The imprinted NPAP1/C15orf2 gene in the Prader-Willi syndrome region encodes a nuclear pore complex associated protein

Endocrine features of Prader-Willi syndrome: a narrative review focusing on genotype-phenotype correlation

Prader-Willi syndrome (PWS) is a complex genetic disorder caused by three different types of molecular genetic abnormalities. The most common defect is a deletion on the paternal 15q11-q13 chromosome, which is seen in about 60% of individuals. The next most common abnormality is maternal disomy 15, found in around 35% of cases, and a defect in the imprinting center that controls the activity of certain genes on chromosome 15, seen in 1-3% of cases. Individuals with PWS typically experience issues with the hypothalamic-pituitary axis, leading to excessive hunger (hyperphagia), severe obesity, various endocrine disorders, and intellectual disability. Differences in physical and behavioral characteristics between patients with PWS due to deletion versus those with maternal disomy are discussed in literature. Patients with maternal disomy tend to have more frequent neurodevelopmental problems, such as autistic traits and behavioral issues, and generally have higher IQ levels compared to those with deletion of the critical PWS region. This has led us to review the pertinent literature to investigate the possibility of establishing connections between the genetic abnormalities and the endocrine disorders experienced by PWS patients, in order to develop more targeted diagnostic and treatment protocols. In this review, we will review the current state of clinical studies focusing on endocrine disorders in individuals with PWS patients, with a specific focus on the various genetic causes. We will look at topics such as neonatal anthropometry, thyroid issues, adrenal problems, hypogonadism, bone metabolism abnormalities, metabolic syndrome resulting from severe obesity caused by hyperphagia, deficiencies in the GH/IGF-1 axis, and the corresponding responses to treatment.

Hormonal Imbalances in Prader-Willi and Schaaf-Yang Syndromes Imply the Evolution of Specific Regulation of Hypothalamic Neuroendocrine Function in Mammals

The hypothalamus regulates fundamental aspects of physiological homeostasis and behavior, including stress response, reproduction, growth, sleep, and feeding, several of which are affected in patients with Prader-Willi (PWS) and Schaaf-Yang syndrome (SYS). PWS is caused by paternal deletion, maternal uniparental disomy, or imprinting defects that lead to loss of expression of a maternally imprinted region of chromosome 15 encompassing non-coding RNAs and five protein-coding genes; SYS patients have a mutation in one of them, MAGEL2. Throughout life, PWS and SYS patients suffer from musculoskeletal deficiencies, intellectual disabilities, and hormonal abnormalities, which lead to compulsive behaviors like hyperphagia and temper outbursts. Management of PWS and SYS is mostly symptomatic and cures for these debilitating disorders do not exist, highlighting a clear, unmet medical need. Research over several decades into the molecular and cellular roles of PWS genes has uncovered that several impinge on the neuroendocrine system. In this review, we will discuss the expression and molecular functions of PWS genes, connecting them with hormonal imbalances in patients and animal models. Besides the observed hormonal imbalances, we will describe the recent findings about how the loss of individual genes, particularly MAGEL2, affects the molecular mechanisms of hormone secretion. These results suggest that MAGEL2 evolved as a mammalian-specific regulator of hypothalamic neuroendocrine function.

Intranasal Carbetocin Reduces Hyperphagia, Anxiousness, and Distress in Prader-Willi Syndrome: CARE-PWS Phase 3 Trial

CONTEXT

Prader-Willi syndrome (PWS) is a rare genetic disorder characterized by endocrine and neuropsychiatric problems including hyperphagia, anxiousness, and distress. Intranasal carbetocin, an oxytocin analog, was investigated as a selective oxytocin replacement therapy.

OBJECTIVE

To evaluate safety and efficacy of intranasal carbetocin in PWS.

DESIGN

Randomized, double-blind, placebo-controlled phase 3 trial with long-term follow-up.

SETTING

Twenty-four ambulatory clinics at academic medical centers.

PARTICIPANTS

A total of 130 participants with PWS aged 7 to 18 years.

