CHARACTERIZATION OF EARLY ALTERATIONS IN GLUCOSE HOMEOSTASIS, INSULIN SECRETION, AND HEPATIC INSULIN EXTRACTION IN NONDIABETIC OBESE PRADER-WILLI SUBJECTS AND HEALTHY OBESE CONTROLS SUBJECTS. † 576

Characterization of alterations in glucose and insulin metabolism in Prader-Willi subjects

Acute illness leads to increased GH, but reduced IGF-I secretion, while both are reduced in chronic illness. Prader-Willi syndrome (PWS) is a genetic obesity syndrome, with GH deficiency a feature independent of obesity. Reduced GH secretion may result from decreased hypothalamic release of GH-releasing hormone (GHRH). To quantify hypothalamic GHRH neurone cell number in control subjects with various lengths of premorbid illness duration, PWS and non-PWS obese subjects. We examined GHRH neurones in the infundibular nucleus/median eminence complex of control subjects (n = 26, including four children), PWS (n = 6) and non-PWS (n = 4) obese adults and PWS children (n = 2), by quantitative immunocytochemistry, using postmortem material. We found: (i) higher GHRH cell number during prolonged illness prior to death in both control adults (r = +0.62, P = 0.002, cell number vs. premorbid illness duration) and PWS adults (r = +0.90, P = 0.02); (ii) higher GHRH cell number in female than male adults [by 53% (95% confidence interval 28-83%) in controls, P = 0.005, correcting for premorbid illness duration]; (iii) no difference in GHRH cell number between PWS adults and control or non-PWS obese adults (P = 0.7 and P = 0.4, adjusting for sex and illness duration); and (iv) low GHRH cell number in only one PWS child (who had been receiving exogenous GH therapy). These findings suggest continued activation of GHRH neurones during prolonged illness. There is no evidence that the GH deficiency in PWS results from reduced GHRH cell number, and GHRH neuronal responses to illness and exogenous GH treatment appear normal in PWS.

