Prader-Willi syndrome: current understanding of cause and diagnosis

Plasma peptide YY and ghrelin levels in infants and children with Prader-Willi syndrome

An insatiable appetite is a cardinal feature of Prader-Willi syndrome (PWS) with stomach rupturing as a reported consequence. Peptide YY, secreted by the intestine and released post-prandially, inhibits appetite, while ghrelin, secreted by the stomach during mealtime hunger, stimulates appetite. Both peptide YY and ghrelin act at the brain level, particularly the hypothalamus. Recently, plasma ghrelin levels were reported to be elevated in children and adults with PWS but peptide YY levels have not been studied in this syndrome or ghrelin in infants with PWS. To further address the abnormal eating behavior in PWS, we obtained fasting plasma peptide YY and ghrelin levels in 12 infants and children with PWS ranging in age from 2.5 months to 13.3 years and compared them with values from normal populations reported in the literature. Plasma ghrelin levels in our patients with PWS were similar to those of other children with PWS and were significantly higher than those reported in obese children without PWS. Our infants with PWS had similar plasma ghrelin levels compared with our children with PWS but peptide YY levels in our children and infants with PWS were lower than reported in similarly aged individuals without PWS. In addition, we performed preliminary gene expression analysis of ghrelin and peptide YY and their receptors in patients with PWS using established lymphoblastoid cell lines but gene expression did not correlate with plasma ghrelin or peptide YY levels.

Isolated hypogonadotropic hypogonadism in a man with a history of head trauma during childhood

OBJECTIVE

To report a case of isolated hypogonadotropic hypogonadism as a delayed consequence of major head injury.

METHODS

We present the relevant history, findings on physical examination, and results of laboratory evaluation, and supportive data from appropriate reports in the literature are reviewed.

RESULTS

A 37-year-old man with progressive loss of libido, impotence, and gradual loss of facial and axillary hair had sustained severe trauma to the head (sufficient to cause blindness in one eye) in a fall from a tree at 7 years of age. Physical examination and laboratory investigations substantiated the presence of isolated hypogonadotropic hypogonadism. Other causes of hypogonadotropic hypogonadism, including Kallmann's syndrome, were excluded.

CONCLUSION

Severe head injury should be considered in the differential diagnosis of isolated hypogonadotropic hypogonadism. Long-term follow-up and endocrine assessment may be important in patients who have sustained severe head injury.

Prader-Willi syndrome with an unusually large 15q deletion due to an unbalanced translocation t(4;15)

Prader-Willi syndrome (PWS) is a neurobehavioral disorder caused by deletions in the 15q11-q13 region, by maternal uniparental disomy of chromosome 15 or by imprinting defects. Structural rearrangements of chromosome 15 have been described in about 5% of the patients with typical or atypical PWS phenotype. An 8-year-old boy with a clinical diagnosis of PWS, severe neurodevelopmental delay, absence of speech and mental retardation was studied by cytogenetic and molecular techniques, and an unbalanced de novo karyotype 45,XY,der(4)t(4;15)(q35;q14),-15 was detected after GTG-banding. The patient was diagnosed by SNURF-SNRPN exon 1 methylation assay, and the extent of the deletions on chromosomes 4 and 15 was investigated by microsatellite analysis of markers located in 4qter and 15q13-q14 regions. The deletion of chromosome 4q was distal to D4S1652, and that of chromosome 15 was located between D15S1043 and D15S1010. Our patient's severely affected phenotype could be due to the extent of the deletion, larger than usually seen in PWS patients, although the unbalance of the derivative chromosome 4 cannot be ruled out as another possible cause. The breakpoint was located in the subtelomeric region, very close to the telomere, a region that has been described as having the lowest gene concentrations in the human genome.

Prader-Willi syndrome resulting from an unbalanced translocation: characterization by array comparative genomic hybridization

Prader-Willi syndrome (PWS) is caused by lack of expression of paternally inherited genes on chromosome 15q11-->15q13. Most cases result from microdeletions in proximal chromosome 15q. The remainder results from maternal uniparental disomy of chromosome 15, imprinting center defects, and rarely from balanced or unbalanced chromosome rearrangements involving chromosome 15. We report a patient with multiple congenital anomalies, including craniofacial dysmorphology, microcephaly, bilateral cryptorchidism, and developmental delay. Cytogenetic analysis showed a de novo 45,XY,der(5)t(5;15)(p15.2;q13), -15 karyotype. In effect, the proband had monosomies of 5p15.2-->pter and 15pter-->15q13. Methylation polymerase chain reaction analysis of the promoter region of the SNRPN gene showed only the maternal allele, consistent with the PWS phenotype. The proband's expanded phenotype was similar to other patients who have PWS as a result of unbalanced translocations and likely reflects the contribution of the associated monosomy. Array comparative genomic hybridization (array CGH) confirmed deletions of both distal 5p and proximal 15q and provided more accurate information as to the size of the deletions and the molecular breakpoints. This case illustrates the utility of array CGH in characterizing complex constitutional structural chromosome abnormalities at the molecular level.

Self concept in people with Williams syndrome and Prader-Willi syndrome

This study explored self concepts in matched groups of adolescents and adults with Williams syndrome (WS) and Prader-Willi syndrome (PWS), using Damon and Hart's semi-structured interview. The main findings were that the WS participants were more productive in their responses to the interview, providing more self characteristics. The WS group also used more social and psychological categories in describing their self concept, and their responses were in general at a higher level than the responses for the PWS group. There were significant age-group differences, with the adolescents offering more self descriptions that were coded as physical and active, whereas the adults gave more social and psychological responses. Different themes were emphasized in the interviews from the two groups. These themes reflected the distinct phenotypes associated with these disorders, the participants life experiences, and their overall attitudes toward their syndrome.

Behavioral differences among subjects with Prader-Willi syndrome and type I or type II deletion and maternal disomy

OBJECTIVE

To determine whether phenotypic differences exist among individuals with Prader-Willi syndrome with either type I or type II deletions of chromosome 15 or maternal disomy 15 leading to a better understanding of cause and pathophysiology of this classical genetic syndrome.

METHODS

We analyzed clinical, anthropometric, and behavioral data in 12 individuals (5 men, 7 women; mean age: 25.9 +/- 8.8 years) with PWS and a type I (TI) deletion, 14 individuals (6 men, 8 women; mean age: 19.6 +/- 6.5 years) with PWS and a type II (TII) deletion, and 21 individuals (10 men, 11 women; mean age: 23.6 +/- 9.2 years) with PWS and maternal disomy 15 (UPD). The deletion type was determined by genotyping of DNA markers between proximal chromosome 15 breakpoints BP1 and BP2. TI deletions are approximately 500 kb larger than TII deletions. Several validated psychological and behavioral tests were used to assess phenotypic characteristics of individuals with PWS representing the 3 genetic subtypes.

RESULTS

Significant differences were found between the 2 deletion groups and those with UPD in multiple psychological and behavioral tests, but no differences were observed in other clinical or anthropometric data studied. Adaptive behavior scores were generally worse in individuals with PWS and the TI deletion, and specific obsessive-compulsive behaviors were more evident in the TI individuals compared with those with UPD. Individuals with PWS with TI deletions also had poorer reading and math skills as well as visual-motor integration.

