Plasma peptide YY and ghrelin levels in infants and children with Prader-Willi syndrome

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.

Prader-Willi syndrome: an update on obesity and endocrine problems

Prader-Willi syndrome (PWS) is a rare complex genetic disorder that results from a lack of expression of the paternally inherited chromosome 15q11-q13. PWS is characterized by hypotonia and feeding difficulty in early infancy and development of morbid obesity aggravated by uncontrolled hyperphagia after childhood and adolescent. Dysmorphic facial features, delayed motor and language development, various degrees of cognitive impairment, and behavioral problems are common in PWS. Without early, intensive nutritional therapy along with behavioral modification, PWS patients develop severe obesity associated with type 2 diabetes, obstructive sleep apnea, right-side heart failure, and other obesity-related metabolic complications. Hypothalamic dysfunction in PWS can lead to several endocrine disorders, including short stature with growth hormone deficiency, hypothyroidism, central adrenal insufficiency, and hypogonadism. In this review, we discuss the natural history of PWS and the mechanisms of hyperphagia and obesity. We also provide an update on obesity treatments and recommendations for screening and monitoring of various endocrine problems that can occur in PWS.

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.

Obesity in Prader-Willi syndrome: physiopathological mechanisms, nutritional and pharmacological approaches

Prader-Willi syndrome (PWS) is a genetic disorder caused by the lack of expression of genes on the paternally inherited chromosome 15q11.2-q13 region. The three main genetic subtypes are represented by paternal 15q11-q13 deletion, maternal uniparental disomy 15, and imprinting defect. Clinical picture of PWS changes across life stages. The main clinical characteristics are represented by short stature, developmental delay, cognitive disability and behavioral diseases. Hypotonia and poor suck resulting in failure to thrive are typical of infancy. As the subjects with PWS age, clinical manifestations such as hyperphagia, temperature instability, high pain threshold, hypersomnia and multiple endocrine abnormalities including growth hormone and thyroid-stimulating hormone deficiencies, hypogonadism and central adrenal insufficiency due to hypothalamic dysfunction occur. Obesity and its complications are the most common causes of morbidity and mortality in PWS. Several mechanisms for the aetiology of obesity in PWS have been hypothesized, which include aberration in hypothalamic pathways of satiety control resulting in hyperphagia, disruption in hormones regulating appetite and satiety and reduced energy expenditure. However, despite the advancement in the research field of the genetic basis of obesity in PWS, there are contradictory data on the management. Although it is mandatory to adopt obesity strategy prevention from infancy, there is promising evidence regarding the management of obesity in adulthood with current obesity drugs along with lifestyle interventions, although the data are limited. Therefore, the current manuscript provides a review of the current evidence on obesity and PWS, covering physiopathological aspects, obesity-related complications and conservative management.

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.

Prader-Willi syndrome: A model for understanding the ghrelin system

Subsequent to the discovery of ghrelin as the endogenous ligand of growth hormone secretagogue receptor 1a, this unique gut peptide has been found to exert numerous physiological effects, such as appetite stimulation and lipid accumulation via the central regulating mechanisms in the hypothalamus, stimulation of gastric motility, regulation of glucose metabolism and brown fat thermogenesis, and modulation of stress, anxiety, taste sensation, reward-seeking behaviour and the sleep/wake cycle. Prader-Willi syndrome (PWS) has been described as a unique pathological state characterised by severe obesity and high circulating levels of ghrelin. It was hypothesised that hyperghrelinaemia would explain at least a part of the feeding behaviour and body composition of PWS patients, who are characterised by hyperphagia, an obsession with food and food-seeking, and increased adiposity. Initially, the link between hyperghrelinaemia and growth hormone deficiency, which is observed in 90% of the children with PWS, was not fully understood. Over the years, however, the increasing knowledge on ghrelin, PWS features and the natural history of the disease has led to a more comprehensive description of the abnormal ghrelin system and its role in the pathophysiology of this rare and complex neurodevelopmental genetic disease. In the present study, we (a) present the current view of PWS; (b) explain its natural history, including recent data on the ghrelin system in PWS patients; and (c) discuss the therapeutic approach of modulating the ghrelin system in these patients and the first promising results.

Mechanisms of obesity in Prader-Willi syndrome

Obesity is the most common cause of metabolic complications and poor quality of life in Prader-Willi syndrome (PWS). Hyperphagia and obesity develop after an initial phase of poor feeding and failure to thrive. Several mechanisms for the aetiology of obesity in PWS are proposed, which include disruption in hypothalamic pathways of satiety control resulting in hyperphagia, aberration in hormones regulating food intake, reduced energy expenditure because of hypotonia and altered behaviour with features of autism spectrum disorder. Profound muscular hypotonia prevents PWS patients from becoming physically active, causing reduced muscle movements and hence reduced energy expenditure. In a quest for the aetiology of obesity, recent evidence has focused on several appetite-regulating hormones, growth hormone, thyroid hormones and plasma adipocytokines. However, despite advancement in understanding of the genetic basis of PWS, there are contradictory data on the role of satiety hormones in hyperphagia and data regarding dietary intake are limited. Mechanistic studies on the aetiology of obesity and its relationship with disease pathogenesis in PWS are required. . In this review, we focused on the available evidence regarding mechanisms of obesity and potential new areas that could be explored to help unravel obesity pathogenesis in PWS.

