Lack of Postprandial Peak in Brain-Derived Neurotrophic Factor in Adults with Prader-Willi Syndrome

The Pivotal Role of Oxytocin's Mechanism of Thermoregulation in Prader-Willi Syndrome, Schaaf-Yang Syndrome, and Autism Spectrum Disorder

Oxytocin (Oxt) regulates thermogenesis, and altered thermoregulation results in Prader-Willi syndrome (PWS), Schaaf-Yang syndrome (SYS), and Autism spectrum disorder (ASD). PWS is a genetic disorder caused by the deletion of the paternal allele of 15q11-q13, the maternal uniparental disomy of chromosome 15, or defects in the imprinting center of chromosome 15. PWS is characterized by hyperphagia, obesity, low skeletal muscle tone, and autism spectrum disorder (ASD). Oxt also increases muscle tonicity and decreases proteolysis while PWS infants are hypotonic and require assisted feeding in early infancy. This evidence inspired us to merge the results of almost 20 years of studies and formulate a new hypothesis according to which the disruption of Oxt's mechanism of thermoregulation manifests in PWS, SYS, and ASD through thermosensory abnormalities and skeletal muscle tone. This review will integrate the current literature with new updates on PWS, SYS, and ASD and the recent discoveries on Oxt's regulation of thermogenesis to advance the knowledge on these diseases.

Hormonal Imbalances in Prader-Willi and Schaaf-Yang Syndromes Imply the Evolution of Specific Regulation of Hypothalamic Neuroendocrine Function in Mammals

The hypothalamus regulates fundamental aspects of physiological homeostasis and behavior, including stress response, reproduction, growth, sleep, and feeding, several of which are affected in patients with Prader-Willi (PWS) and Schaaf-Yang syndrome (SYS). PWS is caused by paternal deletion, maternal uniparental disomy, or imprinting defects that lead to loss of expression of a maternally imprinted region of chromosome 15 encompassing non-coding RNAs and five protein-coding genes; SYS patients have a mutation in one of them, MAGEL2. Throughout life, PWS and SYS patients suffer from musculoskeletal deficiencies, intellectual disabilities, and hormonal abnormalities, which lead to compulsive behaviors like hyperphagia and temper outbursts. Management of PWS and SYS is mostly symptomatic and cures for these debilitating disorders do not exist, highlighting a clear, unmet medical need. Research over several decades into the molecular and cellular roles of PWS genes has uncovered that several impinge on the neuroendocrine system. In this review, we will discuss the expression and molecular functions of PWS genes, connecting them with hormonal imbalances in patients and animal models. Besides the observed hormonal imbalances, we will describe the recent findings about how the loss of individual genes, particularly MAGEL2, affects the molecular mechanisms of hormone secretion. These results suggest that MAGEL2 evolved as a mammalian-specific regulator of hypothalamic neuroendocrine function.

Hyperphagia in Prader-Willi syndrome with obesity: From development to pharmacological treatment

Prader-Willi syndrome (PWS) is a rare genetic disorder due to lack of genes expression inherited from the paternal chromosome 15q11-q13 region usually from paternal deletions, maternal uniparental disomy 15 or imprinting defect. There are two different nutritional stages reported in an individual with PWS; first stage during infancy marked by feeding and growth difficulties and second stage where hyperphagia starts and leads to development of obesity. However, the exact mechanism of hyperphagia development, from having difficulties in feeding during early years to insatiable appetite after they grow is still unknown and is the focused in this review. The keywords used for literature search such as "Prader-Willi syndrome", "hyperphagia", "obesity", and "treatment" were used to create the search strings by using synonyms in order to retrieve the relevant records from PubMed, Scopus and Science Direct. The possible mechanism of hyperphagia can be classed into hormonal abnormalities such as increase in ghrelin and leptin from infancy to adulthood. Low level of hormones was observed in the thyroid, insulin and peptide YY at certain ages. Neuronal abnormalities contributed by Orexin A and brain structure alteration was documented at 4-30 years old. Treatment in the form of drugs such as livoletide, topiramate, and diazoxide could potentially alleviate these abnormalities and make hyperphagia less prominent in PWS. The approaches are important to regulate the hormonal changes and neuronal involvement as potentially controlling hyperphagia and obesity.

