Methods of Determining Energy Expenditure in Individuals with Prader-Willi Syndrome: A Systematic Literature Review

Prader-Willi syndrome (PWS) is a rare disorder characterised by varying nutritional phases that occur throughout the lifespan, ranging from failure to thrive to hyperphagia. If uncontrolled, the imbalance between energy intake and expenditure results in obesity development and increased morbidity and mortality risk. Although measures of energy requirements for accurate nutrition assessment are vital, the evidence appears sparse and heterogeneous; hence, the aim of this review was to examine the available literature on energy expenditure predicted or measured using various methods in individuals with PWS. Studies were sought that presented methods and results on resting energy expenditure or basal metabolic rate. A narrative synthesis was completed to present the study characteristics and results. Methods of determining energy requirements included predictive equations and indirect calorimetry. Differences amongst ages, growth hormone therapy, fasting status, and measures in which results were presented were limitations to appropriately summarising and identifying trends in energy expenditure. Indirect calorimetry was identified as the most accurate method; however, it is not widely available in all settings. Further research is encouraged to support the development of valid and reliable predictive equations that will better inform and improve the efficiency of clinical practice in supporting people with PWS.

Similar metabolic pathways are affected in both Congenital Myasthenic Syndrome-22 and Prader-Willi Syndrome

Loss of prolyl endopeptidase-like (PREPL) encoding a serine hydrolase with (thio)esterase activity leads to the recessive metabolic disorder Congenital Myasthenic Syndrome-22 (CMS22). It is characterized by severe neonatal hypotonia, feeding problems, growth retardation, and hyperphagia leading to rapid weight gain later in childhood. The phenotypic similarities with Prader-Willi syndrome (PWS) are striking, suggesting that similar pathways are affected. The aim of this study was to identify changes in the hypothalamic-pituitary axis in mouse models for both disorders and to examine mitochondrial function in skin fibroblasts of patients and knockout cell lines. We have demonstrated that Prepl is downregulated in the brains of neonatal PWS-IC-p/+m mice. In addition, the hypothalamic-pituitary axis is similarly affected in both Prepl-/- and PWS-IC-p/+m mice resulting in defective orexigenic signaling and growth retardation. Furthermore, we demonstrated that mitochondrial function is altered in PREPL knockout HEK293T cells and can be rescued with the supplementation of coenzyme Q10. Finally, PREPL-deficient and PWS patient skin fibroblasts display defective mitochondrial bioenergetics. The mitochondrial dysfunction in PWS fibroblasts can be rescued by overexpression of PREPL. In conclusion, we provide the first molecular parallels between CMS22 and PWS, raising the possibility that PREPL substrates might become therapeutic targets for treating both disorders.

Metabolomic profiling of Prader-Willi syndrome compared with essential obesity

Introduction

Prader-Willi syndrome (PWS) is a rare disease, which shows a peculiar clinical phenotype, including obesity, which is different from essential obesity (EOB). Metabolomics might represent a valuable tool to reveal the biochemical mechanisms/pathways underlying clinical differences between PWS and EOB. The aim of the present (case-control, retrospective) study was to determine the metabolomic profile that characterizes PWS compared to EOB.

Methods

A validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) targeted metabolomic approach was used to measure a total of 188 endogenous metabolites in plasma samples of 32 patients with PWS (F/M = 23/9; age: 31.6 ± 9.2 years; body mass index [BMI]: 42.1 ± 7.0 kg/m2), compared to a sex-, age- and BMI-matched group of patients with EOB (F/M = 23/9; age: 31.4 ± 6.9 years; BMI: 43.5 ± 3.5 kg/m2).

Results

Body composition in PWS was different when compared to EOB, with increased fat mass and decreased fat-free mass. Glycemia and HDL cholesterol were higher in patients with PWS than in those with EOB, while insulinemia was lower, as well as heart rate. Resting energy expenditure was lower in the group with PWS than in the one with EOB, a difference that was missed after fat-free mass correction. Carrying out a series of Tobit multivariable linear regressions, adjusted for sex, diastolic blood pressure, and C reactive protein, a total of 28 metabolites was found to be associated with PWS (vs. non-PWS, i.e., EOB), including 9 phosphatidylcholines (PCs) ae, 5 PCs aa, all PCs aa, 7 lysoPCs a, all lysoPCs, 4 acetylcarnitines, and 1 sphingomyelin, all of which were higher in PWS than EOB.