Deficiency in prohormone convertase PC1 impairs prohormone processing in Prader-Willi syndrome

Prader-Willi syndrome (PWS) is caused by a loss of paternally expressed genes in an imprinted region of chromosome 15q. Among the canonical PWS phenotypes are hyperphagic obesity, central hypogonadism, and low growth hormone (GH). Rare microdeletions in PWS patients define a 91-kb minimum critical deletion region encompassing 3 genes, including the noncoding RNA gene SNORD116. Here, we found that protein and transcript levels of nescient helix loop helix 2 (NHLH2) and the prohormone convertase PC1 (encoded by PCSK1) were reduced in PWS patient induced pluripotent stem cell-derived (iPSC-derived) neurons. Moreover, Nhlh2 and Pcsk1 expression were reduced in hypothalami of fasted Snord116 paternal knockout (Snord116p-/m+) mice. Hypothalamic Agrp and Npy remained elevated following refeeding in association with relative hyperphagia in Snord116p-/m+ mice. Nhlh2-deficient mice display growth deficiencies as adolescents and hypogonadism, hyperphagia, and obesity as adults. Nhlh2 has also been shown to promote Pcsk1 expression. Humans and mice deficient in PC1 display hyperphagic obesity, hypogonadism, decreased GH, and hypoinsulinemic diabetes due to impaired prohormone processing. Here, we found that Snord116p-/m+ mice displayed in vivo functional defects in prohormone processing of proinsulin, pro-GH-releasing hormone, and proghrelin in association with reductions in islet, hypothalamic, and stomach PC1 content. Our findings suggest that the major neuroendocrine features of PWS are due to PC1 deficiency.

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

Context

Prader-Willi syndrome (PWS) is characterized by severe hyperphagia. Brain-derived neurotrophic factor (BDNF) and leptin are reciprocally involved in energy homeostasis.

Objectives

To analyze the role of BDNF and leptin in satiety in genetic subtypes of PWS.

Design

Experimental study.

Setting

University hospital.

Subjects

90 adults: 30 PWS patients; 30 age-sex-BMI-matched obese controls; and 30 age-sex-matched lean controls.

Interventions

Subjects ingested a liquid meal after fasting ≥10 hours.

Main Outcome Measures

Leptin and BDNF levels in plasma extracted before ingestion and 30’, 60’, and 120’ after ingestion. Hunger, measured on a 100-point visual analogue scale before ingestion and 60’ and 120’ after ingestion.

Results

Fasting BDNF levels were lower in PWS than in controls (p = 0.05). Postprandially, PWS patients showed only a truncated early peak in BDNF, and their BDNF levels at 60' and 120' were lower compared with lean controls (p<0.05). Leptin was higher in PWS patients than in controls at all time points (p<0.001). PWS patients were hungrier than controls before and after eating. The probability of being hungry was associated with baseline BDNF levels: every 50-unit increment in BDNF decreased the odds of being hungry by 22% (OR: 0.78, 95%CI: 0.65–0.94). In uniparental disomy, the odds of being hungry decreased by 66% (OR: 0.34, 90%CI: 0.13–0.9). Postprandial leptin patterns did no differ among genetic subtypes.

Conclusions

Low baseline BDNF levels and lack of postprandial peak may contribute to persistent hunger after meals. Uniparental disomy is the genetic subtype of PWS least affected by these factors.

Single Gene and Syndromic Causes of Obesity: Illustrative Examples

Obesity is a significant health problem in westernized societies, particularly in the United States where it has reached epidemic proportions in both adults and children. The prevalence of childhood obesity has doubled in the past 30 years. The causation is complex with multiple sources, including an obesity promoting environment with plentiful highly dense food sources and overall decreased physical activity noted for much of the general population, but genetic factors clearly play a role. Advances in genetic technology using candidate gene approaches, genome-wide association studies, structural and expression microarrays, and next generation sequencing have led to the discovery of hundreds of genes recognized as contributing to obesity. Polygenic and monogenic causes of obesity are now recognized including dozens of examples of syndromic obesity with Prader-Willi syndrome, as a classical example and recognized as the most common known cause of life-threatening obesity. Genetic factors playing a role in the causation of obesity will be discussed along with the growing evidence of single genes and the continuum between monogenic and polygenic obesity. The clinical and genetic aspects of four classical but rare obesity-related syndromes (ie, Prader-Willi, Alström, fragile X, and Albright hereditary osteodystrophy) will be described and illustrated in this review of single gene and syndromic causes of obesity.

Metabolic profiling in Prader-Willi syndrome and nonsyndromic obesity: sex differences and the role of growth hormone

OBJECTIVES

To identify metabolic factors controlling appetite and insulin sensitivity in PWS and assess effects of GH treatment.

METHODS

We compared amino acids, fatty acids and acylcarnitines in GH-treated and untreated PWS children and obese and lean controls to identify biomarkers associated with ghrelin, peptide YY and markers of insulin sensitivity (adiponectin and HOMA-IR).

RESULTS

Compared with obese controls (OC), children with PWS had fasting hyperghrelinaemia, hyperadiponectinaemia, hypoinsulinaemia and increased ghrelin/PYY. Hyperghrelinaemia, hyperadiponectinaemia and hypoinsulinaemia were more striking in PWS females than males, and decreases in BCAA were detected only in PWS females. GH-treated PWS subjects had lower leptin and higher IGF-1 and adiponectin than untreated subjects; fasting ghrelin, PYY and insulin levels were comparable. Ghrelin correlated inversely with BCAA in PWS but not OC. Adiponectin correlated negatively with BMIz and HOMA-IR in PWS; in contrast, adiponectin correlated more strongly with BCAA than BMIz or HOMA-IR in OC.

