Modeling del(17)(p11.2p11.2) and dup(17)(p11.2p11.2) contiguous gene syndromes by chromosome engineering in mice: phenotypic consequences of gene dosage imbalance

rAAV-CRISPRa therapy corrects Rai1 haploinsufficiency and rescues selective disease features in Smith-Magenis syndrome mice

Haploinsufficiency in retinoic acid induced 1 (RAI1) causes Smith-Magenis syndrome (SMS), a severe neurodevelopmental disorder characterized by neurocognitive deficits and obesity. Currently, curative treatments for SMS do not exist. Here, we take a recombinant adeno-associated virus (rAAV)-clustered regularly interspaced short palindromic repeats activation (CRISPRa) approach to increase expression of the remaining intact Rai1 allele. Building upon our previous work that found the paraventricular nucleus of hypothalamus plays a central role in SMS pathogenesis, we performed paraventricular nucleus of hypothalamus-specific rAAV-CRISPRa therapy by increasing endogenous Rai1 expression in SMS (Rai1^±) mice. We found that rAAV-CRISPRa therapy rescues excessive repetitive behavior, delays the onset of obesity, and partially reduces hyperphagia in SMS mice. Our work provides evidence that rAAV-CRISPRa therapy during early adolescence can boost the expression of healthy Rai1 allele and modify disease progression in a mouse model of Smith-Magenis syndrome.

Biology in balance: human diploid genome integrity, gene dosage, and genomic medicine

The path to completion of the functional annotation of the haploid human genome reference build, exploration of the clan genomics hypothesis, understanding human gene and genome functional biology, and gene genome and organismal evolution, is in reach.

Copy number variations of chromosome 17p11.2 region in children with development delay and in fetuses with abnormal imaging findings

BACKGROUND

Deletion and duplication of the 3.7 Mb region in 17p11.2 result in two syndromes, Smith-Magenis syndrome and Potocki-Lupski syndrome, which are well-known development disorders. The purpose of this study was to determine the prevalence, genetic characteristics and clinical phenotypes of 17p11.2 deletion/duplication in Chinese children with development delay and in fetuses with potential congenital defects.

METHODS

7077 children with development delay and/or intellectual disability were screened by multiplex ligation-dependent probe amplification P245 assay. 7319 fetuses with potential congenital defects were tested using next generation sequencing technique.

RESULTS

417 of 7077 pediatric patients were determined to carry chromosome imbalance. 28 (28/7077, 0.4%) cases had imbalance at chromosome 17p11.2. Among them, 12 cases (42.9%) had heterozygous deletions and 16 cases (57.1%) had heterozygous duplications. The clinical phenotypes were variable, including neurobehavioral disorders, craniofacial/skeletal anomalies, immunologic defects, ocular problems and organ malformations. 263 of 7319 fetuses were recognized to have genomic copy number variations. Only 2 of them were found to harbor 17p11.2 imbalance. The fetus with deletion presented with ventricular septal defect and the fetus with duplication had cerebral ventricle dilation.

CONCLUSION

Our study highlights the phenotypic variability associated with 17p11.2 variations in China. The results further expand the phenotypic spectrum of SMS/PTLS and increase awareness of these disruptive mutations among clinicians.

Dosage-sensitive genes in autism spectrum disorders: From neurobiology to therapy

Autism spectrum disorders (ASDs) are a group of heterogenous neurodevelopmental disorders affecting 1 in 59 children. Syndromic ASDs are commonly associated with chromosomal rearrangements or dosage imbalance involving a single gene. Many of these genes are dosage-sensitive and regulate transcription, protein homeostasis, and synaptic function in the brain. Despite vastly different molecular perturbations, syndromic ASDs share core symptoms including social dysfunction and repetitive behavior. However, each ASD subtype has a unique pathogenic mechanism and combination of comorbidities that require individual attention. We have learned a great deal about how these dosage-sensitive genes control brain development and behaviors from genetically-engineered mice. Here we describe the clinical features of eight monogenic neurodevelopmental disorders caused by dosage imbalance of four genes, as well as recent advances in using genetic mouse models to understand their pathogenic mechanisms and develop intervention strategies. We propose that applying newly developed quantitative molecular and neuroscience technologies will advance our understanding of the unique neurobiology of each disorder and enable the development of personalized therapy.

The CHD4-related syndrome: a comprehensive investigation of the clinical spectrum, genotype-phenotype correlations, and molecular basis

PURPOSE

Sifrim-Hitz-Weiss syndrome (SIHIWES) is a recently described multisystemic neurodevelopmental disorder caused by de novo variants inCHD4. In this study, we investigated the clinical spectrum of the disorder, genotype-phenotype correlations, and the effect of different missense variants on CHD4 function.

METHODS

We collected clinical and molecular data from 32 individuals with mostly de novo variants in CHD4, identified through next-generation sequencing. We performed adenosine triphosphate (ATP) hydrolysis and nucleosome remodeling assays on variants from five different CHD4 domains.

RESULTS

The majority of participants had global developmental delay, mild to moderate intellectual disability, brain anomalies, congenital heart defects, and dysmorphic features. Macrocephaly was a frequent but not universal finding. Additional common abnormalities included hypogonadism in males, skeletal and limb anomalies, hearing impairment, and ophthalmic abnormalities. The majority of variants were nontruncating and affected the SNF2-like region of the protein. We did not identify genotype-phenotype correlations based on the type or location of variants. Alterations in ATP hydrolysis and chromatin remodeling activities were observed in variants from different domains.

CONCLUSION

The CHD4-related syndrome is a multisystemic neurodevelopmental disorder. Missense substitutions in different protein domains alter CHD4 function in a variant-specific manner, but result in a similar phenotype in humans.

Behavioral neuroscience of autism

Autism spectrum disorder (ASD) is a neurodevelopmental disorder. Several genetic causes of ASD have been identified and this has enabled researchers to construct mouse models. Mouse behavioral tests reveal impaired social interaction and communication, as well as increased repetitive behavior and behavioral inflexibility in these mice, which correspond to core behavioral deficits observed in individuals with ASD. However, the connection between these behavioral abnormalities and the underlying dysregulation in neuronal circuits and synaptic function is poorly understood. Moreover, different components of the ASD phenotype may be linked to dysfunction in different brain regions, making it even more challenging to chart the pathophysiological mechanisms involved in ASD. Here we summarize the research on mouse models of ASD and their contribution to understanding pathophysiological mechanisms. Specifically, we emphasize abnormal serotonin production and regulation, as well as the disruption in circadian rhythms and sleep that are observed in a subset of ASD, and propose that spatiotemporal disturbances in brainstem development may be a primary cause of ASD that propagates towards the cerebral cortex.