INTERVENTIONS

Participants were randomized to 9.6 mg/dose carbetocin, 3.2 mg/dose carbetocin, or placebo 3 times daily during an 8-week placebo-controlled period (PCP). During a subsequent 56-week long-term follow-up period, placebo participants were randomly assigned to 9.6 mg or 3.2 mg carbetocin, with carbetocin participants continuing at their previous dose.

MAIN OUTCOME MEASURES

Primary endpoints assessed change in hyperphagia (Hyperphagia Questionnaire for Clinical Trials [HQ-CT]) and obsessive-compulsive symptoms (Children's Yale-Brown Obsessive-Compulsive Scale [CY-BOCS]) during the PCP for 9.6 mg vs placebo, and the first secondary endpoints assessed these same outcomes for 3.2 mg vs placebo. Additional secondary endpoints included assessments of anxiousness and distress behaviors (PWS Anxiousness and Distress Behaviors Questionnaire [PADQ]) and clinical global impression of change (CGI-C).

RESULTS

Because of onset of the COVID-19 pandemic, enrollment was stopped prematurely. The primary endpoints showed numeric improvements in both HQ-CT and CY-BOCS which were not statistically significant; however, the 3.2-mg arm showed nominally significant improvements in HQ-CT, PADQ, and CGI-C scores vs placebo. Improvements were sustained in the long-term follow-up period. The most common adverse event during the PCP was mild to moderate flushing.

CONCLUSIONS

Carbetocin was well tolerated, and the 3.2-mg dose was associated with clinically meaningful improvements in hyperphagia and anxiousness and distress behaviors in participants with PWS.

CLINICAL TRIALS REGISTRATION NUMBER

NCT03649477.

Proteins and Proteases of Prader-Willi Syndrome: A Comprehensive Review and Perspectives

Prader–Willi Syndrome (PWS) is a rare complex genetic disease that is associated with pathological disorders that include endocrine disruption, developmental, neurological, and physical problems as well as intellectual, and behavioral dysfunction. In early stage, PWS is characterized by respiratory distress, hypotonia, and poor sucking ability, causing feeding concern and poor weight gain. Additional features of the disease evolve over time. These include hyperphagia, obesity, developmental, cognitive delay, skin picking, high pain threshold, short stature, growth hormone deficiency, hypogonadism, strabismus, scoliosis, joint laxity, or hip dysplasia. The disease is associated with a shortened life expectancy. There is no cure for PWS, although interventions are available for symptoms management. PWS is caused by genetic defects in chromosome 15q11.2-q13, and categorized into three groups, namely Paternal deletion, Maternal uniparental disomy, and Imprinting defect. PWS is confirmed through genetic testing and DNA-methylation analysis. Studies revealed that at least two key proteins namely MAGEL-2 and NECDIN along with two proteases PCSK1 and PCSK2 are linked to PWS. Herein, we summarize our current understanding and knowledge about the role of these proteins and enzymes in various biological processes associated with PWS. The review also describes how loss and/or impairment of functional activity of these macromolecules can lead to hormonal disbalance by promoting degradation of secretory granules and via inhibition of proteolytic maturation of precursor-proteins. The present review will draw attention of researchers, scientists, and academicians engaged in PWS study and will help to identify potential targets and molecular pathways for PWS intervention and treatment.

Genome-wide association study identifies a role for the progesterone receptor in benign prostatic hyperplasia risk

BACKGROUND

Benign prostatic hyperplasia (BPH) is common noncancerous prostate enlargement, which is usually associated with lower urinary tract symptoms (LUTS) and can lead to complex urinary, bladder, or kidney diseases. The majority of elderly men will be affected by BPH as age increases.

METHODS

Here, we conducted a genome-wide association study (GWAS) of BPH using 1942 cases and 4730 controls from the Electronic Medical Records and Genomics network (eMERGE) as discovery cohort. We then used 5109 cases and 161,911 controls from UK Biobank as validation cohort.

RESULTS

This GWAS discovered 35 genome-wide significant variants (P < 5 × 10-8), located at 22 different loci in discovery cohort. We validated four significant variants located at four different loci in validation cohort: rs8027714 at 15q11.2, rs8136152 at 22q13.2, rs10192133 at 2q24.2, and rs1237696 at 11q22.1. rs1237696 is an intronic variant on chromosome 11 in the progesterone receptor (PGR) gene (P = 4.21 ×10-8, OR [95% CI] = 1.36 [1.22-1.52]). PGR is a known drug target for BPH as the PGR agonist gestonorone caproate has been used to treat BPH in multiple countries.

