IntroductionPrader-Willi syndrome (PWS) is a multisystemic complex genetic disorder caused by lack of expression of genes on the paternally inherited chromosome 15q11.2-q13 region. There are three main genetic subtypes in PWS: paternal 15q11-q13 deletion (65–75 % of cases), maternal uniparental disomy 15 (20–30 % of cases), and imprinting defect (1–3 %). DNA methylation analysis is the only technique that will diagnose PWS in all three molecular genetic classes and differentiate PWS from Angelman syndrome. Clinical manifestations change with age with hypotonia and a poor suck resulting in failure to thrive during infancy. As the individual ages, other features such as short stature, food seeking with excessive weight gain, developmental delay, cognitive disability and behavioral problems become evident. The phenotype is likely due to hypothalamic dysfunction, which is responsible for hyperphagia, temperature instability, high pain threshold, hypersomnia and multiple endocrine abnormalities including growth hormone and thyroid-stimulating hormone deficiencies, hypogonadism and central adrenal insufficiency. Obesity and its complications are the major causes of morbidity and mortality in PWS.MethodsAn extensive review of the literature was performed and interpreted within the context of clinical practice and frequently asked questions from referring physicians and families to include the current status of the cause and diagnosis of the clinical, genetics and endocrine findings in PWS.ConclusionsUpdated information regarding the early diagnosis and management of individuals with Prader-Willi syndrome is important for all physicians and will be helpful in anticipating and managing or modifying complications associated with this rare obesity-related disorder.

Aims There are no treatments for the extreme hyperphagia and obesity in Prader-Willi syndrome (PWS). The bestPWS trial assessed the efficacy, safety, and tolerability of the methionine aminopeptidase 2 (MetAP2) inhibitor, beloranib. Materials and Methods Participants with PWS (12–65 years) were randomly assigned (1:1:1) to biweekly placebo, 1.8 mg beloranib, or 2.4 mg beloranib injection for 26 weeks at 15 US sites. Coprimary endpoints were the changes in hyperphagia (measured by Hyperphagia Questionnaire for Clinical Trials [HQ-CT]; possible score 0–36) and weight by intention-to-treat. ClinicalTrials.gov registration: NCT02179151. Results 107 were included in the intention-to-treat analysis: placebo (n=34), 1.8 mg beloranib (n=36), or 2.4 mg beloranib (n=37). Improvement (reduction) in HQ-CT total score was greater in the 1.8 mg (mean difference −6.3, 95% CI −9.6 to −3.0; p=0.0003) and 2.4 mg beloranib groups (−7.0, 95% CI −10.5 to −3.6; p=0.0001) vs placebo. Compared to placebo, weight change was greater with 1.8 mg (mean difference −8.2%, 95% CI −10.8 to −5.6; p<0.0001) and 2.4 mg beloranib (−9.5%, 95% CI −12.1 to −6.8; p<0.0001). Injection site bruising was the most frequent adverse event with beloranib. Dosing was stopped early due to an imbalance in venous thrombotic events in beloranib-treated participants (two fatal events of pulmonary embolism and two events of deep vein thrombosis) compared to placebo. Conclusions MetAP2 inhibition with beloranib produced statistically significant and clinically meaningful improvements in hyperphagia-related behaviors and weight loss in participants with PWS. Although investigation of beloranib has ceased, inhibition of MetAP2 is a novel mechanism for treating hyperphagia and obesity.

Obesity, short stature, decreased growth rate and delayed skeletal maturation are common features of children with Prader-Willi syndrome (PWS). In contrast to PWS, children with simple exogenous obesity have normal or increased growth rate and normal or advanced skeletal maturation. Decreased growth hormone (GH) secretion evaluated by pharmacological or physiological testing associated with increased plasma insulin-like growth factor (IGF-I) and GH-binding protein (GH-BP) levels are also characteristic of simple obesity. In order to understand whether the suboptimal GH secretion in PWS is an artifact of the obesity, we studied 33 obese and 11 non-obese PWS children, aged 2-16 years.GH secretion was evaluated with three pharmacological stimuli (insulin, clonidine and L-dopa) and by spontaneous 24-hour GH secretion. Skeletal maturation was delayed in 70% whereas plasma IGF-I and GH-BP were either low or normal. Forty subjects, including ten non-obese children, had GH deficiency by standard testing (failure to respond to two pharmacological stimuli), and all but one had blunted spontaneous 24-h GH secretion. No significant correlation between body mass index (wt/ht2) and spontaneous 24-h GH secretion (r = 0.145), p > 0.06) or GH-BP levels (r = 0.19, p > 0.07) was found. Thirty documented GH deficient children have completed at least two years of GH therapy. With treatment the overall mean height SD and weight SD changed from -2.2 to -0.8 and from 3.5 to 2.4 respectively (p < 0.0001). No patient has developed diabetes mellitus. In conclusion, growth velocity, skeletal maturation, GH secretion and GH dependent proteins in PWS resemble GH deficiency more than simple obesity. Our ongoing study suggests that GH deficiency in PWS is not an artifact of obesity. Although it is unlikely that GH deficiency is the only cause of decreased growth velocity and increased adiposity in PWS, it is a common feature and significant contributory factor. Long term observation will be required until achievement of adult height to determine whether GH therapy actually improves final height.

Hyperphagia and obesity are common features in individuals with Prader-Willi syndrome (PWS). Demographic and cause of death data from individuals with PWS were obtained through a national support organization. Four reports of unexpected mortality due to gastric rupture and necrosis were found in 152 reported deaths, accounting for 3% of the causes of mortality. Four additional individuals were suspected to have gastric rupture. Vomiting and abdominal pain, although rare in PWS, were frequent findings in this cohort. The physician should consider an emergent evaluation for gastric rupture and necrosis in individuals with PWS who present with vomiting and abdominal pain.

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