An interaction-based model for neuropsychiatric features of copy-number variants

Variably expressive copy-number variants (CNVs) are characterized by extensive phenotypic heterogeneity of neuropsychiatric phenotypes. Approaches to identify single causative genes for these phenotypes within each CNV have not been successful. Here, we posit using multiple lines of evidence, including pathogenicity metrics, functional assays of model organisms, and gene expression data, that multiple genes within each CNV region are likely responsible for the observed phenotypes. We propose that candidate genes within each region likely interact with each other through shared pathways to modulate the individual gene phenotypes, emphasizing the genetic complexity of CNV-associated neuropsychiatric features.

Revisiting the evolutionary origins of obesity: lazy versus peppy-thrifty genotype hypothesis

The recent global obesity epidemic is attributed to major societal and environmental changes, such as excessive energy intake and sedentary lifestyle. However, exposure to 'obesogenic' environments does not necessarily result in obesity at the individual level, as 40-75% of body mass index variation in population is attributed to genetic differences. The thrifty genotype theory posits that genetic variants promoting efficient food sequestering and optimal deposition of fat during periods of food abundance were evolutionarily advantageous for the early hunter-gatherer and were positively selected. However, the thrifty genotype is likely too simplistic and fails to provide a justification for the complex distribution of obesity predisposing gene variants and for the broad range of body mass index observed in diverse ethnic groups. This review proposes that gene pleiotropy may better account for the variability in the distribution of obesity susceptibility alleles across modern populations. We outline the lazy-thrifty versus peppy-thrifty genotype hypothesis and detail the body of evidence in the literature in support of this novel concept. Future population genetics and mathematical modelling studies that account for pleiotropy may further improve our understanding of the evolutionary origins of the current obesity epidemic.

RAI1 gene mutations: mechanisms of Smith-Magenis syndrome

Smith-Magenis syndrome (SMS; OMIM #182290) is a complex genetic disorder characterized by distinctive physical features, developmental delay, cognitive impairment, and a typical behavioral phenotype. SMS is caused by interstitial 17p11.2 deletions, encompassing multiple genes and including the retinoic acid-induced 1 gene (RAI1), or by mutations in RAI1 itself. About 10% of all the SMS patients, in fact, carry an RAI1 mutation responsible for the phenotype. RAI1 (OMIM *607642) is a dosage-sensitive gene expressed in many tissues and highly conserved among species. Over the years, several studies have demonstrated that RAI1 (or its homologs in animal models) acts as a transcriptional factor implicated in embryonic neurodevelopment, neuronal differentiation, cell growth and cell cycle regulation, bone and skeletal development, lipid and glucose metabolisms, behavioral functions, and circadian activity. Patients with RAI1 pathogenic variants show some phenotypic differences when compared to those carrying the typical deletion. They usually have lower incidence of hypotonia and less cognitive impairment than those with 17p11.2 deletions but more frequently show the behavioral characteristics of the syndrome and overeating issues. These differences reflect the primary pathogenetic role of RAI1 without the pathogenetic contribution of the other genes included in the typical 17p11.2 deletion. The better comprehension of physiological roles of RAI1, its molecular co-workers and interactors, and its contribution in determining the typical SMS phenotype will certainly open a new path for therapeutic interventions.

Revealing hidden complexities of genomic rearrangements generated with Cas9

Modelling human diseases caused by large genomic rearrangements has become more accessible since the utilization of CRISPR/Cas9 in mammalian systems. In a previous study, we showed that genomic rearrangements of up to one million base pairs can be generated by direct injection of CRISPR/Cas9 reagents into mouse zygotes. Although these rearrangements are ascertained by junction PCR, we describe here a variety of unanticipated structural changes often involving reintegration of the region demarcated by the gRNAs in the vicinity of the edited locus. We illustrate here some of this diversity detected by high-resolution fibre-FISH and conclude that extensive molecular analysis is required to fully understand the structure of engineered chromosomes generated by Cas9.

Rodent models of genetic and chromosomal variations in psychiatric disorders

Elucidating the molecular basis of complex human psychiatric disorders is challenging due to the multitude of factors that underpin these disorders. Genetic and chromosomal changes are two factors that have been suggested to be involved in psychiatric disorders. Indeed, numerous risk loci have been identified in autism spectrum disorders, schizophrenia, and related psychiatric disorders. Here, we introduce genetic animal models that disturb excitatory-inhibitory balance in the brain and animal models mirroring human chromosomal abnormalities, both of which may be implicated in autism spectrum disorder pathophysiology. In addition, we discuss recent unique translational research using rodent models, such as Cntnap2 knockout mouse, Mecp2 mutant mouse, Pick1 knockout mouse, and neonatal ventral hippocampal lesion rat. By using these models, several types of drugs are administered during the developmental period to see the effect on psychotic symptoms and neural activities in adults. The accumulating evidence from recent animal studies provides an informative intervention strategy as a translational research.

Rai1 Haploinsufficiency Is Associated with Social Abnormalities in Mice

Background: Autism is characterized by difficulties in social interaction, communication, and repetitive behaviors; with different degrees of severity in each of the core areas. Haploinsufficiency and point mutations of RAI1 are associated with Smith-Magenis syndrome (SMS), a genetic condition that scores within the autism spectrum range for social responsiveness and communication, and is characterized by neurobehavioral abnormalities, intellectual disability, developmental delay, sleep disturbance, and self-injurious behaviors. Methods: To investigate the relationship between Rai1 and social impairment, we evaluated the Rai1^+/− mice with a battery of tests to address social behavior in mice. Results: We found that the mutant mice showed diminished interest in social odors, abnormal submissive tendencies, and increased repetitive behaviors when compared to wild type littermates. Conclusions: These findings suggest that Rai1 contributes to social behavior in mice, and prompt it as a candidate gene for the social behaviors observed in Smith-Magenis Syndrome patients.

Using hiPSCs to model neuropsychiatric copy number variations (CNVs) has potential to reveal underlying disease mechanisms

Schizophrenia is a neuropsychological disorder with a strong heritable component; genetic risk for schizophrenia is conferred by both common variants of relatively small effect and rare variants with high penetrance. Genetically engineered mouse models can recapitulate rare variants, displaying some behavioral defects associated with schizophrenia; however, these mouse models cannot recapitulate the full genetic architecture underlying the disorder. Patient-derived human induced pluripotent stem cells (hiPSCs) present an alternative approach for studying rare variants, in the context of all other risk alleles. Genome editing technologies, such as CRISPR-Cas9, enable the generation of isogenic hiPSC lines with which to examine the functional contribution of single variants within any genetic background. Studies of these rare variants using hiPSCs have the potential to identify commonly disrupted pathways in schizophrenia and allow for the identification of new therapeutic targets. This article is part of a Special Issue entitled SI:StemsCellsinPsychiatry.