Introduction Prader- Willi syndrome (PWS) is a genetic condition commonly associated with hyperphagia and obesity. PWS is thought to have hypothalamic dysfunction which is the head ganglion of autonomic nervous system (ANS). In current literature, ANS is believed to be defective in PWS. ANS may also have a role in controlling orexigenic hormone ghrelin and energy expenditure. One study reported higher resting energy expenditure adjusted for lean body mass in growth hormone naive PWS group but another study found lower activity associated energy expenditure compared to controls. Other studies found adjusted basal and sleeping metabolic rates were not different to the controls. Complete profile of energy expenditure in PWS remains unclear. We hypothesize that there is defective ANS in PWS, as a result of hypothalamus dysfunction, and it leads to high orexigenic hormone, acyl ghrelin, and low energy expenditure that in turn cause obesity. Methods We compared the ANS functions, acyl ghrelin status and energy expenditure in children with PWS and controls. We recruited 16 genetically- confirmed children with PWS and 16 controls. Exclusion criteria were diabetes mellitus, psycho-trophic medications, and other hypothalamic pathologies. We performed a mixed meal challenge to assess ANS function and acyl ghrelin status of PWS and control groups. We used Bodystat 1500® to measure body composition. Orthostatic hypotension, due to gravity, stimulates baroreceptors and activates sympathetic nervous system to counter regulate postural drop in blood pressure by increasing pulse rate, stroke volume and vasoconstriction. We used orthostatic change in pulse rate (PR), blood pressure (BP), and mean arterial pressure (MAP) expressed as per cent change of PR (%ΔPR), BP (%ΔBP), and MAP (%ΔMAP) from lying to standing to access sympathetic nervous function. ANS was further stimulated by a mixed meal and we examined %ΔPR, %ΔBP, and %ΔMAP at 15 and 30 seconds after standing from recumbent position; at fasting, and post-prandial periods. We also measured plasma gastrin, catecholamines (Pcat) and urinary catecholamines (Ucat) at fasting and post- prandial periods to complement autonomic cardiovascular data. Using Actiheart®, we compared weight and fat free mass adjusted total, resting, activity- associated and non- exercise associated thermogenesis between two groups. Results PWS group was younger, shorter, and had reduced lean mass than the controls. Post-prandial %ΔPR at both 15 and 30 seconds were significantly lower in PWS group than controls. The difference in %Δ systolic BP and diastolic BP did not reach statistical significance but %ΔMAP at 60 min and 120 min after meal was significantly lower in PWS. Postprandial plasma gastrin and Ucat were higher in PWS group than controls but Pcat were not different in two groups. Fasting plasma acyl ghrelin (AG) was significantly higher in PWS but it decreased to similar level of controls at 60 and 120 minutes after a meal. The rate of fall of plasma acyl ghrelin was faster in the PWS group than the controls. Fasting AG is negatively correlated to fasting %ΔPR at 30s (r value -0.52, p= 0.04). When adjusted for both weight and fat- free- mass, PWS group had lower total, resting, activity- associated and non- exercise associated thermogenesis than the controls. Conclusions We report that there is dysautonomia, high fasting acyl ghrelin and low energy expenditures in children with PWS. In PWS, there is reduction in GABA-A receptor number and its actions as a result of the deleted genes of β3, α5, and γ3 subunit of GABA-A receptors in the PWS gene region; and probable exaggerated GABA-B receptors actions due to effect of compensatory hyper-gamma- amino- butyric- acidaemia on the normal GABA-B receptors. The abnormities lead to GABA system dysfunction in PWS. GABA is the key neurotransmitter between Nucleus Tractus Solitarius and C1 neurons that connect to the thoracic spinal cord that sends efferent neurons to sympathetic ganglions. GABA system dysfunction, therefore, may be the cause of sympathetic failure. Moreover, GABA is generally an inhibitory neurotransmitter and GABA dysfunction may be the cause of poor vagal inhibitory function that lead to high post-prandial plasma gastrin production, and increased catecholamine production from adrenal medulla probably by increase chromaffin cells gap junction communications. Our findings of dysautonomia can be explained by GABA dysfunction in PWS. Dysautonomia may also be the cause of high fasting acyl ghrelin and low energy expenditures. Therefore in PWS, there is imbalance in energy intake and expenditure resulting in obesity.

The endothelial protein C receptor (EPCR) has a critical role in the regulation of anticoagulant and anti-inflammatory functions of activated protein C (APC). Abnormalities in EPCR might be associated with an increased risk of thrombosis. In this respect, a 23 bp insertion in the exon 3 of the EPCR gene predicts a truncated protein which cannot bind APC. High levels of C-reactive protein (CRP), a strong predictor of cardiovascular events, are found both in the obese and in subjects with Prader-Willi syndrome (PWS). Several cardiovascular risk factors are already present in prepubertal PWS children, but it is uncertain which mechanism contributes to the increased risk of cardiovascular disease in PWS. We analyzed the distribution of 23 bp insertion in the EPCR gene in 81 overweight and obese PWS subjects, 52 adults and 29 children, and in 58 overweight and obese children and adolescents (controls). We found that 1/58 (1.7%) of the controls was heterozygous for the 23 bp insertion, while this mutation was never found in PWS subjects. Furthermore, we evaluated CRP levels, glucose, insulin, and lipid profile, and we found higher CRP values in PWS adults with respect to children with PWS and controls, and a better insulin sensitivity in all PWS subjects than in the controls. This study suggests that in PWS subjects there is no predisposition to develop thrombotic events in association with EPCR gene alteration and demonstrates substantial differences regarding metabolic and inflammatory profile between PWS and non-PWS obese children, with further impairment in adults with PWS.

