Assessment of hyperphagia in Prader-Willi syndrome

Objective: Prader‐Willi syndrome (PWS), the leading known genetic cause of obesity, is characterized by intellectual disabilities, maladaptive and compulsive behaviors, and hyperphagia. Although complications of obesity resulting from hyperphagia are the leading cause of death in PWS, quantifying this drive for food has long been an unmet research need. This study provides factor‐analytic and within‐syndrome analyses of a new measure of hyperphagia in PWS. Research Methods and Procedure: A 13‐item informant measure, the Hyperphagia Questionnaire, was developed and administered to the parents of 153 persons with PWS, 4 to 51 years of age. The intelligence quotients, genetic subtypes of PWS, and BMIs of offspring were obtained, as were measures of their non‐food problem behaviors. Results: Factor analyses with varimax rotation produced three statistically and conceptually robust factors that accounted for 59% of the variance: Hyperphagic Behaviors, Drive, and Severity. Hyperphagic Behavior increased with age, whereas Drive remained stable, and Severity dipped in older adults. Hyperphagic Drive and Severity were positively correlated with non‐food behavior problems, and Hyperphagic Drive differentiated the 36% of participants with extreme obesity from those who had overweight/obese (48%) or healthy (16%) BMI classifications. Discussion: The Hyperphagia Questionnaire is a robust tool for relating breakthroughs in the neurobiology of hyperphagia to in vivo food‐seeking behavior and for examining the psychological and developmental correlates of hyperphagia in PWS. The Hyperphagia Questionnaire also offers a nuanced, real‐life outcome measure for future clinical trials aimed at curbing the life‐threatening drive for food in PWS.     

Behavioral and emotional problems in youngsters with Prader-Willi syndrome.

In this study we document the behavioral/emotional problems of 27 Prader-Willi syndrome (PWS) subjects assessed with the Achenbach Child Behaviour Checklist. Compared with normal subjects of the same age and sex, PW subjects showed significantly more problem behaviour. Of the PWS subjects 87% had total problem scores in the clinical range. No significant difference was found in the proportion of Prader-Willi patients scored in the clinical range on the Internalizing over the Externalizing syndrome. The need for systematic attention towards behavioral/emotional problems when PWS patients enter adolescence is emphasized.     

Hypopigmentation in the Prader-Willi syndrome.

Cutaneous and ocular pigmentation were evaluated in 29 individuals with the Prader-Willi syndrome (PWS). Criteria for hypopigmentation included the presence of type I or II skin, the lightest skin type in the family by history, and iris translucency on globe transillumination. On the basis of these criteria, 48% of the PWS individuals were hypopigmented. The presence of hypopigmentation correlated with a small interstitial deletion on the proximal long arm of chromosome 15; however, this deletion was also found in individuals who did not meet the full criteria for hypopigmentation. Hairbulb tyrosinase activity and glutathione content, as well as urine cysteinyldopa excretion, were low in PWS individuals with and without hypopigmentation and did not separate these two groups. We conclude that hypopigmentation is found in a significant proportion of individuals with PWS and that the hypopigmentation may be associated with a deletion of the long arm of chromosome 15. The mechanism for the hypopigmentation is unknown.     

Molecular characterization of Prader-Willi syndrome by real-time PCR

Prader-Willi syndrome (PWS) is a contiguous gene syndrome caused by the loss of function of genes situated within the 15q11-q13 region. The loss of function arises as a result of paternally derived mutations complemented by maternal imprinting. The molecular events underlying the disorder include interstitial deletions (70%), uniparental disomy (UPD) (25%), imprinting center defects (<5%), and rarely chromosomal translocations (<1%). The standard diagnosis of PWS is based on clinical observations and genetic investigations involving DNA methylation studies and fluorescence in situ hybridization (FISH) analysis. The absence of a paternal methylation pattern within 15q11 is sufficient for a diagnosis of PWS, and FISH analyses are used for the additional categorization of patients as either deletion or nondeletion. The main limitation of these investigations is that they neither determine the size of the molecular deletions nor permit detection of individuals with microdeletions in the PWS imprinting center that regulates imprinting in this region. We have designed and implemented a real-time PCR assay using genomic DNA and SYBR green I intercalating dye to determine the size of the chromosomal deletions in patients with PWS. This has been successfully performed on genomic DNA isolated from both peripheral blood leukocytes and buccal epithelial cells. Through this assay, the two common deletion classes in PWS were observed, and all results were 100% concordant with previous FISH assays performed on the same patients.     