Conclusions

PWS exhibits a specific metabolomic profile when compared to EOB, suggesting a different regulation of some biochemical pathways, fundamentally related to lipid metabolism.

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

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

m6A-Mediated Upregulation of Imprinted in Prader-Willi Syndrome Induces Aberrant Apical-Basal Polarization and Oxidative Damage in RPE Cells

Purpose

To reveal the clinical significance, pathological involvement and molecular mechanism of imprinted in Prader-Willi syndrome (IPW) in RPE anomalies that contribute to AMD.

Methods

IPW expression under pathological conditions were detected by microarrays and qPCR assays. In vitro cultured fetal RPE cells were used to study the pathogenicity induced by IPW overexpression and to analyze its upstream and downstream regulatory networks.

Results

We showed that IPW is upregulated in the macular RPE-choroid tissue of dry AMD patients and in fetal RPE cells under oxidative stress, inflammation and dedifferentiation. IPW overexpression in fetal RPE cells induced aberrant apical-basal polarization as shown by dysregulated polarized markers, disrupted tight and adherens junctions, and inhibited phagocytosis. IPW upregulation was also associated with RPE oxidative damages, as demonstrated by intracellular accumulation of reactive oxygen species, reduced cell proliferation, and accelerated cell apoptosis. Mechanically, N6-methyladenosine level of the IPW transcript regulated its stability with YTHDC1 as the reader. IPW mediated RPE features by suppressing MEG3 expression to sequester its inhibition on the AKT serine-threonine kinase (AKT)/mammalian target of rapamycin (mTOR) pathway. We also noticed that the mTOR inhibitor rapamycin suppresses the AKT/mTOR pathway to alleviate the IPW-induced RPE anomalies.

Conclusions

We revealed that IPW overexpression in RPE induces aberrant apical-basal polarization and oxidative damages, thus contributing to AMD progression. We also annotated the upstream and downstream regulatory networks of IPW in RPE. Our findings shed new light on the molecular mechanisms of RPE dysfunctions, and indicate that IPW blockers may be a promising option to treat RPE abnormalities in AMD.

Insulin secretion deficits in a Prader-Willi syndrome β-cell model are associated with a concerted downregulation of multiple endoplasmic reticulum chaperones

Prader-Willi syndrome (PWS) is a multisystem disorder with neurobehavioral, metabolic, and hormonal phenotypes, caused by loss of expression of a paternally-expressed imprinted gene cluster. Prior evidence from a PWS mouse model identified abnormal pancreatic islet development with retention of aged insulin and deficient insulin secretion. To determine the collective roles of PWS genes in β-cell biology, we used genome-editing to generate isogenic, clonal INS-1 insulinoma lines having 3.16 Mb deletions of the silent, maternal- (control) and active, paternal-allele (PWS). PWS β-cells demonstrated a significant cell autonomous reduction in basal and glucose-stimulated insulin secretion. Further, proteomic analyses revealed reduced levels of cellular and secreted hormones, including all insulin peptides and amylin, concomitant with reduction of at least ten endoplasmic reticulum (ER) chaperones, including GRP78 and GRP94. Critically, differentially expressed genes identified by whole transcriptome studies included reductions in levels of mRNAs encoding these secreted peptides and the group of ER chaperones. In contrast to the dosage compensation previously seen for ER chaperones in Grp78 or Grp94 gene knockouts or knockdown, compensation is precluded by the stress-independent deficiency of ER chaperones in PWS β-cells. Consistent with reduced ER chaperones levels, PWS INS-1 β-cells are more sensitive to ER stress, leading to earlier activation of all three arms of the unfolded protein response. Combined, the findings suggest that a chronic shortage of ER chaperones in PWS β-cells leads to a deficiency of protein folding and/or delay in ER transit of insulin and other cargo. In summary, our results illuminate the pathophysiological basis of pancreatic β-cell hormone deficits in PWS, with evolutionary implications for the multigenic PWS-domain, and indicate that PWS-imprinted genes coordinate concerted regulation of ER chaperone biosynthesis and β-cell secretory pathway function.

Positive effects of ketogenic diet on weight control in children with obesity due to Prader-Willi syndrome

OBJECTIVE

Prader-Willi Syndrome (PWS) is the most common genetic cause of obesity. Prevention and management of obesity, which represents the main cause of morbidity and mortality in these patients, is essential. Ketogenic diet (KD) is used in the treatment of various disorders, however knowledge of its effect in PWS is lacking. The present study assesses the characteristics of patients with PWS who were on KD.