Trans-acting epigenetic effects of chromosomal aneuploidies: lessons from Down syndrome and mouse models

An important line of postgenomic research seeks to understand how genetic factors can influence epigenetic patterning. Here we review epigenetic effects of chromosomal aneuploidies, focusing on findings in Down syndrome (DS, trisomy 21). Recent work in human DS and mouse models has shown that the extra chromosome 21 acts in trans to produce epigenetic changes, including differential CpG methylation (DS-DM), in specific sets of downstream target genes, mostly on other chromosomes. Mechanistic hypotheses emerging from these data include roles of chromosome 21-linked methylation pathway genes (DNMT3L and others) and transcription factor genes (RUNX1, OLIG2, GABPA, ERG and ETS2) in shaping the patterns of DS-DM. The findings may have broader implications for trans-acting epigenetic effects of chromosomal and subchromosomal aneuploidies in other human developmental and neuropsychiatric disorders, and in cancers.

Chromosome engineering in zygotes with CRISPR/Cas9

Deletions, duplications, and inversions of large genomic regions covering several genes are an important class of disease causing variants in humans. Modeling these structural variants in mice requires multistep processes in ES cells, which has limited their availability. Mutant mice containing small insertions, deletions, and single nucleotide polymorphisms can be reliably generated using CRISPR/Cas9 directly in mouse zygotes. Large structural variants can be generated using CRISPR/Cas9 in ES cells, but it has not been possible to generate these directly in zygotes. We now demonstrate the direct generation of deletions, duplications and inversions of up to one million base pairs by zygote injection. genesis 54:78–85, 2016. © 2016 The Authors. genesis Published by Wiley Periodicals, Inc.

Evidence for genetic regulation of mRNA expression of the dosage-sensitive gene retinoic acid induced-1 (RAI1) in human brain

RAI1 (retinoic acid induced-1) is a dosage-sensitive gene that causes Smith-Magenis syndrome (SMS) when mutated or deleted and Potocki-Lupski Syndrome (PTLS) when duplicated, with psychiatric features commonly observed in both syndromes. How common genetic variants regulate this gene, however, is unknown. In this study, we found that RAI1 mRNA expression in Chinese prefrontal and temporal cortex correlate with genotypes of common single nucleotide polymorphisms (SNPs) located in the RAI1 5′-upstream region. Using genotype imputation, “R²-Δ²” analysis, and data from the RegulomeDB database, we identified SNPs rs4925102 and rs9907986 as possible regulatory variants, accounting for approximately 30–40% of the variance in RAI1 mRNA expression in both brain regions. Specifically, rs4925102 and rs9907986 are predicted to disrupt the binding of retinoic acid RXR-RAR receptors and the transcription factor DEAF1 (Deformed epidermal autoregulatory factor-1), respectively. Consistent with these predictions, we observed binding of RXRα and RARα to the predicted RAI1 target in chromatin immunoprecipitation assays. Retinoic acid is crucial for early development of the central neural system, and DEAF1 is associated with intellectual disability. The observation that a significant portion of RAI1 mRNA expression is genetically controlled raises the possibility that common RAI1 5′-region regulatory variants contribute more generally to psychiatric disorders.

Neurodevelopmental Disorders Associated with Abnormal Gene Dosage: Smith-Magenis and Potocki-Lupski Syndromes

Smith-Magenis syndrome (SMS) and Potocki-Lupski syndrome (PTLS) are reciprocal contiguous gene syndromes within the well-characterized 17p11.2 region. Approximately 3.6 Mb microduplication of 17p11.2, known as PTLS, represents the mechanistically predicted homologous recombination reciprocal of the SMS microdeletion, both resulting in multiple congenital anomalies. Mouse model studies have revealed that the retinoic acid-inducible 1 gene (RAI1) within the SMS and PTLS critical genomic interval is the dosage-sensitive gene responsible for the major phenotypic features in these disorders. Even though PTLS and SMS share the same genomic region, clinical manifestations and behavioral issues are distinct and in fact some mirror traits may be on opposite ends of a given phenotypic spectrum. We describe the neurobehavioral phenotypes of SMS and PTLS patients during different life phases as well as clinical guidelines for diagnosis and a multidisciplinary approach once diagnosis is confirmed by array comparative genomic hybridization or RAI1 gene sequencing. The main goal is to increase awareness of these rare disorders because an earlier diagnosis will lead to more timely developmental intervention and medical management which will improve clinical outcome.

Structural variation mutagenesis of the human genome: Impact on disease and evolution

Watson-Crick base-pair changes, or single-nucleotide variants (SNV), have long been known as a source of mutations. However, the extent to which DNA structural variation, including duplication and deletion copy number variants (CNV) and copy number neutral inversions and translocations, contribute to human genome variation and disease has been appreciated only recently. Moreover, the potential complexity of structural variants (SV) was not envisioned; thus, the frequency of complex genomic rearrangements and how such events form remained a mystery. The concept of genomic disorders, diseases due to genomic rearrangements and not sequence-based changes for which genomic architecture incite genomic instability, delineated a new category of conditions distinct from chromosomal syndromes and single-gene Mendelian diseases. Nevertheless, it is the mechanistic understanding of CNV/SV formation that has promoted further understanding of human biology and disease and provided insights into human genome and gene evolution. Environ. Mol. Mutagen. 56:419-436, 2015. © 2015 Wiley Periodicals, Inc.

Characterization of ANKRD11 mutations in humans and mice related to KBG syndrome

Mutations in ANKRD11 have recently been reported to cause KBG syndrome, an autosomal dominant condition characterized by intellectual disability (ID), behavioral problems, and macrodontia. To understand the pathogenic mechanism that relates ANKRD11 mutations with the phenotype of KBG syndrome, we studied the cellular characteristics of wild-type ANKRD11 and the effects of mutations in humans and mice. We show that the abundance of wild-type ANKRD11 is tightly regulated during the cell cycle, and that the ANKRD11 C-terminus is required for the degradation of the protein. Analysis of 11 pathogenic ANKRD11 variants in humans, including six reported in this study, and one reported in the Ankrd11 (Yod/+) mouse, shows that all mutations affect the C-terminal regions and that the mutant proteins accumulate aberrantly. In silico analysis shows the presence of D-box sequences that are signals for proteasome degradation. We suggest that ANKRD11 C-terminus plays an important role in regulating the abundance of the protein, and a disturbance of the protein abundance due to the mutations leads to KBG syndrome.

