Behavioural and cognitive profiles of mouse models for Prader-Willi syndrome

Investigating the correlation between genotype and phenotype in Prader-Willi syndrome: a study of 45 cases from Brazil

BACKGROUND

Prader-Willi syndrome (PWS) is a genetic disorder characterized by abnormalities in the 15q11-q13 region. Understanding the correlation between genotype and phenotype in PWS is crucial for improved genetic counseling and prognosis. In this study, we aimed to investigate the correlation between genotype and phenotype in 45 PWS patients who previously underwent methylation-sensitive high-resolution melting (MS-HRM) for diagnosis.

RESULTS

We employed methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) and Sanger sequencing, along with collecting phenotypic data from the patients for comparison. Among the 45 patients, 29 (64%) exhibited a deletion of 15q11-q13, while the remaining 16 (36%) had uniparental disomy. No statistically significant differences were found in the main signs and symptoms of PWS. However, three clinical features showed significant differences between the groups. Deletion patients had a higher prevalence of myopia than those with uniparental disomy, as well as obstructive sleep apnea and an unusual skill with puzzles.

CONCLUSIONS

The diagnostic tests (MS-HRM, MS-MLPA, and Sanger sequencing) yielded positive results, supporting their applicability in PWS diagnosis. The study's findings indicate a general similarity in the genotype-phenotype correlation across genetic subtypes of PWS.

Effectiveness of the Kaufman Brief Intelligence Test in people with Prader-Willi syndrome

BACKGROUND

Evaluating intelligence using conventional tools is very complex in patients with Prader-Willi Syndrome (PWS), as it is time consuming and requires levels of care that are difficult to sustain for this population. Therefore, we explore the ability of a brief test to assess intelligence in these patients.

METHODS

This study included individuals with a genetically confirmed diagnosis of PWS, with regular attendance at transdisciplinary treatment in an institution dedicated to the care of rare diseases in Argentina. The Wechsler Intelligence Scale for Children (WISC-IV), the Wechsler Adult Intelligence Scale (WAIS-III) and the Kaufman Brief Intelligence Test (K-BIT) were used.

RESULTS

Correlation was obtained between the scales in paediatric and adult populations. Within the paediatric population, no significant differences were identified between the WISC-IV scale (Wechsler for paediatrics) and the K-BIT (56.4 ± 8.6, vs. 53.4 ± 10.1, P = 0.28), with a good agreement between the methods {intraclass correlation 0.79 [95% confidence interval (CI) 0.15-0.95]}. Regarding the adult population, the discrimination of the WAIS-III scale (Wechsler for adults) and the K-BIT of adults (16 years and over) presented an acceptable concordance [0.77 (95% CI -0.09; 0.93)], although also underestimating the results (58.3 ± 7.2 vs. 51.1 ± 11.2, P < 0.0001).

CONCLUSIONS

We observed the feasibility and potential usefulness of a brief intelligence test (K-BIT) in patients with PWS with an acceptable agreement with conventional tools.

Epigenetics in Prader-Willi Syndrome

Prader-Willi Syndrome (PWS) is a rare neurodevelopmental disorder that affects approximately 1 in 20,000 individuals worldwide. Symptom progression in PWS is classically characterized by two nutritional stages. Stage 1 is hypotonia characterized by poor muscle tone that leads to poor feeding behavior causing failure to thrive in early neonatal life. Stage 2 is followed by the development of extreme hyperphagia, also known as insatiable eating and fixation on food that often leads to obesity in early childhood. Other major features of PWS include obsessive-compulsive and hoarding behaviors, intellectual disability, and sleep abnormalities. PWS is genetic disorder mapping to imprinted 15q11.2-q13.3 locus, specifically at the paternally expressed SNORD116 locus of small nucleolar RNAs and noncoding host gene transcripts. SNORD116 is processed into several noncoding components and is hypothesized to orchestrate diurnal changes in metabolism through epigenetics, according to functional studies. Here, we review the current status of epigenetic mechanisms in PWS, with an emphasis on an emerging role for SNORD116 in circadian and sleep phenotypes. We also summarize current ongoing therapeutic strategies, as well as potential implications for more common human metabolic and psychiatric disorders.

Functional diversity of small nucleolar RNAs

Small nucleolar RNAs (snoRNAs) are short non-protein-coding RNAs with a long-recognized role in tuning ribosomal and spliceosomal function by guiding ribose methylation and pseudouridylation at targeted nucleotide residues of ribosomal and small nuclear RNAs, respectively. SnoRNAs are increasingly being implicated in regulation of new types of post-transcriptional processes, for example rRNA acetylation, modulation of splicing patterns, control of mRNA abundance and translational efficiency, or they themselves are processed to shorter stable RNA species that seem to be the principal or alternative bioactive isoform. Intriguingly, some display unusual cellular localization under exogenous stimuli, or tissue-specific distribution. Here, we discuss the new and unforeseen roles attributed to snoRNAs, focusing on the presumed mechanisms of action. Furthermore, we review the experimental approaches to study snoRNA function, including high resolution RNA:protein and RNA:RNA interaction mapping, techniques for analyzing modifications on targeted RNAs, and cellular and animal models used in snoRNA biology research.