CONCLUSIONS

Our study indicates that individuals with TI deletion generally have more behavioral and psychological problems than individuals with the TII deletion or UPD. Four recently identified genes have been identified in the chromosome region between BP1 and BP2 with 1 of the genes (NIPA-1) expressed in mouse brain tissue but not thought to be imprinted. It may be important for brain development or function. These genes are deleted in individuals with TI deletion and are implicated in compulsive behavior and lower intellectual ability in individuals with TI versus TII.

Somatropin Therapy in Adults with Prader-Willi Syndrome

Prader-Willi syndrome is a complex genetic disorder with a characteristic cognitive, behavioral, and endocrinologic phenotype. Obesity, partial growth hormone (GH) secretion, and hypogonadism are common. Results of several somatropin (GH therapy) studies in children with Prader-Willi syndrome have shown improvement in growth, body composition, physical strength, and agility. GH deficiency in adults without Prader-Willi syndrome is associated with abdominal obesity, insulin resistance, and an unfavorable lipid profile, and the partial state of GH deficiency seen in Prader-Willi syndrome thus renders these patients exposed to a lifelong risk of metabolic diseases. The nongrowth effects of somatropin in children with Prader-Willi syndrome have directed interest towards adults in preventing long-term consequences of GH deficiency, but the potential impact of somatropin therapy in adults with Prader-Willi syndrome is not known in detail. To date, only one study has been published. In this study, 17 patients (9 men and 8 women) with a mean age of 25 years and a mean body mass index of 35 +/- 3.2 kg/m2 were examined. Eleven had the Prader-Willi syndrome genotype. They were treated with somatropin (Genotropin) for 12 months after an initial placebo-controlled period of 6 months. Compared with placebo, somatropin increased insulin-like growth factor-1 levels (p < 0.01) and decreased body fat (p = 0.04). During the 12-month period with somatropin therapy, the mean reduction in body fat was 2.5% (p < 0.01), concomitant with a mean increase in lean body mass of 2.2kg (p < 0.05). Lipid profiles were normal in most patients before treatment and did not change. The oral glucose tolerance test was impaired in one patient at study start and in five patients at 12 months. No patients developed diabetes mellitus. Furthermore, insulin levels remained unchanged, and estimation of insulin resistance by homeostasis model assessment did not disclose any change. Transient adverse effects attributed to water retention occurred in three patients. In conclusion, the one published study of somatropin therapy in adults with Prader-Willi syndrome showed beneficial effects on body composition without pronounced adverse effects. However, further studies are required to establish the definite role and optimal dosage of somatropin, as well as long-term effects, in adults with Prader-Willi syndrome.

Energy metabolism in Bardet-Biedl syndrome

INTRODUCTION

Obesity is a consistent presenting feature of the Bardet-Biedl syndrome (BBS), a hereditary disorder caused by a single gene defect. This contrasts sharply with general obesity which, despite a strong hereditary component, has a multifactorial aetiology. For BBS, the phenotypic characterisation of the components of energy balance and the implications for their management remains relatively uninvestigated.

OBJECTIVE

A case-control study to determine whether energy metabolism in subjects with BBS differs from matched obese controls and to inform the clinical management of these patients.

METHODS

A total of 20 overweight and obese subjects with BBS (11 females, 9 males) matched for age, gender and BMI to 20 subjects without BBS. Resting metabolic rate (RMR) was measured by indirect calorimetry, physical activity by CSA accelerometry, body composition by the deuterium dilution technique and dietary intake by 7-day food records.

RESULTS

There was no significant difference between BBS and control subjects in body fat (male: % fat=38, s.d. 2.8 vs 34, s.d. 9.1, female: % fat=45, s.d. 5.9 vs 44, s.d. 8.1; P=0.46] or absolute RMR (male: 6.95, s.d. 1.55 MJ/day vs 7.19, s.d. 1.28 MJ/day; P=0.6). After adjustment for gender, age, fat-free mass and fat mass, there was no significant difference in RMR between BBS and control subjects (F(1, 30)=0.91; P=0.35). A lower level of physical activity was observed in BBS subjects (median cnts/min 259, IQR=153) compared to controls (median cnts/min=306, IQR=119, P=0.02). Reported energy intake, macronutrient composition and magnitude of under-reporting were comparable in both groups.

CONCLUSION

This study reveals no evidence for systematic differences in energy metabolism in subjects with BBS relative to other obese individuals, suggesting that the genetic basis of BBS is not associated with specific abnormalities in energy metabolism. This is an important finding for clinical management and supports the use of energy prescriptions based on RMR for the general obese population plus an appropriate allowance for energy expended via physical activity. Further research is needed on physical activity in BBS.

Coenzyme Q10 levels in Prader-Willi syndrome: comparison with obese and non-obese subjects

Coenzyme Q10 (CoQ10) is an essential component of the mitochondrial respiratory chain and an important scavenger of reactive oxygen species. Low levels are found in individuals with reduced energy expenditure, cardiac and skeletal muscle dysfunction, and mitochondrial disorders, many of these manifestations are seen in individuals with Prader-Willi syndrome (PWS). In addition, CoQ10 supplementation frequently is given to individuals with this syndrome. To determine if CoQ10 levels are decreased in PWS, we studied plasma CoQ10 levels in 16 subjects with PWS, 13 with obesity of unknown cause, and 15 subjects without obesity but of similar age and compared with body composition. Plasma CoQ10 levels were significantly decreased (P < 0.05), using several statistical approaches in subjects with PWS (0.45 +/- 0.16 microg/ml), compared to subjects without obesity (0.93 +/- 0.56 microg/ml), but not different from subjects with obesity (0.73 +/- 0.53 microg/ml). When plasma CoQ10 was normalized relative to cholesterol, triglyceride, and creatinine levels and fat and lean mass [determined by dual energy X-ray absorptiometry (DEXA)] in the subjects with either PWS or obesity, no significant differences were observed. However, a lower muscle mass was found in the PWS subjects.

Hypogonadism and pubertal development in Prader-Willi syndrome

Genital abnormalities and disorders of pubertal development such as hypogonadism are common in Prader-Willi Syndrome (PWS). Depending on age, PWS patients present genital hypoplasia and delayed or incomplete gonadal maturation. Nevertheless, only a few evaluations have been made of these findings in this syndrome; in the cases previously reported the diagnosis of PWS has often been based only on clinical criteria and not confirmed by genetic analysis. In this paper we describe both external genital findings and spontaneous pubertal development in 84 patients aged from 2.1 to 35.4 (42 males, 42 females) affected by PWS. Diagnosis was made using the Holm and Cassidy criteria and was confirmed by genetic analysis (methylation test and/or FISH). We evaluated the presence of cryptorchidism, scrotal development, length of penis and volume of testis in males and outlook of labia minora and/or clitoris, age of menarche and features of menses (when present) in females; in both sexes we also evaluated the onset of puberty. All recruited males showed cryptorchidism, which was bilateral in 36 out of 42 patients (86%); 38 patients (90%) underwent orchidopexy. Small testes and scrotal hypoplasia were present in 76% and 69% of cases, respectively. In 76% of females, hypoplasia or absence of labia minora and/or clitoris was described. Spontaneous menarche occurred only in 14/32 cases (44%) over the age of 15 years, but menstrual cycles were often a periodical vaginal spotting. Primary amenorrhea was diagnosed in 56% of cases. Isolated premature pubarche was present in six males and in six females (14% of cases) while one male and two females were affected by precocious puberty (3.6%).