DESIGN AND PATIENTS

This is a retrospective, cross-sectional descriptive study investigating the subjects with PWS, who had received KD for at least 6 months.

RESULTS

Ten patients with PWS [median age 52.5 (47-77) months] complied with KD. The median treatment period was 16.5 [11-52] months. Of the daily calorie, 75%-85% were from fat, and 15%-25% from protein + carbohydrate. The baseline body weight standard deviation (SD) score before diet therapy was 2.10 [-1.11-4.11], whereas it was 0.05 [-0.92-1.2] at final evaluation (p = .007). The baseline median BMI SD score before diet therapy was 3.05 [-0.21-3.72], whereas it was 0.41 [-0.87-1.57] at final evaluation (p = .002). The height SD score remained unchanged. Mild hypercholesterolaemia was the most common biochemical abnormality during treatment with KD.

CONCLUSION

Our results indicate that KD might have a favourable effect on weight management in PWS.

Analysis of SNHG14: A Long Non-Coding RNA Hosting SNORD116, Whose Loss Contributes to Prader-Willi Syndrome Etiology

The Small Nucleolar Host Gene 14 (SNHG14) is a host gene for small non-coding RNAs, including the SNORD116 small nucleolar C/D box RNA encoding locus. Large deletions of the SNHG14 locus, as well as microdeletions of the SNORD116 locus, lead to the neurodevelopmental genetic disorder Prader-Willi syndrome. This review will focus on the SNHG14 gene, its expression patterns, its role in human cancer, and the possibility that single nucleotide variants within the locus contribute to human phenotypes in the general population. This review will also include new in silico data analyses of the SNHG14 locus and new in situ RNA expression patterns of the Snhg14 RNA in mouse midbrain and hindbrain regions.

Analysis of the hypothalamic oxytocin system and oxytocin receptor-expressing astrocytes in a mouse model of Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a neurodevelopmental disorder characterized by hyperphagia, obesity, developmental delay and intellectual disability. Studies suggest dysfunctional signaling of the neuropeptide oxytocin as one of the key mechanisms in PWS, and administration of oxytocin via intranasal or systemic routes yielded promising results in both humans and mouse models. However, a detailed assessment of the oxytocin system in mouse models of PWS such as the Magel2-deficient Magel2^tm1.Stw mouse, is lacking. In the present study, we performed an automated counting of oxytocin cells in the entire paraventricular nucleus of the hypothalamus of Magel2^tm1.Stw and wild-type control mice and found a significant reduction in the caudal part, which represents the parvocellular subdivision. In addition, based on the recent discovery that some astrocytes express the oxytocin receptor (OTR), we performed detailed analysis of astrocyte numbers and morphology in various brain regions, and assessed expression levels of the astrocyte marker glial fibrillary acidic protein, which was significantly decreased in the hypothalamus, but not other brain regions in Magel2^tm1.Stw mice. Finally, we analyzed the number of OTR-expressing astrocytes in various brain regions and found a significant reduction in the nucleus accumbens of Magel2^tm1.Stw mice, as well as a sex-specific difference in the lateral septum. This study suggests a role for caudal paraventricular nucleus oxytocin neurons as well as OTR-expressing astrocytes in a mouse model of PWS, provides novel information about sex-specific expression of astrocytic OTRs, and presents several new brain regions containing OTR-expressing astrocytes in the mouse brain.

Dysregulated adipose tissue expansion and impaired adipogenesis in Prader-Willi syndrome children before obesity-onset

OBJECTIVE

Prader-Willi syndrome (PWS) is a rare genetic imprinting disorder resulting from the expression loss of genes on the paternally inherited chromosome 15q11-13. Early-onset life-thriving obesity and hyperphagia represent the clinical hallmarks of PWS. The noncoding RNA gene SNORD116 within the minimal PWS genetic lesion plays a critical role in the pathogenesis of the syndrome. Despite advancements in understanding the genetic basis for PWS, the pathophysiology of obesity development in PWS remains largely uncharacterized. Here, we aimed to investigate the signatures of adipose tissue development and expansion pathways and associated adipose biology in PWS children without obesity-onset at an early stage, mainly from the perspective of the adipogenesis process, and further elucidate the underlying molecular mechanisms.