Longitudinal Effects of Developmental Bisphenol A Exposure on Epigenome-Wide DNA Hydroxymethylation at Imprinted Loci in Mouse Blood

BACKGROUND

Epigenetic machinery plays an important role in genomic imprinting, a developmental process that establishes parent-of-origin-specific monoallelic gene expression. Although a number of studies have investigated the role of 5-methylcytosine in imprinting control, the contribution of 5-hydroxymethylcytosine (5-hmC) to this epigenetic phenomenon remains unclear.

OBJECTIVES

Using matched mouse blood samples (from mice at 2, 4, and 10 months of age), our objective was to examine the effects of perinatal bisphenol A (BPA) exposure (50 μg/kg diet) on longitudinal 5-hmC patterns at imprinted regions. We also aimed to test the hypothesis that 5-hmC would show defined patterns at imprinted genes that persist across the life course.

METHODS

Genome-wide 5-hmC levels were measured using hydroxymethylated DNA immunoprecipitation sequencing (HMeDIP-seq). Modeling of differential hydroxymethylation by BPA exposure was performed using a pipeline of bioinformatics tools, including the csaw R package.

RESULTS

Based on BPA exposure, we identified 5,950 differentially hydroxymethylated regions (DHMRs), including 12 DHMRs that were annotated to murine imprinted genes—Gnas, Grb10, Plagl1, Klf14, Pde10a, Snrpn, Airn, Cmah, Ppp1r9a, Kcnq1, Phactr2, and Pde4d. When visualized, these imprinted gene DHMRs showed clear, consistent patterns of differential 5-hmC by developmental BPA exposure that persisted throughout adulthood.

CONCLUSIONS

These data show long-term establishment of 5-hmC marks at imprinted loci during development. Further, the effect of perinatal BPA exposure on 5-hmC at specific imprinted loci indicates that developmental exposure to environmental toxicants may alter long-term imprinted gene regulation via an epigenetic mechanism. https://doi.org/10.1289/EHP3441.

Adult-onset deletion of the Prader-Willi syndrome susceptibility gene Snord116 in mice results in reduced feeding and increased fat mass

BACKGROUND

The imprinted small nucleolar RNA (snoRNA) Snord116 is implicated in the aetiology of Prader-Willi syndrome (PWS), a disease associated with hyperphagia and obesity. Germline deletion of Snord116 in mice has been found to lead to increased food intake but not to the development of obesity. To determine the role of Snord116 independent of potential compensatory developmental factors, we investigated the effects of conditional adult-onset deletion of Snord116 in mice.

METHODS

Deletion of Snord116 was induced at 8 weeks of age by oral administration of tamoxifen to male Snord^lox/lox; ROSA^cre/+ mice, with vehicle-treated mice used as controls. Body weight (BW) was monitored weekly and body composition was measured by dual-energy X-ray absorptiometry and tissue dissection. Non-fasted and fasting-induced food intake was determined, and glucose and insulin tolerance tests were performed. Twenty-four-hour energy expenditure and physical activity were assessed by indirect calorimetry.

RESULTS

Adult-onset deletion of Snord116 led to reduced food intake and increased adiposity, albeit with no concomitant change in BW or lean mass compared to controls. Adult onset Snord116 deletion was also associated with worsened glucose tolerance and insulin sensitivity.

CONCLUSIONS

This study identified a key role for Snord116 in feeding behaviour and growth. Further, it is likely that the effects of this gene are modulated by developmental stage, as mice with adult-onset deletion showed an opposite phenotype, with respect to food intake and body composition, to previously published data on mice with germline deletion.

Maternal transcription of non-protein coding RNAs from the PWS-critical region rescues growth retardation in mice

Prader-Willi syndrome (PWS) is a neurogenetic disorder caused by loss of paternally expressed genes on chromosome 15q11-q13. The PWS-critical region (PWScr) contains an array of non-protein coding IPW-A exons hosting intronic SNORD116 snoRNA genes. Deletion of PWScr is associated with PWS in humans and growth retardation in mice exhibiting ~15% postnatal lethality in C57BL/6 background. Here we analysed a knock-in mouse containing a 5'HPRT-LoxP-Neo(R) cassette (5'LoxP) inserted upstream of the PWScr. When the insertion was inherited maternally in a paternal PWScr-deletion mouse model (PWScr(p-/m5'LoxP)), we observed compensation of growth retardation and postnatal lethality. Genomic methylation pattern and expression of protein-coding genes remained unaltered at the PWS-locus of PWScr(p-/m5'LoxP) mice. Interestingly, ubiquitous Snord116 and IPW-A exon transcription from the originally silent maternal chromosome was detected. In situ hybridization indicated that PWScr(p-/m5'LoxP) mice expressed Snord116 in brain areas similar to wild type animals. Our results suggest that the lack of PWScr RNA expression in certain brain areas could be a primary cause of the growth retardation phenotype in mice. We propose that activation of disease-associated genes on imprinted regions could lead to general therapeutic strategies in associated diseases.

