in mice. In the present study, we looked for the mechanisms that induce hyperphagia in the Ankrd26-/- mice and found defects in primary cilia in regions of the central nervous system that control appetite and energy homeostasis.

The neuropathology of obesity: insights from human disease

Obesity, a pathologic state defined by excess adipose tissue, is a significant public health problem as it affects a large proportion of individuals and is linked with increased risk for numerous chronic diseases. Obesity is the result of fundamental changes associated with modern society including overnutrition and sedentary lifestyles. Proper energy homeostasis is dependent on normal brain function as the master metabolic regulator, which integrates peripheral signals, modulates autonomic outflow and controls feeding behavior. Therefore, many human brain diseases are associated with obesity. This review explores the neuropathology of obesity by examining brain diseases which either cause or are influenced by obesity. First, several genetic and acquired brain diseases are discussed as a means to understand the central regulation of peripheral metabolism. These diseases range from monogenetic causes of obesity (leptin deficiency, MC4R deficiency, Bardet-Biedl syndrome and others) to complex neurodevelopmental disorders (Prader-Willi syndrome and Sim1 deficiency) and neurodegenerative conditions (frontotemporal dementia and Gourmand's syndrome) and serve to highlight the central regulatory mechanisms which have evolved to maintain energy homeostasis. Next, to examine the effect of obesity on the brain, chronic neuropathologic conditions (epilepsy, multiple sclerosis and Alzheimer's disease) are discussed as examples of obesity leading to maladaptive processes which exacerbate chronic disease. Thus, obesity is associated with multiple pathways including abnormal metabolism, altered hormonal signaling and increased inflammation which act in concert to promote downstream neuropathology. Finally, the effect of anti-obesity interventions is discussed in terms of brain structure and function. Together, understanding human diseases and anti-obesity interventions leads to insights into the bidirectional interaction between peripheral metabolism and central brain function, highlighting the need for continued clinicopathologic and mechanistic studies of the neuropathology of obesity.

[Ophthalmologic manifestations of Bardet-Biedl syndrome]

INTRODUCTION

Bardet-Biedl syndrome is characterised by retinal dystrophy, polydactily, obesity and slow mental development.

AIM

The aim of the authors was to present ophthalmologic signs and symptoms of the syndrome.

METHOD

Between 1980 and 2010, 4 children with Bardet-Biedl syndrome were evaluated at the Department of Ophthalmology, University of Szeged, Szeged, Hungary. Their age at the first visit was between 1 and 10 years. Basic ophthalmological and electrophysiological evaluation, as well as orthoptic examinations were performed.

RESULTS

In two cases the electroretinographic curves were subnormal, and in two cases the electroretinographic curves showed no elevation. In the 4 children abnormal electroretinographic curves appeared at the ages of 1, 5, 10, and 18 years. Pigmentary changes on the periphery of the retina were detected in two cases.

CONCLUSIONS

The different signs and symptoms of Bardet-Biedl syndrome may manifest at different ages. Electrophysiological changes failed to correlate with retinal alterations is these patients.

Hyperphagia among patients with Bardet-Biedl syndrome

BACKGROUND

The importance of hyperphagia as a cause for energy imbalance in humans with Bardet-Biedl syndrome (BBS) has not been established. We therefore compared hyperphagic symptoms in patients with BBS vs. controls.

METHODS

We studied 13 patients with BBS and 23 non-syndromic controls with similar age, sex and body mass index (BMI) z-score. A 13-item hyperphagia questionnaire was completed by patients' parents/guardians.

RESULTS

Total hyperphagia questionnaire score was higher in BBS than controls (27.6 ± 9.0 vs. 19.1 ± 7.9, P = 0.005). Behaviour and drive subscales were higher for BBS than controls (12.5 ± 4.1 vs. 7.8 ± 3.2, P = 0.001, and 11.2 ± 4.1 vs. 8.3 ± 3.8, P = 0.04, respectively); severity was not significantly different between groups (3.8 ± 1.5 vs. 3.0 ± 1.3, P = 0.072). After adjustment for demographic variables and BMI z-score, total and behaviour subscale scores remained significantly different between groups, suggesting food-seeking activity, rather than preoccupation with food may be the main hyperphagic feature among patients with BBS.