METHODS

We collected inguinal (subcutaneous) white adipose tissues (ingWATs) from phase 1 PWS and healthy children with normal weight aged from 6 M to 2 Y. Adipose morphology and histological characteristics were assessed. Primary adipose stromal vascular fractions (SVFs) were isolated, cultured in vitro, and used to determine the capacity and function of white and beige adipogenic differentiation. High-throughput RNA-sequencing (RNA-seq) was performed in adipose-derived mesenchymal stem cells (AdMSCs) to analyze transcriptome signatures in PWS subjects. Transient repression of SNORD116 was conducted to evaluate its functional relevance in adipogenesis. The changes in alternative pre-mRNA splicing were investigated in PWS and SNORD116 deficient cells.

RESULTS

In phase 1 PWS children, impaired white adipose tissue (WAT) development and unusual fat expansion occurred long before obesity onset, which was characterized by the massive enlargement of adipocytes accompanied by increased apoptosis. White and beige adipogenesis programs were impaired and differentiated adipocyte functions were disturbed in PWS-derived SVFs, despite increased proliferation capacity, which were consistent with the results of RNA-seq analysis of PWS AdMSCs. We also experimentally validated disrupted beige adipogenesis in adipocytes with transient SNORD116 downregulation. The transcript and protein levels of PPARγ, the adipogenesis master regulator, were significantly lower in PWS than in control AdMSCs as well as in SNORD116 deficient AdMSCs/adipocytes than in scramble (Scr) cells, resulting in the inhibited adipogenic program. Additionally, through RNA-seq, we observed aberrant transcriptome-wide alterations in alternative RNA splicing patterns in PWS cells mediated by SNORD116 loss and specifically identified a changed PRDM16 gene splicing profile in vitro.

CONCLUSIONS

Imbalance in the WAT expansion pathway and developmental disruption are primary defects in PWS displaying aberrant adipocyte hypertrophy and impaired adipogenesis process, in which SNORD116 deficiency plays a part. Our findings suggest that dysregulated adiposity specificity existing at an early phase is a potential pathological mechanism exacerbating hyperphagic obesity onset in PWS. This mechanistic evidence on adipose biology in young PWS patients expands knowledge regarding the pathogenesis of PWS obesity and may aid in developing a new therapeutic strategy targeting disturbed adipogenesis and driving AT plasticity to combat abnormal adiposity and associated metabolic disorders for PWS patients.

Advances in genetic mechanisms of hypothalamic dysfunction in Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a rare congenital developmental disorder mainly due to the absent expression of genes on the paternally inherited chromosome 15q11-q13 region. Most of the clinical symptoms of PWS are related to hypothalamic dysfunction, including hyperphagia, morbid obesity, mental retardation, and hypogonadism. However, the molecular genetic mechanism of PWS is not fully understood, especially the relationship between genotype and phenotype. In this review, we focus on the genetic mechanisms behind the hypothalamus dysfunction, summarizing the latest research progress of the roles of PWS candidate genes in chromosome 15q11-q13 region (NIPA1, NIPA2, TUBGCP5, CYFIP1, MAGEL2, NDN, MKRN3 and SNORD116) in hypothalamic disorders such as hyperphagia and obesity, hypogonadism, sleep-disordered breathing, growth retardation in PWS patients, to deepen the understanding of PWS syndrome and explore potential new drug targets.

Prader-Willi Syndrome and PCSK1 mutation: a novel presentation of combined syndromic and monogenic obesity

OBJECTIVE

Prader-Willi syndrome (PWS) is a genomic imprinting disorder predominantly caused by the absence of paternally expressed imprinted genes at chromosome 15q11.2-q13. The PCSK1 gene is vital for the processing of hypothalamic POMC to ACTH and α-MSH, leading to food intake suppression and increased energy expenditure. The aim of this study was to investigate whether our PWS patient had a defect in genes involved in the hypothalamic melanocortin-4 receptor (MC4R) pathway.

PATIENTS AND METHODS

A 27-year-old Greek man with PWS presented to the Adult Endocrine Clinic with morbid obesity and hyperphagia. He also had obstructive sleep apnea, growth hormone deficiency, gonadal failure and metabolic disturbances. At 6 years of age, chromosomal testing confirmed PWS with a deletion in the q11q13 region of the long arm of paternal chromosome 15.

RESULTS

At the age of 27 years, further genetic testing was conducted, and next generation sequencing revealed a PCSK1_pN221D_HET mutation which was confirmed by Sanger sequencing.

CONCLUSIONS

Our findings suggest that different genetic abnormalities may be present in an individual with PWS and that patients with PWS may need to be investigated for PCSK1 mutations, as the finding may potentially offer a novel treatment perspective for them.