CONCLUSION

Hypogonadism represents a common clinical feature in PWS, confirming the importance of such a major diagnostic criterion. Cryptorchidism was consistently present in all our cases. Patients with PWS commonly fail to spontaneously complete puberty, although some patients may have early pubarche or, more rarely, precocious puberty. In older subjects, hormonal replacement therapy is not always necessary and it must be reserved for selected patients.

Prader-Willi syndrome and the evolution of human childhood

The kinship theory of genomic imprinting predicts that imprinted genes have effects on asymmetric kin (relatives with different degrees of matrilineal and patrilineal relatedness). The most important interaction with such a relative is a child's interaction with its mother. Therefore, the study of imprinted genes and their phenotypic effects promises to provide insights into the evolution of mother-child relations. Prader-Willi syndrome (PWS) is caused by the absence of expression of genes at 15q11-q13 that are normally expressed only when paternally derived. The kinship theory predicts that children with PWS will fail to express behaviors that have increased mothers' costs of child-rearing. Our analysis focuses on aspects of the PWS phenotype that affect appetite and feeding. Immediately after birth, children with PWS have little appetite and are usually unable to suckle, but at some stage (usually within the first 2 years) they develop a voracious appetite and an obsession with food. We conjecture that this change in appetite reflects evolutionary forces associated with weaning. Immediately after birth, when a child is completely dependent on the breast, poor appetite reduced maternal costs. However, once a child was able to consume supplemental foods, maternal costs would have been reduced by children with increased, nonfastidious appetites.

Unexpected death and critical illness in Prader-Willi syndrome: Report of ten individuals

Individuals with Prader-Willi syndrome (PWS) generally survive into adulthood. Common causes of death are obesity related cor pulmonale and respiratory failure. We report on a case series of eight children and two adults with unexpected death or critical illness. Our data show age-specific characteristics of PWS patients with fatal or life-threatening illnesses. Under the age of 2 years, childhood illnesses in general were associated with high fever and rapid demise or near-demise. Hypothalamic dysfunction likely plays a role in exaggerated fever response, but also perhaps in central regulation of adrenal function. Below average sized adrenal glands were found in three children, which raises the possibility of unrecognized adrenal insufficiency in a subset of individuals with PWS and emphasizes the vital role of autopsy. The tub drowning death of an adult patient could be related to central hypersomnia, which has been reported in PWS. We suggest that increased risk for critical illness be considered in the discussion of anticipatory guidance for the care of infants with PWS. Since a number of children died while hospitalized, particularly close observation of PWS children who are ill enough to warrant hospital admission is recommended.

Imprinting disorders: non-Mendelian mechanisms affecting growth

Most autosomal genes are expressed from both maternal and paternal alleles. However, imprinted genes are an example of non-Mendelian genetics, in which only one member of the gene pair is expressed and expression is determined by the parent of origin. Imprinted genes may account for 0.1-1% of all mammalian genes. At least 50 imprinted genes have been identified in humans, and imprinted genes frequently cluster under the control of an imprinting center. Many imprinted genes contribute to growth, either as growth factors, such as insulin-like growth factors (IGF2 in Beckwith-Wiedemann syndrome), or as growth inhibitors, such as the GRB10 gene in Russell-Silver syndrome. Imprinted genes have evolved over time in mammals to fine-tune the growth of the fetus. Paternally expressed genes generally enhance growth, whereas maternally expressed genes appear to suppress growth. In addition, normal and abnormal genomic imprinting and loss of heterozygosity contribute to a wide range of malignancies. A common process for controlling gene activity is methylation, which can be changed during male or female gametogenesis. Examples of classic human disorders related to genomic imprinting are Beckwith-Wiedemann syndrome (chromosome 11), Prader-Willi/Angelman syndromes (chromosome 15), Russell-Silver syndrome (chromosome 7), and Albright hereditary osteodystrophy (chromosome 20). Several of these disorders are discussed and illustrated.

Cutaneous blood flow and thermoregulation in Prader-Willi syndrome patients

We examined adrenergic controlled cutaneous blood flow and temperature regulation in Prader-Willi syndrome. A body mass index was calculated for each participant. Thermal and laser Doppler finger probes were applied for continuous simultaneous surface temperature and capillary blood flow recording. Analysis with respect to group, age, body mass index, and genetic cause were performed. There were 32 patients (mean = 17.5 years of age) and five control subjects (mean = 15.6 years of age). There were no significant differences in mean ages or sex between groups. There was no significant difference in averaged blood flow measures with respect to group (P = 0.81), age (P = 0.16), body mass index (P = 0.54), or genetic identification (P = 0.81). There was no significant difference in average temperature measures as a function of group (P = 0.95), body mass index (P = 0.82), or genetic identification (P = 0.95). There was a significant difference in average temperature (P = 0.008) and trend in temperature change over time (P = 0.07) with respect to age for both patients and control subjects. Younger participants had higher average temperatures (30.6 degrees C vs 28.4 degrees C) in both study groups. We conclude that the central regulation and adrenergic control of cutaneous temperature and blood flow regulation in Prader-Willi syndrome at rest is not different from control subjects. These observations strengthen prior observations that a primary disturbance in parasympathetic autonomic regulation exists in Prader-Willi syndrome.

The behavioral impact of growth hormone treatment for children and adolescents with Prader-Willi syndrome: a 2-year, controlled study

INTRODUCTION

Prader-Willi syndrome (PWS) is characterized by obesity, hypotonia, hypogonadism, hyperphagia, short stature, and a neurobehavioral profile that includes cognitive deficits, learning problems, and behavioral difficulties that increase in both quantity and severity over time. PWS results from an alteration in the molecular composition of a critical region of C#15q. Morbid obesity resulting from hyperphagia is amplified by decreased energy expenditure and reduced physical activity. The hyperphagia has proven refractory to all psychopharmocologic intervention; the behavioral components are equally resistant to psychotropic intervention. PWS patients' body composition resembles that of individuals with growth hormone (GH) deficiency, including short stature and reduced lean body mass with concomitant increased fat mass. We hypothesized that GH administration to children with PWS, in addition to stimulating linear growth, would improve body composition, increase energy expenditure and fat utilization, and improve muscle strength, physical agility, and pulmonary function. Two recent reports from this study document significant positive effects of GH treatment on these children's physical parameters measured in a 2-year, controlled study. However, the behavioral impact of GH treatment in this population remains incompletely described. A psychosocial burden, including emotional, behavioral, and cognitive disturbances associated with short stature, has been previously described in a non-PWS population with GH deficiency and idiopathic short stature. An impaired quality of life and psychosocial status is also documented in otherwise normal adults with GH deficiency. In both populations, growth hormone replacement therapy (GHRT) is reported to improve alertness, activity level, endurance, irritability, tendency to worry, and extroversion resulting in better personal relationships with fewer conflicts. This report focuses on that portion of the study investigating the behavioral and psychosocial outcomes accompanying increased stature and improved physical status for persons with PWS treated with GHRT. We hypothesized that, as in other populations, GHRT for persons with PWS would have a significant positive effect on their psychosocial status as well as an improvement in their growth parameters.