Hyperghrelinemia is a common feature of Prader-Willi syndrome and pituitary stalk interruption: a pathophysiological hypothesis

BACKGROUND: Elevated plasma ghrelin levels have recently been reported in adults and children with Prader-Willi syndrome (PWS). The aim of the study is to investigate the relationship between obesity, growth hormone (GH) deficiency (GHD) and ghrelinemia in PWS and to examine whether hyperghrelinemia is specific to PWS. METHODS: We measured fasting ghrelinemia in children with PWS, idiopathic GHD (iGHD), obese children, controls and in 6 children presenting another congenital syndrome associated with GHD: pituitary stalk interruption (PSI). RESULTS: Children with PWS exhibited significantly higher ghrelin levels (995 pg/ml (801/1,099, median 1st/3rd quartile)) than iGHD (517 pg/ml (392/775)), obese (396 pg/ml (145/610)) and control (605 ng/ml (413/753)) children. Similar to PWS hyperghrelinemia was found in PSI children (1,029 pg/ml (705/1,151)), and was not modified by GH treatment. CONCLUSION: We conclude that hyperghrelinemia in PWS and PSI is not related to GH secretion. We hypothesize that a major site of ghrelin action is at the hypothalamic level and that a 'ghrelin resistance' syndrome may be present in these patients, primarily due to a hypothalamic defect. Combined alterations such as impaired serotonin receptor regulation associated with abnormal ghrelin responsiveness are probably responsible for obesity in PWS.     

Prader-Willi Syndrome: Relationship of Adiposity to Plasma Leptin Levels

Objective : Prader-Willi syndrome (PWS) is an autosomal dominant disorder involving the proximal long arm of chromosome 15, in which obesity is common. However, there is limited information on the underlying physiological mechanisms promoting obesity in this population. We tested whether there was a significant positive association between leptin and total body fat (TBF) in subjects with PWS, and whether this association was stronger among subjects with than without PWS. Research Methods and Procedures : We studied 21 PWS patients and 64 non-PWS controls on whom we measured serum leptin, total body fat, glucose, insulin, and resting energy expenditure. We tested whether the slope of the regression line between leptin and TBF (in kg), measured by dual energy X-ray absorptiometry, was the same for PWS patients and aon-PWS controls. Results : Regression analyses indicated that the leptin-TBF association was significantly stronger among PWS patients. In contrast, the slope of the leptin-body mass index association did not significantly differ between PWS patients and non-PWS controls. None of the other outcome variables showed associations with leptin. Discussion : Results suggest that the role of leptin in promoting obesity may be greater among subjects with PWS than among non-PWS controls.     

A molecular and cytogenetic study in Finnish Prader-Willi patients

The Prader-Willi syndrome (PWS) is a developmental disorder caused by a deficiency of paternal contributions, arising from differently sized deletions, uniparental disomy or rare imprinting mutations, in the chromosome region 15q11–q13. We studied 41 patients with suspected PWS and their parents using cytogenetic and molecular techniques. Of the 27 clinically typical PWS patients, 23 (85%) had a molecular deletion that could be classified into four size categories. Only 15 of them (71%) could be detected cytogenetically. Maternal uniparental heterodisomy was observed in four cases. The rest of the patients showed no molecular defects including rare imprinting mutations. In our experience, the use of the methylation test with the probe PW71 (D15S63), together with the probe hN4HS (SNRPN), which distinguishes between a deletion and uniparental disomy, is the method of choice for the diagnosis of PWS.     

Psychological profile and behavioural characteristics in 12 patients with Prader-Willi syndrome.

In the present study medical, psychological and behavioural aspects in 12 patients with Prader-Willi syndrome (PWS), aged between 13 months and 28 years are presented. In half of the patients the diagnosis of PWS was made before the age of one year. The contribution of cytogenetic investigations with the detection of a 15q11 deletion in half of the PWS patients is discussed. In the evaluation of the intellectual performances IQ levels were spread between 45 and 95 with a mean IQ of 54. A specific behavioral profile in all patients with characteristic fluctuations with age was observed. Rapid changes in behaviour increased with age and after puberty, mostly related with withholding of food. The present study reinforces the importance of early diagnosis in the PWS with adequate and intelligible information towards the parents. It may prevent the dramatic obesity which leads to severe physical problems and psychological burdens in PWS adolescents and adults.     