Circulating Irisin in Children and Adolescents With Prader-Willi Syndrome: Relation With Glucose Metabolism

Irisin is a myokine involved in the browning of white adipose tissue and regulation of energy expenditure, glucose homeostasis and insulin sensitivity. Debated evidence exists on the metabolic role played by irisin in children with overweight or obesity, while few information exist in children with Prader Willi Syndrome (PWS), a condition genetically prone to obesity. Here we assessed serum irisin in relation to the metabolic profile and body composition in children and adolescents with and without PWS. In 25 PWS subjects [age 6.6-17.8y; body mass index standard deviation score (BMI SDS) 2.5 ± 0.3] and 25 age, and BMI-matched controls (age 6.8-18.0y; BMI SDS, 2.8 ± 0.1) we assessed irisin levels and metabolic profile inclusive of oral glucose tolerance test (OGTT), and body composition by dual-energy X-ray absorptiometry (DXA). In PWS, we recorded lower levels of fat-free mass (FFM) (p <0.05), fasting (p<0.0001) and 2h post-OGTT insulin (p<0.05) and lower insulin resistance as expressed by homeostatic model of insulin resistance (HOMA-IR) (p<0.0001). Irisin levels were significantly lower in PWS group than in controls with common obesity (p<0.05). In univariate correlation analysis, positive associations linked irisin to insulin OGTT₀ (p<0.05), insulin OGTT₁₂₀ (p<0.005), HOMA-IR (p<0.05) and fasting C-peptide (p<0.05). In stepwise multivariable regression analysis, irisin levels were independently predicted by insulin OGTT₁₂₀. These results suggest a link between irisin levels and insulin sensitivity in two divergent models of obesity.

Case Report: Hepatic Adenomatosis in a Patient With Prader-Willi Syndrome

Prader-Willi syndrome (PWS) is a genetic disorder caused by the lack of expression of genes on the paternally inherited chromosome region 15q11.2-q13. It is a multisystem disorder that is characterized by severe hypotonia with poor suck and feeding difficulties in early infancy, followed in early childhood by excessive eating and gradual development of morbid obesity. The incidence of type 2 diabetes mellitus is high, particularly in obese patients. Non-alcoholic fatty liver disease has also been reported in some patients with PWS. Liver adenomatosis is a benign vascular lesion of the liver, defined by the presence of >10 adenomas, in the otherwise healthy liver parenchyma. We report the first case of a patient with PWS with severe obesity, type 2 diabetes mellitus, and non-alcoholic fatty liver who also developed liver adenomatosis, review the pediatric literature on liver adenomatosis, and discuss the potential underlying mechanisms.

Hypothalamic neuropeptides and neurocircuitries in Prader Willi syndrome

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

Stimulated GH levels during the transition phase in Prader-Willi syndrome

PURPOSE

Early institution of GH therapy in children with Prader-Willi syndrome (PWS) yields beneficial effects on their phenotype and is associated with a persistent improvement of body composition, both in the transition age and in adulthood. Reports from GH stimulation testing in PWS adults, however, suggest that GH deficiency (GHD) is not a universal feature of the syndrome, and the current Consensus Guidelines suggest to perform a reassessment of persistent GHD so as to continue GH therapy after reaching adult height. Few data about GH responsiveness to stimulation testing throughout the transitional period in PWS are available to date. Thus, we investigated the prevalence of GHD in a large cohort of patients with PWS during the transition phase.

PATIENTS AND METHODS

One hundred forty-one PWS patients, 72 females and 69 males, aged 15.4-24.9 years, were evaluated by dynamic testing with growth hormone-releasing hormone (GHRH) plus arginine (GHRH + ARG). To define GHD, both BMI-dependent and BMI-independent diagnostic cut-off limits were considered.

RESULTS

According to BMI-dependent criteria, 10.7% of normal weight (NW), 18.5% of overweight and 22.1% of obese PWS maintained a status of GHD. Similar results were obtained by adopting a cut-off limit specific for the adult age (26.2%), as well as criteria for the transition phase in NW subjects (25%).

CONCLUSION

Our study shows that about 20% of patients with PWS fulfilled the criteria for GHD during the transitional age, suggesting the need of an integrated analysis of GH/IGF-I axis, in the context of the general clinical picture and other endocrine abnormalities, in all subjects after attainment of final stature.