CONCLUSIONS

BCAA levels were lower in PWS females than OC females and correlated inversely with ghrelin. Low BCAA in PWS females may promote hyperghrelinaemia and hyperphagia, while hyperadiponectinaemia may maintain insulin sensitivity despite excess weight gain. GH treatment may reduce leptin and increase adiponectin, but does not affect fasting ghrelin or PYY.

Macronutrient Regulation of Ghrelin and Peptide YY in Pediatric Obesity and Prader-Willi Syndrome

BACKGROUND

The roles of macronutrients and GH in the regulation of food intake in pediatric obesity and Prader-Willi Syndrome (PWS) are poorly understood.

OBJECTIVE

We compared effects of high-carbohydrate (HC) and high-fat (HF) meals and GH therapy on ghrelin, insulin, peptide YY (PYY), and insulin sensitivity in children with PWS and body mass index (BMI) -matched obese controls (OCs).

METHODS

In a randomized, crossover study, 14 PWS (median, 11.35 y; BMI z score [BMI-z], 2.15) and 14 OCs (median, 11.97 y; BMI-z, 2.35) received isocaloric breakfast meals (HC or HF) on separate days. Blood samples were drawn at baseline and every 30 minutes for 4 hours. Mixed linear models were adjusted for age, sex, and BMI-z.

RESULTS

Relative to OCs, children with PWS had lower fasting insulin and higher fasting ghrelin and ghrelin/PYY. Ghrelin levels were higher in PWS across all postprandial time points (P < .0001). Carbohydrate was more potent than fat in suppressing ghrelin levels in PWS (P = .028); HC and HF were equipotent in OCs but less potent than in PWS (P = .011). The increase in PYY following HF was attenuated in PWS (P = .037); thus, postprandial ghrelin/PYY remained higher throughout. A lesser increase in insulin and lesser decrease in ghrelin were observed in GH-treated PWS patients than in untreated patients; PYY responses were comparable.

CONCLUSION

Children with PWS have fasting and postprandial hyperghrelinemia and an attenuated PYY response to fat, yielding a high ghrelin/PYY ratio. GH therapy in PWS is associated with increased insulin sensitivity and lesser postprandial suppression of ghrelin. The ratio Ghrelin/PYY may be a novel marker of orexigenic drive.

Hyperghrelinemia in Prader-Willi syndrome begins in early infancy long before the onset of hyperphagia

Circulating total ghrelin levels are elevated in older children and adults with Prader-Willi syndrome (PWS). However, the presence or absence of hyperghrelinemia in young children with PWS remains controversial. We hypothesized that a more robust way to analyze appetite-regulating hormones in PWS would be by nutritional phases rather than age alone. Our objectives were to compare total serum ghrelin levels in children with PWS by nutritional phase as well as to compare total ghrelin levels in PWS (5 weeks to 21 years of age) to normal weight controls and individuals with early-onset morbid obesity (EMO) without PWS. Fasting serum total ghrelin levels were measured in 60 subjects with PWS, 39 subjects with EMO of unknown etiology, and in 95 normal non-obese sibling controls of PWS or EMO subjects (SibC) in this 12 year longitudinal study. Within PWS, total ghrelin levels were significantly (P < 0.001) higher in earlier nutritional phases: phase 1a (7,906  ±  5,887); 1b (5,057 ± 2,624); 2a (2,905 ± 1,521); 2b (2,615 ± 1,370) and 3 (2,423 ± 1,350). Young infants with PWS also had significantly (P = 0.009) higher total ghrelin levels than did the sibling controls. Nutritional phase is an important independent prognostic factor of total ghrelin levels in individuals with PWS. Circulating ghrelin levels are elevated in young children with PWS long before the onset of hyperphagia, especially during the early phase of poor appetite and feeding. Therefore, it seems unlikely that high ghrelin levels are directly responsible for the switch to the hyperphagic nutritional phases in PWS.

Unexpectedly increased anorexigenic postprandial responses of PYY and GLP-1 to fast ice cream consumption in adult patients with Prader-Willi syndrome

OBJECTIVE

The effect of eating rate on the release of anorexigenic gut peptides in Prader-Willi syndrome (PWS), a neurogenetic disorder clinically characterized by hyperphagia and excessive obesity, has not been investigated so far.

DESIGN AND PATIENTS

Postprandial PYY and GLP-1 levels to fast (5 min) and slow (30 min) ice cream consumption were measured in PWS adult patients and age-matched patients with simple obesity and normal-weighted subjects. Visual analog scales (VASs) were used to evaluate the subjective feelings of hunger and satiety.

RESULTS

Fast ice cream consumption stimulated GLP-1 release in normal subjects, a greater increase being observed with slow feeding. Fast or slow feeding did not change circulating levels of GLP-1 in obese patients, while, unexpectedly, fast feeding (but not slow feeding) stimulated GLP-1 release in PWS patients. Plasma PYY concentrations increased in all groups, irrespective of the eating rate. Slow feeding was more effective in stimulating PYY release in normal subjects, while fast feeding was more effective in PWS patients. Slow feeding evoked a lower hunger and higher satiety compared with fast feeding in normal subjects, this finding being not evident in obese patients. Unexpectedly, fast feeding evoked a lower hunger and higher satiety in PWS patients in comparison with slow feeding.

