**5. Prader-Willi and Angelman syndromes**

age in four brain regions that may be relevant for autism, including the olfactory bulbs,

In-cage neurobehavioral phenotypes were assessed in these mice to determine what, if any, affect these CNVs had on autistic-like behaviors. As expected, deletion mice displayed the most abnormal phenotypes, while duplication mice had fewer and milder symptoms. Inter‐ estingly, reciprocal phenotypes were sometimes observed for mice harboring reciprocal CNVs. For example, the amount of time spent resting in the cage was lower in deletion mice but higher in duplication mice relative to controls, indicating that 16p11.2 CNVs affect the rate and timing of specific behaviors in a dosage-dependent manner. Deletion mice dis‐ played an abnormal ceiling-climbing behavior where they demonstrated marked stereotypic and nonprogressive motor behaviors, similar to what is often observed in patients with au‐ tism or patients with lateral hypothalamic and nigrostriatal lesions in the brain. These ab‐ normal behaviors were accompanied by volumetric and morphological changes in several brain regions, including the lateral hypothalamus. Importantly, the difference between dele‐ tion mice and duplication mice was greater than that between deletion mice and controls,

No significant abnormal social behavior was observed in these animal models in the 3 chamber test for sociability, indicating either that these animals do not display social abnor‐ malities, or that further investigation into the social behavior of these animals is required. Indeed, with the subtle nature of many social interactions in rodents, it is quite possible that social abnormalities exist in these mice but have not yet been described. It is also distinctly possible that the 'in-cage' environment does not elicit a social deficit that might perhaps be observed in the wild or natural environment of the animal. An extensive battery of tests for

Many of the genes mapped to the altered region have unknown function, and therefore, unknown significance or contribution to the disease phenotype. In order to further delin‐ eate the function of the dosage-sensitive genes within the common duplication/deletion region, zebrafish models were generated [57, 58]. The first study aimed to investigate the diametric head size phenotypes linked to this locus, as in addition to ASD, deletion is known to result in macrocephaly, and duplication gives rise to microcephaly [36, 57]. In this study, zebrafish were utilized for an *in vivo* overexpression screen, which identified the gene *KCTD13* as the likely candidate for the neurodevelopmental phenotypes associ‐ ated with CNVs at 16p11.2. Interestingly, this gene was also one of the 5 genes found in a minimal critical deletion interval for ASD [54]. Overexpression of this gene in zebrafish resulted in microcephaly, while the reciprocal reduced expression of this locus by mor‐ pholino oligonucelotides resulted in macrocephaly, thereby mirroring the phenotypes seen in humans harboring CNVs at this locus [57]. Further study revealed that the func‐ tion of this gene is likely conserved across species, and it is required to maintain the proliferative status of cortical progenitor cells in mice [57]. Furthermore, this gene is af‐ fected in a complex genomic rearrangement identified in a patient with autism [57]. Tak‐ en together, these results indicate that *KCTD13* is a likely candidate for further study of

social behavior will be required to rule out the possibility of further abnormalities.

cortex, cerebellum, and brainstem [29].

256 Recent Advances in Autism Spectrum Disorders - Volume I

indicating that these effects are reciprocal or opposing in nature.

the neurological phenotypes associated with CNV at this locus.

Chromosome 15q11-13 is enriched for LCRs, providing a mechanism for LCR-mediated NAHR, and generating a series of recurrent breakpoints along this chromosome. As a result, interstitial deletion or duplication of this region is common. LCRs can also mediate triplica‐ tions, or, alternatively, the presence of supernumerary isodicentric chromosome 15 (idic(15)) can lead to crossing over between these LCRs, and ultimately, duplication of the region. A bipartite imprinting center lies at this locus and directs the expression of a number of genes, resulting in a tissue-specific parent-of-origin effect. As a result, many of the phenotypes caused by these structural rearrangements also display parent-of-origin effects.