Effects of growth hormone therapy on glucose metabolism and insulin sensitivity indices in prepubertal children with Prader-Willi syndrome

In Prader-Willi syndrome (PWS) growth hormone therapy (GHT) improves height, body composition, agility and muscular strength. In such patients it is necessary to consider the potential diabetogenic effect of GHT, since they tend to develop type 2 diabetes, particularly after the pubertal age. The aim of our study was to investigate the effects of GHT on glucose and insulin homeostasis in PWS children. An oral glucose tolerance test (OGTT) was performed in 24 prepubertal PWS children (15 male, 9 female, age: 5.8 +/- 2.8 years), 16 were obese (group A) and 8 had normal weight (group B), before and after 2.7 +/- 1.3 years GHT (0.22 +/- 0.03 mg/kg/week) and, only at baseline, in 35 prepubertal children with simple obesity (19 male, 16 female) (group C). Fasting glucose and insulin, glucose tolerance, insulin sensitivity index (ISI), homeostasis model assessment of insulin resistance (HOMA-IR), quick insulin check index (QUICKI), area under the curves (AUC) of glucose and insulin were estimated. At the start of GHT, all PWS children were normoglycaemic and normotolerant but two developed impaired glucose tolerance after 2.2 and 1.9 years of therapy, respectively. At baseline, group A showed lower fasting insulin levels, HOMA-IR and AUC of insulin, higher ISI, QUICKI and AUC of glucose than group C. Comparing groups A and B, AUC of insulin was higher and ISI lower in group A. During GHT, a significant increase of fasting insulin and glucose, a worsening of insulin resistance (HOMA-IR) and insulin sensitivity (QUICKI) was found only in group A while ISI did not change. The AUC of glucose decreased in both groups instead AUC of insulin did not change. BMI-SDS decreased in group A and increased in group B. The increased insulin resistance and decreased insulin sensitivity in obese PWS patients, as well as the occurrence of impaired glucose tolerance during GHT, suggest that a close monitoring of glucose and insulin homeostasis is mandatory, especially in treated obese PWS children.     

A genetic model for the Prader-Willi syndrome and its implication for angelman syndrome

Summary Sporadic cases of Prader-Willi syndrome (PWS) are associated with the physical absence of the paternal Prader-Willi chromosome region (PWCR) by deletion 15q11–13, by segmental maternal heterodisomy or by chromosome rearrangements resulting in homozygosity for maternal PWCR. In isolated/familial cases, it is proposed that the expression of PWS depends on the functional absence caused by mutated gene(s) within the paternal PWCR. The same mutation on a maternally derived chromosome 15 is not able to express PWS. An epigenetic mechanism associated with the paternal meiosis is essential. In the Angelman syndrome (AS), inverse mechanisms are postulated. There is convincing evidence for specific PWS and AS genes or alleles within PWCR. This is compatible with the observations of interstitial chromosome deletions of the critical region in normal individuals or in probands with phenotypes other than PWS or AS. The new ideas of the model stated here are: (1) the proposed epigenetic mechanism in PWCR is obviously common in humans, but is usually of no phenotypic relevance; (2) interactions with specific chromosomal or gene mutations are required for the clinical expression of PWS or AS; (3) each factor alone is not able to produce an abnormal phenotype.     

Parent-specific complementary patterns of histone H3 lysine 9 and H3 lysine 4 methylation at the Prader-Willi syndrome imprinting center

The Prader-Willi syndrome (PWS)/Angelman syndrome (AS) region, on human chromosome 15q11-q13, exemplifies coordinate control of imprinted gene expression over a large chromosomal domain. Establishment of the paternal state of the region requires the PWS imprinting center (PWS-IC); establishment of the maternal state requires the AS-IC. Cytosine methylation of the PWS-IC, which occurs during oogenesis in mice, occurs only after fertilization in humans, so this modification cannot be the gametic imprint for the PWS/AS region in humans. Here, we demonstrate that the PWS-IC shows parent-specific complementary patterns of H3 lysine 9 (Lys9) and H3 lysine 4 (Lys4) methylation. H3 Lys9 is methylated on the maternal copy of the PWS-IC, and H3 Lys4 is methylated on the paternal copy. We suggest that H3 Lys9 methylation is a candidate maternal gametic imprint for this region, and we show how changes in chromatin packaging during the life cycle of mammals provide a means of erasing such an imprint in the male germline.     