Serum alpha-melanocyte-stimulating hormone (a-MSH), brain-derived neurotrophic factor (BDNF), and agouti-related protein (AGRP) levels in children with Prader-Willi or Bardet-Biedl syndromes

BACKGROUND

Although leptin/melanocortin pathway pathologies in hypothalamus are thought to be the main cause of early-onset obesity and hyperphagia in PWS and BBS, the exact mechanism is still not known.

OBJECTIVE

To measure serum concentrations of a-MSH, BDNF and AGRP in a group of children with BBS or PWS.

METHODS

We recruited 12 subjects with PWS, 12 subjects with BBS, 28 obese controls (OC) and 26 lean controls (LC) matched for age, sex and puberty. Serum a-MSH, BDNF and AGRP levels were measured by the ELISA method.

RESULTS

The mean a-MSH level was lower in PWS than those of OC and LC (3729 ± 1319, 5211 ± 829 and 5681 ± 565 pg/ml, respectively, p < 0.001), and mean a-MSH was lower in OC than LC (p < 0.05). The mean BDNF level of PWS was higher than those of OC and LC (565 ± 122, 482 ± 102 and 391 ± 74 pg/ml, respectively, p < 0.001). On the other hand, mean a-MSH level of BBS was lower than those of OC and LC (4543 ± 658, 5211 ± 829 and 5681 ± 565 pg/ml, respectively, p < 0.001), and mean a-MSH was lower in OC than LC (p < 0.05). The mean BDNF level of BBS was higher than those of OC and LC (583 ± 115, 482 ± 102 and 391 ± 74 pg/ml, respectively, p < 0.001). Additionally, both in PWS and BBS, the mean BDNF level was higher in OC than LC (p < 0.01). Regarding AGRP level, there was no difference both in BBS and PWS compared to OC.

CONCLUSION

We found that the serum a-MSH levels of PWS and BBS groups are significantly lower compared to those of obese and lean controls. Therefore, we can speculate that the circulating a-MSH level does properly reflect its central production, and the serum a-MSH level might be a good biomarker to detect a-MSH deficiency in individuals suspected to have BBS or PWS, and also in those with POMC, PCSK1, and LEPR deficiency.

Hunger and Satiety Peptides: Is There a Pattern to Classify Patients with Prader-Willi Syndrome?

Hyperphagia is one of the main problems of patients with Prader-Willi syndrome (PWS) to cope with everyday life. The underlying mechanisms are not yet well understood. Gut-brain hormones are an interrelated network that may be at least partially involved. We aimed to study the hormonal profile of PWS patients in comparison with obese and healthy controls. Thirty adult PWS patients (15 men; age 27.5 ± 8.02 years; BMI 32.4 ± 8.14 kg/m²), 30 obese and 30 healthy controls were studied before and after eating a hypercaloric liquid diet. Plasma brain-derived neurotrophic factor (BDNF), leptin, total and active ghrelin, peptide YY (PYY), pancreatic polypeptide (PP), Glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and amylin were determined at times 0′, 30′, 60′ and 120′. Cluster analysis was used. When considering all peptides together, two clusters were established according to fasting hormonal standardized concentrations. Cluster 1 encompassed most of obese (25/30) and healthy controls (28/30). By contrast, the majority of patients with PWS were located in Cluster 2 (23/27) and presented a similar fasting profile with hyperghrelinemia, high levels of leptin, PYY, GIP and GLP-1, compared to Cluster 1; that may reflect a dysfunction of these hunger/satiety hormones. When peptide behavior over the time was considered, PP concentrations were not sustained postprandially from 60 min onwards in Cluster 2. BDNF and amylin did not help to differentiate the two clusters. Thus, cluster analysis could be a good tool to distinguish and characterize the differences in hormone responses between PWS and obese or healthy controls.

