Carbohydrate metabolism is not impaired after 3 years of growth hormone therapy in children with Prader-Willi syndrome

Body Fat Distribution Contributes to Defining the Relationship between Insulin Resistance and Obesity in Human Diseases

The risk for metabolic and cardiovascular complications of obesity is defined by body fat distribution rather than global adiposity. Unlike subcutaneous fat, visceral fat (including hepatic steatosis) reflects insulin resistance and predicts type 2 diabetes and cardiovascular disease. In humans, available evidence indicates that the ability to store triglycerides in the subcutaneous adipose tissue reflects enhanced insulin sensitivity. Prospective studies document an association between larger subcutaneous fat mass at baseline and reduced incidence of impaired glucose tolerance. Case-control studies reveal an association between genetic predisposition to insulin resistance and a lower amount of subcutaneous adipose tissue. Human peroxisome proliferator-activated receptorgamma (PPAR-γ) promotes subcutaneous adipocyte differentiation and subcutaneous fat deposition, improving insulin resistance and reducing visceral fat. Thiazolidinediones reproduce the effects of PPAR-γ activation and therefore increase the amount of subcutaneous fat while enhancing insulin sensitivity and reducing visceral fat. Partial or virtually complete lack of adipose tissue (lipodystrophy) is associated with insulin resistance and its clinical manifestations, including essential hypertension, hypertriglyceridemia, reduced HDL-c, type 2 diabetes, cardiovascular disease, and kidney disease. Patients with Prader Willi syndrome manifest severe subcutaneous obesity without insulin resistance. The impaired ability to accumulate fat in the subcutaneous adipose tissue may be due to deficient triglyceride synthesis, inadequate formation of lipid droplets, or defective adipocyte differentiation. Lean and obese humans develop insulin resistance when the capacity to store fat in the subcutaneous adipose tissue is exhausted and deposition of triglycerides is no longer attainable at that location. Existing adipocytes become large and reflect the presence of insulin resistance.

Do patients with Prader-Willi syndrome have favorable glucose metabolism?

Background

In recent years, more studies have observed that patients with Prader–Willi syndrome have lower insulin levels and lower insulin resistance than body mass index-matched controls, which may suggest protected glucose metabolism.

Method

The PubMed and Web of Science online databases were searched to identify relevant studies published in the English language using the terms “Prader–Willi syndrome” with “glucose”, “insulin”, “diabetes mellitus”, “fat”, “adipo*”, “ghrelin”, “oxytocin”, “irisin” or “autonomic nervous system”.

Results

The prevalence of impaired glucose intolerance, type 2 diabetes mellitus and some other obesity-associated complications in patients with Prader–Willi syndrome tends to be lower when compared to that in general obesity, which is consistent with the hypothetically protected glucose metabolism. Factors including adipose tissue, adiponectin, ghrelin, oxytocin, irisin, growth hormone and the autonomic nervous system possibly modulate insulin sensitivity in patients with Prader–Willi syndrome.

Conclusion

Although lower insulin levels, lower IR and protected glucose metabolism are widely reported in PWS patients, the causes are still mysterious. Based on existing knowledge, we cannot determine which factor is of utmost importance and what are the underlying mechanisms, and further research is in urgent need.

Early start of growth hormone is associated with positive effects on auxology and metabolism in Prader-Willi-syndrome

BACKGROUND

Prader-Willi-Syndrome (PWS) is characterized by hypothalamic-pituitary dysfunction. Recent research suggests starting growth hormone-treatment (GHT) as soon as possible. The aim of this study is to analyze possible differences in auxological parameters, carbohydrate and lipid metabolism between two groups of children with PWS that started GHT either during or after their first year of life.

STUDY DESIGN

Retrospective longitudinal study of 62 children (31 males) with genetically confirmed PWS. Upon diagnosis all children were offered GHT, some started immediately, others commenced later. Cohort A (n = 21; 11 males) started GHT at 0.3-0.99 yrs. (mean 0.72 yrs) and Cohort B (n = 41; 20 males) commenced GHT at 1.02-2.54 yrs. (mean 1.42 yrs) of age. Fasting morning blood samples and auxological parameters were obtained before the start of therapy and semi-annually thereafter. Differences between the two cohorts were estimated with a linear mixed-effect model.