Overview of mouse models of autism spectrum disorders

This overview describes many well characterized mouse models of autism spectrum disorders (ASDs). Mouse models considered here were selected because they are examples of genetically engineered models where human genetic evidence supports a causative relationship between the targeted mutation and the behavioral phenotype. As the ASD diagnosis is based primarily on behavioral evaluations in humans in the domains of social interaction, communication, and restricted interests, the murine phenotypes analogous to human autistic behaviors are highlighted for the different models and behaviors. Although genetically engineered mouse models with good construct and face validity are valuable for identifying and defining underlying pathophysiological mechanisms and for developing potential therapeutic interventions for the human condition, the translational value of various rodent behavioral assays remains a subject of debate. Significant challenges associated with modeling ASDs in rodents because of the clinical and molecular heterogeneity that characterize this disorder are also considered.

SCRIB and PUF60 are primary drivers of the multisystemic phenotypes of the 8q24.3 copy-number variant

Copy-number variants (CNVs) represent a significant interpretative challenge, given that each CNV typically affects the dosage of multiple genes. Here we report on five individuals with coloboma, microcephaly, developmental delay, short stature, and craniofacial, cardiac, and renal defects who harbor overlapping microdeletions on 8q24.3. Fine mapping localized a commonly deleted 78 kb region that contains three genes: SCRIB, NRBP2, and PUF60. In vivo dissection of the CNV showed discrete contributions of the planar cell polarity effector SCRIB and the splicing factor PUF60 to the syndromic phenotype, and the combinatorial suppression of both genes exacerbated some, but not all, phenotypic components. Consistent with these findings, we identified an individual with microcephaly, short stature, intellectual disability, and heart defects with a de novo c.505C>T variant leading to a p.His169Tyr change in PUF60. Functional testing of this allele in vivo and in vitro showed that the mutation perturbs the relative dosage of two PUF60 isoforms and, subsequently, the splicing efficiency of downstream PUF60 targets. These data inform the functions of two genes not associated previously with human genetic disease and demonstrate how CNVs can exhibit complex genetic architecture, with the phenotype being the amalgam of both discrete dosage dysfunction of single transcripts and also of binary genetic interactions.

Evolution and diversity of copy number variation in the great ape lineage

Copy number variation (CNV) contributes to disease and has restructured the genomes of great apes. The diversity and rate of this process, however, have not been extensively explored among great ape lineages. We analyzed 97 deeply sequenced great ape and human genomes and estimate 16% (469 Mb) of the hominid genome has been affected by recent CNV. We identify a comprehensive set of fixed gene deletions (n = 340) and duplications (n = 405) as well as >13.5 Mb of sequence that has been specifically lost on the human lineage. We compared the diversity and rates of copy number and single nucleotide variation across the hominid phylogeny. We find that CNV diversity partially correlates with single nucleotide diversity (r² = 0.5) and recapitulates the phylogeny of apes with few exceptions. Duplications significantly outpace deletions (2.8-fold). The load of segregating duplications remains significantly higher in bonobos, Western chimpanzees, and Sumatran orangutans—populations that have experienced recent genetic bottlenecks (P = 0.0014, 0.02, and 0.0088, respectively). The rate of fixed deletion has been more clocklike with the exception of the chimpanzee lineage, where we observe a twofold increase in the chimpanzee–bonobo ancestor (P = 4.79 × 10⁻⁹) and increased deletion load among Western chimpanzees (P = 0.002). The latter includes the first genomic disorder in a chimpanzee with features resembling Smith-Magenis syndrome mediated by a chimpanzee-specific increase in segmental duplication complexity. We hypothesize that demographic effects, such as bottlenecks, have contributed to larger and more gene-rich segments being deleted in the chimpanzee lineage and that this effect, more generally, may account for episodic bursts in CNV during hominid evolution.

Phenotypic impact of genomic structural variation: insights from and for human disease

Genomic structural variants have long been implicated in phenotypic diversity and human disease, but dissecting the mechanisms by which they exert their functional impact has proven elusive. Recently however, developments in high-throughput DNA sequencing and chromosomal engineering technology have facilitated the analysis of structural variants in human populations and model systems in unprecedented detail. In this Review, we describe how structural variants can affect molecular and cellular processes, leading to complex organismal phenotypes, including human disease. We further present advances in delineating disease-causing elements that are affected by structural variants, and we discuss future directions for research on the functional consequences of structural variants.

Opposing phenotypes in mice with Smith-Magenis deletion and Potocki-Lupski duplication syndromes suggest gene dosage effects on fluid consumption behavior

A quantitative long-term fluid consumption and fluid-licking assay was performed in two mouse models with either an ∼2 Mb genomic deletion, Df(11)17, or the reciprocal duplication copy number variation (CNV), Dp(11)17, analogous to the human genomic rearrangements causing either Smith-Magenis syndrome [SMS; OMIM #182290] or Potocki-Lupski syndrome [PTLS; OMIM #610883], respectively. Both mouse strains display distinct quantitative alterations in fluid consumption compared to their wild-type littermates; several of these changes are diametrically opposing between the two chromosome engineered mouse models. Mice with duplication versus deletion showed longer versus shorter intervals between visits to the waterspout, generated more versus less licks per visit and had higher versus lower variability in the number of licks per lick-burst as compared to their respective wild-type littermates. These findings suggest that copy number variation can affect long-term fluid consumption behavior in mice. Other behavioral differences were unique for either the duplication or deletion mutants; the deletion CNV resulted in increased variability of the licking rhythm, and the duplication CNV resulted in a significant slowing of the licking rhythm. Our findings document a readily quantitated complex behavioral response that can be directly and reciprocally influenced by a gene dosage effect.

The Human Obesity Gene Map: The 2003 Update

This is the tenth update of the human obesity gene map, incorporating published results up to the end of October 2003 and continuing the previous format. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) from human genome-wide scans and animal crossbreeding experiments, and association and linkage studies with candidate genes and other markers is reviewed. Transgenic and knockout murine models relevant to obesity are also incorporated (N = 55). As of October 2003, 41 Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. QTLs reported from animal models currently number 183. There are 208 human QTLs for obesity phenotypes from genome-wide scans and candidate regions in targeted studies. A total of 35 genomic regions harbor QTLs replicated among two to five studies. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 272 studies reporting positive associations with 90 candidate genes. Fifteen such candidate genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, more than 430 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful sites can be found at http://obesitygene.pbrc.edu.