Hypothalamic neuropeptides and neurocircuitries in Prader Willi syndrome

Prader-Willi Syndrome (PWS) is a rare and incurable congenital neurodevelopmental disorder, resulting from the absence of expression of a group of genes on the paternally acquired chromosome 15q11-q13. Phenotypical characteristics of PWS include infantile hypotonia, short stature, incomplete pubertal development, hyperphagia and morbid obesity. Hypothalamic dysfunction in controlling body weight and food intake is a hallmark of PWS. Neuroimaging studies have demonstrated that PWS subjects have abnormal neurocircuitry engaged in the hedonic and physiological control of feeding behavior. This is translated into diminished production of hypothalamic effector peptides which are responsible for the coordination of energy homeostasis and satiety. So far, studies with animal models for PWS and with human post-mortem hypothalamic specimens demonstrated changes particularly in the infundibular and the paraventricular nuclei of the hypothalamus, both in orexigenic and anorexigenic neural populations. Moreover, many PWS patients have a severe endocrine dysfunction, e.g. central hypogonadism and/or growth hormone deficiency, which may contribute to the development of increased fat mass, especially if left untreated. Additionally, the role of non-neuronal cells, such as astrocytes and microglia in the hypothalamic dysregulation in PWS is yet to be determined. Notably, microglial activation is persistently present in non-genetic obesity. To what extent microglia, and other glial cells, are affected in PWS is poorly understood. The elucidation of the hypothalamic dysfunction in PWS could prove to be a key feature of rational therapeutic management in this syndrome. This review aims to examine the evidence for hypothalamic dysfunction, both at the neuropeptidergic and circuitry levels, and its correlation with the pathophysiology of PWS.

Behavioral features in Prader-Willi syndrome (PWS): consensus paper from the International PWS Clinical Trial Consortium

Prader-Willi syndrome (PWS) is a rare neurodevelopmental genetic disorder associated with a characteristic behavioral phenotype that includes severe hyperphagia and a variety of other behavioral challenges such as temper outbursts and anxiety. These behaviors have a significant and dramatic impact on the daily functioning and quality of life for the person with PWS and their families. To date, effective therapies addressing these behavioral challenges have proven elusive, but several potential treatments are on the horizon. However, a limiting factor for treatment studies in PWS is the lack of consensus in the field regarding how to best define and measure the complex and interrelated behavioral features of this syndrome. The International PWS Clinical Trials Consortium (PWS-CTC, www.pwsctc.org) includes expert PWS scientists, clinicians, and patient advocacy organization representatives focused on facilitating clinical trials in this rare disease. To address the above gap in the field, members of the PWS-CTC “Behavior Outcomes Working Group” sought to develop a unified understanding of the key behavioral features in PWS and build a consensus regarding their definition and description. The primary focus of this paper is to present consensus definitions and descriptions of key phenotypic PWS behaviors including hyperphagia, temper outbursts, anxiety, obsessive–compulsive behaviors, rigidity, and social cognition deficits. Patient vignettes are provided to illustrate the interrelatedness and impact of these behaviors. We also review some available assessment tools as well as new instruments in development which may be useful in measuring these behavioral features in PWS.