RESULTS

Mean length/height-SDS_PWS differed significantly between the groups [1 yr: A: 0.37 (±0.83) vs B: 0.05 (±0.56); 5 yrs.: A: 0.81 (±0.67) vs B: 0.54 (±0.64); p = 0.012]. No significant differences were found in BMI, lean body mass or body fat. Low-density cholesterol was significantly lower in A than in B [LDL: 1 yr: A: 79 (±20) mg/dl vs B: 90 (±19) mg/dl; 5 yrs.: A: 91(±18) mg/dl vs 104 (±26) mg/dl; p = 0.024]. We found significant differences in the glucose homeostasis between the groups [fasting insulin: p = 0.012; HOMA-IR: p = 0.006; HbA1c: p < 0.001; blood glucose: p = 0.022].

CONCLUSIONS

An early start of GHT during the first year of life seems to have a favorable effect on height-SDS and metabolic parameters.

Update on Diabetes Mellitus and Glucose Metabolism Alterations in Prader-Willi Syndrome

PURPOSE OF REVIEW

This review summarizes our current knowledge on type 2 diabetes mellitus (T2DM) and glucose metabolism alterations in Prader-Willi syndrome (PWS), the most common syndromic cause of obesity, and serves as a guide for future research and current best practice.

RECENT FINDINGS

Diabetes occurs in 10-25% of PWS patients, usually in adulthood. Severe obesity is a significant risk factor for developing of T2DM in PWS. Paradoxically, despite severe obesity, a relative hypoinsulinemia, without the expected insulin resistance, is frequently observed in PWS. The majority of PWS subjects with T2DM are asymptomatic and diabetes-related complications are infrequent. Long-term growth hormone therapy does not adversely influence glucose homeostasis in all ages, if weight gain does not occur. Early intervention to prevent obesity and the regular monitoring of glucose levels are recommended in PWS subjects. However, further studies are required to better understand the physiopathological mechanisms of T2DM in these patients.

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.

Prevalence and risk factors for type 2 diabetes mellitus with Prader-Willi syndrome: a single center experience

BACKGROUND

Prader-Willi syndrome (PWS) is often related to severe obesity and type-2 diabetes mellitus (T2DM). However, few studies, and none in Korea, have examined prevalence of T2DM and other variables in PWS. The aim of this study was to identify the prevalence and associated risk factors for T2DM in Korean patients with PWS.

METHODS

We performed a retrospective cohort study of the 84 PWS patients aged 10 or over (10.3-35.8 years of age) diagnosed with PWS at Samsung Medical Center from 1994 to 2016. We estimated occurrence of T2DM according to age (10-18 years versus >18 years), body mass index (BMI), genotype, history of growth hormone therapy, homeostasis model of assessment-insulin resistance (HOMA-IR), and the presence of dyslipidemia, hypogonadism, or central precocious puberty. Additionally, we investigated cutoff values of risk factors for development of T2DM.

RESULTS

Twenty-nine of a total 211 patients, diagnosed with PWS over the study period, were diagnosed as having T2DM (13.7%, mean age 15.9 ± 3.6 years). In the >18 years group, obesity, HOMA-IR, and presence of dyslipidemia, hypogonadism, or central precocious puberty were associated with the occurrence of T2DM in univariate analysis. In multivariate logistic regression analysis, only obesity (p = 0.001) and HOMA-IR (p < 0.001) were significant predictive factors for T2DM. Based on the receiver operating a characteristic curve analysis, the cutoff values of HOMA-IR and BMI for predicting T2DM were >2.7 and >28.49 kg/m2, respectively. Of the 29 patients, seven had ≥1 microvascular complication, with non-proliferative diabetic retinopathy in 6 of 7 cases. Advanced age and HOMA-IR were positively correlated with diabetic microvascular complications (p < 0.05, Spearman correlation coefficient 0.393 and 0.434, respectively).

CONCLUSIONS

The prevalence of diabetes in Korean PWS was similar to that in previous results. BMI and HOMA-IR were strong predictive factors for the development of T2DM in PWS. We specifically suggest the regular monitoring of glucose homeostasis parameters through a detailed settlement of ethnically specific cutoff values for BMI and HOMA-IR in PWS to prevent progression of T2DM and diabetic microvascular complications.

Cellular and disease functions of the Prader-Willi Syndrome gene MAGEL2

Melanoma antigen L2 (MAGEL2 or MAGE-L2) is a member of the MAGE family of ubiquitin ligase regulators. It is maternally imprinted and often paternally deleted or mutated in the related neurodevelopmental syndromes, Prader-Willi Syndrome (PWS) and Schaaf-Yang Syndrome (SHFYNG). MAGEL2 is highly expressed in the hypothalamus and plays an important role in a fundamental cellular process that recycles membrane proteins from endosomes through the retromer sorting pathway. MAGEL2 is part of a multi-subunit protein complex consisting of MAGEL2, the TRIM27 E3 ubiquitin ligase, and the USP7 deubiquitinating enzyme. The MAGEL2-USP7-TRIM27 (or MUST) complex facilitates the retromer recycling pathway through ubiquitination and activation of the WASH actin nucleation promoting factor. This review provides an overview of the MAGE protein family of ubiquitin ligases regulators and details the molecular and cellular role of MAGEL2 in ubiquitination, actin regulation and endosomal sorting processes, as well as MAGEL2 implications in PWS and SHFYNG disorders. The physiological functions of MAGEL2, elucidated through the study of Magel2 knockout mouse models, are also discussed.