Neural mechanisms underlying hyperphagia in Prader-Willi syndrome

Objective: Prader‐Willi syndrome (PWS) is a genetic disorder associated with developmental delay, obesity, and obsessive behavior related to food consumption. The most striking symptom of PWS is hyperphagia; as such, PWS may provide important insights into factors leading to overeating and obesity in the general population. We used functional magnetic resonance imaging to study the neural mechanisms underlying responses to visual food stimuli, before and after eating, in individuals with PWS and a healthy weight control (HWC) group. Research Methods and Procedures: Participants were scanned once before (pre‐meal) and once after (post‐meal) eating a standardized meal. Pictures of food, animals, and blurred control images were presented in a block design format during acquisition of functional magnetic resonance imaging data. Results: Statistical contrasts in the HWC group showed greater activation to food pictures in the pre‐meal condition compared with the post‐meal condition in the amygdala, orbitofrontal cortex, medial prefrontal cortex (medial PFC), and frontal operculum. In comparison, the PWS group exhibited greater activation to food pictures in the post‐meal condition compared with the pre‐meal condition in the orbitofrontal cortex, medial PFC, insula, hippocampus, and parahippocampal gyrus. Between‐group contrasts in the pre‐ and post‐meal conditions confirmed group differences, with the PWS group showing greater activation than the HWC group after the meal in food motivation networks. Discussion: Results point to distinct neural mechanisms associated with hyperphagia in PWS. After eating a meal, the PWS group showed hyperfunction in limbic and paralimbic regions that drive eating behavior (e.g., the amygdala) and in regions that suppress food intake (e.g., the medial PFC).     

Prader-Willi syndrome: clinical genetics, cytogenetics and molecular biology

Prader-Willi syndrome (PWS) is a neurodevelopmental disorder that arises from lack of expression of paternally inherited genes known to be imprinted and located in the chromosome 15q11-q13 region. PWS is considered the most common syndromal cause of life-threatening obesity and is estimated at 1 in 10,000 to 20,000 individuals. A de novo paternally derived chromosome 15q11-q13 deletion is the cause of PWS in about 70% of cases, and maternal disomy 15 accounts for about 25% of cases. The remaining cases of PWS result either from genomic imprinting defects (microdeletions or epimutations) of the imprinting centre in the 15q11-q13 region or from chromosome 15 translocations. Here, we describe the clinical presentation of PWS, review the current understanding of causative cytogenetic and molecular genetic mechanisms, and discuss future directions for research.     

Adrenarche in Prader-Willi syndrome appears not related to insulin sensitivity and serum adiponectin

Prader-Willi syndrome (PWS) is a genetic disorder characterized by dysmorphic features, obesity, hypogonadism, hypotonia and mental retardation. Obesity has been linked to insulin resistance and the latter has also been associated with premature adrenarche. Since up to date a controlled study to investigate adrenarche and its hormonal regulation was lacking in PWS, our aim was to assess whether prepubertal PWS patients develop premature adrenarche and its relationship with markers of insulin sensitivity. Fourteen prepubertal children with PWS (6 M, 8 F) and 10 non-syndromal simple obese matched controls (5 M, 5 F) participated (mean age: 7.62 +/- 1.84 years). A fasting blood sample was obtained for adrenal and ovarian androgens, sex hormone binding globulin, insulin-like growth factor-I (IGF-I), insulin-like growth factor binding protein-1, leptin, adiponectin and a lipid profile. Thereafter an oral glucose tolerance test was performed. PWS patients were smaller at birth and a higher proportion displayed premature pubarche. No differences were found in testosterone, androstenedione, sex hormone binding globulin, free androgen index, homeostatic model assessment-IR, 2-hour insulin, leptin or adiponectin levels. 17-hydroxyprogesterone and DHEAS levels however, were significantly higher in PWS. IGF-I levels were significantly lower in PWS and correlated significantly with height SDS (p < 0.05). In conclusion, a higher proportion of premature adrenarche in our PW patients was observed, which was not explained by differences in insulin sensitivity or plasma levels of adipokines and IGF-I.     