Appetite- and weight-inducing and -inhibiting neuroendocrine factors in Prader-Willi syndrome, Bardet-Biedl syndrome and craniopharyngioma versus anorexia nervosa

Obesity is reaching an epidemic state and has a major impact on health and economy. In most cases, obesity is caused by lifestyle factors. However, the risk of becoming obese differs highly between people. Individual's differences in lifestyle, genetic, and neuroendocrine factors play a role in satiety, hunger and regulation of body weight. In a small percentage of children and adults with obesity, an underlying hormonal or genetic cause can be found. The aim of this review is to present and compare data on the extreme ends of the obesity and undernutrition spectrum in patients with Prader-Willi syndrome (PWS), Bardet-Biedl syndrome (BBS), acquired hypothalamic obesity in craniopharyngioma patients, and anorexia nervosa. This may give more insight into the role of neuroendocrine factors and might give direction for future research in conditions of severe obesity and underweight.

Endocrine disorders in Prader-Willi syndrome: a model to understand and treat hypothalamic dysfunction

Prader-Willi syndrome is a rare genetic neurodevelopmental disorder resulting from the loss of expression of maternally imprinted genes located in the paternal chromosomal region, 15q11-13. Impaired hypothalamic development and function is the cause of most of the phenotypes comprising the developmental trajectory of Prader-Willi syndrome: from anorexia at birth to excessive weight gain preceding hyperphagia, and early severe obesity with hormonal deficiencies, behavioural problems, and dysautonomia. Growth hormone deficiency, hypogonadism, hypothyroidism, premature adrenarche, corticotropin deficiency, precocious puberty, and glucose metabolism disorders are the main endocrine dysfunctions observed. Additionally, as a result of hypothalamic dysfunction, oxytocin and ghrelin systems are impaired in most patients. Standard pituitary and gonadal hormone replacement therapies are required. In this Review, we discuss Prader-Willi syndrome as a model of hypothalamic dysfunction, and provide a comprehensive description of the accumulated knowledge on genetics, pathophysiology, and treatment approaches of this rare disorder.

Alpha-Melanocyte-Stimulating Hormone is Elevated in Hypothalamic Obesity Associated with Childhood Craniopharyngioma

OBJECTIVE

The purpose of this study was to investigate the peripheral concentrations of leptin and neuropeptides taking part in the melanocortin pathway in hypothalamic obesity (HO) associated with craniopharyngioma (CP) and to find a peripheral marker for diagnosis.

METHODS

Thirty-one patients (52% girls; median age 16 years) with CP were enrolled in the study group. They were grouped as CP with obesity (CP^obesity , n = 17) and CP without obesity (CP^nonobesity , n = 14). Two control groups without CP consisted of 27 children with obesity (OC) (55% girls; median age 13.8 years) and 25 children without obesity (normal control [NC]) (72% girls; median age 14.5 years). Obesity was defined as BMI percentile ≥ 95%. Fasting serum concentrations of leptin, brain-derived neurotrophic factor (BDNF), and alpha-melanocyte-stimulating hormone (α-MSH) were measured in the groups.

RESULTS

Leptin and BDNF concentrations were correlated with BMI SD score (SDS) in controls (OC + NC) and CP. However, there was no correlation between α-MSH and BMI-SDS in CP or control groups. After adjusting for age, sex, and BMI-SDS, α-MSH was found to be significantly higher in CP^obesity than in other groups, whereas leptin and BDNF were comparable among the four groups.

CONCLUSIONS

Serum BDNF, just like leptin, increased with BMI, regardless of hypothalamic damage. On the contrary, α-MSH concentration was significantly high in HO, designating a potential biomarker for HO in CP.

What can we learn from PWS and SNORD116 genes about the pathophysiology of addictive disorders?

Addictive disorders have been much investigated and many studies have underlined the role of environmental factors such as social interaction in the vulnerability to and maintenance of addictive behaviors. Research on addiction pathophysiology now suggests that certain behavioral disorders are addictive, one example being food addiction. Yet, despite the growing body of knowledge on addiction, it is still unknown why only some of the individuals exposed to a drug become addicted to it. This observation has prompted the consideration of genetic heritage, neurodevelopmental trajectories, and gene-environment interactions in addiction vulnerability. Prader-Willi syndrome (PWS) is a rare neurodevelopmental disorder in which children become addicted to food and show early social impairment. PWS is caused by the deficiency of imprinted genes located on the 15q11-q13 chromosome. Among them, the SNORD116 gene was identified as the minimal gene responsible for the PWS phenotype. Several studies have also indicated the role of the Snord116 gene in animal and cellular models to explain PWS pathophysiology and phenotype (including social impairment and food addiction). We thus present here the evidence suggesting the potential involvement of the SNORD116 gene in addictive disorders.