The GHRH + arginine stimulated pituitary GH secretion in children and adults with Prader–Willi syndrome shows age- and BMI-dependent and genotype-related differences

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. 11 adults with PWS were compared with 12 adiposity-matched and 10 lean subjects. Indirect calorimetry was conducted at baseline and 210 min after a standardized 600 kCal breakfast to assess energy expenditure and substrate utilization. Circulating glucose, insulin, C-peptide, glucagon, nonesterified fatty acids, and triglycerides were measured up to 240 min. Insulin sensitivity and insulin secretion rate were assessed by HOMA-IR and C-peptide deconvolution, respectively. Body composition was determined by dual-energy X-ray absorptiometry. The PWS group had lower lean mass than the obesity control group. Corrected for lean mass, there were no differences between the PWS and obesity groups in resting metabolic rate or metabolic flexibility. Total and abdominal fat mass, insulin sensitivity, and insulin secretion rate were also similar between these groups. This study did not detect an intrinsic metabolic defect in individuals with PWS. Rather, lower lean mass, combined with lower physical activity, may contribute to weight gain on an apparent weight-maintenance diet.

Influence of age, gender, and glucose tolerance on fasting and fed acylated ghrelin in Prader Willi syndrome

The Prader-Willi syndrome (PWS) is characterized by short stature, mild mental retardation, and a characteristic face. Approximately 75% of all patients have a del (15q). Cephalometric roentgenograms of 20 PWS patients of both sexes (12 adults, 8 children, age 4.5-50.0 years) were analyzed to determine if the facial appearance is reflected in changes in the bony architecture, a characteristic which might be useful in diagnosis and/or dental treatment of these individuals. PWS subjects were compared with chronologic age and sex-matched control individuals derived from the Denver Growth study using 52 point computer analyzed lateral head-plate tracings performed by the same individual (RS). The mean Z-score differences for mandibular and maxillary total length, ramus height, mandibular corpus length, posterior facial height, and mid-facial height were all significantly smaller in greater than 65% of the PWS subjects; this was more evident in the PWS children. The Z-score difference for posterior cranial base was very large in most PWS adults and children whereas lower facial height was small or normal in all subjects. No statistical difference in mean Z-score measurements was found for all these measures in PWS subjects with or without the 15q chromosome deletion. The overall small bony structures contrast with the relatively large soft tissue draping seen especially in obese adults. The data suggest that a characteristic bony model might be created for PWS which could be of use in diagnosis and in the treatment of PWS patients by their orthodontist.

Diagnosis and treatment of GH deficiency in Prader–Willi syndrome

Prader-Willi syndrome (PWS), the most frequent syndrome of obesity, is a model of early fat mass (FM) development, but scarce data exist on adipose tissue characteristics. The objective of the study was to compare metabolic, fat distribution, and transcriptomic signatures of sc adipose tissue (scAT) in PWS adults, with matched obese adults with primary obesities. Hormonal and metabolic assessments, systemic inflammation, and gene expression in scAT were compared between PWS patients and obese controls (OCs). Each 42nd PWS patient was matched with one randomly paired control with primary obesity. Matching factors were age, gender, fat mass (percentage), and diabetic status. Compared with OCs, the PWS group had a decreased percentage of trunk FM and a better metabolic profile with decreased insulin and homeostasis model assessment, an index of insulin-resistance, and increased concentrations of serum adiponectin and ghrelin. Adipocyte size relative to body fat was significantly higher in PWS vs OCs. scAT in PWS patients was characterized by a transcriptomic functional signature with enrichment of themes related to immunoinflammation, the extracellular matrix, and angiogenesis. A RT-PCR targeted study revealed that candidate genes encoding proinflammatory markers and remodeling molecules, CD68, CD3e, IL-1β, chemokine (C-C motif) ligand 5, collagen type 4-α, and lysyl oxidase, were down-regulated. Matched for FM, PWS subjects have a better metabolic profile, a phenotype that could be linked to changes in scAT remodeling and promotion of adipocyte growth.

