Whole genome microarray analysis of gene expression in an imprinting center deletion mouse model of Prader-Willi syndrome

Prader-Willi syndrome (PWS) is caused by loss of paternally expressed genes in the 15q11-q13 region. To further characterize alterations in gene expression in this classical obesity syndrome we used whole genome microarrays to study a PWS mouse model resulting from a paternally derived imprinting center (IC) deletion (PWS IC deletion). These mice die generally within 2-3 days of life (reflective of failure to thrive in infants with PWS) and therefore, the analysis was performed on RNA extracted from the whole brain of PWS IC deletion mice and normal littermates at less than 24 hr after birth. Of more than 45,000 probes examined, 26,471 (59%) were detected for further analysis, and 69 had a significant change in expression of at least 1.5-fold and a false discovery rate (FDR) of 5%. Eight of the genes with differential expression were imprinted and from the PWS critical region (PWSCR). The three genes with the highest expression in the PWS IC mice were pro-opiomelanocortin (Pomc) and two transcripts of unknown function. Pomc knockout mice have been shown to develop obesity. Therefore, elevated Pomc RNA in PWS IC deletion neonatal mice may be an important genetic factor in the survival of these mice as it may affect eating behavior. Interestingly, Mc5r, a melanocortin receptor known to directly respond to Pomc expression changes, was upregulated as well. Mc5r is known to be involved with thermoregulation which is reportedly abnormal in PWS infants. These observations support a role for Pomc and the network of genes involved in regulating energy homeostasis in the early clinical findings of failure to thrive observed in PWS. Other notable patterns include three previously unstudied transcripts that are expressed only from the paternal allele under regulatory control of the IC and include AK013560, BB3144814, and BB182944 (whose genes are located in the mouse PWSCR on chromosome 7B). As expected, all the known paternally expressed genes from the PWSCR had detection signals below the threshold in the PWS IC deletion mice but were clearly detectable in control littermates. Several of the genes in this study were further examined by quantitative reverse transcription-PCR (RT-PCR) to confirm their expression status. Further analysis of gene expression in these mice may lead to novel pathways affected in PWS. These results, along with other recent reports, suggest that the cumulative effect of modest changes in expression of many genes, especially genes involved in energy metabolism, contribute to the failure to thrive of infants with PWS.

Neurocognitive findings in Prader-Willi syndrome and early-onset morbid obesity

OBJECTIVES

To examine whether early-onset morbid obesity is associated with cognitive impairment, neuropathologic changes, and behavioral problems.

STUDY DESIGN

This case-control study compared head MRI scans and cognitive, achievement, and behavioral evaluations of subjects with Prader-Willi syndrome (PWS), early-onset morbid obesity (EMO), and normal-weight sibling control subjects from both groups. Head MRI was done on 17 PWS, 18 EMO, and 21 siblings, and cognitive, achievement, and behavioral evaluations were done on 19 PWS, 17 EMO, and 24 siblings.

RESULTS

The mean General Intellectual Ability score of the EMO group was 77.4 +/- 17.8; PWS, 63.3 +/- 14.2; and control subjects, 106.4 +/- 13.0. Achievement scores for the three groups were EMO, 78.7 +/- 18.8; PWS, 71.2 +/- 17.0; and control subjects, 104.8 +/- 17.0. Significant negative behaviors and poor adaptive skills were found in the EMO group. White matter lesions were noted on brain MRI in 6 subjects with PWS and 5 with EMO. None of the normal-weight control subjects had these findings.

CONCLUSIONS

Individuals with EMO have significantly lower cognitive function and more behavioral problems than control subjects with no history of childhood obesity. Both EMO and PWS subjects have white matter lesions on brain MRI that have not previously been described.