CONCLUSION

Appetite dysregulation may contribute to obesity in BBS.

Common FSNP variants of fourteen Bardet-Biedl syndrome genes and adult body mass

OBJECTIVE

Bardet-Biedl syndrome (BBS) is a rare monogenic multi-systemic disorder manifesting with marked obesity. Fourteen BBS genes have been identified to date and additional loci are expected. Mutations of several BBS genes were shown to affect fat cell differentiation. The purpose was to Investigate the association between common polymorphisms in all 14 genes as a group and body weight.

DESIGN AND METHODS

We investigated association between tagging single nucleotide polymorphisms (tSNPs) located between 10 kb upstream and downstream from the transcribed sequences of each of 14 BBS genes, and body weight and fat in 2462 adult women from the UK Twins study. Significant results were further tested in a confirmation sample of 2003 women from the same cohort and additionally in the GIANT consortium population (n = 123,865).

RESULTS

105 SNPs in 14 BBS genes were selected and tested in the first cohort of women for association with the body weight and fat related phenotypes, i.e. weight, body mass index (BMI), total body fat (assessed by DEXA), total fat/height(2), and total fat/weight. We used principal component (PC) derived using the latter five traits as a primary phenotype for this study. Of the 105 SNPs, 3 variants in BBS9 and BBS11 showed evidence of nominally significant association with elevated body weight and fat. However, none of the associations survived multiple-testing correction.

CONCLUSIONS

The results suggest that common variation in 14 BBS genes (within or adjacent to the genes) are unlikely to have a substantial effect on body weight and fat in the European population.

Obesity in patients with Bardet-Biedl syndrome: influence of appetite-regulating hormones

BACKGROUND

Bardet-Biedl syndrome (BBS) is a genetic disorder with obesity as one of the major phenotypic criterion, which is proposed to be of neuroendocrine origin. Therefore, disturbances in appetite-regulating hormones have been considered as causative factors. Acyl ghrelin is an orexigenic hormone, whereas its desacylated form, obestatin, and leptin have the opposite functions. Ghrelin is negatively regulated in relation to nutritional status. The aim of this study was to evaluate the impact of hormone alterations on obesity development in BBS patients.

METHODS

Total and acylated ghrelin, obestatin, leptin and adiponectin were measured in eight children with BBS. The results were analyzed in relation to auxological parameters [body mass index (BMI), height].

RESULTS

The mean BMI was significantly increased in BBS patients compared to the controls. Plasma levels of acylated ghrelin, total ghrelin and obestatin were slightly elevated in BBS patients compared to controls, as was the acyl/total ghrelin ratio. Leptin levels were significantly elevated in BBS patients.

CONCLUSION

BBS patients lack the negative regulatory mechanisms of appetite-regulating hormones with respect to nutritional status and exhibit resistance to anorexigenic leptin. This results in a shift towards the orexigenic effects of this self-regulating system. These alterations may in part be responsible for the disturbed appetite regulation in BBS patients.

Bardet-Biedl syndrome

Bardet-Biedl syndrome (BBS) is a rare autosomal recessive ciliopathy characterised by retinal dystrophy, obesity, post-axial polydactyly, renal dysfunction, learning difficulties and hypogonadism. Many associated minor features can be helpful in making a diagnosis and are important in the clinical management of BBS. The diagnosis is based on clinical findings and can be confirmed by sequencing of known disease-causing genes in 80% of patients. BBS genes encode proteins that localise to the cilia and basal body and are involved in cilia biogenesis and function. Mutations lead to defective cilia accounting in part for the pleiotropic effects observed in BBS. We provide an overview of BBS including the clinical findings, current understanding of cilia biology, and a practical approach to diagnosis, genetic counselling and up-to-date management.