Paternally- or maternally-inherited deletions of human chromosome 15q11-13 result in Prader-Willi syndrome (PWS) or Angelman syndrome (AS), respectively. Alternatively, these disorders can be caused by uniparental disomy (UPD), or by balanced translocations involving this region. Less frequently, imprinting errors, leading to aberrant methylation of the PWS imprinting center can also cause PWS, and mutations or deletions in the gene *UBE3A* can cause AS [11, 59]. The critical region for AS lies 35 kb telomeric to the PWS criti‐ cal region [60]. PWS is characterized by intellectual disability, hypotonia, hyperphagia, obe‐ sity, compulsive and repetitive behaviors, skin picking, tantrums, irritability. In addition, congenital abnormalities are often observed, including hypogonadism, facial dysmorphism, and small hands and feet, among others. PWS can also be associated with psychosis, mood disorders, and ASD [61].

AS is a neurodevelopmental disorder that is characterized by severe developmental de‐ lay, intellectual disability, microcephaly, seizures, lack of speech, ataxia, and dysmorphic facial features [11, 59]. Patients with AS are often described as having happy demeanors, however hyperactivity, attention deficits, aggression, and repetitive or stereotypic behav‐ iors have also been described [59]. AS has been associated with ASD in several studies, however, the severity of the cognitive impairments in most patients with AS may pre‐ clude an accurate diagnosis [11, 59].

**7. Modeling 15q11-13 CNVs in mice**

notypes is necessary.

The first mouse model for PWS was generated by targeted deletion of part of the imprinting center on chromosome 15q11-13 [68]. While these mice model several aspects of PWS, in‐ cluding hypersensitivity to sensory input in the form of increased acoustic startle response and decreased prepulse inhibition, it is not known whether these mice exhibit other autisticlike behaviors, such as impaired social interactions or altered communication [69]. Further behavioral characterization is needed to determine whether these mice accurately recapitu‐

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Mouse models for Angelman syndrome were initially generated by disrupting maternal ex‐ pression of *Ube3a*; these mice exhibit increased anxiety-like behavior that may be due to the disruption of a glucocorticoid receptor transactivation in the brain [70]. They also display various motor defects [71], abnormal cerebellum-driven licking behavior [72], sleep disturb‐ ance [73], abnormal EEG patterns, and cognitive defects in the conditioned fear and Morris water maze tests [74]. However, these mice displayed hypoactivity and normal social seek‐ ing behavior, in contrast to what is seen in human patients with AS and/or ASD [75]. Impor‐ tantly, human patients with mutations in *UBE3A* typically have a milder phenotype than those patients harboring interstitial deletions, so this mouse model may not accurately re‐ flect the majority of AS patients, who have a deletion containing this gene, as well as many other genes at this locus. Indeed, when a larger 1.6 Mb deletion model was generated by chromosome engineering that encompasses the genomic region from *Ube3a* to *Gabrb3*, the phenotype of these mice was more severe than that of mice with deletion of *Ube3a* alone [76]. Similar to *Ube3a* deficient mice, large deletion mice had significant motor impairment, anxiety-like behavior, and abnormal EEG, but they also had learning and memory defects and abnormal communication [76]. These larger deletion mice may be an appropriate model for CNV-associated ASD, however further investigation into the social neurobehavioral phe‐

Chromosome-engineered mouse models harboring a duplication of 6.3 Mb on mouse chro‐ mosome 7 syntenic to the duplication of human chromosome 15q11-13 associated with ASD were developed to study the underlying mechanism behind the phenotypes associated with this CNV in humans [28]. The core features of autism, including abnormal social interac‐ tions, stereotypic or ritualistic behavior, and impaired communication were all evaluated in this mouse model, and patDp/+, but not matDp/+ mice were determined to have reduced so‐ ciability compared to wild-type mice. Ultrasonic vocalizations were evaluated in pups sepa‐ rated from the dam, and an abnormal USV pattern was observed in patDp/+ but not matDp/+ mice. Specifically, patDp/+ mice appeared to have delayed development of com‐ munication, they emitted a greater number of USVs, and some pups emitted vocalizations at abnormally high frequencies (>70 kHz). In order to evaluate communication between older mice, pairs of mice 7-8 weeks of age were observed in a resident intruder paradigm and the pattern of USVs was measured during this interaction. Vocal communication between pairs of pat/Dp/+ mice was significantly reduced compared to the vocalization recorded between WT pairs, giving further support to the notion that patDp/+ mice have a defect in social

late the neurobehavioral phenotypes seen in patients with PWS and/or ASD.