Transcriptomics of the Prader-Willi syndrome hypothalamus

Prader-Willi syndrome (PWS) is a complex neurodevelopmental disorder, arising from a loss of paternity expressed genetic material on the imprinted chromosome locus 15q11-q13. Despite increasing clarity on the underlying genetic defects, the molecular basis of the condition remains poorly understood. Hypothalamic dysfunction is widely recognized as the basis of the core symptoms of PWS, which include a deficiency in growth hormone and reproductive hormones, circadian rhythm abnormalities, and a lack of satiety, leading to an extreme obesity, among others. Genome-wide gene expression analysis (transcriptomics) offers an unbiased interrogation of complex disease pathogenesis and a potential window into the dysregulated pathways involved in disease. In this chapter, we review the findings from recent work investigating the PWS hypothalamic transcriptome, discuss the significance of the findings in relation to the clinical presentation and molecular underpinnings of PWS, and highlight future research directions.

Influence of the BDNF Val66Met polymorphism on weight loss after bariatric surgery: a 24-month follow-up

BACKGROUND

Bariatric surgery is currently the most effective long-term treatment for severe obesity. However, interindividual variation in surgery outcome has been observed, and research suggests a moderating effect of several factors including baseline co-morbidities (e.g., type 2 diabetes [T2D] and genetic factors). No data are currently available on the interaction between T2D and variants in brain derived neurotrophic factor (BDNF) and its effect on weight loss after surgery.

OBJECTIVES

To examine the role of the BDNF Val66Met polymorphism (rs6265) and the influence of T2D and their interaction on weight loss after bariatric surgery in a cohort of patients with severe obesity.

SETTING

University hospital in Spain.

METHODS

The present study evaluated a cohort of 158 patients with obesity submitted to bariatric surgery (Roux-en-Y gastric bypass or sleeve gastrectomy) followed up for 24 months (loss to follow-up: 0%). During the postoperative period, percentage of excess body mass index loss (%EBMIL), percentage of excess weight loss (%EWL), and total weight loss (%TWL) were evaluated.

RESULTS

Longitudinal analyses showed a suggestive effect of BDNF genotype on the %EWL (P = .056) and indicated that individuals carrying the methionine (Met) allele may experience a better outcome after bariatric surgery than those with the valine/valine (Val/Val) genotype. We found a negative effect of a T2D diagnosis at baseline on %EBMIL (P = .004). Additionally, we found an interaction between BDNF genotype and T2D on %EWL and %EBMIL (P = .027 and P = .0004, respectively), whereby individuals with the Met allele without T2D displayed a greater %EWL and greater %EBMIL at 12 months and 24 months than their counterparts with T2D or patients with the Val/Val genotype with or without T2D.

CONCLUSION

Our data showed an association between the Met variant and greater weight loss after bariatric surgery in patients without T2D. The presence of T2D seems to counteract this positive effect.

Postprandial leptin and adiponectin in response to sugar and fat in obese and normal weight individuals

PURPOSE

Adipokines produced by white adipose tissue are central in the development of lifestyle diseases. Individuals in industrialized countries spend a substantial part of life in the non-fasting, postprandial state, which is associated with increased oxidation and inflammation. The aim was to study postprandial adiponectin and leptin levels after an oral fat tolerance test (OFTT) and an oral glucose tolerance test (OGTT) in obese (OB) and healthy, normal weight individuals (NW).