Genomic Imprinting

BACKGROUND:

Genomic imprinting is the inheritance out of Mendelian borders. Many of inherited diseases and human development violates Mendelian law of inheritance, this way of inheriting is studied by epigenetics.

AIM:

The aim of this review is to analyze current opinions and options regarding to this way of inheriting.

RESULTS:

Epigenetics shows that gene expression undergoes changes more complex than modifications in the DNA sequence; it includes the environmental influence on the gametes before conception. Humans inherit two alleles from mother and father, both are functional for the majority of the genes, but sometimes one is turned off or “stamped” and doesn’t show in offspring, that gene is imprinted. Imprinting means that that gene is silenced, and gene from other parent is expressed. The mechanisms for imprinting are still incompletely defined, but they involve epigenetic modifications that are erased and then reset during the creation of eggs and sperm. Genomic imprinting is a process of silencing genes through DNA methylation. The repressed allele is methylated, while the active allele is unmethylated. The most well-known conditions include Prader-Willi syndrome, and Angelman syndrome. Both of these syndromes can be caused by imprinting or other errors involving genes on the long arm of chromosome 15.

CONCLUSIONS:

Genomic imprinting and other epigenetic mechanisms such as environment is shown that plays role in offspring neurodevelopment and autism spectrum disorder.

Behavioural characteristics of the Prader-Willi syndrome related biallelic Snord116 mouse model

Prader-Willi syndrome (PWS) is the predominant genetic cause of obesity in humans and is associated with several behavioural phenotypes such as altered motoric function, reduced activity, and learning disabilities. It can include mood instability and, in some cases, psychotic episodes. Recently, the Snord116 gene has been associated with the development of PWS, however, it's contribution to the behavioural aspects of the disease are unknown. Here we show that male and female mice lacking Snord116 on both alleles exhibit normal motor behaviours and exploration but do display task-dependent alterations to locomotion and anxiety-related behaviours. Sociability is well developed in Snord116 deficient mice as are social recognition memory, spatial working memory, and fear-associated behaviours. No sex-specific effects were found. In conclusion, the biallelic Snord116 deficiency mouse model exhibits particular endophenotypes with some relevance to PWS, suggesting partial face validity for the syndrome.

From Prader-Willi syndrome to psychosis: translating parent-of-origin effects into schizophrenia research

Prader-Willi syndrome (PWS) is a relatively rare disorder that originates from paternally inherited deletions and maternal disomy (mUPD) within the 15q11-q13 region or alterations in the PWS imprinting center. Evidence is accumulating that mUPD underlies high prevalence of psychosis among PWS patients. Several genes involved in differentiation and survival of neurons as well as neurotransmission known to act in the development of PWS have been also implicated in schizophrenia. In this article, we provide an overview of genetic and epigenetic underpinnings of psychosis in PWS indicating overlapping points in the molecular background of PWS and schizophrenia. Simultaneously, we highlight the need for studies investigating genetic and epigenetic makeup of the 15q11-q13 in schizophrenia indicating promising candidate genes.

Calorie seeking, but not hedonic response, contributes to hyperphagia in a mouse model for Prader-Willi syndrome

Prader–Willi syndrome (PWS) is a neurodevelopmental disorder caused by deletion or inactivation of paternally expressed imprinted genes on human chromosome 15q11‐q13, the most recognised feature of which is hyperphagia. This is thought to arise as a consequence of abnormalities in both the physiological drive for food and the rewarding properties of food. Although a number of mouse models for PWS exist, the underlying variables dictating maladaptive feeding remain unknown. Here, feeding behaviour in a mouse model in which the imprinting centre (IC) of the syntenic PWS interval has been deleted (PWS^ICdel mice) is characterised. It is demonstrated that PWS^ICdel mice show hyperghrelinaemia and increased consumption of food both following overnight fasting and when made more palatable with sucrose. However, hyperphagia in PWS^ICdel mice was not accompanied by any changes in reactivity to the hedonic properties of palatable food (sucrose or saccharin), as measured by lick‐cluster size. Nevertheless, overall consumption by PWS^ICdel mice for non‐caloric saccharin in the licking test was significantly reduced. Combined with converging findings from a continuous reinforcement schedule, these data indicate that PWS^ICdel mice show a marked heightened sensitivity to the calorific value of food. Overall, these data indicate that any impact of the rewarding properties of food on the hyperphagia seen in PWS^ICdel mice is driven primarily by calorie content and is unlikely to involve hedonic processes. This has important implications for understanding the neural systems underlying the feeding phenotype of PWS and the contribution of imprinted genes to abnormal feeding behaviour more generally.