METHODS

A 2-year, controlled study with control group crossover in the second year was used. Fifty-four consecutive children with genetically confirmed PWS were enrolled. Patients were 4 to 16 years of age at time of enrollment, had skeletal maturation <13 for girls and <15 for boys; all but 3 participants remained prepubertal (Tanner stage 1) throughout the study. Children who had previous therapy with GH were excluded, as were children with a scoliosis >20 degrees. After a 6-month growth assessment were randomized into a 60:40 treatment:control ratio. Treatment consisted of Nutropin (Genentech), 1 mg/m2/day. A modified Offord Survey Diagnostic Instrument (SDI) was used to monitor behavior at 6-month intervals. The SDI is a 165-item behavioral checklist with items rated on a scale of 0 = Never or Not True, 1 = Sometimes or Somewhat True, and 2 = Often or Very True. The items are balanced between positively and negatively scored items. The present instrument was designed to derive diagnoses for the following Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition categories: Depression, Obsessive-Compulsive Disorder, Anxiety Disorder, Somatization Disorder, Conduct Disorder, and Attention-Deficit/Hyperactivity Disorder. The SDI was modified to include 10 items specifically inquiring about PWS (eg, denies having PWS, picks excessively at skin, nose, or other body parts). Because diagnoses are not mutually exclusive, an individual can meet criteria for 1 or more diagnostic categories. The SDI contains a second section measuring behavior functioning in the school environment, in the family, and in personal and social relationships. A wider scoring range is used and is question-specific. Parallel forms of this measure are available for parents, teachers, and the child him/herself. We gathered data from both parents and teachers at 6-month intervals. No questionnaire was scored until the completion of the entire study to avoid any possibility of an inadvertent "feedback" or "self-fulfilling prophecy" effect. All questionnaires were scored by a Bachelor's level research assistant blind to study assignment. Family stress was monitored with the Family Inventory of Life Events. At study completion, the impact of GH was measured with a 13-item summary interview adapted from Wiren et al. After completion of all final study visits, a single research assistant blind to treatment assignment interviewed all families by phone. This method was chosen to minimize any positively biased demand characteristics.

RESULTS

Both between-group and within-group contrasts were computed for baseline, 12 (time 1) and 24 month (time 2) measures. Because behavioral deterioration, as well as improvement, was a possibility, a 2-tailed hypothesis test was used for all comparisons. No differences were found between treatment and control groups, nor within groups across measurement points for attentional symptoms, anxiety, obsessive-compulsive complex, violence, or psychotic symptoms. Similarly, no differences were noted between groups on depressive symptoms; however, a significant positive effect (reduction of depressive symptoms) was noted for the treatment group from baseline to time 1, and was retained at time 2. The group was divided by age, with those 11.0 years and younger comprising one group and those older the second group. This analysis indicated that the major reduction in depressive symptoms occurred in those over 11 years old. When divided by age, a second unexpected finding emerged. There was a significant increase in attention-deficit/hyperactivity disorder symptoms from baseline to 24 months in those children 11 and under, independent of treatment status. The groups were subsequently further broken down by sex and by genetic status (deletion versus disomy) with no significant findings. At no time was the expected behavioral deterioration reported. We conclude that in addition to the previously detailed improvements in physical parameters for these children, behavioral improvement, including a lack of predictable behavioral deterioration during the treatment period, is a strong argument for the use of GHRT for this difficult syndrome.

Genome organization, function, and imprinting in Prader-Willi and Angelman syndromes

The chromosomal region, 15q11-q13, involved in Prader-Willi and Angelman syndromes (PWS and AS) represents a paradigm for understanding the relationships between genome structure, epigenetics, evolution, and function. The PWS/AS region is conserved in organization and function with the homologous mouse chromosome 7C region. However, the primate 4 Mb PWS/AS region is bounded by duplicons derived from an ancestral HERC2 gene and other sequences that may predispose to chromosome rearrangements. Within a 2 Mb imprinted domain, gene function depends on parental origin. Genetic evidence suggests that PWS arises from functional loss of several paternally expressed genes, including those that function as RNAs, and that AS results from loss of maternal UBE3A brain-specific expression. Imprinted expression is coordinately controlled in cis by an imprinting center (IC), a genetic element functional in germline and/or early postzygotic development that regulates the establishment of parental specific allelic differences in replication timing, DNA methylation, and chromatin structure.

Decreased bone mineral density in Prader-Willi syndrome: comparison with obese subjects

Bone density, anthropometric data, and markers of bone turnover were collected on 21 subjects diagnosed with Prader-Willi syndrome (PWS) and compared with 9 subjects with obesity of unknown cause. In addition, urinary N-telopeptide levels were obtained in all subjects. N-telopeptides are the peptide fragments of type I collagen, the major bone matrix material. During periods of active bone degradation or high bone turnover, high levels of N-telopeptides are excreted in the urine. However, no significant difference was detected in the urinary N-telopeptide levels when corrected for creatinine excretion (raw or transformed data) between our subjects with obesity or PWS and the observed effect size of the between-group difference was small. Although N-telopeptide levels were higher but not significantly different in the subjects with PWS compared with obese controls, the subjects with PWS had significantly decreased total bone and spine mineral density and total bone mineral content (all P < 0.001). No differences in N-telopeptide levels or bone mineral density were observed between subjects with PWS and chromosome 15q deletion or maternal disomy. Thus, decreased bone mineral density in subjects with PWS may relate to the lack of depositing bone mineral during growth when bones are becoming more dense (e.g., during adolescence), possibly because of decreased production of sex or growth hormones and/or long-standing hypotonia. It may not be caused by loss, or active degradation, of bone matrix measurable by the methods described in this study further supporting the possible need for hormone therapy during adolescence.

[Rectal self-mutilation, rectal bleeding and Prader-Willi syndrome]

Prader-Willi syndrome is a genetic disorder characterized by infantile hypotonia, obesity, hypogonadism and mental retardation. Individuals with Prader-Willi syndrome manifest a severe skin picking behavior, including rectal picking.

CASE REPORT

We report the case of a girl (12 years old) with this syndrome in whom rectal picking resulted in rectal bleeding and solitary rectal ulcer.

CONCLUSION

Caregivers of children with Prader-Willi syndrome should be aware of a potential rectal picking behavior, which results in significant bleeding. Early recognition of such a behavior helps to avoid misdiagnosis.