CONCLUSIONS

Fast feeding leads to higher concentrations of anorexigenic gut peptides and favours satiety in PWS adult patients, this pattern being not evident in age-matched patients with simple obesity, thus suggesting the existence of a different pathophysiological substrate in these two clinical conditions.

Postprandial cardiac autonomic function in Prader-Willi syndrome

CONTEXT

Individuals with Prader-Willi syndrome (PWS) have a high cardiovascular risk, the mechanism of which is unclear. There may be dysfunction in the autonomic nervous system (ANS) in PWS.

OBJECTIVE

To measure, as indicators of cardiac autonomic function, postprandial heart rate variability (HRV) and arterial stiffness in adults with PWS.

METHODS

Ten adults with PWS were compared with 11 matched healthy obese subjects and 9 healthy lean subjects. Electrocardiographic traces and arterial stiffness were recorded over a period of 10 minutes at -60, 0, 30, 60, 120 and 240 minutes after consumption of a standardized 600-kCal breakfast. Frequency domain analysis was performed using fast Fourier transform to estimate power spectral density in the full spectrum and in low-frequency (LF 0·04-0·15 Hz) and high-frequency (HF 0·15-0·40 Hz) bands.

RESULTS

ANCOVA revealed a reduced LF HRV meal response in adults with PWS compared with obese controls, with no differences in HF HRV, LF/HF ratio, heart rate, total power or arterial stiffness meal responses.

CONCLUSIONS

This study assessed cardiac autonomic function in adults with PWS compared with matched obese and lean subjects in response to a meal. Results suggest impaired postprandial ANS responsiveness in PWS, which could contribute to both the known increased cardiovascular risk and obesity.

Role of ghrelin in the pathophysiology of eating disorders: implications for pharmacotherapy

Ghrelin is the only known circulating orexigenic hormone. It increases food intake by interacting with hypothalamic and brainstem circuits involved in energy balance, as well as reward-related brain areas. A heightened gut-brain ghrelin axis is an emerging feature of certain eating disorders such as anorexia nervosa and Prader-Willi syndrome. In common obesity, ghrelin levels are lowered, whereas post-meal ghrelin levels remain higher than in lean individuals. Agents that interfere with ghrelin signalling have therapeutic potential for eating disorders, including obesity. However, most of these drugs are only in the preclinical phase of development. Data obtained so far suggest that ghrelin agonists may have potential in the treatment of anorexia nervosa, while ghrelin antagonists seem promising for other eating disorders such as obesity and Prader-Willi syndrome. However, large clinical trials are needed to evaluate the efficacy and safety of these drugs.

In adults with Prader-Willi syndrome, elevated ghrelin levels are more consistent with hyperphagia than high PYY and GLP-1 levels

OBJECTIVE

Prader-Willi syndrome (PWS) is a leading genetic cause of obesity, characterized by hyperphagia, endocrine and developmental disorders. It is suggested that the intense hyperphagia could stem, in part, from impaired gut hormone signaling. Previous studies produced conflicting results, being confounded by differences in body composition between PWS and control subjects.

DESIGN

Fasting and postprandial gut hormone responses were investigated in a cross-sectional cohort study including 10 adult PWS, 12 obese subjects matched for percentage body fat and central abdominal fat, and 10 healthy normal weight subjects.

METHODS

PYY[total], PYY[3-36], GLP-1[active] and ghrelin[total] were measured by ELISA or radioimmunoassay. Body composition was assessed by dual energy X-ray absorptiometry. Visual analog scales were used to assess hunger and satiety.

RESULTS

In contrast to lean subjects (p<0.05), PWS and obese subjects were similarly insulin resistant and had similar insulin levels. Ghrelin[total] levels were significantly higher in PWS compared to obese subjects before and during the meal (p<0.05). PYY[3-36] meal responses were higher in PWS than in lean subjects (p=0.01), but not significantly different to obese (p=0.08), with an additional non-significant trend in PYY[total] levels. There were no significant differences in self-reported satiety between groups, however PWS subjects reported more hunger throughout (p=0.003), and exhibited a markedly reduced meal-induced suppression of hunger (p=0.01) compared to lean or obese subjects.

CONCLUSIONS

Compared to adiposity-matched control subjects, hyperphagia in PWS is not related to a lower postprandial GLP-1 or PYY response. Elevated ghrelin levels in PWS are consistent with increased hunger and are unrelated to insulin levels.