METHODS

Fifty adults with obesity (BMI ≥ 30) and 17 healthy, NW were included. Postprandial triglyceride (TG), adiponectin, and leptin levels were measured every second hour during an 8 h OFTT, and every half hour during a 2 h OGTT.

RESULTS

Compared with the basal level, postprandial levels of adiponectin following OFTT showed a slight initial peak, followed by a significant decrease at 8 h, in the NW. In the OB these changes were abolished. Postprandial levels of leptin decreased significantly from basal levels in the OFTT, in the NW, whereas in the OB, leptin was unchanged except for a slight increase from 2 to 8 h. During the OGTT both adiponectin and leptin levels remained unchanged in the NW, but decreased significantly in the OB. In addition, the OB had delayed TG clearance at 6 h.

CONCLUSIONS

A fatty meal gives postprandial changes in the secretion of adiponectin and leptin in NW, but not in OB. Our observations indicate that a potential postprandial regulatory role of adiponectin and leptin is impaired in OB, and of importance in a more comprehensive understanding of the delayed postprandial TG clearance in obese individuals.

Psychopathological disorders in Prader-Willi syndrome

Prader-Willi syndrome is a genetic disorder caused by chromosomal changes in segment 15q11-q13 including cognitive, mental, and behavioral symptoms, as well as a specific physical phenotype. Both the most common psychopathological changes (intellectual disability, obsessions, impulsivity, autism spectrum disorders, self-injuries) and the main psychiatric comorbidities (affective disorders, psychosis, obsessive-compulsive disorder, autism spectrum disorder) are characterized by a great heterogeneity, which warrants the need for better identification of their frequency and clinical signs. In addition to its effects on body compositionand hypotony, growth hormone has been shown to be useful for regulating patient behavior, and psychoactive drugs are also an option. Other alternatives have shown promising results in experimental trials. Adequate understanding of the psychopathology associated to Prader-Willi syndrome would allow for improving clinical approach, symptom identification, detection of comorbidities, and administration of more effective treatments, leading to better clinical outcomes.

Obesity management in Prader-Willi syndrome: current perspectives

Prader-Willi syndrome (PWS) is a complex multisystem disorder due to the absent expression of the paternally active genes in the PWS critical region on chromosome 15 (15q11.2-q13). The syndrome is considered the most common genetic cause of obesity, occurring in 1:10,000-1:30,000 live births. Its main characteristics include neonatal hypotonia, poor feeding, and lack of appetite in infancy, followed by weight gain, lack of satiety, and uncontrolled appetite, frequently after the age of 2-3 years. The clinical picture includes short stature, multiple endocrine abnormalities (hypogonadism, growth hormone/insulin-like growth factor-I axis dysfunction, hypothyroidism, central adrenal insufficiency), dysmorphic features, scoliosis, osteoporosis, mental retardation, and behavioral and psychiatric problems. Subjects with PWS will become severely obese unless their food intake is strictly controlled. Constant and obsessive food seeking behavior can make life very difficult for both the family and caretakers. Prevention of obesity is mandatory in these patients from the first years of life, because once obesity develops it is difficult to maintain the control of food intake. In fact, PWS subjects die prematurely from complications conventionally related to obesity, including diabetes mellitus, metabolic syndrome, sleep apnea, respiratory insufficiency, and cardiovascular disease. The mechanisms underlying hyperphagia in PWS are not completely known, and to date no drugs have proven their efficacy in controlling appetite. Consequently, dietary restriction, physical activity, and behavior management are fundamental in the prevention and management of obesity in PWS. In spite of all available therapeutic tools, however, successful weight loss and maintenance are hardly accomplished. In this context, clinical trials with new drugs have been initiated in order to find new possibilities of a therapy for obesity in these patients. The preliminary results of these studies seem to be encouraging. On the other hand, until well-proven medical treatments are available, bariatric surgery can be taken into consideration, especially in PWS patients with life-threatening comorbidities.