Kinetic form discrimination in Prader-Willi syndrome

Discrimination of the shape of motion-produced forms generated by random elements (i.e. second-order stimuli varying in element density and temporal correlation) was tested in four groups: (1) subjects with Prader-Willi syndrome (PWS), chromosome 15q deletion subtype; (2) subjects with PWS, uniparental maternal disomy (UPD) subtype; (3) equivalent non-PWS controls; and (4) normal controls. The performance of the normal controls exceeded that of all other groups (78% correct, P < 0.009). The PWS deletion (66%) and the equivalent control groups (59%) did not differ (P < 0.95). The UPD group performed significantly less well (38%, P < 0.04) than all the other groups. The performance of the PWS deletion and equivalent control groups is consistent with other data indicating that these populations encounter difficulty meeting the processing demands posed by second-order stimuli. The inferior performance of the UPD group may be attributed to receiving two active alleles of a maternally expressed gene influencing neural development. One candidate is the ubiquitin protein ligase gene (UBE3A), which is maternally expressed only and localized to the 15q region. Other possibilities include the requirement of a paternally expressed gene, residual mosaic trisomy 15 in the brain tissue or complex interactions including specific ratios of differentially spliced gene products.

Hyperphagic short stature and Prader--Willi syndrome: a comparison of behavioural phenotypes, genotypes and indices of stress

BACKGROUND

The clinical features of hyperphagic short stature (HSS) include short stature secondary to growth hormone insufficiency, excessive appetite (hyperphagia) and mild learning disabilities. Affected children characteristically live in conditions of high psychosocial stress. Symptoms resolve when the child is removed from the stressful environment. Family studies indicate a genetic predisposition.

AIMS

To compare the behavioural and stress profiles of HSS with those of Prader--Willi syndrome (PWS), and to test the hypothesis that the genetic locus that predisposes to HSS co-inherits with the PWS locus at 15q11--13.

METHOD

Twenty-five children with HSS, mean age 9.1 (s.d. 3.8) years, 28% female, were compared with 30 children with PWS, mean age 8.8 (s.d. 2.8) years, 33% female.

RESULTS

The clinical profiles were largely similar across the conditions, but no evidence was found in HSS of co-inheritance of the PWS critical region.

CONCLUSIONS

Hyperphagic short stature is one of the very few behavioural diseases associated with a pathognomonic physiological abnormality. Investigations of the suggested genetic dysregulation, which is so sensitive to environmental influences, may well be of importance in a broader context.

Prader-Willi and Angelman syndromes: sister imprinted disorders

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are clinically distinct complex disorders mapped to chromosome 15q11-q13. They both have characteristic neurologic, developmental, and behavioral phenotypes plus other structural and functional abnormalities. However, the cognitive and neurologic impairment is more severe in AS, including seizures and ataxia. The behavioral and endocrine disorders are more severe in PWS, including obsessive-compulsive symptoms and hypothalamic insufficiency. Both disorders can result from microdeletion, uniparental disomy, or an imprinting center defect in 15q11-q13, although the abnormality is on the paternally derived chromosome 15 for PWS and the maternally derived 15 for AS because of genomic imprinting. Although the same gene may control imprinting for both disorders, the gene(s) causing their phenotypes differ. AS results from underexpression of a single gene, UBE3A, which codes for E6-AP, a protein that functions to transfer small ubiquitin molecules to certain target proteins, to enable their degradation. The genes responsible for PWS are not determined, although several maternally imprinted genes in 15q11-q13 are known. The most likely candidate is SNRPN, which codes for a small nuclear ribonucleoprotein, a ribosome-associated protein that controls gene splicing and thus synthesis of critical proteins in the brain. Animal models exist for both disorders. The genetic relationship between PWS and AS makes them unique and potentially highly instructive disorders that contribute substantially to the population burden of cognitive impairment.

Experimental analyses of gene-brain-behavior relations: some notes on their application

The fields of genetics and neuroscience are yielding findings useful in understanding complex behavior-environment relations. We believe that these developments in interdisciplinary basic research are of interest to applied behavior analysts because of the long history of basic findings being used by the readership of the Journal of Applied Behavior Analysis to improve everyday human activities. An awareness of contemporary developments in a range of basic research disciplines may facilitate the systematic replication of those functional relations in applied settings. In this context, we selectively review papers published in the Journal of the Experimental Analysis of Behavior and other basic research journals that relate to gene-brain-behavior relations.

Emergence of compulsive behavior and tantrums in children with Prader-Willi syndrome

Many adults with Prader-Willi syndrome are affected by behaviors such as tantrums, skin-picking, and compulsions. The nature and extent of these problems suggest more attention be directed to their emergence in childhood. Our purpose was to investigate behavior problems in children with this syndrome and identify the age at which these behaviors emerge. Parents of children with Prader-Willi syndrome, Down syndrome, and those developing typically completed questionnaires. Children with Prader-Willi syndrome exhibited more compulsions, skin-picking, and tantrums than did the other groups. A discriminant analysis of behavior variables derived two statistically significant functions that were interpreted as developmental milestones and problematic behavior. These functions correctly predicted membership for 79% of grouped cases.

Emergence of compulsive behavior and tantrums in children with Prader-Willi syndrome

Many adults with Prader-Willi syndrome are affected by behaviors such as tantrums, skin-picking, and compulsions. The nature and extent of these problems suggest more attention be directed to their emergence in childhood. Our purpose was to investigate behavior problems in children with this syndrome and identify the age at which these behaviors emerge. Parents of children with Prader-Willi syndrome, Down syndrome, and those developing typically completed questionnaires. Children with Prader-Willi syndrome exhibited more compulsions, skin-picking, and tantrums than did the other groups. A discriminant analysis of behavior variables derived two statistically significant functions that were interpreted as developmental milestones and problematic behavior. These functions correctly predicted membership for 79% of grouped cases.

Genomic imprinting: genetic mechanisms and phenotypic consequences in Prader-Willi and Angelman syndromes

Chromosomal 15q11-q13 region is of great interest in Human Genetics because many structural rearrangements have been described for it (deletions, duplications and translocations) leading to phenotypes resulting in conditions such as the Prader-Willi (PWS) and Angelman (AS) syndromes which were the first human diseases found to be related to the differential expression of parental alleles (genomic imprinting). Contrary to Mendelian laws where the parental inheritance of genetic information does not influence gene expression, genomic imprinting is characterized by DNA modifications that produce different phenotypes depending on the parental origin of the mutation. Clinical manifestation of PWS appears when the loss of paternally expressed genes occurs and AS results from the loss of a maternally expressed gene. Different genetic mechanisms can lead to PWS or AS, such as deletions, uniparental disomy or imprinting mutation. In AS patients an additional class occurs with mutations on the UBE3A gene. Studies of PWS and AS patients can help us to understand the imprinting process, so that other genomic regions with similar characteristics can be located, and different syndromes can have their genetic mechanisms elucidated.