Molecular basis of the obesity associated with Bardet-Biedl syndrome

Bardet-Biedl Syndrome (BBS) is a rare human hereditary disorder associated with several features including obesity, retinopathy, renal defects, polydactyly, learning disabilities and hypogenitalism. This article discusses the abnormalities accounting for energy imbalance leading to obesity in BBS, with emphasis on the recent evidence pointing to aberrations in hypothalamic action of leptin. Indeed, BBS proteins have emerged as important mediators of leptin receptor trafficking, and loss of BBS genes results in leptin resistance that could be due to abnormal leptin receptor handling in a subset of leptin-responsive neurons. These recent discoveries hold promise for improved clinical management of BBS patients. The relevance of these findings to non-syndromic common obesity is also discussed.

Patients with Bardet-Biedl syndrome have hyperleptinemia suggestive of leptin resistance

OBJECTIVE

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous disorder of the primary cilium associated with obesity. In BBS mouse models, ciliary dysfunction leads to impaired leptin signaling and hyperleptinemia before obesity onset. To study the pathophysiology of obesity in BBS, we compared patients with BBS and body mass index Z-score (BMI-Z)-matched controls.

DESIGN AND METHODS

Fifty patients with BBS were matched 2:1 by age, sex, race, and BMI-Z with 100 controls. Patients with BBS and controls were compared for differences in body composition (dual-energy x-ray absorptiometry, abdominal magnetic resonance imaging), blood pressure Z-score (BP-Z; standardized for age, sex, and height), and fasting concentrations of leptin, lipids, insulin, and glucose. Patients with BBS were also compared by genotype.

RESULTS

Leptin, triglycerides, intraabdominal fat mass, and diastolic BP-Z were significantly greater in patients with BBS than in the controls. BBS1 (27%) and BBS10 (30%) mutations were the most prevalent. Patients with BBS10 mutations had significantly higher BMI-Z, greater visceral adiposity, and greater insulin resistance than those with BBS1 mutations.

CONCLUSIONS

Patients with BBS had higher leptin than expected for their degree of adiposity, consistent with the notion that ciliopathy-induced leptin signaling dysfunction is associated with leptin resistance. The preferential deposition of fat intraabdominally in patients with BBS may indicate a predisposition for metabolic complications, including hypertension and hypertriglyceridemia. The observation of disparate results in the BBS10 vs. BBS1 mutation groups is the first demonstration of physiological differences among patients with BBS caused by mutations in distinct genes. These results suggest that the obesity of BBS is distinct from nonsyndromic obesity.

Expanding the definition of hypothalamic obesity

Hypothalamic obesity (HyOb) was first defined as the significant polyphagia and weight gain that occurs after extensive suprasellar operations for excision of hypothalamic tumours. However, polyphagia and weight gain complicate other disorders related to the hypothalamus, including those that cause structural damage to the hypothalamus like tumours, trauma, radiotherapy; genetic disorders such as Prader-Willi syndrome; side effects of psychotropic drugs; and mutations in several genes involved in hypothalamic satiety signalling. Moreover, 'simple' obesity is associated with polymorphisms in several genes involved in hypothalamic weight-regulating pathways. Thus, understanding HyOb may enhance our understanding of 'simple' obesity. This review will claim that HyOb is a far wider phenomenon than hitherto understood by the narrow definition of post-surgical weight gain. It will emphasize the similarity in clinical characteristics and therapeutic approaches for HyOb, as well as its mechanisms. HyOb, regardless of its aetiology, is a result of impairment in hypothalamic regulatory centres of body weight and energy expenditure. The pathophysiology includes loss of sensitivity to afferent peripheral humoral signals, such as, leptin on the one hand and dysfunctional afferent signals, on the other hand. The most important afferent signals deranged are energy regulation by the sympathetic nervous system and regulation of insulin secretion. Dys-regulation of 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) activity and melatonin may also have a role in the development of HyOb. The complexity of the syndrome requires simultaneous targeting of several mechanisms that are deranged in the HyOb patient. We review the studies evaluating possible treatment strategies, including sympathomimetics, somatostatin analogues, triiodothyronine, sibutramine, and surgery.