CONCLUSIONS

Our results suggest that genetic variants identified from BPH GWAS can identify pharmacologic targets for BPH treatment.

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

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

Prader-Willi syndrome: reflections on seminal studies and future therapies

Prader-Willi syndrome (PWS) is caused by the loss of function of the paternally inherited 15q11-q13 locus. This region is governed by genomic imprinting, a phenomenon in which genes are expressed exclusively from one parental allele. The genomic imprinting of the 15q11-q13 locus is established in the germline and is largely controlled by a bipartite imprinting centre. One part, termed the Prader-Willi syndrome imprinting center (PWS-IC), comprises a CpG island that is unmethylated on the paternal allele and methylated on the maternal allele. The second part, termed the Angelman syndrome imprinting centre, is required to silence the PWS_IC in the maternal germline. The loss of the paternal contribution of the imprinted 15q11-q13 locus most frequently occurs owing to a large deletion of the entire imprinted region but can also occur through maternal uniparental disomy or an imprinting defect. While PWS is considered a contiguous gene syndrome based on large-deletion and uniparental disomy patients, the lack of expression of only non-coding RNA transcripts from the SNURF-SNRPN/SNHG14 may be the primary cause of PWS. Patients with small atypical deletions of the paternal SNORD116 cluster alone appear to have most of the PWS related clinical phenotypes. The loss of the maternal contribution of the 15q11-q13 locus causes a separate and distinct condition called Angelman syndrome. Importantly, while much has been learned about the regulation and expression of genes and transcripts deriving from the 15q11-q13 locus, there remains much to be learned about how these genes and transcripts contribute at the molecular level to the clinical traits and developmental aspects of PWS that have been observed.

Linkage and exome analysis implicate multiple genes in non-syndromic intellectual disability in a large Swedish family

Background

Non-syndromic intellectual disability is genetically heterogeneous with dominant, recessive and complex forms of inheritance. We have performed detailed genetic studies in a large multi-generational Swedish family, including several members diagnosed with non-syndromic intellectual disability. Linkage analysis was performed on 22 family members, nine affected with mild to moderate intellectual disability and 13 unaffected family members.

Methods

Family members were analyzed with Affymetrix Genome-Wide Human SNP Array 6.0 and the genetic data was used to detect copy number variation and to perform genome wide linkage analysis with the SNP High Throughput Linkage analysis system and the Merlin software. For the exome sequencing, the samples were prepared using the Sure Select Human All Exon Kit (Agilent Technologies, Santa Clara, CA, USA) and sequenced using the Ion Proton™ System. Validation of identified variants was performed with Sanger sequencing.

Results

The linkage analysis results indicate that intellectual disability in this family is genetically heterogeneous, with suggestive linkage found on chromosomes 1q31-q41, 4q32-q35, 6p25 and 14q24-q31 (LOD scores of 2.4, simulated p-value of 0.000003 and a simulated genome-wide p-value of 0.06). Exome sequencing was then performed in 14 family members and 7 unrelated individuals from the same region. The analysis of coding variation revealed a pathogenic and candidate variants in different branches of the family. In three patients we find a known homozygous pathogenic mutation in the Homo sapiens solute carrier family 17 member 5 (SLC17A5), causing Salla disease. We also identify a deletion overlapping KDM3B and a duplication overlapping MAP3K4 and AGPAT4, both overlapping variants previously reported in developmental disorders.

Conclusions

DNA samples from the large family analyzed in this study were initially collected based on a hypothesis that affected members shared a major genetic risk factor. Our results show that a complex phenotype such as mild intellectual disability in large families from genetically isolated populations may show considerable genetic heterogeneity.