A Comprehensive Review of Genetically Engineered Mouse Models for Prader-Willi Syndrome Research

Prader-Willi syndrome (PWS) is a neurogenetic multifactorial disorder caused by the deletion or inactivation of paternally imprinted genes on human chromosome 15q11-q13. The affected homologous locus is on mouse chromosome 7C. The positional conservation and organization of genes including the imprinting pattern between mice and men implies similar physiological functions of this locus. Therefore, considerable efforts to recreate the pathogenesis of PWS have been accomplished in mouse models. We provide a summary of different mouse models that were generated for the analysis of PWS and discuss their impact on our current understanding of corresponding genes, their putative functions and the pathogenesis of PWS. Murine models of PWS unveiled the contribution of each affected gene to this multi-facetted disease, and also enabled the establishment of the minimal critical genomic region (PWScr) responsible for core symptoms, highlighting the importance of non-protein coding genes in the PWS locus. Although the underlying disease-causing mechanisms of PWS remain widely unresolved and existing mouse models do not fully capture the entire spectrum of the human PWS disorder, continuous improvements of genetically engineered mouse models have proven to be very powerful and valuable tools in PWS research.

Glucagon stimulation test to assess growth hormone status in Prader-Willi syndrome

PURPOSE

Growth hormone deficiency (GHD) must be confirmed before starting treatment in adults with Prader-Willi syndrome (PWS). Most studies use the growth-hormone-releasing hormone plus arginine (GHRH-arginine) test. No data are available on the glucagon stimulation test (GST) in PWS. We compared the utility of fixed-dose (1 mg) GST versus GHRH-arginine test in diagnosing GHD.

METHODS

Adults and late adolescents with PWS underwent both tests on separate days. In the GHRH-arginine test, GHD was defined according to body mass index. In the GST, two cutoffs were analyzed: peak GH concentration < 3 ng/mL and < 1 ng/mL. For analyses, patients were divided into two groups according to body weight (≤ 90 kg and > 90 kg).

RESULTS

We analyzed 34 patients: 22 weighing ≤ 90 kg and 12 weighing > 90 kg. In patients weighing ≤ 90 kg, the two tests were concordant in 16 (72.72%) patients (k = 0.476, p = 0.009 with GST cutoff < 3 ng/mL, and k = 0.450, p = 0.035 with GST cutoff < 1 ng/mL). In patients weighing > 90 kg, the two tests were not concordant with GST cutoff < 3 ng/mL, but were concordant in 11 (91.6%) patients (k = 0.833, p = 0.003) with GST cutoff < 1 ng/mL. GH peaks on the two tests correlated (r = 0.725, p = 0.008).

CONCLUSION

Fixed-dose (1 mg) GST using a peak GH cutoff of < 3 ng/mL or < 1 ng/mL promises to be useful for screening for GHD in adults and late adolescents with PWS. However, in those weighing > 90 kg, the < 1 ng/mL cutoff seems better. Larger studies are necessary to establish definitive glucagon doses and cutoffs, especially in extremely obese patients.

Hair cortisol-a method to detect chronic cortisol levels in patients with Prader-Willi syndrome

BACKGROUND

Prader-Willi syndrome (PWS) is a multisymptomatic, rare, genetic, neurodevelopmental disorder in adults mainly characterized by hyperphagia, cognitive dysfunction, behavioral problems and risk of morbid obesity. Although endocrine insufficiencies are common, hypocortisolism is rare and knowledge on long-term cortisol concentrations is lacking. The aim of this study was to evaluate long-term cortisol levels in PWS by measurements of hair cortisol.

METHODS

Twenty-nine adults with PWS, 15 men and 14 women, median age 29 years, median BMI 27 kg/m², were included. Scalp hair samples were analyzed for cortisol content using liquid-chromatography tandem-mass spectrometry. In addition, a questionnaire on auxology, medication and stress were included. For comparison, 105 age- and sex-matched participants from the population-based Lifelines Cohort study were included as controls. The mean hair cortisol between the groups were compared and associations between BMI and stress were assessed by a generalized linear regression model.

RESULTS

In the PWS group large variations in hair cortisol was seen. Mean hair cortisol was 12.8 ± 25.4 pg/mg compared to 3.8 ± 7.3 pg/mg in controls (p = 0.001). The linear regression model similarly showed higher cortisol levels in patients with PWS, which remained consistent after adjusting for BMI and stress (p = 0.023). Furthermore, hair cortisol increased with BMI (p = 0.012) and reported stress (p = 0.014).

CONCLUSION

Long-term cortisol concentrations were higher in patients with PWS compared to controls and increased with BMI and stress, suggesting an adequate cortisol response to chronic stress. Hair cortisol demonstrate promising applications in the context of PWS treatment and disease management.