The Human Obesity Gene Map: The 2004 Update

This paper presents the eleventh update of the human obesity gene map, which incorporates published results up to the end of October 2004. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTLs) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2004, 173 human obesity cases due to single-gene mutations in 10 different genes have been reported, and 49 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 166 genes which, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 221. The number of human obesity QTLs derived from genome scans continues to grow, and we have now 204 QTLs for obesity-related phenotypes from 50 genome-wide scans. A total of 38 genomic regions harbor QTLs replicated among two to four studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably with 358 findings of positive associations with 113 candidate genes. Among them, 18 genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, >600 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful publications and genomic and other relevant sites can be found at http://obesitygene.pbrc.edu.

Animal models of psychiatric disorders that reflect human copy number variation

The development of genetic technologies has led to the identification of several copy number variations (CNVs) in the human genome. Genome rearrangements affect dosage-sensitive gene expression in normal brain development. There is strong evidence associating human psychiatric disorders, especially autism spectrum disorders (ASDs) and schizophrenia to genetic risk factors and accumulated CNV risk loci. Deletions in 1q21, 3q29, 15q13, 17p12, and 22q11, as well as duplications in 16p11, 16p13, and 15q11-13 have been reported as recurrent CNVs in ASD and/or schizophrenia. Chromosome engineering can be a useful technology to reflect human diseases in animal models, especially CNV-based psychiatric disorders. This system, based on the Cre/loxP strategy, uses large chromosome rearrangement such as deletion, duplication, inversion, and translocation. Although it is hard to reflect human pathophysiology in animal models, some aspects of molecular pathways, brain anatomy, cognitive, and behavioral phenotypes can be addressed. Some groups have created animal models of psychiatric disorders, ASD, and schizophrenia, which are based on human CNV. These mouse models display some brain anatomical and behavioral abnormalities, providing insight into human neuropsychiatric disorders that will contribute to novel drug screening for these devastating disorders.

Definition of a critical genetic interval related to kidney abnormalities in the Potocki-Lupski syndrome

Potocki-Lupski syndrome is a genomic disorder caused by duplication of 17p11.2. It is characterized by failure to thrive, intellectual disability, hypotonia, and behavioral difficulties. Structural renal anomalies have been observed in <10% of affected individuals. We present detailed clinical and molecular data on six patients with Potocki-Lupski syndrome, two of whom had renal abnormalities, and investigate the prevalence of kidney abnormalities in the mouse model for the syndrome. In contrast to affected humans, the mouse model does not demonstrate a renal phenotype. Comparison of the duplicated segment in patients with Potocki-Lupski syndrome and the renal phenotype and the syntenic duplicated region in the mouse model allowed us to suggest a 0.285 Mb critical region, including the FLCN gene that may be important for development of renal abnormalities in patients with this duplication.

A duplication CNV that conveys traits reciprocal to metabolic syndrome and protects against diet-induced obesity in mice and men

The functional contribution of CNV to human biology and disease pathophysiology has undergone limited exploration. Recent observations in humans indicate a tentative link between CNV and weight regulation. Smith-Magenis syndrome (SMS), manifesting obesity and hypercholesterolemia, results from a deletion CNV at 17p11.2, but is sometimes due to haploinsufficiency of a single gene, RAI1. The reciprocal duplication in 17p11.2 causes Potocki-Lupski syndrome (PTLS). We previously constructed mouse strains with a deletion, Df(11)17, or duplication, Dp(11)17, of the mouse genomic interval syntenic to the SMS/PTLS region. We demonstrate that Dp(11)17 is obesity-opposing; it conveys a highly penetrant, strain-independent phenotype of reduced weight, leaner body composition, lower TC/LDL, and increased insulin sensitivity that is not due to alteration in food intake or activity level. When fed with a high-fat diet, Dp(11)17/+ mice display much less weight gain and metabolic change than WT mice, demonstrating that the Dp(11)17 CNV protects against metabolic syndrome. Reciprocally, Df(11)17/+ mice with the deletion CNV have increased weight, higher fat content, decreased HDL, and reduced insulin sensitivity, manifesting a bona fide metabolic syndrome. These observations in the deficiency animal model are supported by human data from 76 SMS subjects. Further, studies on knockout/transgenic mice showed that the metabolic consequences of Dp(11)17 and Df(11)17 CNVs are not only due to dosage alterations of Rai1, the predominant dosage-sensitive gene for SMS and likely also PTLS. Our experiments in chromosome-engineered mouse CNV models for human genomic disorders demonstrate that a CNV can be causative for weight/metabolic phenotypes. Furthermore, we explored the biology underlying the contribution of CNV to the physiology of weight control and energy metabolism. The high penetrance, strain independence, and resistance to dietary influences associated with the CNVs in this study are features distinct from most SNP–associated metabolic traits and further highlight the potential importance of CNV in the etiology of both obesity and MetS as well as in the protection from these traits.

Genetic factors play a large role in obesity. However, despite recent technical progress in the search for genetic variants, the identities of causative and contributory genetic factors remain largely unknown. Whereas nucleotide sequence variation has been studied extensively with respect to its potential contribution to obesity, copy number variations (CNV), in which genes exist in abnormal numbers of copies mostly due to duplication or deletion, have only more recently been observed to be associated with human obesity. In this report, we utilize chromosome engineered mouse strains harboring a deletion or duplication CNV to address the potential functional impact of CNVs on weight control and metabolism. We show that the duplication CNV leads to lower body weight; it is also metabolically advantageous and protects from diet-induced obesity and metabolic syndrome (MetS). The deletion CNV causes a “mirror” phenotype with increased body weight and MetS–like phenotypes. Importantly, these effects manifest regardless of the genetic background and do not appear to be attributable to any single gene. These findings demonstrate experimentally that CNV can be causative for weight and metabolic phenotypes and highlight the potential relevance and importance of CNV in the etiology of obesity/MetS and the protection from these traits.