Management strategy for very mild aortic valve stenosis

It is unclear how often patients with very mild aortic stenosis (gradients < 25 mmHg) need interval follow-up. The purpose of this study was to define the determinants of disease severity progression and to propose appropriate management strategies. It is known that congenital aortic stenosis is a progressive disease that requires long-term follow-up at consistent intervals. We studied 89 patients with very mild aortic stenosis. Cox proportional hazard modeling was performed to ascertain predictors of morbidity and mortality. Events were defined as valve surgery or death. Of the original 89 patients, 7 died (92% survival); one death was sudden and unexplained and six were noncardiac. Eighteen individuals were lost to follow-up (10 not located and 8 refused participation). Twelve (17%) had valve surgery. The minimum time interval between initial diagnosis of very mild aortic stenosis and surgery was 4.6 years (mean, 14.0). Age at diagnosis, gender, initial gradient, initial gradient/age, and aortic regurgitation were found not to be predictive of outcome. However, the slope of the transaortic gradient [change of gradient/time (years)] was predictive of outcome (hazard ratio of 1.69; confidence interval, 1.4-2.2). At least 17% of these patients progress to require operation. For patients with a gradient slope < 1.1, evaluation every 4 or 5 years is recommended. For patients with a gradient slope > 1.2, evaluation every 1 or 2 years seems prudent.

Histone H3 lysine 4 dimethylation is enriched on the inactive sex chromosomes in male meiosis but absent on the inactive X in female somatic cells

Inactivation of the X chromosome occurs in female somatic cells and in male meiosis. In both cases, the inactive X chromosome undergoes changes in histone modifications including deacetylation of core histone proteins and enrichment with histone H3 lysine 9 (H3-K9) dimethylation. In this study we show that while the inactive X in female somatic cells is largely devoid of H3-K4 dimethylation, the inactive X in male meiosis is enriched with this modification. However, the inactive X chromosome in female somatic cells and the inactive X and Y in male meiosis are devoid of H3-K4 trimethylation. Further, trimethylation of H3-K4 is present at discrete regions along most of the autosomes, while H3-K4 dimethylation shows a more homogenous staining. Also, the Y chromosome is largely devoid of H3-K4 di- and trimethylation in somatic cells of both humans and mice, however, the Y chromosome is enriched with H3-K4 di- but not trimethylation throughout spermatogenesis. Our results provide insights into the differences between female somatic cells and male germ cells in inactivating the X chromosome, and suggest that trimethylation, and not dimethylation, of H3-K4 is a more robust indicator of the active regions of the genome.

Short-term effects of growth hormone on sleep abnormalities in Prader-Willi syndrome

CONTEXT

GH was approved for Prader-Willi Syndrome (PWS) in 2000. Fatalities in individuals with PWS soon after beginning GH treatment prompted concern about GH worsening sleep apnea.

OBJECTIVE

We sought to determine whether GH affects sleep apnea in individuals with PWS.

DESIGN

Twenty-five patients with PWS had overnight polysomnography (PSA) at baseline and 6 wk after starting GH.

SETTING

The study was conducted in a sleep lab using a standardized procedure.

PATIENTS

The patients studied had genetically confirmed PWS.

MAIN OUTCOME MEASURES

PSA results were analyzed for frequency and severity of central and obstructive apnea/hypopnea events and total apnea/hypopnea index.

RESULTS

As a group, GH improved apnea/hypopnea index by a mean of 1.2 events per hour (P = 0.02) and central events by a median of 1.7 events per hour (P < 0.001). Fourteen patients had improvement in obstructive events by a mean of 1.7 events per hour. Six patients had worsening of obstructive events on GH. Four of these patients had upper respiratory tract infections at the time of the second PSA and had tonsil/adenoid hypertrophy on otorhinolaryngological evaluation. Two patients with high serum IGF-I levels had increased obstructive events.

CONCLUSIONS

Most of our PWS patients had improvement after short-term GH treatment, but 32% had worsening of sleep disturbance. A subset of PWS patients are at risk during this window of vulnerability shortly after initiation of GH. Because it is difficult to predict who will worsen with GH, patients with PWS should have PSA before and after starting GH and should be monitored for sleep apnea with upper respiratory tract infections. Otorhinolaryngological evaluation is warranted if sleep apnea worsens on GH. IGF-I levels should be monitored, with the goal being physiological levels.

Lupus-like disease and high interferon levels corresponding to trisomy of the type I interferon cluster on chromosome 9p

OBJECTIVE

Systemic lupus erythematosus (SLE) is associated with type I interferons (IFNs) and can be induced by IFNalpha treatment. This study looked for evidence of autoimmunity in a pedigree consisting of 4 family members with a balanced translocation 9;21 and 2 members with an unbalanced translocation resulting in trisomy of the short (p) arm and part of the long (q) arm of chromosome 9. These latter 2 subjects had 3 copies of the IFN gene cluster.