Plasma cholecystokinin levels in Prader-Willi syndrome and obese subjects

The cardinal feature of individuals with Prader-Willi syndrome (PWS) is severe hyperphagia-mediated obesity resulting from a faulty satiety mechanism. PWS is the most common genetic cause of marked obesity. Cholecystokinin (CCK) is a 33-amino-acid peptide found in high levels in the gut and brain involved in mediating the satiety response to meals. Free fatty acids (FFA) are responsible for the stimulation of CCK release after a fatty meal, and CCK and plasma FFA levels rise in tandem in normal individuals. Fasting plasma CCK levels were measured by radio-immunoassay in 33 PWS subjects with a mean age of 22.2 years +/- 8.1 years and 24 obese control subjects without a known cause of their obesity with a mean age of 28.7 years +/- 12.9 years. Consistent with previous findings, neither fasting plasma FFA levels (617.5 versus 486.8 microm/mL) or CCK levels (21.0 versus 19.1 pg/mL) were significantly different in PWS or control subjects, respectively. However, there was a significant correlation between fasting plasma FFA and CCK levels in obese subjects (r = 0. 64, P < 0.01), this correlation was completely lacking in PWS subjects (r = -0.06, P = 0.79). This difference in correlation coefficients constitutes a large effect. There were no significant effects observed for genetic subtypes (15q11-q13 deletion or maternal disomy 15), body mass index, percentage of fat, plasma levels of insulin, C-peptide, glucagon or leptin, age, or gender on CCK levels in our PWS subjects. These results suggest that differences in the peripheral CCK response to FFA levels may be a factor contributing to the altered satiety response in PWS subjects.

A componential view of theory of mind: evidence from Williams syndrome

In this paper we argue that there are two distinct components of a theory of mind: a social-cognitive and a social-perceptual component. Evidence for this proposal is presented from various sources, including studies of children with Williams syndrome, a rare genetic neurodevelopmental disorder. Earlier work has demonstrated that people with Williams syndrome appear to be spared in the social-perceptual component of a theory of mind. In this paper we present evidence that they are not spared in the social-cognitive component of theory of mind. Three experiments with young children with Williams syndrome were conducted. In each experiment the children with Williams syndrome were compared to age-, IQ-, and language-matched children with Prader-Willi syndrome, and children with non-specific mental retardation. The experiments used different measures of theory of mind ability, including false belief (Experiment 1), explanation of action (Experiment 2), and recognition of emotional expressions (Experiment 3). In none of these experiments did the children with Williams syndrome evidence superior performance compared to the control groups. The results from this and other studies on Williams syndrome support the view that the social-cognitive and social-perceptual components of a theory of mind are dissociable. In Williams syndrome only the latter components, which are linked to distinct neurobiological substrates, are spared.

Prader-Willi Syndrome: Clinical and Genetic Findings

Since the initial medical description by Prader, Labhart and Willi in 1956 of individuals with overlapping features, the Prader-Willi syndrome has become recognized as a classical but sporadic genetic syndrome. Prader-Willi syndrome is the most common genetic cause of life-threatening obesity in humans. It is estimated that there are 350,000-400,000 people with this syndrome worldwide. Prader-Willi Syndrome Association USA knows of more than 3,400 persons with Prader-Willi syndrome in the USA out of an approximate 17,000-22,000. Prader-Willi syndrome with an incidence of 1 in 10,000 to 25,000 individuals and Angelman syndrome, an entirely different clinical condition, were the first examples in humans of genetic imprinting. Genetic imprinting or the differential expression of genetic information depending on the parent of origin plays a significant role in other conditions including malignancies.

Unbalanced translocation t(15;22) in "severe" Prader-Willi syndrome

A 13-year-old girl with an unbalanced karyotype 45,XX,-15,der(22)t(15;22)(q13;q13.3) de novo had Prader-Willi syndrome (PWS), (score 13.5), but with features of mental and physical retardation more severe than usually seen in PWS. The clinical diagnosis of PWS was confirmed by methylation analysis that showed absence of the paternal band. With GTG banding, the cytogenetic breakpoint on chromosome 15q13, with 15q14 intact, encompassed the PWS region, while the breakpoint on 22q was terminal. Investigations with FISH utilised ten different probes/combinations, namely SNRPN/PML, TUPLE1/22q13.3, TUPLE/ARSA, GABRB3, three YAC clones and one cosmid for specific regions within chromosome 15q, painting probes for the long arm of chromosomes 15 and 22 and a pantelomere probe. Deletion of SNRPN,TYAC 9 (at 15q11-12), TYAC19 (at 15q13) and GABRB3 (within the PWS locus), was evident on the derivative (22) chromosome, while TYAC10 (at 15q22), cos15-5 (at 15q22) and PML (15q22) were not deleted. On the der(22), 22q13.3 and ARSA were not deleted, but the most distal non specific pantelomeric probe was deleted. Thus, the severe phenotype could be attributable to deletion on chromosome 15q extending beyond q13 to q14, (further than the usual chromosome 15q deletion (q11-13) in PWS), or be related to loss of the very terminal 22q region (from ARSA to the pantelomere) or be due to genetic factors elsewhere in the genome.

Intellectual characteristics of Prader-Willi syndrome: comparison of genetic subtypes

Advances in genetics have led to an increased understanding of the role of the genotype on behavioural functioning. The purpose of the present study was to examine differences in intellectual functioning in individuals with Prader-Willi syndrome (PWS) with a paternal 15q11-q13 deletion versus maternal uniparental disomy (UPD) of chromosome 15. Measures of intelligence and academic achievement were administered to 38 individuals with PWS (24 with deletion and 14 with UPD). The subjects with UPD had significantly higher verbal IQ scores than those with deletion (P< 0.01). The magnitude of the difference in verbal IQ was 9.1 points (69.9 versus 60.8 for UPD and deletion PWS subjects, respectively). Only 17% of subjects with the 15q11-q13 deletion had a verbal IQ > or = 70, while 50% of those with UPD had a verbal IQ > or = 70. Performance IQ scores did not differ between the two PWS genetic subtype groups. This is the first report to document the difference between verbal and performance IQ score patterns among subjects with PWS of the deletion versus the UPD subtype.

Appetitive behavior, compulsivity, and neurochemistry in Prader-Willi syndrome

Advances in genetic research have led to an increased understanding of genotype-phenotype relationships. Excessive eating and weight gain characteristic of Prader-Willi syndrome (PWS) have been the understandable focus of much of the research. The intense preoccupation with food, lack of satiation, and incessant food seeking are among the most striking features of PWS. It has become increasingly clear that the behavioral phenotype of PWS also includes symptoms similar to obsessive compulsive disorder, which in all probability interact with the incessant hunger and lack of satiation to engender the intense preoccupation and food seeking behavior that is characteristic of this disorder. Several lines of evidence suggest that genetic material on chromosome 15 may alter synthesis, release, metabolism, binding, intrinsic activity, or reuptake of specific neurotransmitters, or alter the receptor numbers and/or distribution involved in modulating feeding. Among the likely candidates are GABAnergic, serotonergic, and neuropeptidergic mechanisms. This review summarizes what is known about the appetitive behavior and compulsivity in PWS and discusses the possible mechanisms underlying these behaviors. MRDD Research Reviews 2000;6:125-130.

A 68-year-old white female with Prader-Willi syndrome

A 68-year-old white female with Prader-Willi syndrome is described. The clinical features are described and the progression of her condition is discussed and illustrated.

Leptin concentrations in Prader-Willi syndrome before and after growth hormone replacement

OBJECTIVE

This study explored leptin concentrations in Prader-Willi syndrome (PWS), a genetic disorder characterized by significant obesity and presumed hypothalamic dysfunction. The potential interaction of leptin metabolism with the growth hormone (GH) axis was also studied.