Nutritional phases in Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a complex neurobehavioral condition which has been classically described as having two nutritional stages: poor feeding, frequently with failure to thrive (FTT) in infancy (Stage 1), followed by hyperphagia leading to obesity in later childhood (Stage 2). We have longitudinally followed the feeding behaviors of individuals with PWS and found a much more gradual and complex progression of the nutritional phases than the traditional two stages described in the literature. Therefore, this study characterizes the growth, metabolic, and laboratory changes associated with the various nutritional phases of PWS in a large cohort of subjects. We have identified a total of seven different nutritional phases, with five main phases and sub-phases in phases 1 and 2. Phase 0 occurs in utero, with decreased fetal movements and growth restriction compared to unaffected siblings. In phase 1 the infant is hypotonic and not obese, with sub-phase 1a characterized by difficulty feeding with or without FTT (ages birth-15 months; median age at completion: 9 months). This phase is followed by sub-phase 1b when the infant grows steadily along a growth curve and weight is increasing at a normal rate (median age of onset: 9 months; age quartiles 5-15 months). Phase 2 is associated with weight gain-in sub-phase 2a the weight increases without a significant change in appetite or caloric intake (median age of onset 2.08 years; age quartiles 20-31 months;), while in sub-phase 2b the weight gain is associated with a concomitant increased interest in food (median age of onset: 4.5 years; quartiles 3-5.25 years). Phase 3 is characterized by hyperphagia, typically accompanied by food-seeking and lack of satiety (median age of onset: 8 years; quartiles 5-13 years). Some adults progress to phase 4 which is when an individual who was previously in phase 3 no longer has an insatiable appetite and is able to feel full. Therefore, the progression of the nutritional phases in PWS is much more complex than previously recognized. Awareness of the various phases will aid researchers in unraveling the pathophysiology of each phase and provide a foundation for developing rational therapies. Counseling parents of newly diagnosed infants with PWS as to what to expect with regard to these nutritional phases may help prevent or slow the early-onset of obesity in this syndrome.

Psychiatric adverse effects of rimonobant in adults with Prader Willi syndrome

BACKGROUND

Prader Willi syndrome (PWS) without strict environmental modifications can lead to obesity associated with significant morbidity and mortality. In addition to increased appetite, these individuals have decreased energy expenditure with lower insulin like growth factor 1 (IGF1), which contributes to adiposity. No effective treatment is available for this condition. Endocannabinoid receptor CB1 antagonist, rimonobant, has been effective for treatment of obesity in adult subjects. Rimonabant promotes weight loss by multiple proposed mechanisms, including decreased appetite and lipogenesis, and increased energy expenditure. Therefore, we conducted this pilot study to evaluate the effect of rimonabant on body weight and composition of adults with PWS.

METHOD

This was a double blind placebo controlled study. Body weight, total fat mass, fasting ghrelin, leptin, IGF1 and insulin like growth factor binding protein (IGFBP-3) were collected at baseline, and after 90 and 180 days of treatment with placebo or 20 mg of rimonabant.

RESULTS

Due to psychiatric adverse effects, 50% of subjects in the rimonabant group withdrew, and the study was terminated early (N=10) for safety concerns. There was a trend for weight loss, lower fat mass and higher IGF1 level at the end of study in this group. Leptin followed the fat mass and decreased with rimonabant treatment.

CONCLUSION

Rimonabant administration may be efficacious for weight loss in adults with PWS; unfortunately it is associated with an unacceptably high risk of psychiatric side effects. Future CB1 antagonists will need a better psychiatric profile before considered in the treatment of obesity in this genetic condition.

Imprinted genes and neuroendocrine function

Imprinted genes are monoallelically expressed in a parent-of-origin dependent manner. Whilst the full functional repertoire of these genes remains obscure, they are generally highly expressed in the brain and are often involved in fundamental neural processes. Besides influencing brain neurochemistry, imprinted genes are important in the development and function of the hypothalamus and pituitary gland, key sites of neuroendocrine regulation. Moreover, imprinted genes may directly modulate hormone-dependent signalling cascades, both in the brain and elsewhere. Much of our knowledge about imprinted gene function has come from studying knockout mice and human disorders of imprinting. One such disorder is Prader-Willi syndrome, a neuroendocrine disorder characterised by hypothalamic abnormalities and aberrant feeding behaviour. Through examining the role of imprinted genes in neuroendocrine function, it may be possible to shed light on the neurobiological basis of feeding and aspects of social behaviour and underlying cognition, and to provide insights into disorders where these functions go awry.

Altered distribution of adiponectin isoforms in children with Prader-Willi syndrome (PWS): association with insulin sensitivity and circulating satiety peptide hormones

OBJECTIVE

Prader-Willi syndrome (PWS) is a genetic syndrome characterized by relative hypoinsulinaemia and normal or increased insulin sensitivity despite profound obesity. We hypothesized that this increased insulin sensitivity is mediated by increased levels of total and high molecular weight adiponectin and associated with changes in levels of satiety hormones.

DESIGN, PATIENTS AND MEASUREMENTS

We measured total adiponectin and its isoforms [high molecular weight (HMW), middle molecular weight (MMW) and low molecular weight (LMW) adiponectin] and satiety hormones in 14 children with PWS [median age 11.35 years, body mass index (BMI) Z-score 2.15] and 14 BMI-matched controls (median age 11.97 years, BMI Z-score 2.34).

RESULTS

Despite comparable BMI Z-scores and leptin levels, the PWS children exhibited lower fasting insulin and HOMA-IR (homeostasis model assessment of insulin resistance) scores compared to obese controls. For any given BMI Z-score, the PWS children showed higher concentrations of fasting total and HMW adiponectin and higher HMW/total adiponectin ratios. The HMW/total adioponectin ratio was preserved in children with PWS at high degrees of obesity. In PWS children, fasting plasma total adiponectin, HMW adiponectin and HMW/total adiponectin ratio correlated negatively with age (P < 0.05), HOMA-IR (P < 0.01), BMI Z-score (P < 0.05), insulin (P < 0.01) and leptin (P < 0.05). In addition to higher fasting ghrelin concentrations, the PWS children showed significantly higher fasting levels of total peptide YY (PYY) and gastric inhibitory polypeptide (GIP) compared to obese controls.