Enriched rearing improves behavioral responses of an animal model for CNV-based autistic-like traits

Potocki-Lupski syndrome (PTLS; MIM #610883), characterized by neurobehavioral abnormalities, intellectual disability and congenital anomalies, is caused by a 3.7-Mb duplication in 17p11.2. Neurobehavioral studies determined that ∼70-90% of PTLS subjects tested positive for autism or autism spectrum disorder (ASD). We previously chromosomally engineered a mouse model for PTLS (Dp(11)17/+) with a duplication of a 2-Mb genomic interval syntenic to the PTLS region and identified consistent behavioral abnormalities in this mouse model. We now report extensive phenotyping with behavioral assays established to evaluate core and associated autistic-like traits, including tests for social abnormalities, ultrasonic vocalizations, perseverative and stereotypic behaviors, anxiety, learning and memory deficits and motor defects. Alterations were identified in both core and associated ASD-like traits. Rearing this animal model in an enriched environment mitigated some, and even rescued selected, neurobehavioral abnormalities, suggesting a role for gene-environment interactions in the determination of copy number variation-mediated autism severity.

Mouse models of aneuploidy

Abnormalities of chromosome copy number are called aneuploidies and make up a large health load on the human population. Many aneuploidies are lethal because the resulting abnormal gene dosage is highly deleterious. Nevertheless, some whole chromosome aneuploidies can lead to live births. Alterations in the copy number of sections of chromosomes, which are also known as segmental aneuploidies, are also associated with deleterious effects. Here we examine how aneuploidy of whole chromosomes and segmental aneuploidy of chromosomal regions are modeled in the mouse. These models provide a whole animal system in which we aim to investigate the complex phenotype-genotype interactions that arise from alteration in the copy number of genes. Although our understanding of this subject is still in its infancy, already research in mouse models is highlighting possible therapies that might help alleviate the cognitive effects associated with changes in gene number. Thus, creating and studying mouse models of aneuploidy and copy number variation is important for understanding what it is to be human, in both the normal and genomically altered states.

Dosage-dependent phenotypes in models of 16p11.2 lesions found in autism

Recurrent copy number variations (CNVs) of human 16p11.2 have been associated with a variety of developmental/neurocognitive syndromes. In particular, deletion of 16p11.2 is found in patients with autism, developmental delay, and obesity. Patients with deletions or duplications have a wide range of clinical features, and siblings carrying the same deletion often have diverse symptoms. To study the consequence of 16p11.2 CNVs in a systematic manner, we used chromosome engineering to generate mice harboring deletion of the chromosomal region corresponding to 16p11.2, as well as mice harboring the reciprocal duplication. These 16p11.2 CNV models have dosage-dependent changes in gene expression, viability, brain architecture, and behavior. For each phenotype, the consequence of the deletion is more severe than that of the duplication. Of particular note is that half of the 16p11.2 deletion mice die postnatally; those that survive to adulthood are healthy and fertile, but have alterations in the hypothalamus and exhibit a "behavior trap" phenotype-a specific behavior characteristic of rodents with lateral hypothalamic and nigrostriatal lesions. These findings indicate that 16p11.2 CNVs cause brain and behavioral anomalies, providing insight into human neurodevelopmental disorders.

Mouse models of genomic syndromes as tools for understanding the basis of complex traits: an example with the smith-magenis and the potocki-lupski syndromes

Each human's genome is distinguished by extra and missing DNA that can be “benign” or powerfully impact everything from development to disease. In the case of genomic disorders DNA rearrangements, such as deletions or duplications, correlate with a clinical specific phenotype. The clinical presentations of genomic disorders were thought to result from altered gene copy number of physically linked dosage sensitive genes. Genomic disorders are frequent diseases (~1 per 1,000 births). Smith-Magenis syndrome (SMS) and Potocki-Lupski syndrome (PTLS) are genomic disorders, associated with a deletion and a duplication, of 3.7 Mb respectively, within chromosome 17 band p11.2. This region includes 23 genes. Both syndromes have complex and distinctive phenotypes including multiple congenital and neurobehavioral abnormalities. Human chromosome 17p11.2 is syntenic to the 32-34 cM region of murine chromosome 11. The number and order of the genes are highly conserved. In this review, we will exemplify how genomic disorders can be modeled in mice and the advantages that such models can give in the study of genomic disorders in particular and gene copy number variation (CNV) in general. The contributions of the SMS and PTLS animal models in several aspects ranging from more specific ones, as the definition of the clinical aspects of the human clinical spectrum, the identification of dosage sensitive genes related to the human syndromes, to the more general contributions as the definition of genetic locus impacting obesity and behavior and the elucidation of general mechanisms related to the pathogenesis of gene CNV are discussed.

Retinoic Acid Induced 1, RAI1: A Dosage Sensitive Gene Related to Neurobehavioral Alterations Including Autistic Behavior

Genomic structural changes, such as gene Copy Number Variations (CNVs) are extremely abundant in the human genome. An enormous effort is currently ongoing to recognize and catalogue human CNVs and their associations with abnormal phenotypic outcomes. Recently, several reports related neuropsychiatric diseases (i.e. autism spectrum disorders, schizophrenia, mental retardation, behavioral problems, epilepsy) with specific CNV. Moreover, for some conditions, both the deletion and duplication of the same genomic segment are related to the phenotype. Syndromes associated with CNVs (microdeletion and microduplication) have long been known to display specific neurobehavioral traits. It is important to note that not every gene is susceptible to gene dosage changes and there are only a few dosage sensitive genes. Smith-Magenis (SMS) and Potocki-Lupski (PTLS) syndromes are associated with a reciprocal microdeletion and microduplication within chromosome 17p11.2. in humans. The dosage sensitive gene responsible for most phenotypes in SMS has been identified: the Retinoic Acid Induced 1 (RAI1). Studies on mouse models and humans suggest that RAI1 is likely the dosage sensitive gene responsible for clinical features in PTLS. In addition, the human RAI1 gene has been implicated in several neurobehavioral traits as spinocerebellar ataxia (SCA2), schizophrenia and non syndromic autism. In this review we discuss the evidence of RAI1 as a dosage sensitive gene, its relationship with different neurobehavioral traits, gene structure and mutations, and what is known about its molecular and cellular function, as a first step in the elucidation of the mechanisms that relate dosage sensitive genes with abnormal neurobehavioral outcomes.

Controlled somatic and germline copy number variation in the mouse model

Changes in the number of chromosomes, but also variations in the copy number of chromosomal regions have been described in various pathological conditions, such as cancer and aneuploidy, but also in normal physiological condition. Our classical view of DNA replication and mitotic preservation of the chromosomal integrity is now challenged as new technologies allow us to observe such mosaic somatic changes in copy number affecting regions of chromosomes with various sizes. In order to go further in the understanding of copy number influence in normal condition we could take advantage of the novel strategy called Targeted Asymmetric Sister Chromatin Event of Recombination (TASCER) to induce recombination during the G2 phase so that we can generate deletions and duplications of regions of interest prior to mitosis. Using this approach in the mouse we could address the effects of copy number variation and segmental aneuploidy in daughter cells and allow us to explore somatic mosaics for large region of interest in the mouse.