Genotype-Phenotype Relationships and Endocrine Findings in Prader-Willi Syndrome

Prader-Willi syndrome (PWS) is a complex imprinting disorder related to genomic errors that inactivate paternally-inherited genes on chromosome 15q11-q13 with severe implications on endocrine, cognitive and neurologic systems, metabolism, and behavior. The absence of expression of one or more genes at the PWS critical region contributes to different phenotypes. There are three molecular mechanisms of occurrence: paternal deletion of the 15q11-q13 region; maternal uniparental disomy 15; or imprinting defects. Although there is a clinical diagnostic consensus criteria, DNA methylation status must be confirmed through genetic testing. The endocrine system can be the most affected in PWS, and growth hormone replacement therapy provides improvement in growth, body composition, and behavioral and physical attributes. A key feature of the syndrome is the hypothalamic dysfunction that may be the basis of several endocrine symptoms. Clinical and molecular complexity in PWS enhances the importance of genetic diagnosis in therapeutic definition and genetic counseling. So far, no single gene mutation has been described to contribute to this genetic disorder or related to any exclusive symptoms. Here we proposed to review individually disrupted genes within the PWS critical region and their reported clinical phenotypes related to the syndrome. While genes such as MKRN3, MAGEL2, NDN, or SNORD115 do not address the full spectrum of PWS symptoms and are less likely to have causal implications in PWS major clinical signs, SNORD116 has emerged as a critical, and possibly, a determinant candidate in PWS, in the recent years. Besides that, the understanding of the biology of the PWS SNORD genes is fairly low at the present. These non-coding RNAs exhibit all the hallmarks of RNA methylation guides and can be incorporated into ribonucleoprotein complexes with possible hypothalamic and endocrine functions. Also, DNA conservation between SNORD sequences across placental mammals strongly suggests that they have a functional role as RNA entities on an evolutionary basis. The broad clinical spectrum observed in PWS and the absence of a clear genotype-phenotype specific correlation imply that the numerous genes involved in the syndrome have an additive deleterious effect on different phenotypes when deficiently expressed.

Muscle dysfunction caused by loss of Magel2 in a mouse model of Prader-Willi and Schaaf-Yang syndromes

Prader-Willi syndrome is characterized by severe hypotonia in infancy, with decreased lean mass and increased fat mass in childhood followed by severe hyperphagia and consequent obesity. Scoliosis and other orthopaedic manifestations of hypotonia are common in children with Prader-Willi syndrome and cause significant morbidity. The relationships among hypotonia, reduced muscle mass and scoliosis have been difficult to establish. Inactivating mutations in one Prader-Willi syndrome candidate gene, MAGEL2, cause a Prader-Willi-like syndrome called Schaaf-Yang syndrome, highlighting the importance of loss of MAGEL2 in Prader-Willi syndrome phenotypes. Gene-targeted mice lacking Magel2 have excess fat and decreased muscle, recapitulating altered body composition in Prader-Willi syndrome. We now demonstrate that Magel2 is expressed in the developing musculoskeletal system, and that loss of Magel2 causes muscle-related phenotypes in mice consistent with atrophy caused by altered autophagy. Magel2-null mice serve as a preclinical model for therapies targeting muscle structure and function in children lacking MAGEL2 diagnosed with Prader-Willi or Schaaf-Yang syndrome.

Efficient Generation of Human Embryonic Stem Cell-Derived Corneal Endothelial Cells by Directed Differentiation

Aim

To generate human embryonic stem cell derived corneal endothelial cells (hESC-CECs) for transplantation in patients with corneal endothelial dystrophies.

Materials and Methods

Feeder-free hESC-CECs were generated by a directed differentiation protocol. hESC-CECs were characterized by morphology, expression of corneal endothelial markers, and microarray analysis of gene expression.

Results

hESC-CECs were nearly identical morphologically to primary human corneal endothelial cells, expressed Zona Occludens 1 (ZO-1) and Na⁺/K⁺ATPaseα1 (ATPA1) on the apical surface in monolayer culture, and produced the key proteins of Descemet’s membrane, Collagen VIIIα1 and VIIIα2 (COL8A1 and 8A2). Quantitative PCR analysis revealed expression of all corneal endothelial pump transcripts. hESC-CECs were 96% similar to primary human adult CECs by microarray analysis.