METHODS

Subjects were evaluated clinically and serologically for autoimmune disease. Expression levels of IFNalpha4, IFNbeta, the type I IFN-inducible gene Mx1, the type I IFN receptor, interleukin-6, and tumor necrosis factor alpha were determined by real-time polymerase chain reaction. Circulating plasmacytoid dendritic cells, the main IFN-producing cells, were quantified by flow cytometry.

RESULTS

Both subjects with trisomy of chromosome 9p had a lupus-like syndrome with joint manifestations and antinuclear antibodies: one had anti-RNP and antiphospholipid autoantibodies, and the other had anti-Ro 60. The 3 family members with a balanced translocation 9;21 had no clinical or serologic evidence of autoimmunity, similar to that in relatives who were unaffected by the chromosomal translocation. In the 2 subjects with trisomy of 9p, high levels of IFNalpha/beta (comparable with those found in patients with SLE), increased signaling through the IFN receptor (as indicated by high Mx1 expression), and low levels of circulating plasmacytoid dendritic cells (as observed in patients with SLE) were evident. These abnormalities were not seen in individuals with a balanced translocation.

CONCLUSION

Trisomy of the type I IFN cluster of chromosome 9p was associated with lupus-like autoimmunity and increased IFNalpha/beta and IFN receptor signaling. The data support the idea that abnormal regulation of type I IFN production is involved in the pathogenesis of SLE.

Characterization of cis- and trans-acting elements in the imprinted human SNURF-SNRPN locus

The imprinted SNRPN locus is a complex transcriptional unit that encodes the SNURF and SmN polypeptides as well as multiple non-coding RNAs. SNRPN is located within the Prader-Willi and Angelman syndrome (PWS/AS) region that contains multiple imprinted genes, which are coordinately regulated by a bipartite imprinting center (IC). The SNRPN 5′ region co-localizes with the PWS-IC and contains two DNase I hypersensitive sites, DHS1 at the SNRPN promoter, and DHS2 within intron 1, exclusively on the paternally inherited chromosome. We have examined DHS1 and DHS2 to identify cis- and trans-acting regulatory elements within the endogenous SNRPN 5′ region. Analysis of DHS1 by in vivo footprinting and chromatin immunoprecipitation identified allele-specific interaction with multiple regulatory proteins, including NRF-1, which regulates genes involved in mitochondrial and metabolic functions. DHS2 acted as an enhancer of the SNRPN promoter and contained a highly conserved region that showed allele-specific interaction with unphosphorylated RNA polymerase II, YY1, Sp1 and NRF-1, further suggesting a key role for NRF-1 in regulation of the SNRPN locus. We propose that one or more of the regulatory elements identified in this study may also contribute to PWS-IC function.

Satiety dysfunction in Prader-Willi syndrome demonstrated by fMRI

The neurobiology relating to the insatiable appetite observed in Prader-Willi syndrome (PWS) has not been fully characterised. Two functional magnetic resonance imaging (fMRI) scans were performed on each of three adults with PWS. The scans were carried out pre- and post-treatment with the antiepileptic topiramate, which had little effect on body weight and appetite in these subjects. Subjects fasted overnight and drank a 75 g dextrose solution prior to fMRI scans for measurement of brain activation levels during/after glucose ingestion. Following glucose administration, there was a significant delay in activation at the hypothalamus and other brain regions associated with satiety compared with previous data on obese volunteers. These regions include the insula, ventromedial prefrontal cortex, and nucleus accumbens. Individuals with PWS showed a mean latency of 24 min while in a previous study obese volunteers had shown a latency of 15 min and lean volunteers a latency of 10 min in the hypothalamus. Our results provide evidence towards a satiety dysfunction in the central nervous system of PWS patients.