Inherited cerebrorenal syndromes

Abnormalities in the central nervous system and renal function are seen together in a variety of congenital syndromes. This Review examines the clinical presentation and the genetic basis of several such syndromes. The X-linked oculocerebrorenal syndrome of Lowe is characterized by developmental delay, blindness, renal tubular dysfunction, and progressive renal failure. This syndrome results from mutations in the OCRL gene, which encodes a phosphatase involved in endosomal trafficking. Mutations in OCRL also occur in Dent disease, which has a milder disease phenotype than Lowe syndrome. Patients with Joubert syndrome have cerebellar ataxia, pigmentary retinopathy, and nephronophthisis. Joubert syndrome is a genetically heterogeneous condition associated with mutations in at least five genes that encode ciliary proteins. Bardet-Biedl syndrome is a clinically variable condition associated with learning disabilities, progressive visual loss, obesity, polydactyly, hypogonadism, and cystic and fibrotic renal changes that can lead to renal failure. Most of the 12 genes mutated in Bardet-Biedl syndrome are also involved in ciliary function, as are the genes implicated in other 'ciliopathies' with similar phenotypes, including Meckel syndrome.

The nonmotile ciliopathies

Over the last 5 years, disorders of nonmotile cilia have come of age and their study has contributed immeasurably to our understanding of cell biology and human genetics. This review summarizes the main features of the ciliopathies, their underlying genetics, and the functions of the proteins involved. We describe some of the key findings in the field, including new animal models, the role of ciliopathy proteins in signaling pathways and development, and the unusual genetics of these diseases. We also discuss the therapeutic potential for these diseases and finally, discuss important future work that will extend our understanding of this fascinating organelle and its associated pathologies.

Roux-en-Y gastric bypass in an adolescent patient with Bardet-Biedl syndrome, a monogenic obesity disorder

Bardet-Biedl syndrome (BBS) is a rare genetic disorder characterized by a wide range of phenotypic variability and associated with the development of life-threatening obesity. Birth weight tends to be normal, but rapid weight gain begins after the first year, probably due to polyphagia rather than abnormalities in energy metabolism. A morbidly obese 16-year-old male patient with BBS was referred to our institution, after nonsurgical methods of weight control had failed, for surgical treatment of his obesity. His preoperative body mass index (BMI) was 52.28 kg/m(2) (height, 1.84 m; weight, 177 kg) and was above the 99th centile for age and gender. The patient underwent laparoscopic Roux-en-Y gastric bypass (RYGBP). The postoperative period was uneventful. Three and a half years after the operation, the patient's weight has decreased to 118 kg (BMI, 34.85 kg/m(2)), while significant improvement in his hypertension, hyperuricemia, and mobility has been noted. In our BBS patient, RYGBP proved to be safe and effective; nevertheless, longer follow-up is required to evaluate the weight loss durability and to assess the lasting beneficial effect of surgical intervention on genetically determined co-morbidities.

Pleiotropic genetic syndromes with developmental abnormalities associated with obesity

Childhood obesity is a common and complex problem that may persist in adulthood. It may present as a component of genetic syndromes associated with dysmorphic features, developmental abnormalities, mental retardation and/or learning disabilities and often neuroendocrine dysfunction. Although the chromosomal abnormalities of these rare syndromes are already known, the specific genetic and pathophysiological mechanisms leading to the distinct phenotypes and obesity still remain unclarified. New exciting genetic pathways contributing to syndrome phenotype and leading to obesity have recently been identified. Prader-Willi syndrome is caused by loss of expression of the C/D box HBII-84 cluster of snoRNAs. Dysfunction of the primary cilium, thought to have important signalling functions, may contribute to disease phenotype and obesity in Bardet-Biedl, Alstrom and Carpenter syndromes. In this mini-review current knowledge of clinical and genetic characteristics is summarized as well as the pathogenesis of these syndromes with special emphasis on the pathogenesis of obesity.

Lessons from extreme human obesity: monogenic disorders

Human obesity has a strong genetic component. Most genes that influence an individual's predisposition to gain weight are not yet known. However, the study of extreme human obesity caused by single gene defects has provided a glimpse into the long-term regulation of body weight. These monogenic obesity disorders have confirmed that the hypothalamic leptin-melanocortin system is critical for energy balance in humans, because disruption of these pathways causes the most severe obesity phenotypes. Approximately 20 different genes and at least three different mechanisms have been implicated in monogenic causes of obesity; however, they account for fewer than 5% of all severe obesity cases. This finding suggests that the genetic basis for human obesity is likely to be extremely heterogeneous, with contributions from numerous genes acting by various, yet undiscovered, molecular mechanisms.