Conclusion

hESC-CECs are morphologically similar, express corneal endothelial cell markers and express a nearly identical complement of genes compared to human adult corneal endothelial cells. hESC-CECs may be a suitable alternative to donor-derived corneal endothelium.

Expression of imprinted genes in placenta is associated with infant neurobehavioral development

Genomic imprinting disorders often exhibit delayed neurobehavioral development, suggesting this unique mechanism of epigenetic regulation plays a role in mental and neurological health. While major errors in imprinting have been linked to adverse health outcomes, there has been little research conducted on how moderate variability in imprinted gene expression within a population contributes to differences in neurobehavioral outcomes, particularly at birth. Here, we profiled the expression of 108 known and putative imprinted genes in human placenta samples from 615 infants assessed by the Neonatal Intensive Care Unit (NICU) Network Neurobehavioral Scales (NNNS). Data reduction identified 10 genes (DLX5, DHCR24, VTRNA2-1, PHLDA2, NPAP1, FAM50B, GNAS-AS1, PAX8-AS1, SHANK2, and COPG2IT1) whose expression could distinguish between newborn neurobehavioral profiles derived from the NNNS. Clustering infants based on the expression pattern of these genes identified 2 groups of infants characterized by reduced quality of movement, increased signs of asymmetrical and non-optimal reflexes, and increased odds of demonstrating increased signs of physiologic stress and abstinence. Overall, these results suggest that common variation in placental imprinted gene expression is linked to suboptimal performance on scales of neurological functioning as well as with increased signs of physiologic stress, highlighting the central importance of the control of expression of these genes in the placenta for neurobehavioral development.

Altering TET dioxygenase levels within physiological range affects DNA methylation dynamics of HEK293 cells

The TET family of dioxygenases (TET1/2/3) can convert 5-methylcytosine (5 mC) into 5-hydroxymethylcytosine (5 hmC) and has been shown to be involved in active and passive DNA demethylation. Here, we demonstrate that altering TET dioxygenase levels within physiological range can affect DNA methylation dynamics of HEK293 cells. Overexpression of TET1 increased global 5 hmC levels and was accompanied by mild DNA demethylation of promoters, gene bodies and CpG islands. Conversely, the simultaneous knockdown of TET1, TET2, and TET3 led to decreased global 5 hmC levels and mild DNA hypermethylation of above-mentioned regions. The methylation changes observed in the overexpression and knockdown studies were mostly non-reciprocal and occurred with different preference depending on endogenous methylation and gene expression levels. Single-nucleotide 5 hmC profiling performed on a genome-wide scale revealed that TET1 overexpression induced 5 mC oxidation without a distribution bias among genetic elements and structures. Detailed analysis showed that this oxidation was related to endogenous 5 hmC levels. In addition, our results support the notion that the effects of TET1 overexpression on gene expression are generally unrelated to its catalytic activity.

The small RNA content of human sperm reveals pseudogene-derived piRNAs complementary to protein-coding genes

At the end of mammalian sperm development, sperm cells expel most of their cytoplasm and dispose of the majority of their RNA. Yet, hundreds of RNA molecules remain in mature sperm. The biological significance of the vast majority of these molecules is unclear. To better understand the processes that generate sperm small RNAs and what roles they may have, we sequenced and characterized the small RNA content of sperm samples from two human fertile individuals. We detected 182 microRNAs, some of which are highly abundant. The most abundant microRNA in sperm is miR-1246 with predicted targets among sperm-specific genes. The most abundant class of small noncoding RNAs in sperm are PIWI-interacting RNAs (piRNAs). Surprisingly, we found that human sperm cells contain piRNAs processed from pseudogenes. Clusters of piRNAs from human testes contain pseudogenes transcribed in the antisense strand and processed into small RNAs. Several human protein-coding genes contain antisense predicted targets of pseudogene-derived piRNAs in the male germline and these piRNAs are still found in mature sperm. Our study provides the most extensive data set and annotation of human sperm small RNAs to date and is a resource for further functional studies on the roles of sperm small RNAs. In addition, we propose that some of the pseudogene-derived human piRNAs may regulate expression of their parent gene in the male germline.