STUDY DESIGN

Plasma leptin concentrations and percent body fat were determined by radioimmunoassay and dual energy x-ray absorptionmetry, respectively, in 23 children with Prader-Willi syndrome and 23 children with exogenous obesity.

RESULTS

Log plasma leptin concentrations were positively correlated with percentage body fat in PWS (r = 0.844) and exogenous obesity (r = 0.869). When the regression lines for the two groups were compared, there were no differences in their slopes (P = 0.737) or intercepts (P = 0.701). Administration of recombinant human growth hormone to PWS children for 12 months significantly reduced both percentage body fat and plasma leptin concentrations, but the relationship of log plasma leptin to percentage body fat was unchanged.

CONCLUSION

Prader-Willi syndrome is not accompanied by deranged leptin concentrations and there was no evidence of an interaction of the GH axis with leptin metabolism in these GH-deficient children.

Central precocious puberty and abnormal chromosomal patterns

Central precocious puberty (PP) can be caused by chromosomal aberrations. We report three patients presenting with central PP in whom karyotype analysis demonstrated abnormal chromosomal patterns. The first patient was affected by the triple-X syndrome, commonly characterized by premature ovarian failure. The second patient, a girl with inv dup(15)(pter-->q12::q12-->pter), had a chromosomal aberration involving an imprinted region of the human genome, whose deletion is commonly associated with Prader-Willi syndrome (PWS) and hypogonadotrophic hypogonadism. The third patient was a boy carrying a rare chromosome abnormality, the duplication of chromosome 9 (q22-->qter). All patients had mental retardation, which was mild in patient 1, moderate in patient 2, and severe in case 3. They underwent treatment with luteinizing hormone releasing hormone (LHRH) analogs, which were able to stop the progression of the sexual development. We confirm that chromosomal aberrations are an important cause of central PP, and that karyotype analysis in patients with PP and mental retardation, even if mild, is necessary because chromosomal abnormalities can be present.

Appetitive behavior, compulsivity, and neurochemistry in Prader-Willi syndrome

Advances in genetic research have led to an increased understanding of genotype-phenotype relationships. Excessive eating and weight gain characteristic of Prader-Willi syndrome (PWS) have been the understandable focus of much of the research. The intense preoccupation with food, lack of satiation, and incessant food seeking are among the most striking features of PWS. It has become increasingly clear that the behavioral phenotype of PWS also includes symptoms similar to obsessive compulsive disorder, which in all probability interact with the incessant hunger and lack of satiation to engender the intense preoccupation and food seeking behavior that is characteristic of this disorder. Several lines of evidence suggest that genetic material on chromosome 15 may alter synthesis, release, metabolism, binding, intrinsic activity, or reuptake of specific neurotransmitters, or alter the receptor numbers and/or distribution involved in modulating feeding. Among the likely candidates are GABAnergic, serotonergic, and neuropeptidergic mechanisms. This review summarizes what is known about the appetitive behavior and compulsivity in PWS and discusses the possible mechanisms underlying these behaviors. MRDD Research Reviews 2000;6:125-130.

Second-order belief attribution in Williams syndrome: intact or impaired?

Second-order mental state attribution in a group of children with Williams syndrome was investigated. The children were compared to age, IQ, and language-matched groups of children with Prader-Willi syndrome or nonspecific mental retardation. Participants were given two trials of a second-order reasoning task. No significant differences between the Williams syndrome and Prader-Willi or mentally retarded groups on any of the test questions were found. Results contrast with the view that individuals with Williams syndrome have an intact theory of mind and suggest that in their attributions of second-order mental states, children with Williams syndrome perform no better than do other groups of children with mental retardation.

Visual capacity and Prader-Willi syndrome

PURPOSE

Prader-Willi syndrome (PWS) refers to a genetic disorder induced by an anomaly on chromosome 15 occurring with a frequency of one in 10,000 to 20,000. It is characterized by a unique set of features including infantile hypotonia, obesity in childhood, small hands and feet, hypogonadism, and mental retardation. Reported here are the results of ophthalmic examinations of persons with PWS, together with results from controls comparable in age, percentage of body fat, and intelligence. These data bear on the hypothesis that the ocular anomalies in PWS are unique to this syndrome.

METHOD

A comprehensive investigation of PWS brought children and adults to Vanderbilt University for extended testing, which included an ophthalmic examination. Genetic analysis determined unequivocally the PWS diagnosis and identified subgroups-deletion and maternal disomy. A group of persons without PWS but generally comparable in age, body composition, and intelligence served as controls.

RESULTS

Significant differences between the deletion and disomy subgroups were not found for the clinical ophthalmic measures. The incidence of anomalies in the combined PWS was similar to those reported in previous studies. A similar pattern was present in the control group except for myopia and stereopsis. An effect of genetic subgroup, however, was observed for random element stereopsis with the maternal disomy group having a greater degree of impairment.

CONCLUSION

The overall similarity between the PWS and control groups on all measures except myopia and stereopsis suggest that many of the anomalies in PWS found in prior studies are due to factors inherent in a general dysfunctional population, rather than reflective of an ocular signature unique to PWS.

Chromosome breakage in the Prader-Willi and Angelman syndromes involves recombination between large, transcribed repeats at proximal and distal breakpoints

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are distinct neurobehavioral disorders that most often arise from a 4-Mb deletion of chromosome 15q11-q13 during paternal or maternal gametogenesis, respectively. At a de novo frequency of approximately.67-1/10,000 births, these deletions represent a common structural chromosome change in the human genome. To elucidate the mechanism underlying these events, we characterized the regions that contain two proximal breakpoint clusters and a distal cluster. Novel DNA sequences potentially associated with the breakpoints were positionally cloned from YACs within or near these regions. Analyses of rodent-human somatic-cell hybrids, YAC contigs, and FISH of normal or rearranged chromosomes 15 identified duplicated sequences (the END repeats) at or near the breakpoints. The END-repeat units are derived from large genomic duplications of a novel gene (HERC2), many copies of which are transcriptionally active in germline tissues. One of five PWS/AS patients analyzed to date has an identifiable, rearranged HERC2 transcript derived from the deletion event. We postulate that the END repeats flanking 15q11-q13 mediate homologous recombination resulting in deletion. Furthermore, we propose that active transcription of these repeats in male and female germ cells may facilitate the homologous recombination process.

Analysis of imprinted genes in subjects with Prader-Willi syndrome and chromosome 15 abnormalities

PURPOSE

To determine gene expression of five imprinted genes or transcripts from the 15q11-q13 chromosome region using reverse transcription polymerase chain reaction (RT-PCR) in a relatively large survey of Prader-Willi syndrome (PWS) and control subjects with several different chromosome 15 abnormalities.

METHODS

RT-PCR was undertaken on mRNA isolated from tissue (e.g., mostly lymphoblasts) from 38 PWS and 10 control subjects. DNA primers were used for five imprinted genes or transcripts (ZNF127, SNRPN, PAR5, IPW, and PAR1) from 15q11-q13 and fibrillin, a control gene from 15q21.

RESULTS

One PWS subject with maternal disomy 15 showed weak but detectable expression of PAR1, whereas SNRPN expression was detected in two PWS subjects [one with the 15q11-q13 deletion and one with a t(15;15) karyotype and maternal disomy 15], and the remaining typical PWS subjects showed no expression of the imprinted genes or transcripts.