CONCLUSIONS

Relative to controls of similar age and BMI Z-score, the PWS children had significantly higher levels of total and HMW adiponectin, and increased ratios of HMW/total adiponectin. These findings may explain in part the heightened insulin sensitivity of PWS children relative to BMI-matched controls.

Prader-Willi syndrome: an update and review for the primary pediatrician

Prader-Willi syndrome, the first known human genomic imprinting disorder, is one of the most common micro-deletion syndromes. Prader-Willi syndrome is caused by the absence of certain paternally inherited genes on the long arm of chromosome 15, resulting in a complete absence of the active copy of the genetic information in this region. It is most commonly known for its food-related characteristics of hyperphagia, food-seeking behavior, and consequent obesity. Primary care physicians play an important role in the care of children with Prader-Willi syndrome, from recognizing the presenting signs and symptoms at its various stages to understanding their unique medical, developmental, behavioral, and dietary issues. They can also serve as a valuable source of support and advocacy for the family. This article reviews the current state of knowledge about Prader-Willi syndrome and discusses up-to-date understanding of the management of this condition.

Peptide YY, cholecystokinin, insulin and ghrelin response to meal did not change, but mean serum levels of insulin is reduced in children with Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a contiguous gene syndrome characterized by uncontrollable eating or hyperphagia. Several studies have confirmed that plasma ghrelin levels are markedly elevated in PWS adults and children. The study of anorexigenic hormones is of interest because of their regulation of appetite by negative signals. To study the pattern and response of the anorexigenic hormones such as cholecystokinin (CCK) and peptide YY (PYY) to a meal in PWS, we measured the plasma CCK, PYY, ghrelin and serum insulin levels in PWS patients (n=4) and in controls (n=4) hourly for a day, and analyzed hormone levels and hormonal responses to meals. Repeated measures of ANOVA of hormone levels demonstrated that only insulin levels decreased (p=0.013) and CCK (p=0.005) and ghrelin (p=0.0007) increased in PWS over 24 hr. However, no significant group x time interactions (ghrelin: p=0.89, CCK: p=0.93, PYY: p=0.68 and insulin: p=0.85) were observed; in addition, there were no differences in an assessment of a three-hour area under the curve after breakfast. These results suggest that the response pattern of hormones to meals in PWS patients parallels that of normal controls. In addition, the decrease of insulin levels over 24 hr, in spite of obesity and elevated ghrelin levels, suggests that the baseline insulin level, not the insulin response to meals, may be abnormal in patients with PWS.

Plasma obestatin and ghrelin levels in subjects with Prader-Willi syndrome

Prader-Willi syndrome (PWS) is an obesity syndrome characterized by rapid weight gain and excessive food intake. Food intake is regulated by the hypothalamus but directly influenced by gastrointestinal peptides responding to the nutritional status and body composition of an individual. Ghrelin, derived from preproghrelin, is secreted by the stomach and increases appetite while obestatin, a recently identified peptide derived post-translationally from preproghrelin, works in opposition to ghrelin by decreasing appetite. The objective of this study was to measure fasting obestatin and ghrelin levels in peripheral blood of subjects with PWS and compare to age and gender matched control subjects. Plasma obestatin and ghrelin levels were measured in subjects with PWS (n = 16, mean age = 16.0 +/- 13.3 years; age range 1-44 years) and age and gender matched control subjects (n = 16). Significantly higher obestatin levels were seen in the 16 PWS subjects (398 +/- 102 pg/ml) compared with 16 controls (325 +/- 109 pg/ml; matched t-test, P = 0.04), particularly in 5 young (< or =3 years old) PWS subjects (460 +/- 49 pg/ml) compared with 5 young controls (369 +/- 96 pg/ml; matched t-test, P = 0.03). No significant difference in ghrelin levels was seen between the PWS and comparison groups. No significant correlation was observed for either peptide when compared with body mass index but a significant negative correlation was seen for ghrelin and age in PWS subjects. Our observations suggest that obestatin may be higher in infants with PWS compared to comparison infants. The possibility that obestatin may contribute to the failure to thrive which is common in infants with PWS warrants further investigation.

The effect of growth hormone on the response of total and acylated ghrelin to a standardized oral glucose load and insulin resistance in children with Prader-Willi syndrome

CONTEXT

Fasting levels of plasma ghrelins are grossly elevated in children with Prader-Willi syndrome (PWS). The cause of this elevation and the regulation of ghrelins in PWS is largely unknown. The regulatory role of individual nutritional components and of GH is not well characterized.

OBJECTIVE

We investigated the influence of GH on acylated (aGhr) and total ghrelin (tGhr) concentrations before and after an oral glucose load, and on insulin resistance in PWS children.

DESIGN, PATIENTS, AND INTERVENTIONS

In a clinical follow-up study, plasma ghrelins were measured during an oral glucose tolerance test, and parameters of insulin resistance were determined in 28 PWS children before and/or 1.18 (0.42-9.6) yr (median, range) after start of GH therapy (0.035 mg/kg body weight per day).

MAIN OUTCOME MEASURES

Fasting and postglucose concentrations of aGhr and tGhr and homeostasis model assessment 2 insulin resistance were the main outcome measures.

SETTING

The study was conducted in a single center (University Children's Hospital).