The imprinted NPAP1 gene in the Prader-Willi syndrome region belongs to a POM121-related family of retrogenes

We have recently shown that the human Nuclear pore-associated protein (NPAP1)/C15orf2 gene encodes a nuclear pore-associated protein. This gene is one of several paternally expressed imprinted genes in the genomic region 15q11q13. Because the Prader–Willi syndrome is known to be caused by the loss of function of paternally expressed genes in 15q11q13, a phenotypic contribution of NPAP1 cannot be excluded. NPAP1 appears to be under strong positive Darwinian selection in primates, suggesting an important function in primate biology. Interestingly, however, in contrast to all other protein-coding genes in 15q11q13, NPAP1 has no ortholog in the mouse. Our investigation of the evolutionary origin of NPAP1 showed that the gene is specific to primate species and absent from the 15q11q13-orthologous regions in all nonprimate mammals. However, we identified a group of paralogous genes, which we call NPAP1L, in all placental mammals except rodents. Phylogenetic analysis revealed that NPAP1, NPAP1L, and another group of genes (UPF0607), which is also restricted to primates, are closely related to the vertebrate transmembrane nucleoporin gene POM121, although they lack the transmembrane domain. These three newly identified groups of genes all lack conserved introns, and hence, are likely retrogenes. We hypothesize that, in the common ancestor of placentals, the POM121 gene retrotransposed and gave rise to an NPAP1-ancestral retrogene NPAP1L/NPAP1/UPF0607. Our results suggest that the nuclear pore-associated gene NPAP1 originates from the vertebrate nucleoporin gene POM121 and—after several steps of retrotransposition and duplication—has been subjected to genomic imprinting and positive selection after integration into the imprinted SNRPN-UBE3A chromosomal domain.

Differential regulation of non-protein coding RNAs from Prader-Willi Syndrome locus

Prader-Willi Syndrome (PWS) is a neurogenetic disorder caused by the deletion of imprinted genes on the paternally inherited human chromosome 15q11-q13. This locus harbours a long non-protein-coding RNA (U-UBE3A-ATS) that contains six intron-encoded snoRNAs, including the SNORD116 and SNORD115 repetitive clusters. The 3′-region of U-UBE3A-ATS is transcribed in the cis-antisense direction to the ubiquitin-protein ligase E3A (UBE3A) gene. Deletion of the SNORD116 region causes key characteristics of PWS. There are few indications that SNORD115 might regulate serotonin receptor (5HT2C) pre-mRNA processing. Here we performed quantitative real-time expression analyses of RNAs from the PWS locus across 20 human tissues and combined it with deep-sequencing data derived from Cap Analysis of Gene Expression (CAGE-seq) libraries. We found that the expression profiles of SNORD64, SNORD107, SNORD108 and SNORD116 are similar across analyzed tissues and correlate well with SNORD116 embedded U-UBE3A-ATS exons (IPW116). Notable differences in expressions between the aforementioned RNAs and SNORD115 together with the host IPW115 and UBE3A cis-antisense exons were observed. CAGE-seq analysis revealed the presence of potential transcriptional start sites originated from the U-UBE3A-ATS spanning region. Our findings indicate novel aspects for the expression regulation in the PWS locus.

Copy number variation findings among 50 children and adolescents with autism spectrum disorder

OBJECTIVES

Autism spectrum disorders (ASDs) are a heterogeneous group of neurodevelopment disorders with a complex genetic aetiology. The aim of this study was to identify copy number variations (CNVs) with a clinical significance for ASD.

MATERIALS AND METHODS

Array-based comparative genomic hybridization was applied to detect CNVs in a clinically well-characterized population of 50 children and adolescents with ASD.

RESULTS

Nine CNVs with predicted clinical significance were identified among eight individuals (detection rate 16%). Three of the CNVs are recurrently associated with ASDs (15q11.2q13.1) or have been identified in ASD populations [3p14.2 and t(8;12)(p23.1;p13.31)]. The remaining regions (15q11.2, 10q21.1, Xp22.2, 16p13.3 and 22q13.1) have not been reported previously as candidate genes for ASD.