We tested the hypothesis that the levels of bone remodeling mediators may be altered in Prader-Willi syndrome (PWS). We assessed RANKL, OPG, sclerostin, DKK-1 serum levels, and bone metabolism markers in 12 PWS children (7.8 ± 4.3years), 14 PWS adults (29.5 ± 7.2years), and 31 healthy controls matched for sex and age. Instrumental parameters of bone mineral density (BMD) were also evaluated. Lumbar spine BMD Z-scores were reduced in PWS children (P < 0.01), reaching osteopenic levels in PWS adults. PWS patients showed lower 25(OH)-vitamin D serum levels than controls (P < 0.001). Osteocalcin was increased in PWS children but reduced in adults respect to controls (P < 0.005 and P < 0.01, respectively). RANKL levels were higher in both pediatric and PWS adults than controls (P < 0.004), while OPG levels were significantly reduced (P < 0.004 and P < 0.006, respectively). Sclerostin levels were increased in children (P < 0.04) but reduced in adults compared to controls (P < 0.01). DKK-1 levels did not show significant difference between patients and controls. In PWS patients, RANKL, OPG, and sclerostin significantly correlated with metabolic and bone instrumental parameters. Consistently, with adjustment for age, multiple linear regression analysis showed that BMD and osteocalcin were the most important predictors for RANKL, OPG, and sclerostin in children, and GH and sex steroid replacement treatment in PWS adults. We demonstrated the involvement of RANKL, OPG, and sclerostin in the altered bone turnover of PWS subjects suggesting these molecules as markers of bone disease and new potential pharmacological targets to improve bone health in PWS.

Lipid metabolism is closely linked to adiposity. Prader-Willi syndrome (PWS) is a typical genetic disorder causing obesity; however, the distinct lipidomic profiles in PWS children have not been thoroughly investigated. Herein, serum lipidomics analyses were simultaneously explored in PWS, simple obesity (SO), and normal children (Normal). Results indicated that the total concentration of phosphatidylcholine (PC) and lysophosphatidylcholine (LPC) in the PWS group were significantly deceased compared with both the SO and the Normal group. In contrast, compared with the Normal group, there was an overall significant increase in triacylglycerol (TAG) levels in both the PWS and the SO groups, with the highest found in SO group. Thirty-nine and 50 differential lipid species were screened among 3 groups: between obesity (PWS and SO) and the Normal group. Correlation analysis revealed distinct profiles in PWS that was different from other 2 groups. Notably, PC (P16:0/18:1), PE (P18:0-20:3), PE (P18:0-20:4)) showed significant negative correlation with body mass index (BMI) only in the PWS group. PE (P16:0-18:2) showed a negative association with BMI and weight in the PWS group, but significant positive correlation in the SO group; no statistically significant association was found in the Normal group. We also found a significant negative correlation between Blautia genus abundance and several significantly changed lipids, including LPC (14:0), LPC (16:0), TAG (C50:2/C51:9), TAG (C52:2/C53:9), TAG (C52:3/C53:10), and TAG (C52:4/C53:11), but no significant correlation in the Normal group and the SO group. Similarly, in the PWS group, the Neisseria genus was significantly negatively associated with acylcarnitine (CAR) (14:1), CAR (18:0), PE (P18:0/20:3), and PE (P18:0/20:4), and extremely positively associated with TAG (C52:2/C53:9); no obvious correlations were observed in the Normal group and the SO group.

Prader–Willi syndrome (PWS) is characterized by a dysregulation of growth hormone (GH)/insulin-like growth factor I axis, as the consequence of a complex hypothalamic involvement. PWS’ clinical picture seems to resemble the classic non-PWS GH deficiency (GHD), including short stature, excessive body fat, decreased muscle mass, and impaired quality of life. GH therapy is able to ameliorate the phenotypic appearance of the syndrome, as well as to improve body composition, physical strength, and cognitive level. In this regard, however, some pathophysiologic and clinical questions still remain, representing a challenge to give the most appropriate care to PWS patients. Data about the prevalence of GHD in PWS children are not unequivocal, ranging from 40% to 100%. In this context, to establish whether the presence (or not) of GHD may have a different effect on clinical course during GH therapy may be helpful. In addition, the comparison of GH effects in PWS children diagnosed as small for gestational age with those obtained in subjects born appropriate for gestational age is of potential interest for future trials. Emerging information seems to demonstrate the maintenance of beneficial effects of GH therapy in PWS subjects after adolescent years. Thus, GH retesting after achievement of final height should be taken into consideration for all PWS patients. However, it is noteworthy that GH administration exerts positive effects both in PWS adults with and without GHD. Another critical issue is to clarify whether the genotype–phenotype correlations may be relevant to specific outcome measures related to GH therapy. Moreover, progress of our understanding of the role of GH replacement and concomitant therapies on bone characteristics of PWS is required. Finally, a long-term surveillance of benefits and risks of GH therapy is strongly recommended for PWS population, since most of the current studies are uncontrolled and of short duration.