An unexpected function of the Prader-Willi syndrome imprinting center in maternal imprinting in mice

Genomic imprinting is a phenomenon that some genes are expressed differentially according to the parent of origin. Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are neurobehavioral disorders caused by deficiency of imprinted gene expression from paternal and maternal chromosome 15q11-q13, respectively. Imprinted genes at the PWS/AS domain are regulated through a bipartite imprinting center, the PWS-IC and AS-IC. The PWS-IC activates paternal-specific gene expression and is responsible for the paternal imprint, whereas the AS-IC functions in the maternal imprint by allele-specific repression of the PWS-IC to prevent the paternal imprinting program. Although mouse chromosome 7C has a conserved PWS/AS imprinted domain, the mouse equivalent of the human AS-IC element has not yet been identified. Here, we suggest another dimension that the PWS-IC also functions in maternal imprinting by negatively regulating the paternally expressed imprinted genes in mice, in contrast to its known function as a positive regulator for paternal-specific gene expression. Using a mouse model carrying a 4.8-kb deletion at the PWS-IC, we demonstrated that maternal transmission of the PWS-IC deletion resulted in a maternal imprinting defect with activation of the paternally expressed imprinted genes and decreased expression of the maternally expressed imprinted gene on the maternal chromosome, accompanied by alteration of the maternal epigenotype toward a paternal state spread over the PWS/AS domain. The functional significance of this acquired paternal pattern of gene expression was demonstrated by the ability to complement PWS phenotypes by maternal inheritance of the PWS-IC deletion, which is in stark contrast to paternal inheritance of the PWS-IC deletion that resulted in the PWS phenotypes. Importantly, low levels of expression of the paternally expressed imprinted genes are sufficient to rescue postnatal lethality and growth retardation in two PWS mouse models. These findings open the opportunity for a novel approach to the treatment of PWS.     

Evaluation of methylation analysis for diagnostic testing in 258 referrals suspected of Prader-Willi or Angelman syndromes

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are distinct neurodevelopmental disorders with interrelated genetic mechanisms because genomic imprinting within the chromosome 15q11–13 region affects both the PWS and the AS locus. Methylation analysis is one method of distinguishing between the maternally and paternally inherited chromosome 15. Here we present clinical and molecular data on a large series of 258 referred patients, evaluated with methylation analysis: 115 with suspected PWS and 143 with suspected AS. In these patients, the clinical phenotype was graded into three groups: classical (group 1); not classical but possible (group 2); not classical and unlikely (group 3). For PWS, a fourth group consisted of hypotonic babies. DNA methylation analysis confirmed the diagnosis of PWS in 30 patients (26%) and AS in 28 patients (20%). For 21 PWS patients the mechanism was established: 15 had deletions, 4 had uniparental disomy (UPD) and 2 a presumed imprinting defect. Clinically all those with an abnormal methylation pattern had the classical phenotype and none of those with a normal methylation pattern had classical PWS. For 23 AS patients in whom a mechanism was established, 17 had a deletion, 3 had UPD and 3 had a presumed imprinting defect. There was greater clinical overlap in AS, with 26 classical AS patients having a normal methylation pattern while an abnormal methylation pattern was seen in one patient from group 2. In addition, there were a further 40 patients with a normal methylation pattern in whom AS was still a possible diagnosis. Our conclusion is that methylation analysis provides an excellent screening test for both syndromes, providing ∼99% diagnosis for PWS and for AS, a 75% diagnostic rate, supplemented for the remaining 25% with an essential basic starting point to further investigations. Received: 10 February 1998 / Accepted: 7 July 1998     

Classical Prader-Willi syndrome with trisomy 15(pter----q12) plus de novo variant 15p11

We describe a boy with the classical Prader Willi syndrome (PWS), clinically, who had a chromosome abnormality not previously described in PWS. The karyotype was 47,XY,+mar, var(15)(p11). The marker was a fragment of 15 from 15pter----q12 and the variant 15p11 was de novo in origin. Overall, this karyotype contains increased 15 heterochromatin and we discuss alteration in the amount of 15 heterochromatin in PWS.