CONCLUSION

This study identified five novel CNVs among the individuals. The causal relationship between identified CNVs and the ASD phenotype is not fully established. However, the genes involved are associated with ASD and/or other neuropsychiatric disorders, or implicated in synaptic and neuronal activity, thus suggesting clinical significance. Further identification of ASD-associated CNVs is required, together with a broad clinical characterization of affected individuals to identify genotype-phenotype correlations.

Recommendations for the investigation of animal models of Prader-Willi syndrome

Prader-Willi syndrome (PWS) occurs in about 1 in 15,000 individuals and is a contiguous gene disorder causing developmental disability, hyperphagia usually with obesity, and behavioral problems, including an increased incidence of psychiatric illness. The genomic imprinting that regulates allele-specific expression of PWS candidate genes, the fact that multiple genes are typically inactivated, and the presence of many genes that produce functional RNAs rather than proteins has complicated the identification of the underlying genetic pathophysiology of PWS. Over 30 genetically modified mouse strains that have been developed and characterized have been instrumental in elucidating the genetic and epigenetic mechanisms for the regulation of PWS genes and in discovering their physiological functions. In 2011, a PWS Animal Models Working Group (AMWG) was established to generate discussions and facilitate exchange of ideas regarding the best use of PWS animal models. Here, we summarize the goals of the AMWG, describe current animal models of PWS, and make recommendations for strategies to maximize the utility of animal models and for the development and use of new animal models of PWS.

Leptin signaling defects in a mouse model of Prader-Willi syndrome: An orphan genetic obesity syndrome no more?

Prader-Willi syndrome (PWS) is a rare (~1 in 12,000) genetic disorder that involves at least six genes on chromosome 15q11–q13. Children with PWS not only rapidly gain weight and become severely obese because of reduced voluntary activity and increased food intake, but also exhibit growth hormone deficiency, excessive daytime sleepiness, endocrine dysregulation and infertility. These phenotypes suggest dysfunction of the hypothalamus, the brain region that regulates short- and long-term energy balance and other body functions. The physiological basis for obesity in children with PWS has eluded researchers for decades. Mercer et al. now demonstrate that Magel2, the murine ortholog of one of the PWS genes, is a component of the hypothalamic leptin-melanocortin pathway that is critical for energy balance. Most interestingly, disruptions of other components of this pathway cause obesity in both mice and humans, suggesting a mechanistic link between PWS and other rare genetic forms of severe childhood-onset obesity.

RNAs of the human chromosome 15q11-q13 imprinted region

The human chromosome 15q11-q13 region hosts a wide variety of coding and noncoding RNAs, and is also the site of nearly every imaginable type of RNA processing. To deepen the intrigue, the transcripts in the human chromosome 15q11-q13 region are subject to regulation by genomic imprinting, and some of these transcripts are imprinted in a tissue-specific manner. As the region is critically important for three human neurogenetic disorders, Angelman syndrome, Prader-Willi syndrome, and 15q duplication syndrome, there is intense interest in understanding the types of RNA and RNA processing that occurs among the imprinted genes. This review summarizes what is known about the various RNAs within the imprinted domain, including a novel type of RNA that was only very recently identified.

FTO levels affect RNA modification and the transcriptome

A block of single-nucleotide polymorphisms within intron 1 of the FTO (fat mass and obesity associated) gene is associated with variation in body weight. Previous works suggest that increased expression of FTO, which encodes a 2-oxoglutarate-dependent nucleic acid demethylase, leads to increased body weight, although the underlying mechanism has remained unclear. To elucidate the function of FTO, we examined the consequences of altered FTO levels in cultured cells and murine brain. Here we show that a knockdown of FTO in HEK293 cells affects the transcripts levels of genes involved in the response to starvation, whereas overexpression of FTO affects the transcript levels of genes related to RNA processing and metabolism. Subcellular localization of FTO further strengthens the latter notion. Using immunocytochemistry and confocal laser scanning microscopy, we detected FTO in nuclear speckles and--to a lesser and varying extent--in the nucleoplasm and nucleoli of HEK293, HeLa and MCF-7 cells. Moreover, RNA modification analyses revealed that loss of Fto affects the 3-methyluridine/uridine and pseudouridine/uridine ratios in total brain RNA. We conclude that altered levels of FTO have multiple and diverse consequences on RNA modifications and the transcriptome.