CONCLUSION

No obvious clinical differences were identified in those PWS subjects with weak expression of genes compared with those showing no expression. Although the reason(s) for weak expression is unknown, possible explanations include relaxation of imprinting caused by failure to reset the imprinted genes or transcripts in the maternal germ line or by postzygotic gene expression or undetected chromosome 15 mosaicism in the deletion PWS subjects. The timing, tissue source, and other factors relating to partial expression of genes that are thought to be imprinted may play a role in clinical variability and allow for a better understanding of molecular mechanisms in PWS and other abnormalities of proximal chromosome 15q.

Multiple endocrine neoplasia type 1 concomitant with Prader-Willi syndrome: case report and genetic diagnosis

A case of multiple endocrine neoplasia type 1 (MEN 1) accompanied with Prader-Willi syndrome (PWS) was reported. Diagnosis of both diseases have been genetically confirmed. Delay in the diagnosis and management for PWS made surgery for endocrine tumors difficult. This is the first report on the concomitance of MEN 1 with PWS.

Prader-Willi and Angelman syndromes: update on genetic mechanisms and diagnostic complexities

Significant advances have been made in determining the genetic basis of the Prader-Willi and Angelman syndromes; disorders in which genomic imprinting is abnormal. These advances will be instrumental in unravelling the pathogenesis that underlies these neurobehavioural disorders.

The neonatal presentation of Prader-Willi syndrome revisited

We describe 6 newborns evaluated for hypotonia, later diagnosed with Prader-Willi syndrome despite the absence of the classical neonatal features of this syndrome. Specific genetic testing for Prader-Willi syndrome should be considered for all neonates with undiagnosed central hypotonia even in the absence of the other major features of this syndrome.

Plasma leptin concentrations in lean and obese human subjects and Prader-Willi syndrome: comparison of RIA and ELISA methods

Immunoassays for circulating leptin are important research tools for examining the role and regulation of leptin expression in human obesity. However, uncertainty exists regarding the comparability between studies of reported plasma or serum leptin concentrations. The purpose of the present study was to directly compare plasma leptin concentrations by using two of the most widely reported immunoassay methods-namely, a commercially available radioimmunoassay (RIA) and a proprietary enzyme-linked immunosorbent assay (ELISA). Plasma leptin concentrations were measured in healthy lean and obese volunteers and in patients with Prader-Willi syndrome (PWS). Over a wide range of plasma concentrations (2 to 70 ng/mL), leptin measurements obtained with the RIA and ELISA methods were highly correlated (r = 0.957, P<.0001) and were essentially indistinguishable. Leptin levels measured by RIA and ELISA were highly correlated with body mass index (BMI) overall (r = 0.784, P<.0001 and r = 0.732, P<.0001, respectively) and in the lean and obese subgroups. When compared with the results in the lean individuals (mean +/- SEM, 11.6+/-3.2 ng/mL), plasma leptin was significantly higher in both the obese (35.5+/-4.0 ng/mL, P<.0001) and the PWS subjects (30.7+/-6.9 ng/mL, P<.05). However, after we controlled for differences in BMI, the leptin levels were similar in all three groups. In conclusion, we found that the RIA and ELISA used in the present study yield plasma leptin concentrations that are essentially indistinguishable. Our findings should facilitate comparisons of leptin levels measured by these two widely used immunoassays in previous and future studies that examine the role of leptin in body weight regulation.

The latent variable structure of the Compulsive Behaviour Checklist in people with Prader-Willi syndrome

The presence and severity of compulsive behaviours may be evaluated via the Compulsive Behaviour Checklist (CBC) and this instrument has been successfully employed in people with intellectual disability. However, the applicability of the overall CBC scoring system, which entails tallying the number of behavioural categories represented (i.e. five) as well as the number of individual behaviours endorsed (i.e. 25), is not known in the population with Prader-Willi syndrome (PWS). The present investigation examined the latent variable structure of the CBC in people with PWS in order to identify possible population-specific scoring and interpretation considerations. The 25 behaviour-specific items of the CBC were analysed for 75 people with PWS (44 females and 31 males) aged between 4 and 41 years (mean +/- SD = 11.4+/-9.4) via factor analysis with principal component extraction and equamax rotation. The most suitable solution was determined on the basis of multiple empirical criteria: (1) the scree test; (2) eigenvalues >1.00; (3) salient loadings >0.30; (4) the clarity of item assignment to a single latent dimension; (5) the internal consistency of the latent dimension(s) (coefficient alpha > or = 0.70); and (6) item-total correlations between 0.20 and 0.79. In addition, solutions were examined with respect to psychological theory and previous research. A 'general factor' (i.e. single latent dimension) solution which adhered to all a priori criteria was indicated. Twenty-four out of 25 items achieved salient loadings ranging from 0.46 to 0.80 on the general factor. The single item which failed to achieve salience, 'deviant grooming-skin picking', exhibited both substantial unique variance (0.997) and moderate reliability (r = 0.59, P<0.001). The internal consistency of the general factor was strong (alpha = 0.93) and all salient items were suitably correlated with the unit-weighted total score (r(item-total) = 0.41-0.77). The traditional CBC scoring system, which includes tallying the number of categories represented, would not be relevant in this PWS sample. In addition, the recommended tallying of the number of individual behaviours endorsed does not reflect the empirically indicated notion of compulsive behaviour in this special population. These findings indicate that the 24 salient items should be scored as a unit-weighted composite and that the score on the substantially unique item (skin picking) should be considered a separate measure when evaluating compulsive behaviours via the CBC in people with PWS.

Genetic variants of the human obesity (OB) gene in subjects with and without Prader-Willi syndrome: comparison with body mass index and weight

We investigated whether an association exists between genetic variants of the human obesity (OB or leptin) gene and body mass index (BMI) or weight in subjects with Prader Willi syndrome (PWS) and in age- and gender-matched lean and obese subjects without PWS. The study included 51 subjects with PWS (mean age = 17.7 +/- 9.5 years, BMI = 29.7 +/- 8.3 kg/m2); 50 non-PWS obese subjects (mean age = 18.2 +/- 10.8 years, BMI = 33.3 +/- 9.5 kg/m2); and 53 non-PWS lean subjects (mean age = 17.8 +/- 9.5 years, BMI = 19.5 +/- 2.9 kg/m2). Allele sizes were determined via standard polymerase chain reaction of the D7S1875 locus, a dinucleotide repeat polymorphism close to the OB gene and classified as trichotomous (homozygous < 208 bp, heterozygous < 208/ > or = 208 bp, homozygous > or = 208 bp) or dichotomous (homozygous < 208 bp or not). Non-PWS males showed a marked decrease in weight with larger alleles while females did not (interaction effect, p < 0.05). Comparable effects were not observed among the PWS subjects. Associations between BMI and genotype were statistically significant (r = 0.22, one-tailed p < 0.05) and comparable to previous research among the non-PWS subjects < 18 years, but not the adults (r = 0.05, one-tailed p = 0.38). Correlations were not statistically significant among either the adult or non-adult PWS subjects.