Learning by observation and learning by doing in Prader-Willi syndrome

BACKGROUND

New competencies may be learned through active experience (learning by doing) or observation of others' experience (learning by observation). Observing another person performing a complex action accelerates the observer's acquisition of the same action, limiting the time-consuming process of learning by doing. Here, we compared learning by observation and learning by doing in individuals with Prader-Willi syndrome (PWS). It is hypothesized that PWS individuals could show more difficulties with learning by observation than learning by doing because of their specific difficulty in interpreting and using social information.

METHODS

The performance of 24 PWS individuals was compared with that of 28 mental age (MA)- and gender-matched typically developing (TD) children in tasks of learning a visuo-motor sequence by observation or by doing. To determine whether the performance pattern exhibited by PWS participants was specific to this population or whether it was a nonspecific intellectual disability effect, we compared the PWS performances with those of a third MA- and gender-matched group of individuals with Williams syndrome (WS).

RESULTS

PWS individuals were severely impaired in detecting a sequence by observation, were able to detect a sequence by doing, and became as efficient as TD children in reproducing an observed sequence after a task of learning by doing. The learning pattern of PWS children was reversed compared with that of WS individuals.

CONCLUSIONS

The observational learning deficit in PWS individuals may be rooted, at least partially, in their incapacity to understand and/or use social information.

Dosage-sensitivity of imprinted genes expressed in the brain: 15q11-q13 and neuropsychiatric illness

Imprinted genes, those genes subject to parent-of-origin-specific epigenetic marking resulting in monoallelic parent-specific expression, are sensitive to subtle changes in expression dosage. This has been illustrated in a number of experimental models and the fact that both decreased (or complete loss) and increased imprinted gene expression can lead to human diseases. In the present paper, we discuss the consequence of increased dosage of imprinted genes for brain function, focusing on the PWS (Prader-Willi syndrome) locus on human chromosome 15q11-q13 and how predicted increases in dosage of maternally expressed imprinted genes from this interval are associated with a higher risk of developing psychotic illness. The evidence for this comes from individuals with PWS itself and also non-syndromic cases of psychosis in carriers of a maternally derived copy number variant spanning this locus. Of the known imprinted genes in this region, the prime candidate is maternally expressed UBE3A, which encodes E6-AP (E6-associated protein) ubiquitin ligase and has an influence on a number of important neurotransmitter systems. Furthermore, these findings point to the fact that brain function is exquisitely sensitive to both decreases and increases in the expression of imprinted genes.

An unexpected function of the Prader-Willi syndrome imprinting center in maternal imprinting in mice

Genomic imprinting is a phenomenon that some genes are expressed differentially according to the parent of origin. Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are neurobehavioral disorders caused by deficiency of imprinted gene expression from paternal and maternal chromosome 15q11–q13, respectively. Imprinted genes at the PWS/AS domain are regulated through a bipartite imprinting center, the PWS-IC and AS-IC. The PWS-IC activates paternal-specific gene expression and is responsible for the paternal imprint, whereas the AS-IC functions in the maternal imprint by allele-specific repression of the PWS-IC to prevent the paternal imprinting program. Although mouse chromosome 7C has a conserved PWS/AS imprinted domain, the mouse equivalent of the human AS-IC element has not yet been identified. Here, we suggest another dimension that the PWS-IC also functions in maternal imprinting by negatively regulating the paternally expressed imprinted genes in mice, in contrast to its known function as a positive regulator for paternal-specific gene expression. Using a mouse model carrying a 4.8-kb deletion at the PWS-IC, we demonstrated that maternal transmission of the PWS-IC deletion resulted in a maternal imprinting defect with activation of the paternally expressed imprinted genes and decreased expression of the maternally expressed imprinted gene on the maternal chromosome, accompanied by alteration of the maternal epigenotype toward a paternal state spread over the PWS/AS domain. The functional significance of this acquired paternal pattern of gene expression was demonstrated by the ability to complement PWS phenotypes by maternal inheritance of the PWS-IC deletion, which is in stark contrast to paternal inheritance of the PWS-IC deletion that resulted in the PWS phenotypes. Importantly, low levels of expression of the paternally expressed imprinted genes are sufficient to rescue postnatal lethality and growth retardation in two PWS mouse models. These findings open the opportunity for a novel approach to the treatment of PWS.