Prader-Willi syndrome (PWS) is one of the most commonly recognized causes of early-onset childhood obesity. Individuals with PWS have significant hyperphagia and decreased recognition of satiety. The exact etiology of the hyperphagia remains unknown and, therefore, untreatable. We conducted a pilot, open-label study of response to metformin in 21 children with PWS and six with early morbid obesity (EMO). Participants had significant insulin resistance and glucose intolerance on oral glucose tolerance testing (OGTT) and were started on metformin for these biochemical findings. We administered the Hyperphagia Questionnaire to parents of patients before and after starting metformin treatment. Both the PWS and EMO groups showed significant improvements in food-related distress, anxiety, and ability to be redirected away from food on the Hyperphagia Questionnaire. In the PWS group, improvements were predominantly seen in females. Within the PWS group, responders to metformin had higher 2-h glucose levels on OGTT (7.48 mmol/L vs. 4.235 mmol/L; p=0.003) and higher fasting insulin levels (116 pmol/L vs. 53.5 pmol/L; p=0.04). Additionally, parents of 5/13 individuals with PWS and 5/6 with EMO reported that their child was able to feel full while on metformin (for many this was the first time they had ever described a feeling of fullness). Metformin may improve sense of satiety and decrease anxiety about food in some individuals with PWS and EMO. Positive response to metformin may depend on the degree of hyperinsulinism and glucose intolerance. Nonetheless, the results of this pilot study bear further investigation.

Prader-Willi syndrome (PWS), the most common genetic cause of marked obesity in humans, is usually due to a de novo paternally derived chromosome 15q11-q13 deletion or maternal disomy 15 [(uniparental disomy (UPD)]. Obesity is due to energy imbalance, but few studies have examined fat patterning and obesity-related factors in subjects with PWS (deletions and UPD) compared with subjects with simple obesity. We examined for differences in fatness patterning and lipid, leptin, and glucose and insulin levels in subjects with simple obesity and PWS and adjusted for gender, age, and body mass index (BMI). Fasting peripheral blood samples and cross-sectional magnetic resonance image scans at the level of the umbilicus were obtained in 55 subjects ranging in age from 10.4 to 49 years: 20 PWS deletion, 17 PWS UPD, and 18 obese controls. Subcutaneous fat area (SFA) and intra-abdominal visceral fat area (VFA) were calculated. No significant difference was seen between the PWS deletion subjects or PWS UPD subjects for fatness measurements or leptin levels. Twenty-three of 37 PWS subjects met the criteria for obesity (BMI > 95th percentile). No significant differences were observed for SFA and VFA between the PWS subjects judged to be obese and control subjects with simple obesity. There was an overall trend for decreased VFA in the PWS subjects but not significantly different. VFA was significantly positively correlated with both fasting insulin and total cholesterol in PWS deletion subjects but not in PWS UPD subjects or obese controls. Fasting insulin level was significantly lower in the obese PWS subjects compared with subjects with simple obesity, and insulin sensitivity (QUICKI) was significantly higher in PWS subjects with obesity. Homeostasis model assessment (HOMA) and QUICKI values were correlated and in opposite directions with triglycerides in the obese PWS subjects but not in the obese controls. Subjects in each group were stratified according to published criteria on the basis of their level of visceral fat (e.g. > or = 130 cm(2)) to assess the influence of VFA on metabolic abnormalities. In the obese PWS subjects, the fasting triglyceride, glucose, and insulin levels, and HOMA value were significantly elevated, while the QUICKI value was significantly lower in those with VFA > or = 130 cm(2). Such significant differences were not seen in the obese control group. Our results indicate that VFA may be regulated differently in PWS subjects compared to individuals with simple obesity. Insulin resistance is lower in PWS subjects and insulin sensitivity is higher compared with obese controls. PWS subjects with increased VFA may be at a higher risk of obesity-related complications compared to PWS subjects without increased VFA.