Microarray analysis of gene/transcript expression in Angelman syndrome: deletion versus UPD

Angelman syndrome (AS) is a neurodevelopmental disorder due to a functional deficit, usually a deletion, of the UBE3A gene located in the 15q11-q13 chromosome region. We report the first microarray analysis of gene expression in AS using a custom cDNA microarray to compare expression patterns from lymphoblastoid cell lines from control males and AS subjects with a 15q deletion or uniparental paternal disomy 15. Expression patterns of genes known to be biallelically expressed or paternally or maternally expressed were consistent with expectations. We detected paternal or maternal allelic bias in the expression of several genes and transcripts (e.g., GABRA5, GABRB3, WI-14946). Additionally, mechanisms controlling paternal allele expression appear to be faithfully replicated in each paternal chromosome in individuals with paternal disomy. Our results indicate that interconnected mechanisms can produce subtle and unexpected changes in gene expression that may help explain the phenotypic differences observed among the genetic subtypes of AS.

Dynamic histone modifications mark sex chromosome inactivation and reactivation during mammalian spermatogenesis

Based on the formation of the XY body at pachytene and expression studies of a few X-linked genes, the X and Y chromosomes seem to undergo transcriptional inactivation during mammalian spermatogenesis. However, the extent and the mechanism of X and Y inactivation are not known. Here, we show that both the X and Y chromosomes undergo sequential changes in their histone modifications beginning at the pachytene stage of meiosis. These changes usually are associated with transcriptional inactivation in somatic cells, and they coincide with the exclusion of the phosphorylated (active) form of RNA polymerase II from the XY body. Both sex chromosomes undergo extensive deacetylation at histones H3 and H4 and (di)methylation of lysine (K)9 on histone H3; however, there are no changes in H3-K4 methylation. These changes persist even when the XY body disappears in late pachytene, and the X and Y chromosomes segregate from one another after the first meiotic division. By the spermatid stage, histone modifications of the X and Y chromosomes revert to those of active chromatin and RNA polymerase II reengages with both chromosomes. Our observations indicate that X and Y inactivation is extensive and persists even when the X and Y chromosomes are separated in secondary spermatocytes. These findings provide insights into epigenetic programming and chromatin dynamics in the male germ line.

Effects of topiramate in adults with Prader-Willi syndrome

Prader-Willi syndrome is a multisystem neurogenetic obesity disorder with behavioral manifestations, including hyperphagia, compulsive behavior, self-injury, and mild to moderate mental retardation. In an 8-week open-label study, we evaluated adjunctive therapy with the anticonvulsant topiramate in 8 adults with Prader-Willi syndrome. Appetite was measured by a 1-hour access to food four times throughout the study and quantified with a visual analogue scale. Topiramate did not significantly change calories consumed, Body Mass Index, or increase self-reported appetite. In addition, there were no significant changes in compulsions. Surprisingly, topiramate treatment resulted in a clinically significant improvement in the self-injury (i.e., skin-picking) that is characteristic of this syndrome. Potential benefits of topiramate for self-injury should be evaluated further in controlled trials.

Progression of familial and non-familial dilated cardiomyopathy: long term follow up

BACKGROUND

It is unknown whether progression of familial idiopathic dilated cardiomyopathy differs from progression in the non-familial form. It has been suggested that familial disease indicates a worse prognosis, and that this should be considered when planning the timing of heart transplantation.

OBJECTIVE

To compare five year survival or time to heart transplantation in an unselected series of patients with dilated cardiomyopathy who had been evaluated for familial v non-familial disease through the echocardiographic investigation of first degree relatives.

DESIGN

Medical records were reviewed and questionnaires were mailed to all patients who had previously participated in a family based study of dilated cardiomyopathy. Information was gathered about survival, heart transplantation, and left ventricular ejection fraction (LVEF) measurements. Survival data were censored at the time of cardiac transplantation.

RESULTS

Follow up data were obtained for 99 of 101 patients (69 with non-familial and 30 with familial disease). Five year survival was 55% for non-familial and 51% for familial patients (NS). The main predictor of mortality was an LVEF of < 30%. Familial status did not predict mortality. There was no significant difference in follow up LVEF values between the groups.

CONCLUSIONS

Five year survival is not significantly different in the familial and non-familial forms of dilated cardiomyopathy.

