Louise Purtell

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.

Effects of a Single Dose of Exenatide on Appetite, Gut Hormones, and Glucose Homeostasis in Adults with Prader-Willi Syndrome

CONTEXT Prader-Willi syndrome (PWS) is associated with hyperphagia and obesity, without effective pharmacological treatment. Exenatide, recently developed for treatment of type 2 diabetes, induces appetite suppression and weight loss with common side effects. OBJECTIVE The objective of the study was to investigate the initial safety and effectiveness of exenatide in adult PWS subjects compared with obese controls (OBESE). DESIGN, SETTING, PATIENTS, AND INTERVENTION Eight PWS and 11 OBESE patients underwent standardized meal studies after a single sc injection of 10 μg exenatide or placebo in a single-blinded, crossover design. MAIN OUTCOME MEASURES Glucose, insulin, C-peptide, glucagon, peptide YY (PYY; total)/PYY (3-36), glucagon-like peptide-1, and ghrelin (total) were measured fasting and postprandially. Appetite and satiety were assessed by visual analog scales. Energy expenditure (EE) was measured by indirect calorimetry. Side effects were screened during and for 24 h after the meal. RESULTS PWS and OBESE patients were matched for gender, age, body mass index, and central/total body fat. In both groups, exenatide increased satiety and lowered glucose and insulin levels but increased insulin secretion rate. Side effects were absent in PWS but common in OBESE patients. During the meal, PYY (total) and ghrelin were elevated in PWS patients. Exenatide decreased PYY (total) and glucagon-like peptide-1, whereas ghrelin remained unchanged. Energy expenditure was unchanged by exenatide. CONCLUSIONS Our pilot study demonstrates that exenatide is well tolerated in PWS patients. It increases satiety independently of measured appetite hormones, exerting glucose lowering, and insulinotropic effects similarly in PWS and OBESE patients. Larger prospective studies should investigate whether chronic exenatide administration will reduce hyperphagia and overweight in PWS patients without side effects.

Snord116 is critical in the regulation of food intake and body weight.

Prader-Willi syndrome (PWS) is the predominant genetic cause of obesity in humans. Recent clinical reports have suggested that micro-deletion of the Snord116 gene cluster can lead to PWS, however, the extent of the contributions of the encoded snoRNAs is unknown. Here we show that mice lacking Snord116 globally have low birth weight, increased body weight gain, energy expenditure and hyperphagia. Consistent with this, microarray analysis of hypothalamic gene expression revealed a significant alteration in feeding related pathways that was also confirmed by in situ hybridisation. Importantly, selective deletion of Snord116 only from NPY expressing neurons mimics almost exactly the global deletion phenotype including the persistent low birth weight, increased body weight gain in early adulthood, increased energy expenditure and hyperphagia. Mechanistically, the lack of Snord116 in NPY neurons leads to the upregulation of NPY mRNA consistent with the hyperphagic phenotype and suggests a critical role of Snord116 in the control of NPY neuronal functions that might be dysregulated in PWS.

Prader-Willi Critical Region, a Non-Translated, Imprinted Central Regulator of Bone Mass: Possible Role in Skeletal Abnormalities in Prader-Willi Syndrome.

Prader-Willi Syndrome (PWS), a maternally imprinted disorder and leading cause of obesity, is characterised by insatiable appetite, poor muscle development, cognitive impairment, endocrine disturbance, short stature and osteoporosis. A number of causative loci have been located within the imprinted Prader-Willi Critical Region (PWCR), including a set of small non-translated nucleolar RNA’s (snoRNA). Recently, micro-deletions in humans identified the snoRNA Snord116 as a critical contributor to the development of PWS exhibiting many of the classical symptoms of PWS. Here we show that loss of the PWCR which includes Snord116 in mice leads to a reduced bone mass phenotype, similar to that observed in humans. Consistent with reduced stature in PWS, PWCR KO mice showed delayed skeletal development, with shorter femurs and vertebrae, reduced bone size and mass in both sexes. The reduction in bone mass in PWCR KO mice was associated with deficiencies in cortical bone volume and cortical mineral apposition rate, with no change in cancellous bone. Importantly, while the length difference was corrected in aged mice, consistent with continued growth in rodents, reduced cortical bone formation was still evident, indicating continued osteoblastic suppression by loss of PWCR expression in skeletally mature mice. Interestingly, deletion of this region included deletion of the exclusively brain expressed Snord116 cluster and resulted in an upregulation in expression of both NPY and POMC mRNA in the arcuate nucleus. Importantly, the selective deletion of the PWCR only in NPY expressing neurons replicated the bone phenotype of PWCR KO mice. Taken together, PWCR deletion in mice, and specifically in NPY neurons, recapitulates the short stature and low BMD and aspects of the hormonal imbalance of PWS individuals. Moreover, it demonstrates for the first time, that a region encoding non-translated RNAs, expressed solely within the brain, can regulate bone mass in health and disease.