RESULTS

High fasting [1060 +/- 292 (sd) pg/ml; n = 12] and postglucose trough (801 +/- 303 pg/ml; n = 10) tGhr concentrations in GH-untreated PWS children were found to be decreased in the GH-treated group (fasting 761 +/- 247 pg/ml, n = 24, P = 0.006; postglucose 500 +/- 176 pg/ml, n = 20; P = 0.006). In contrast, aGhr concentrations and insulin resistance were not changed by GH treatment. Both aGhr and tGhr concentrations were decreased by oral carbohydrate administration, independent of the GH treatment status.

CONCLUSIONS

Our results indicate that, in PWS children, aGhr and tGhr are differentially regulated by GH.

A lesser postprandial suppression of plasma ghrelin in Prader-Willi syndrome is associated with low fasting and a blunted postprandial PYY response

OBJECTIVE

Ghrelin and polipeptide YY (PYY) are involved in the regulation of food intake. We evaluated these two peptides and their possible relationship in adult patients with Prader-Willi syndrome (PWS).

PATIENTS

Seven patients with PWS, 16 age-sex-BMI matched obese and 42 age-sex matched lean subjects.

DESIGN AND MEASUREMENTS

Fasting plasma PYY and ghrelin levels were measured in all subjects and, postprandially until 6 h, in seven matched subjects of each group.

RESULTS

Fasting ghrelin levels were higher in PWS than in the other two groups. Fasting PYY levels were lower in patients with PWS than in lean subjects but similar to those in obese subjects. The postprandial decrease in ghrelin concentrations was lower in PWS as compared to the other two groups and therefore the 6-h-postprandial area under the curve (AUC) for ghrelin was higher in PWS than in obese subjects. PYY response after the meal was blunted in patients with PWS, but not in the other two groups that showed a peak at 60 min The AUC for PYY was lower in PWS as compared to the other two groups. Fasting PYY levels correlated negatively with fasting ghrelin levels and with ghrelin AUC and they were the only predictor for ghrelin AUC (beta = -0.464, P = 0.034). The increase in PYY correlated negatively with the decrease in ghrelin at times 60 min and 120 min in PWS.

CONCLUSIONS

In PWS, the low decrease in postprandial ghrelin levels could be related to the low fasting PYY concentrations and their blunted postprandial response.

Obestatin is not elevated or correlated with insulin in children with Prader-Willi syndrome

CONTEXT

Obestatin is a peptide hormone derived from the proteolytic cleavage of ghrelin preprohormone. In Prader-Willi syndrome (PWS), the levels of total ghrelin (TG) and acylated ghrelin (AG) are increased, and these hormones are regulated by insulin.

OBJECTIVE

Our objective was to analyze the changes in the obestatin levels after glucose loading and to characterize the correlations of obestatin with TG, AG, and insulin.

DESIGN

Plasma obestatin, TG, AG, and insulin levels were measured in PWS children (n = 15) and controls (n = 18) during an oral glucose tolerance test.

SETTING

All subjects were admitted to the Samsung Medical Center.

INTERVENTIONS

An oral glucose tolerance test was performed after an overnight fast.

MAIN OUTCOME MEASURES

The plasma levels of obestatin, TG, AG, and serum insulin were measured at 0, 30, 60, 90, and 120 min after glucose challenge, and areas under the curves (AUCs) were calculated.

RESULTS

No significant difference in AUC of the plasma obestatin was found between the PWS children and normal obese controls (P = 0.885), although AUC of AG (P = 0.002) and TG (P = 0.003) were increased in the PWS children. Moreover, There was a negative correlation between the AUC of AG and AUC of insulin both in PWS (r = -0.432; P = 0.049) and in controls (r = -0.507; P = 0.016). However, AUC of obestatin was not significantly correlated with AUC of insulin (in PWS, r = 0.168 and P = 0.275; in controls, r = -0.331 and P = 0.09).

CONCLUSIONS

Our results indicate that plasma obestatin is not elevated in PWS children and is not regulated by insulin both in PWS children and in obese controls.

Ghrelin and the short- and long-term regulation of appetite and body weight

Ghrelin, an acylated upper gastrointestinal peptide, is the only known orexigenic hormone. Considerable evidence implicates ghrelin in mealtime hunger and meal initiation. Circulating levels decrease with feeding and increase before meals, achieving concentrations sufficient to stimulate hunger and food intake. Preprandial ghrelin surges occur before every meal on various fixed feeding schedules and also among individuals initiating meals voluntarily without time- or food-related cues. Ghrelin injections stimulate food intake rapidly and transiently, primarily by increasing appetitive feeding behaviors and the number of meals. Preprandial ghrelin surges are probably triggered by sympathetic nervous output. Postprandial suppression is not mediated by nutrients in the stomach or duodenum, where most ghrelin is produced. Rather, it results from post-ingestive increases in lower intestinal osmolarity (information probably relayed to the foregut via enteric nervous signaling), as well as from insulin surges. Consequently, ingested lipids suppress ghrelin poorly compared with other macronutrients. Beyond a probable role in meal initiation, ghrelin also fulfills established criteria for an adiposity-related hormone involved in long-term body-weight regulation. Ghrelin levels circulate in relation to energy stores and manifest compensatory changes in response to body-weight alterations. Ghrelin crosses the blood-brain barrier and stimulates food intake by acting on several classical body-weight regulatory centers, including the hypothalamus, hindbrain, and mesolimbic reward system. Chronic ghrelin administration increases body weight via diverse, concerted actions on food intake, energy expenditure, and fuel utilization. Congenital ablation of the ghrelin or ghrelin-receptor gene causes resistance to diet-induced obesity, and pharmacologic ghrelin blockade reduces food intake and body weight. Ghrelin levels are high in Prader-Willi syndrome and low after gastric bypass surgery, possibly contributing to body-weight alterations in these settings. Extant evidence favors roles for ghrelin in both short-term meal initiation and long-term energy homeostasis, making it an attractive target for drugs to treat obesity and/or wasting disorders.