Anorexigenic melanocortin signaling in the hypothalamus is augmented in association with failure-to-thrive in a transgenic mouse model for Prader-Willi syndrome

As in Prader-Willi syndrome (PWS) infants, mouse models of PWS display failure-to-thrive during the neonatal period. In rodents, the hypothalamic neuropeptide, Neuropeptide Y (NPY) and Agouti-related peptide (AgrP) stimulate while alpha-melanocyte stimulating hormone (alpha-MSH) inhibits appetite. We hypothesized that altered expression of these neuropeptides in the hypothalamus may underlie the failure-to-thrive in PWS neonatal mice. To test this hypothesis we evaluated mRNA expression of Npy, Agrp, and Pomc by in situ hybridization in the hypothalamic arcuate nucleus (ARC) of 3-day-old female and male PWS neonates. The results showed that Agrp mRNA expression was decreased relative to wild-type (WT) controls in neonates of both sexes, while mRNA expression of Pomc was upregulated in PWS neonates. Since AgrP and the Pomc-derived peptide, alpha-MSH, are functional antagonists at melanocortin 4 receptors in the hypothalamic regulation of appetitive behavior, these results show that robust anorexigenic melanocortin signaling, may contribute to the failure-to-thrive in PWS neonatal mice.

Topiramate attenuates self-injurious behaviour in Prader-Willi Syndrome

Self-injurious behaviour (SIB), most notably skin picking, has been described by various terms in the literature ranging from neurotic/psychogenic excoriations to compulsive/pathological skin picking. Prader-Willi Syndrome (PWS) is a neurogenetic multisystem disorder characterized by infantile hypotonia, mental retardation, short stature, hypogonadism, dysmorphic features, and hyperphagia with a high risk of obesity. Psychiatric manifestations include SIBs in the form of skin picking, nail biting and rectal gouging. Topiramate is a novel anti-epileptic medication without significant liability of weight gain. There are no published reports of topiramate being utilized in PWS or SIB. We report attenuation of SIB with resultant lesion healing in three PWS adults treated with topiramate in an 8-wk open-label trial. Although our findings should be treated with caution, they suggest that double-blind or cross-over studies with topiramate are warranted to establish the possible role of topiramate in attenuating SIB in PWS and other disorders that involve SIB.

Secondary organic aerosol formation from the irradiation of simulated automobile exhaust

A laboratory study was conducted to evaluate the potential for secondary organic aerosol formation from emissions from automotive exhaust. The goal was to determine to what extent photochemical oxidation products of these hydrocarbons contribute to secondary organic aerosol (SOA) and how well their formation is described by recently developed models for SOA formation. The quality of a surrogate was tested by comparing its reactivity with that from irradiations of authentic automobile exhaust. Experiments for secondary particle formation using the surrogate were conducted in a fixed volume reactor operated in a dynamic mode. The mass concentration of the aerosol was determined from measurements of organic carbon collected on quartz filters and was corrected for the presence of hydrogen, nitrogen, and oxygen atoms in the organic species. A functional group analysis of the aerosol made by Fourier transform infrared (FTIR) spectroscopy indicated

A family with a grand-maternally derived interstitial duplication of proximal 15q

About 1% of individuals with autism or types of pervasive developmental disorder have a duplication of the 15q11-q13 region. These abnormalities can be detected by routine G-banded chromosome study, showing an extra marker chromosome, or demonstrated by fluorescence in situ hybridization (FISH) analysis, revealing an interstitial duplication. We report here the molecular, cytogenetic, clinical and neuropsychiatric evaluations of a family in whom 3 of 4 siblings inherited an interstitial duplication of 15q11-q13. This duplication was inherited from their mother who also had a maternally derived duplication. Affected family members had apraxia of speech, phonological awareness deficits, developmental language disorder, dyslexia, as well as limb apraxia but did not have any dysmorphic clinical features. The observations in this family suggest that the phenotypic manifestations of proximal 15q duplications may also involve language-based learning disabilities.

Distinct phenotypes distinguish the molecular classes of Angelman syndrome

BACKGROUND

Angelman syndrome (AS) is a severe neurobehavioural disorder caused by defects in the maternally derived imprinted domain located on 15q11-q13. Most patients acquire AS by one of five mechanisms: (1) a large interstitial deletion of 15q11-q13; (2) paternal uniparental disomy (UPD) of chromosome 15; (3) an imprinting defect (ID); (4) a mutation in the E3 ubiquitin protein ligase gene (UBE3A); or (5) unidentified mechanism(s). All classical patients from these classes exhibit four cardinal features, including severe developmental delay and/or mental retardation, profound speech impairment, a movement and balance disorder, and AS specific behaviour typified by an easily excitable personality with an inappropriately happy affect. In addition, patients can display other characteristics, including microcephaly, hypopigmentation, and seizures.