Behavioural characteristics of the Prader-Willi syndrome related biallelic Snord116 mouse model.

Prader-Willi syndrome (PWS) is the predominant genetic cause of obesity in humans and is associated with several behavioural phenotypes such as altered motoric function, reduced activity, and learning disabilities. It can include mood instability and, in some cases, psychotic episodes. Recently, the Snord116 gene has been associated with the development of PWS, however, its contribution to the behavioural aspects of the disease are unknown. Here we show that male and female mice lacking Snord116 on both alleles exhibit normal motor behaviours and exploration but do display task-dependent alterations to locomotion and anxiety-related behaviours. Sociability is well developed in Snord116 deficient mice as are social recognition memory, spatial working memory, and fear-associated behaviours. No sex-specific effects were found. In conclusion, the biallelic Snord116 deficiency mouse model exhibits particular endophenotypes with some relevance to PWS, suggesting partial face validity for the syndrome.

Postprandial metabolism in adults with prader–willi syndrome

Individuals with Prader–Willi syndrome (PWS) are commonly restricted to 60‐75% of height‐appropriate calorie intake because they rapidly become obese on a normal diet. This study measured changes in energy expenditure, glucose and lipid homeostasis, and metabolic flexibility in response to a meal in PWS adults.

Adult-onset deletion of the Prader-Willi syndrome susceptibility gene Snord116 in mice results in reduced feeding and increased fat mass

BACKGROUND The imprinted small nucleolar RNA (snoRNA) Snord116 is implicated in the aetiology of Prader-Willi syndrome (PWS), a disease associated with hyperphagia and obesity. Germline deletion of Snord116 in mice has been found to lead to increased food intake but not to the development of obesity. To determine the role of Snord116 independent of potential compensatory developmental factors, we investigated the effects of conditional adult-onset deletion of Snord116 in mice. METHODS Deletion of Snord116 was induced at 8 weeks of age by oral administration of tamoxifen to male Snordlox/lox; ROSAcre/+ mice, with vehicle-treated mice used as controls. Body weight (BW) was monitored weekly and body composition was measured by dual-energy X-ray absorptiometry and tissue dissection. Non-fasted and fasting-induced food intake was determined, and glucose and insulin tolerance tests were performed. Twenty-four-hour energy expenditure and physical activity were assessed by indirect calorimetry. RESULTS Adult-onset deletion of Snord116 led to reduced food intake and increased adiposity, albeit with no concomitant change in BW or lean mass compared to controls. Adult onset Snord116 deletion was also associated with worsened glucose tolerance and insulin sensitivity. CONCLUSIONS This study identified a key role for Snord116 in feeding behaviour and growth. Further, it is likely that the effects of this gene are modulated by developmental stage, as mice with adult-onset deletion showed an opposite phenotype, with respect to food intake and body composition, to previously published data on mice with germline deletion.

Ambient temperature modulates the effects of the Prader-Willi syndrome candidate gene Snord116 on energy homeostasis