Long-term side effects of growth hormone treatment in children with Prader-Willi syndrome

The main motivations of growth hormone (GH) treatment of Prader-Willi syndrome (PWS) are the stimulation of growth and lean muscle mass. Furthermore GH therapy in Prader-Willi children seems to favorably affect their behavior and mental performances. It is still a matter of discussion whether GH therapy in PWS should be considered responsible for specific adverse events. The most significant of them are scoliosis and breathing disorders, the latter considered being responsible for some deaths, reported in children with PWS, mainly at the beginning of GH therapy. Obstructive sleep apnea was occasionally reported also in patients treated with GH for several years. The review reports and discusses the latest data related to side effects of long-term GH treatment in children with PWS.

Clinical Effects of Treatment for Hypogonadism in Male Adolescents with Prader-Labhart-Willi Syndrome

BACKGROUND

In boys with Prader-Labhart-Willi syndrome (PWS), hypogonadism causes pubertal arrest and reduces pubertal muscle growth. Formerly, it was assumed that therapy with gonadal hormones accentuates behaviour abnormalities in PWS. Our aim was to assess the clinical effects of human chorionic gonadotropin (hCG) therapy on pubertal development, muscle mass and behaviour in adolescents with PWS.

METHODS

6 peripubertal boys with PWS undergoing long-term treatment with growth hormone were examined 6-monthly for at least 2 years before and after pubertal arrest (13.5 +/- 0.3 years, mean +/- SEM) and the beginning of hCG therapy (500-1,500 IU twice weekly, intramuscularly). Height, weight, pubertal stage, bone age, body composition (by dual-energy X-ray absorptiometry), testosterone levels and behaviour abnormalities (obtained from parents) were assessed.

RESULTS

Testicular volume and lean mass were reduced in pubertal boys with PWS. During hCG therapy, testosterone levels and lean mass significantly increased (at the beginning and after 2 years of hCG therapy: 2.3 +/- 0.9 and 10.7 +/- 1.3 nmol/l, -3.1 +/- 0.3 and -1.4 +/- 0.6 SD, respectively), and fat mass stabilized at 38%. The characteristically observed PWS-associated problems, mood instability, aggressiveness and difficulties in social interaction, did not deteriorate during therapy.

CONCLUSION

In the present study, timely application of hCG to treat hypogonadism in boys with PWS promoted virilization and normalized muscle mass without detrimental effects on behaviour. Larger studies comparing hCG therapy with testosterone replacement would be useful.

Insulin sensitivity in growth hormone-deficient children: influence of replacement treatment

OBJECTIVE

In adults, excessive GH secretion may lead to secondary diabetes mellitus, while prolonged GH treatment may accelerate the onset of type 2 diabetes mellitus in predisposed children. The aim of the study was to evaluate insulin sensitivity (IS) and glucose tolerance (GT) in a group of GH-deficient children treated with GH for a period of 6 years.

PATIENTS AND DESIGN

One hundred and twenty-eight children (40 females, 88 males) were included in the study. At the beginning of treatment chronological age was 8.9 +/- 3.2 years, height standard deviation score (SDS) -2.43 +/- 0.90 and body mass index (BMI) SDS 0.18 +/- 1.60. At the end of the study chronological age was 13.0 +/- 2.9 years, height SDS -1.24 +/- 1.27 and BMI SDS 0.23 +/- 1.54. GH was administered at a mean weekly dosage of 0.3 mg/kg, injected subcutaneously over 6-7 days. GT was assessed according to the criteria of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. IS was evaluated with the quantitative insulin sensitivity check index (QUICKI).

RESULTS

No cases of impaired GT or diabetes were recorded during the follow-up period. IS, already lower than in controls before starting treatment with GH, decreased significantly during the first year of therapy (QUICKI: 0.346 +/- 0.033 vs. 0.355 +/- 0.044, P < 0.05), with no further decrease in the following years. No correlation was found between QUICKI, BMI, years of treatment and onset of puberty.

CONCLUSIONS

GH treatment in GH-deficient children does not lead to an impaired GT or type 2 diabetes mellitus, although it does significantly decrease IS.