ADHD and genetic syndromes

A high rate of Attention Deficit/Hyperactivity Disorder (ADHD)-like characteristics has been reported in a wide variety of disorders including syndromes with known genetic causes. In this article, we review the genetic and the neurobiological links between ADHD symptoms and some genetic syndromes such as: Fragile X Syndrome, Neurofibromatosis 1, DiGeorge Syndrome, Tuberous Sclerosis Complex, Turner Syndrome, Williams Syndrome and Klinefelter Syndrome. Although each syndrome may arise from different genetic abnormalities with multiple molecular functions, the effects of these abnormalities may give rise to common effects downstream in the biological pathways or neural circuits, resulting in the presentation of ADHD symptoms. Early diagnosis of ADHD allows for earlier treatment, and has the potential for a better outcome in children with genetic syndromes.

Smith–Magenis syndrome: haploinsufficiency of RAI1 results in altered gene regulation in neurological and metabolic pathways

Smith–Magenis syndrome (SMS) is a complex neurobehavioural disorder characterised by intellectual disability, self-injurious behaviours, sleep disturbance, obesity, and craniofacial and skeletal anomalies. Diagnostic strategies are focused towards identification of a 17p11.2 microdeletion encompassing the gene RAI1 (retinoic acid induced 1) or a mutation of RAI1. Molecular evidence shows that most SMS features are due to RAI1 haploinsufficiency, whereas variability and severity are modified by other genes in the 17p11.2 region for 17p11.2 deletion cases. The functional role of RAI1 is not completely understood, but it is probably a transcription factor acting in several different biological pathways that are dysregulated in SMS. Functional studies based on the hypothesis that RAI1 acts through phenotype-specific pathways involving several downstream genes have shown that RAI1 gene dosage is crucial for normal regulation of circadian rhythm, lipid metabolism and neurotransmitter function. Here, we review the clinical and molecular features of SMS and explore more recent studies supporting possible therapeutic strategies for behavioural management.

Potocki-Lupski syndrome: a microduplication syndrome associated with oropharyngeal dysphagia and failure to thrive

OBJECTIVE

Failure to thrive (FTT) is a feature of children with Potocki-Lupski syndrome (PTLS) [duplication 17p11.2]. This study was designed to describe the growth characteristics of 24 subjects with PTLS from birth through age 5 years in conjunction with relevant physical features and swallow function studies.

STUDY DESIGN

We evaluated 24 individuals with PTLS who were ascertained by chromosome analysis and/or array comparative genome hybridization. Clinical assessments included review of medical records, physical examination, otolaryngological examination, and swallow function studies. Measures of height and weight were converted to Z-scores.

RESULTS

The mean weight-for-age and weight-for-length Z-scores at birth were lower (P < .01) than the reference standard and did not change with age. A history of poor feeding, hypotonia, and FTT were reported in 92%, 88%, and 71%, respectively. Individuals with hypotonia had lower weight-for-age and body mass index-for-age Z-scores (P = .01). Swallow function studies demonstrated at least one abnormality in all subjects.

CONCLUSIONS

FTT is common in children with PTLS. We hypothesize that oropharyngeal dysphagia and hypotonia likely contribute to FTT in patients with PTLS and recommend that once a diagnosis is established, the individual be assessed for feeding and growth issues and be availed of oromotor therapy and nutritional services.

Phenotypic consequences of copy number variation: insights from Smith-Magenis and Potocki-Lupski syndrome mouse models

The characterization of mice with different number of copies of the same genomic segment shows that structural changes influence the phenotypic outcome independently of gene dosage.

A large fraction of genome variation between individuals is comprised of submicroscopic copy number variation of genomic DNA segments. We assessed the relative contribution of structural changes and gene dosage alterations on phenotypic outcomes with mouse models of Smith-Magenis and Potocki-Lupski syndromes. We phenotyped mice with 1n (Deletion/+), 2n (+/+), 3n (Duplication/+), and balanced 2n compound heterozygous (Deletion/Duplication) copies of the same region. Parallel to the observations made in humans, such variation in gene copy number was sufficient to generate phenotypic consequences: in a number of cases diametrically opposing phenotypes were associated with gain versus loss of gene content. Surprisingly, some neurobehavioral traits were not rescued by restoration of the normal gene copy number. Transcriptome profiling showed that a highly significant propensity of transcriptional changes map to the engineered interval in the five assessed tissues. A statistically significant overrepresentation of the genes mapping to the entire length of the engineered chromosome was also found in the top-ranked differentially expressed genes in the mice containing rearranged chromosomes, regardless of the nature of the rearrangement, an observation robust across different cell lineages of the central nervous system. Our data indicate that a structural change at a given position of the human genome may affect not only locus and adjacent gene expression but also “genome regulation.” Furthermore, structural change can cause the same perturbation in particular pathways regardless of gene dosage. Thus, the presence of a genomic structural change, as well as gene dosage imbalance, contributes to the ultimate phenotype.

Mammalian genomes contain many forms of genetic variation. For example, some genome segments were shown to vary in their number of copies between individuals of the same species, i.e. there is a range of number of copies in the normal population instead of the usual two copies (one per chromosome). These genetic differences play an important role in determining the phenotype (the observable characteristics) of each individual. We do not know, however, if such influences are brought about solely through changes in the number of copies of the genomic segments (and of the genes that map within) or if the structural modification of the genome per se also plays a role in the outcome. We use mouse models with different number of copies of the same genomic region to show that rearrangements of the genetic materials can affect the phenotype independently of the dosage of the rearranged region.