Leptin resistance contributes to obesity and hypertension in mouse models of Bardet-Biedl syndrome

Bardet-Biedl syndrome (BBS) is a heterogeneous genetic disorder characterized by many features, including obesity and cardiovascular disease. We previously developed knockout mouse models of 3 BBS genes: BBS2, BBS4, and BBS6. To dissect the mechanisms involved in the metabolic disorders associated with BBS, we assessed the development of obesity in these mouse models and found that BBS-null mice were hyperphagic, had low locomotor activity, and had elevated circulating levels of the hormone leptin. The effect of exogenous leptin on body weight and food intake was attenuated in BBS mice, which suggests that leptin resistance may contribute to hyperleptinemia. In other mouse models of obesity, leptin resistance may be selective rather than systemic; although mice became resistant to leptin's anorectic effects, the ability to increase renal sympathetic nerve activity (SNA) was preserved. Although all 3 of the BBS mouse models were similarly resistant to leptin, the sensitivity of renal SNA to leptin was maintained in Bbs4 -/- and Bbs6 -/- mice, but not in Bbs2 -/- mice. Consequently, Bbs4 -/- and Bbs6 -/- mice had higher baseline renal SNA and arterial pressure and a greater reduction in arterial pressure in response to ganglionic blockade. Furthermore, we found that BBS mice had a decreased hypothalamic expression of proopiomelanocortin, which suggests that BBS genes play an important role in maintaining leptin sensitivity in proopiomelanocortin neurons.

Modeling ciliopathies: Primary cilia in development and disease

Primary (nonmotile) cilia are currently enjoying a renaissance in light of novel ascribed functions ranging from mechanosensory to signal transduction. Their importance for key developmental pathways such as Sonic Hedgehog (Shh) and Wnt is beginning to emerge. The function of nodal cilia, for example, is vital for breaking early embryonic symmetry, Shh signaling is important for tissue morphogenesis and successful Wnt signaling for organ growth and differentiation. When ciliary function is perturbed, photoreceptors may die, kidney tubules develop cysts, limb digits multiply and brains form improperly. The etiology of several uncommon disorders has recently been associated with cilia dysfunction. The causative genes are often similar and their cognate proteins certainly share cellular locations and/or pathways. Animal models of ciliary gene ablation such as Ift88, Kif3a, and Bbs have been invaluable for understanding the broad function of the cilium. Herein, we describe the wealth of information derived from the study of the ciliopathies and their animal models.

Childhood obesity and insulin resistance

Insulin resistance (IR) in childhood has importance to the understanding and prevention of the growing epidemic of insulin resistance syndrome (IRS) in adults with attendant obesity, type 2 diabetes (T2DM), atherosclerotic diseases, hypertension, gout, non-alcoholic, steato-hepatitis (NASH), gall bladder disease, nephropathy, polycystic ovarian disease (PCOS), infertility and premature senility. The severity of IR and its' complications in children unfortunately and usually progresses in their pubertal transition to adulthood; affected young children are more likely than adults to have underlying causal monogenic disorders; the sequence of natural history and events give insights into disease pathogeneses, and optimal life style choices that last are best made during the early formative years. Some features of IR in children discussed herein are: a strong tendency to low birth weight for gestational age, adverse effects of adrenarche and therapeutic steroid therapy, predisposition to premature pubarche, acanthosis nigricans, tall stature despite pituitary GH suppression, allergic diathesis, hyperandrogenism and PCOS, dyslipidemia and fatty liver disease, and diagnosis by clinical and biochemical markers of IR including insulin regulated hepatic hormonal binding proteins such as IGFBP-1. The national preoccupation with the "metabolic syndrome" T2DM and obesity, should be appropriately directed to an improved understanding of IR in children and their management, if the looming health crisis in affected adults is to be seriously addressed. The nation is facing its' first generation of children who will be less healthy and die younger than the previous generation (Marks (2005) Presentation to the American Association of Diabetes Educators 32nd Annual Meeting and Exhibition, August 10-13, Washington, DC).