The physiology and potential clinical applications of ghrelin, a novel peptide hormone

Ghrelin, a peptide hormone originally identified as the endogenous ligand of the growth hormone secretagogue receptor, is secreted primarily from the stomach and secondarily from the small intestine and colon. Ghrelin may also be expressed in the pancreatic islets, hypothalamus, pituitary, and several tissues in the periphery. The growth hormone secretagogue receptor is widely expressed, suggesting diverse physiologic roles for ghrelin. A growing body of evidence suggests that, in addition to its predictable effect on growth hormone secretion, ghrelin has an important role in the short-term regulation of appetite and the long-term regulation of energy balance and glucose homeostasis. Recent studies have implicated ghrelin in the regulation of gastrointestinal, cardiovascular, and immune function and have suggested a role for ghrelin in bone physiology. The identification of obestatin, a novel peptide hormone derived from the same gene as ghrelin, has recently added further complexity to ghrelin physiology. Obestatin appears to have actions opposite of ghrelin on energy homeostasis and gastrointestinal function. Despite the rapid progress, many questions remain unanswered, including the regulation of ghrelin and obestatin secretion, the downstream pathways that mediate their effects, and their precise physiologic endocrine and paracrine roles. This review presents data on ghrelin structure, expression, and function, with emphasis placed on human studies, highlighting areas that require future investigation and providing speculation about potential clinical applications of ghrelin agonists or antagonists.

A 9-year-old male with a duplication of chromosome 3p25.3p26.2: clinical report and gene expression analysis

We describe a 9-year-old male referred for genetic evaluation for Prader-Willi syndrome (PWS). PWS is the most common genetically defined cause of life-threatening obesity and results from a functional loss of paternally expressed genes from the chromosome 15q11-q13 region. The patient presented with pervasive developmental disorder, delayed speech, and rapid onset of obesity at age 4 years, all features similar to PWS. However, chromosome 15q11-q13 methylation testing and fragile X studies were normal. GTG-banding and fluorescence in situ hybridization (FISH) with whole chromosome 3 paint probe (WCP3) and a chromosome 3p subtelomeric probe suggested a duplication of 3p25.3p26.2, a finding supported by comparative genomic hybridization (CGH). This region of chromosome 3p contains genes which contribute to obesity and behavioral problems, most notably, ghrelin (GHRL), an oxytocin receptor (OXTR), solute carrier family six members (gamma-aminobutyric acid (GABA) neurotransmitter transporters, SLC6A1 and SLC6A11), and peroxisome proliferator-activated receptor gamma (PPARG). To characterize these obesity and behavior related genes in our subject, we performed quantitative RT-PCR and compared expression levels with similarly aged male subjects (four non-obese males, four obese males, and four PWS males-two with 15q11-q13 deletions and two with maternal disomy 15). Our studies suggest increased expression of several genes in the 3p duplication region, including GHRL and PPARG, which may contribute to the phenotypic features in our 3p duplication subject.

Prader-Willi syndrome: clinical genetics, cytogenetics and molecular biology

Prader-Willi syndrome (PWS) is a neurodevelopmental disorder that arises from lack of expression of paternally inherited genes known to be imprinted and located in the chromosome 15q11-q13 region. PWS is considered the most common syndromal cause of life-threatening obesity and is estimated at 1 in 10,000 to 20,000 individuals. A de novo paternally derived chromosome 15q11-q13 deletion is the cause of PWS in about 70% of cases, and maternal disomy 15 accounts for about 25% of cases. The remaining cases of PWS result either from genomic imprinting defects (microdeletions or epimutations) of the imprinting centre in the 15q11-q13 region or from chromosome 15 translocations. Here, we describe the clinical presentation of PWS, review the current understanding of causative cytogenetic and molecular genetic mechanisms, and discuss future directions for research.

Ghrelin, peptide YY and their receptors: gene expression in brain from subjects with and without Prader-Willi syndrome

Ghrelin and peptide YY (PYY) are peptides generally produced by the gastrointestinal organs which are involved in appetite regulation via highly specialized centers in the brain. Abnormal plasma ghrelin and PYY levels compared with controls have been reported for subjects with Prader-Willi syndrome (PWS) which is characterized by infantile hypotonia, poor suck reflex and failure to thrive followed by hyperphagia and marked obesity in early childhood. We studied gene expression of ghrelin, peptide YY, and their receptors (i.e., GHS-R1a, GHS-R1b, and NPY2R) in six different brain regions (frontal cortex, temporal cortex, visual cortex, pons, medulla, and hypothalamus) obtained from three subjects with PWS, two individuals with Angelman syndrome, and six controls to determine if expression of these genes is detectable in different regions of the brain in subjects with and without PWS. In general, expression of these genes using RT-PCR was detected in all subjects and no obvious differences were seen in their pattern of expression between subjects with or without PWS. Additional studies including quantitative gene expression measurements will be required to further evaluate the role of these genes in the eating disorder seen in PWS.