METHODS

We restricted the present study to 104 patients (93 families) with a classical AS phenotype. All of our patients were evaluated for 22 clinical variables including growth parameters, acquisition of motor skills, and history of seizures. In addition, molecular and cytogenetic analyses were used to assign a molecular class (I-V) to each patient for genotype-phenotype correlations.

RESULTS

In our patient repository, 22% of our families had normal DNA methylation analyses along 15q11-q13. Of these, 44% of sporadic patients had mutations within UBE3A, the largest percentage found to date. Our data indicate that the five molecular classes can be divided into four phenotypic groups: deletions, UPD and ID patients, UBE3A mutation patients, and subjects with unknown aetiology. Deletion patients are the most severely affected, while UPD and ID patients are the least. Differences in body mass index, head circumference, and seizure activity are the most pronounced among the classes.

CONCLUSIONS

Clinically, we were unable to distinguish between UPD and ID patients, suggesting that 15q11-q13 contains the only significant maternally expressed imprinted genes on chromosome 15.

Pulmonary atresia with ventricular septal defect and persistent airway hyperresponsiveness

OBJECTIVE

We and others have observed significant hyperinflation and airflow obstruction after the surgical repair of pulmonary atresia and ventricular septal defect. This study sought to objectively characterize this problem and determine the prevalence of airway hyperresponsiveness in these patients.

METHODS

We performed a prospective study of children and young adults with pulmonary atresia and ventricular septal defect between June 1996 and December 1998. The participants were stratified into 2 distinct molecular genotypes on the basis of chromosome 22q11.2 microdeletion. A clinical diagnosis of asthma and an objective assessment of airway hyperresponsiveness were determined by means of an asthma inventory scale and methacholine challenge testing, respectively. Thirty-three patients were enrolled. Thirteen had velocardiofacial syndrome, each with chromosome 22q11.2 microdeletion.

RESULTS

None of the nonsyndromic patients had evidence for haploinsufficiency. Overall, 66.7% (22/33) met criteria for a clinical diagnosis of airway hyperresponsiveness: 62% (8/13) from the microdeletion genotype and 70% (14/20) from the nonsyndromic group.

CONCLUSIONS

We have identified an extremely strong association between pulmonary atresia and ventricular septal defect and persistent airway hyperresponsiveness. Haploinsufficiency at chromosome 22q11.2 did not contribute to this predilection for airway hyperresponsiveness. These results provide a basis to anticipate persistent respiratory difficulties after operations in patients with pulmonary atresia and ventricular septal defect. Moreover, this at-risk patient population may yield unique insights into fundamental mechanisms involved in the pathogenesis of airway hyperresponsiveness.

Molecular autopsy of sudden unexplained death in the young

Sudden unexplained death (SUD) claims over 4,000 persons between the age of 1 and 22 each year in the United States. Nearly half of all pediatric SUD cases have a normal structural autopsy evaluation and are dismissed without a diagnosis. With the discovery of the genetic basis for potentially fatal arrhythmias associated with the inherited long QT syndrome (LQTS), postmortem molecular diagnosis of this disorder is possible. The authors describe the results of a molecular autopsy performed on a 17-year-old boy found dead in bed. A novel clinical test involving an epinephrine challenge in the decedent's mother implicated a potential defect in the phase 3 potassium current encoded by the gene KVLQT1. Exon-specific amplification by polymerase chain reaction and direct DNA sequencing of KVLQT1 revealed a 5-base pair deletion in the genetic material recovered from the decedent's paraffin-embedded heart tissue. The ability to perform molecular autopsies on archived necropsy material undoubtedly will transform the forensic evaluation of SUD. The combination of catecholamine provocation testing in survivors and a postmortem LQTS gene analysis may unmask families with "concealed" LQTS and establish the cause and manner of death in SUDS.