Effects of Bifidobacterium animalis Subsp. lactis (BPL1) Supplementation in Children and Adolescents with Prader-Willi Syndrome: A Randomized Crossover Trial

Prader-Willi syndrome (PWS) is a rare genetic disorder characterized by a wide range of clinical manifestations, including obesity, hyperphagia, and behavioral problems. Bifidobacterium animalis subsp. lactis strain BPL1 has been shown to improve central adiposity in adults with simple obesity. To evaluate BPL1's effects in children with PWS, we performed a randomized crossover trial among 39 patients (mean age 10.4 years). Participants were randomized to placebo-BPL1 (n = 19) or BPL1-placebo (n = 20) sequences and underwent a 12-week period with placebo/BPL1 treatments, a 12-week washout period, and a 12-week period with the crossover treatment. Thirty-five subjects completed the study. The main outcome was changes in adiposity, measured by dual-energy X-ray absorptiometry. Secondary outcomes included lipid and glucose metabolism, hyperphagia, and mental health symptoms. Generalized linear modeling was applied to assess differences between treatments. While BPL1 did not modify total fat mass compared to placebo, BPL1 decreased abdominal adiposity in a subgroup of patients older than 4.5 years (n = 28). BPL1 improved fasting insulin concentration and insulin sensitivity. Furthermore, we observed modest improvements in some mental health symptoms. A follow-up trial with a longer treatment period is warranted to determine whether BPL1 supplementation can provide a long-term therapeutic approach for children with PWS (ClinicalTrials.gov NCT03548480).

Structural Models for the Dynamic Effects of Loss-of-Function Variants in the Human SIM1 Protein Transcriptional Activation Domain

Single-minded homologue 1 (SIM1) is a transcription factor with numerous different physiological and developmental functions. SIM1 is a member of the class I basic helix-loop-helix-PER-ARNT-SIM (bHLH-PAS) transcription factor family, that includes several other conserved proteins, including the hypoxia-inducible factors, aryl hydrocarbon receptor, neuronal PAS proteins, and the CLOCK circadian regulator. Recent studies of HIF-a-ARNT and CLOCK-BMAL1 protein complexes have revealed the organization of their bHLH, PASA, and PASB domains and provided insight into how these heterodimeric protein complexes form; however, experimental structures for SIM1 have been lacking. Here, we describe the first full-length atomic structural model for human SIM1 with its binding partner ARNT in a heterodimeric complex and analyze several pathogenic variants utilizing state-of-the-art simulations and algorithms. Using local and global positional deviation metrics, deductions to the structural basis for the individual mutants are addressed in terms of the deleterious structural reorganizations that could alter protein function. We propose new experiments to probe these hypotheses and examine an interesting SIM1 dynamic behavior. The conformational dynamics demonstrates conformational changes on local and global regions that represent a mechanism for dysfunction in variants presented. In addition, we used our ab initio hybrid model for further prediction of variant hotspots that can be engineered to test for counter variant (restoration of wild-type function) or basic research probe.

A 24-Week Physical Activity Intervention Increases Bone Mineral Content without Changes in Bone Markers in Youth with PWS

Bone mineral density (BMD) is of concern in Prader-Willi syndrome (PWS). This study compared responses to a physical activity intervention in bone parameters and remodeling markers in youth with PWS (n = 45) and youth with non-syndromic obesity (NSO; n = 66). Measurements occurred at baseline (PRE) and after 24 weeks (POST) of a home-based active games intervention with strengthening and jumping exercises (intervention group = I) or after a no-intervention period (control group = C). Dual x-ray absorptiometry scans of the hip and lumbar spine (L1-L4) determined BMD and bone mineral content (BMC). Bone markers included fasting bone-specific alkaline phosphatase (BAP) and C-terminal telopeptide of type I collagen (CTx). Both I and C groups increased their hip BMD and BMC (p < 0.001). Youth with PWS-I increased their spine BMC from PRE to POST (p < 0.001) but not youth with PWS-C (p = 1.000). Youth with NSO (I and C) increased their spine BMC between PRE and POST (all p < 0.001). Youth with PWS showed lower BAP (108.28 ± 9.19 vs. 139.07 ± 6.41 U/L; p = 0.006) and similar CTx (2.07 ± 0.11 vs.1.84 ± 0.14 ng/dL; p = 0.193) than those with NSO regardless of time. Likely, the novelty of the intervention exercises for those with PWS contributed to gains in spine BMC beyond growth. Bone remodeling markers were unaltered by the intervention.