Bardet-Biedl syndrome: beyond the cilium

The Bardet-Biedl syndrome (BBS) is a significant genetic cause of chronic and end-stage renal failure in children. Despite being a relatively rare recessive condition, BBS has come to prominence during the past few years owing to revelations of primary cilia dysfunction underlying pathogenesis. The study of this multi-system disorder, which includes obesity, cognitive impairment, genito-urinary tract malformations and limb deformities, is beginning to reveal insights into several aspects of mammalian development and organogenesis. Involvement of BBS proteins in disparate pathways such as the non-canonical Wnt and Sonic Hedgehog pathways is highlighting their interplay in disease pathogenesis. Here we review the recent developments in this emerging field, with the emphasis on the renal component of the syndrome and potential future directions.

Temporal expression pattern of Bardet-Biedl syndrome genes in adipogenesis

Bardet-Biedl syndrome (BBS) is an autosomal recessive disorder associated with marked obesity. Research in rare forms of obesity has identified genes with significant roles in common obesity etiology. To date, 11 BBS genes have been cloned (BBS1-BBS11). However, the function of BBS genes in adipogenesis is unknown. Moreover, not all BBS genes have been shown to be expressed in adipose tissue. The aim of our study was to investigate the expression of BBS genes throughout adipogenesis. 3T3-F442A preadipocyte cells were harvested throughout the adipogenesis process (from day 1 to 8) at 1-day intervals. Levels of BBS genes transcripts were analyzed by quantitative real-time polymerase chain reaction (PCR). Additionally, transcript levels of BBS5-9 and BBS11 were studied in mouse (C57BL/6) adipose tissue. We have shown for the first time that BBS5-9 and BBS11 are expressed in adipose tissue. Significant variations in the transcript levels of the BBS genes were identified throughout adipogenesis. Compared to the their levels in non-differentiated preadipocytes, transcript levels of BBS1-4, 6-9 and 11 were significantly augmented through differentiation, reaching maximum values at day 3 (BBS1-4, 6-8) and 4 (BBS9 and 11) by 3.5, 4, 2.9, 3, 5, 1.9, 2, 2.9 and 2.6-fold, respectively. These findings show for the first time a unique, temporal and synchronized expression of BBS genes during adipogenesis. These findings highlight the importance of BBS genes functional studies in adipogenesis.

Molecular physiology of syndromic obesities in humans

Obesity has become an increasingly prevalent public health problem and represents the complex interaction of genetic, developmental, behavioral and environmental influences. Although rare, the study of syndromic forms of obesity provides insight into underlying molecular and physiological mechanisms by which adiposity is regulated through food intake, energy expenditure and partitioning of stored calories.

Fat chance: genetic syndromes with obesity

Although obesity shows high heritability, we are aware of only a small number of genes that affect adipose mass in humans. Genetic syndromes with obesity represent unique opportunities to gain insight into the control of energy balance. The majority of obesity syndromes can be distinguished by the presence of mental retardation. We performed a systematic search of such syndromes and reviewed the literature with a focus on distinguishing clinical features, the characteristics of their obesity, and the underlying pathogenetic mechanisms. We predict that the study of these conditions will shed light on common forms of obesity.

What have rare genetic syndromes taught us about the pathophysiology of the common forms of obesity?

Obesity is a central feature for several congenital syndromes, including Prader-Willi, Angelman, Bardet-Biedl, Cohen, Alström, and Börjeson-Forssman-Lehmann syndromes, and Albright's hereditary osteodystrophy. Although a role for the central nervous system, including the hypothalamus-pituitary axis, has been suggested for the etiology of obesity in these syndromes, the pathophysiologic pathways are as yet not well defined, and in many cases may identify currently unknown mechanisms. Nevertheless, many of the causative genes and unusual mechanisms, including parental imprinting of genes and complex patterns of inheritance, have been identified. We review the latest advances in understanding congenital syndromes in which obesity is purely genetic, drawing on comparisons to genetic studies of obesity in the human population as well as to those in experimental and agricultural animal models. An understanding of the genetic basis for these syndromes will provide a more comprehensive picture of the mechanisms that control food intake and energy balance in humans.