Germline deletion of the Prader-Willi syndrome (PWS) candidate gene Snord116 in mice leads to some classical symptoms of human PWS, notably reductions in body weight, linear growth and bone mass. However, Snord116 deficient mice (Snord116-/-) do not develop an obese phenotype despite their increased food intake and the underlying mechanism for that is unknown. We tested the phenotypes of germline Snord116-/- as well as neuropeptide Y (NPY) neuron specific Snord116lox/lox/NPYcre/+ mice at 30°C, the thermoneutral temperature of mice, and compared these to previous reports studies conducted at normal room temperature. Snord116-/- mice at 30°C still weighed less than wild type but had increased body weight gain. Importantly, food intake and energy expenditure were no longer different at 30°C, and the reduced bone mass and nasal-anal length observed in Snord116-/- mice at room temperature were also normalized. Mechanistically, the thermoneutral condition led to the correction of the mRNA expression of NPY and pro-opiomelanocortin (POMC), which were both previously observed to be significantly up-regulated at room temperature. Importantly, almost identical phenotypes and NPY/POMC mRNA expression alterations were also observed in Snord116lox/lox/NPYcre/+ mice, which lack the Snord116 gene only in NPY neurons. These data illustrate that mild cold stress is a critical factor preventing the development of obesity in Snord116-/- mice via the NPY system. Our study highlights that the function of Snord116 in the hypothalamus may be to enhance energy expenditure, likely via the NPY system, and also indicates that Snord116 function in mice is strongly dependent on environmental conditions such as cold exposure.

Postprandial cardiac autonomic function in Prader–Willi syndrome

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.

Vitamin D levels in primary growth hormone deficiency disorder Prader–Willi syndrome

To the Editor, We read with interest the research article by Savanelli et al. (Endocrine, October 2015) [1], in which the authors report that low vitamin D levels predict dyslipidaemia and hypertension in patients with growth hormone (GH) deficiency. Given that vitamin D modulates gene expression of the GH/IGF-1 pathway and its administration augments circulating IGF-1 [2], the relationships of vitamin D and GH with cardiovascular risk are likely to intersect. Individuals in their study cohort had GH deficiency with disparate causes (including numerous types of pituitary tumours and idiopathic GH deficiency) and, presumably, age of onset. It is therefore of interest to investigate whether vitamin D levels are similarly affected in a cohort in which GH deficiency arises from a common cause which is present from early life. Prader–Willi syndrome (PWS) is a genetic imprinting disorder associated with hyperphagia, muscular hypotonia and endocrine dysfunction. Hypothalamic GH deficiency is a hallmark of PWS, contributing to the short stature, poor muscular development and low bone mineral density in individuals with this disorder. Many children and (in recent years) adults with PWS now receive GH replacement therapy, which has beneficial effects on height, muscle mass, obesity and physical activity. Individuals with PWS have increased risk of adverse cardiovascular events independent of obesity status; low-grade inflammation, low GH/IGF-1 levels and impaired autonomic function have been suggested as possible mechanisms but to our knowledge no research into vitamin D in PWS has been conducted. Approval for this study was obtained from the St Vincent’s Hospital Human Research Ethics Committee. Study participants or their parents/guardians gave written informed consent prior to participation. To determine vitamin D status in a cohort with GH deficiency and increased cardiovascular risk, we assessed 10 GH-naı̈ve adults with PWS (age 27.9 ± 2.7; BMI 37.0 ± 2.9) in comparison to 12 obese controls (age 31.9 ± 2.5; BMI 34.3 ± 1.2) and 10 lean controls (age 28.9 ± 1.3; BMI 21.3 ± 0.5). Blood samples were collected after an overnight (10 h) fast, and plasma was obtained by centrifugation and stored at -80 C prior to being assayed. Circulating 25(OH) vitamin D levels were measured in plasma by ELISA (Enzo Life Sciences, Farmingdale, USA). Group means were compared using ANOVA (GraphPad Prism 6.0, GraphPad Software, San Diego, CA, USA) and classified according to the guidelines established by Nowson et al. [3]. 25(OH) vitamin D levels in the three groups are shown in Fig. 1. While group differences were not statistically significant, group means fell within different categories of vitamin D status. The lean group had a mean plasma 25(OH) vitamin D concentration of 23.4 ± 4.4 ng/mL, placing them in the optimal range for adults in Australia and New Zealand [3]. Obese subjects had mean levels of 18.6 ± 3.1 ng/mL, placing them in the mild vitamin D deficiency category. The individuals with PWS, with mean levels of 12.7 ± 1.5 ng/mL, exhibited mild-to-moderate vitamin D deficiency. From this cross-sectional study, we cannot conclude whether the low levels of vitamin D in individuals in the PWS group are an intrinsic feature of the disease or secondary to environmental factors. Sunlight accounts for 90–95 % of vitamin D in Australians; as the PWS group, & Louise Purtell l.purtell@garvan.org.au