Epigenetics meets GPCR: inhibition of histone H3 methyltransferase (G9a) and histamine H3 receptor for Prader-Willi Syndrome

The role of epigenetic regulation is in large parts connected to cancer, but additionally, its therapeutic claim in neurological disorders has emerged. Inhibition of histone H3 lysine N-methyltransferase, especially G9a, has been recently shown to restore candidate genes from silenced parental chromosomes in the imprinting disorder Prader-Willi syndrome (PWS). In addition to this epigenetic approach, pitolisant as G-protein coupled histamine H3 receptor (H3R) antagonist has demonstrated promising therapeutic effects for Prader-Willi syndrome. To combine these pioneering principles of drug action, we aimed to identify compounds that combine both activities, guided by the pharmacophore blueprint for both targets. However, pitolisant as selective H3R inverse agonist with FDA and EMA-approval did not show the required inhibition at G9a. Pharmacological characterization of the prominent G9a inhibitor A-366, that is as well an inhibitor of the epigenetic reader protein Spindlin1, revealed its high affinity at H3R while showing subtype selectivity among subsets of the histaminergic and dopaminergic receptor families. This work moves prominent G9a ligands forward as pharmacological tools to prove for a potentially combined, symptomatic and causal, therapy in PWS by bridging the gap between drug development for G-protein coupled receptors and G9a as an epigenetic effector in a multi-targeting approach.

Firing activity of locus coeruleus noradrenergic neurons decreases in necdin-deficient mice, an animal model of Prader-Willi syndrome

BACKGROUND

Prader-Willi syndrome (PWS) is a neurodevelopmental disorder characterized by multiple respiratory, cognitive, endocrine, and behavioral symptoms, such as central apnea, intellectual disabilities, exaggerated stress responses, and temper tantrums. The locus coeruleus noradrenergic system (LC-NE) modulates a diverse range of behaviors, including arousal, learning, pain modulation, and stress-induced negative affective states, which are possibly correlated with the pathogenesis of PWS phenotypes. Therefore, we evaluated the LC-NE neuronal activity of necdin-deficient mice, an animal model of PWS.

METHODS

Heterozygous necdin-deficient mice (B6.Cg-Ndntm1ky) were bred from wild-type (WT) females to generate WT (+m/+p) and heterozygotes (+m/-p) animals, which were examined of LC-NE neuronal activity, developmental reflexes, and plethysmography.

RESULTS

On slice electrophysiology, LC-NE neurons of Ndntm1ky mice with necdin deficiency showed significantly decreased spontaneous activities and impaired excitability, which was mediated by enhanced A-type voltage-dependent potassium currents. Ndntm1ky mice also exhibited the neonatal phenotypes of PWS, such as hypotonia and blunt respiratory responses to hypercapnia.

CONCLUSIONS

LC-NE neuronal firing activity decreased in necdin-deficient mice, suggesting that LC, the primary source of norepinephrine in the central nervous system, is possibly involved in PWS pathogenesis.

Gut microbiota of obese subjects with Prader-Willi syndrome is linked to metabolic health

OBJECTIVE

The gut microbiota has been implicated in the aetiology of obesity and associated comorbidities. Patients with Prader-Willi syndrome (PWS) are obese but partly protected against insulin resistance. We hypothesised that the gut microbiota of PWS patients differs from that of non-genetically obese controls and correlate to metabolic health. Therefore, here we used PWS as a model to study the role of gut microbiota in the prevention of metabolic complications linked to obesity.

DESIGN

We conducted a case-control study with 17 adult PWS patients and 17 obese subjects matched for body fat mass index, gender and age. The subjects were metabolically characterised and faecal microbiota was profiled by 16S ribosomal RNA gene sequencing. The patients' parents were used as a non-obese control group. Stool samples from two PWS patients and two obese controls were used for faecal microbiota transplantations in germ-free mice to examine the impact of the microbiota on glucose metabolism.

RESULTS

The composition of the faecal microbiota in patients with PWS differed from that of obese controls, and was characterised by higher phylogenetic diversity and increased abundance of several taxa such as Akkermansia, Desulfovibrio and Archaea, and decreased abundance of Dorea. Microbial taxa prevalent in the PWS microbiota were associated with markers of insulin sensitivity. Improved insulin resistance of PWS was partly transmitted by faecal microbiota transplantations into germ-free mice.

CONCLUSION

The gut microbiota of PWS patients is similar to that of their non-obese parents and might play a role for the protection of PWS patients from metabolic complications.