Altered ultrasonic vocalization and impaired learning and memory in Angelman syndrome mouse model with a large maternal deletion from Ube3a to Gabrb3

Angelman syndrome (AS) is a neurobehavioral disorder associated with mental retardation, absence of language development, characteristic electroencephalography (EEG) abnormalities and epilepsy, happy disposition, movement or balance disorders, and autistic behaviors. The molecular defects underlying AS are heterogeneous, including large maternal deletions of chromosome 15q11–q13 (70%), paternal uniparental disomy (UPD) of chromosome 15 (5%), imprinting mutations (rare), and mutations in the E6-AP ubiquitin ligase gene UBE3A (15%). Although patients with UBE3A mutations have a wide spectrum of neurological phenotypes, their features are usually milder than AS patients with deletions of 15q11–q13. Using a chromosomal engineering strategy, we generated mutant mice with a 1.6-Mb chromosomal deletion from Ube3a to Gabrb3, which inactivated the Ube3a and Gabrb3 genes and deleted the Atp10a gene. Homozygous deletion mutant mice died in the perinatal period due to a cleft palate resulting from the null mutation in Gabrb3 gene. Mice with a maternal deletion (m−/p+) were viable and did not have any obvious developmental defects. Expression analysis of the maternal and paternal deletion mice confirmed that the Ube3a gene is maternally expressed in brain, and showed that the Atp10a and Gabrb3 genes are biallelically expressed in all brain sub-regions studied. Maternal (m−/p+), but not paternal (m+/p−), deletion mice had increased spontaneous seizure activity and abnormal EEG. Extensive behavioral analyses revealed significant impairment in motor function, learning and memory tasks, and anxiety-related measures assayed in the light-dark box in maternal deletion but not paternal deletion mice. Ultrasonic vocalization (USV) recording in newborns revealed that maternal deletion pups emitted significantly more USVs than wild-type littermates. The increased USV in maternal deletion mice suggests abnormal signaling behavior between mothers and pups that may reflect abnormal communication behaviors in human AS patients. Thus, mutant mice with a maternal deletion from Ube3a to Gabrb3 provide an AS mouse model that is molecularly more similar to the contiguous gene deletion form of AS in humans than mice with Ube3a mutation alone. These mice will be valuable for future comparative studies to mice with maternal deficiency of Ube3a alone.

Deficiencies in the region syntenic to human 21q22.3 cause cognitive deficits in mice

Copy-number variation in the human genome can be disease-causing or phenotypically neutral. This type of genetic rearrangement associated with human chromosome 21 (Hsa21) underlies partial Monosomy 21 and Trisomy 21. Mental retardation is a major clinical manifestation of partial Monosomy 21. To model this human chromosomal deletion disorder, we have generated novel mouse mutants carrying heterozygous deletions of the 2.3- and 1.1-Mb segments on mouse chromosome 10 (Mmu10) and Mmu17, respectively, which are orthologous to the regions on human 21q22.3, using Cre/loxP-mediated chromosome engineering. Alterations of the transcriptional levels of genes within the deleted intervals reflect gene-dosage effects in the mutant mice. The analysis of cognitive behaviors shows that the mutant mice carrying the deletion on either Mmu10 or Mmu17 are impaired in learning and memory. Therefore, these mutants represent mouse models for Monosomy 21-associated mental retardation, which can serve as a powerful tool to study the molecular mechanism underlying the clinical phenotype and should facilitate efforts to identify the haploinsufficient causative genes.

Chromosome engineering in ES cells

Chromosomal rearrangements, such as deletions, duplications, inversions and translocations, occur frequently in humans and can be disease-associated or phenotypically neutral. To understand the genetic consequences of such genomic changes, these mutations need to be modelled in experimentally tractable systems. The mouse is an excellent organism for this analysis because of its biological and genetic similarity to humans, the ease with which its genome can be manipulated and the similarity of observed affects. Through chromosome engineering, defined rearrangements can be introduced into the mouse genome. The resulting mouse models are leading to a better understanding of the molecular and cellular basis of dosage alterations in human disease phenotypes, in turn opening new diagnostic and therapeutic opportunities.

Distorted Mendelian transmission as a function of genetic background in Rai1-haploinsufficient mice

The retinoic acid induced 1 gene (RAI1) is the primary causative gene for Smith-Magenis syndrome (SMS). Chromosomal deletion encompassing RAI1 or mutation in RAI1 is responsible for the majority of SMS features. Mouse models with targeted disruption of Rai1 have recapitulated overt SMS phenotypes, including craniofacial abnormalities, obesity, and neurobehavioral anomalies. Penetrance and expressivity of most phenotypes in mice were incomplete due to the mixed genetic background in which they were created. While increased penetrance of craniofacial phenotypes was observed in relatively homogeneous backgrounds, the effect of Rai1 haploinsufficiency on breeding outcome and fitness has not been studied. We analyzed mating results of Rai1+/- mice in a pure C57BL/6J background (>or=N10 generations). A significant distortion (P<0.05) of Mendelian transmission ratio with skewing against Rai1+/- mice was observed. Consequently, a decreased number of Rai1+/- pups and no Rai1-/- pups were obtained from all the breeding pairs. The decreased yield of Rai1+/- pups precluded penetrance studies of other phenotypes in these mice. However, when Rai1+/- alleles were transferred to a slightly variable (approximately 1% 129/approximately 99% C57BL/6J) genetic background expected numbers of Rai1+/- pups were obtained. Our results indicate that selection against Rai1-haploinsufficient alleles is governed primarily by modifier genes. Our data show that genetic background or modifier genes also significantly contribute to the severity of the phenotypes in SMS mouse models, mirroring the phenotypic variation observed in humans with Smith-Magenis syndrome and support the need for investigation of modifier loci for both single gene and complex genetic syndromes.

Abnormal social behaviors and altered gene expression rates in a mouse model for Potocki-Lupski syndrome

The Potocki-Lupski syndrome (PTLS) is associated with a microduplication of 17p11.2. Clinical features include multiple congenital and neurobehavioral abnormalities and autistic features. We have generated a PTLS mouse model, Dp(11)17/+, that recapitulates some of the physical and neurobehavioral phenotypes present in patients. Here, we investigated the social behavior and gene expression pattern of this mouse model in a pure C57BL/6-Tyr(c-Brd) genetic background. Dp(11)17/+ male mice displayed normal home-cage behavior but increased anxiety and increased dominant behavior in specific tests. A subtle impairment in the preference for a social target versus an inanimate target and abnormal preference for social novelty (the preference to explore an unfamiliar mouse versus a familiar one) was also observed. Our results indicate that these animals could provide a valuable model to identify the specific gene(s) that confer abnormal social behaviors and that map within this delimited genomic deletion interval. In a first attempt to identify candidate genes and for elucidating the mechanisms of regulation of these important phenotypes, we directly assessed the relative transcription of genes within and around this genomic interval. In this mouse model, we found that candidates genes include not only most of the duplicated genes, but also normal-copy genes that flank the engineered interval; both categories of genes showed altered expression levels in the hippocampus of Dp(11)17/+ mice.