Prader-Willi (PWS) and Angelman (AS) syndromes were the first examples in humans with errors in genomic imprinting, usually from de novo 15q11-q13 deletions of different parent origin (paternal in PWS and maternal in AS). Dozens of genes and transcripts are found in the 15q11-q13 region, and may play a role in PWS, specifically paternally expressed SNURF-SNRPN and MAGEL2 genes, while AS is due to the maternally expressed UBE3A gene. These three causative genes, including their encoding proteins, were targeted. This review article summarizes and illustrates the current understanding and cause of both PWS and AS using strategies to include the literature sources of key words and searchable web-based programs with databases for integrated gene and protein interactions, biological processes, and molecular mechanisms available for the two imprinting disorders. The SNURF-SNRPN gene is key in developing complex spliceosomal snRNP assemblies required for mRNA processing, cellular events, splicing, and binding required for detailed protein production and variation, neurodevelopment, immunodeficiency, and cell migration. The MAGEL2 gene is involved with the regulation of retrograde transport and promotion of endosomal assembly, oxytocin and reproduction, as well as circadian rhythm, transcriptional activity control, and appetite. The UBE3A gene encodes a key enzyme for the ubiquitin protein degradation system, apoptosis, tumor suppression, cell adhesion, and targeting proteins for degradation, autophagy, signaling pathways, and circadian rhythm. PWS is characterized early with infantile hypotonia, a poor suck, and failure to thrive with hypogenitalism/hypogonadism. Later, growth and other hormone deficiencies, developmental delays, and behavioral problems are noted with hyperphagia and morbid obesity, if not externally controlled. AS is characterized by seizures, lack of speech, severe learning disabilities, inappropriate laughter, and ataxia. This review captures the clinical presentation, natural history, causes with genetics, mechanisms, and description of established laboratory testing for genetic confirmation of each disorder. Three separate searchable web-based programs and databases that included information from the updated literature and other sources were used to identify and examine integrated genetic findings with predicted gene and protein interactions, molecular mechanisms and functions, biological processes, pathways, and gene-disease associations for candidate or causative genes per disorder. The natural history, review of pathophysiology, clinical presentation, genetics, and genetic-phenotypic findings were described along with computational biology, molecular mechanisms, genetic testing approaches, and status for each disorder, management and treatment options, clinical trial experiences, and future strategies. Conclusions and limitations were discussed to improve understanding, clinical care, genetics, diagnostic protocols, therapeutic agents, and genetic counseling for those with these genomic imprinting disorders.

Angelman Syndrome (AS) is a severe neurodevelopmental disorder with only symptomatic treatment currently available. The primary cause of AS is loss of functional UBE3A protein. This can be caused by deletions in the maternal 15q11-q13 region, maternal AS-imprinting center defects (mICD), paternal uniparental disomy of chromosome 15 (UPD) or mutations within the UBE3A gene. Current mouse models are Ube3a-centric and do not address expression changes of other genes in the 15q11-q13 locus on the pathophysiology of AS. This limits the ability to discern differences in therapeutic responses to current UBE3A-targeting strategies and hampers the identification of novel therapeutics/co-therapeutics. Using a mouse line that harbors a maternally inherited mutation affecting the AS-PWS imprinting center ('mICD mice'), we studied the impact of the mICD or UPD AS subtype on behavior, seizure susceptibility and proteome. Additionally, by using mice overexpressing two copies of Ube3a or antisense oligonucleotide (ASO) targeting Ube3a-ATS, we analyzed the impact of bi-allelic Ube3a activation on behavior and proteome. mICD mice showed 80% reduction in UBE3A protein, bi-allelic expression of Ube3a-ATS and Mkrn3-Snord115 gene cluster, leading to robust AS behavioral deficits and proteome alterations similar to Ube3am-/p+ mice. Genetic UBE3A overexpression in mICD mice, mimicking therapeutic strategies that effectively activate the biallelic silenced Ube3a gene, resulted in a complete rescue of all behavioral phenotypes, seizure susceptibility and proteome alterations. Subsequently, treatment with an antisense oligonucleotide (ASO) to directly activate the biallelic silenced Ube3a gene in mICD mice also resulted in efficient reinstatement of UBE3A, 30% higher relative to WT, alongside a partial rescue of behavioral phenotypes. Despite using a highly robust AS-specific behavioral battery, we did not investigate readouts such as neuronal activity and sleep, for which impairments in Ube3am-/p+ mice were described. Taken together, these findings demonstrate that the loss of UBE3A protein is the primary factor underlying AS phenotypes in this mICD/UPD mouse model of AS, while the biallelic expressed genes in this locus play either a marginal or yet unidentified role. These findings also corroborate UBE3A reinstatement as an attractive therapeutic strategy for AS individuals carrying an mICD or UPD mutation.

Prader-Willi syndrome (PWS) is the most common genetic syndrome with obesity and results from loss of expression of paternally inherited genes on chromosome 15q11-q13 by a variety of mechanisms which include large deletions (70%-75%), maternal uniparental disomy (UPD) (20%-30%), and imprinting defects (2%-5%) or balanced translocations. Individuals often have a characteristic behavior disorder with mild intellectual disability, infantile hypotonia associated with poor sucking, short stature, and obesity. PWS is characterized by hypothalamic-pituitary axis dysfunction with growth hormone (GH) deficiency, hypogonadism, and several other hormonal deficiencies resulting in short stature, centrally driven excessive appetite (hyperphagia), central obesity, cryptorchidism, and decreased lean body mass. In this study, we determined and sought differences in the incidence of thyroid abnormalities among the common genetic subtypes in a cohort of 52 subjects with PWS because there was limited literature available. We also sought the effects of growth hormone (GH) treatment on the thyroid profile. Fifty-two subjects with a genetically confirmed diagnosis of PWS were included in this study at the University of California, Irvine. Blood samples for baseline thyroxine stimulating hormone (TSH) and free thyroxine (fT4) levels were obtained in the morning after an overnight fast for 8-12 h. Statistical analyses were performed with SPSS (SPSS Inc., 21.0). Mean values were analyzed by one-way ANOVA, and student's t-test and statistical significance were set at p < 0.05. The subjects included 26 males and 26 females with an age range of 3-38 years. There were 29 subjects with chromosome 15q11-q13 deletions and 23 with UPD; 28 were GH treated currently or in the past, and 24 never received GH. There was no significant difference in age or body mass index (BMI) (kg/m2) between GH-treated versus non-GH-treated groups. BMI was higher in the deletion group compared to the UPD group (p = 0.05). We identified two individuals who were clinically diagnosed and treated for hypothyroidism, one of whom was on GH supplements. We identified two additional individuals with subclinical hypothyroidism who were not on GH treatment, giving a frequency of 7.6% (4/52) in this cohort of patients. We did not find significant differences in thyroid function (TSH) in the deletion versus UPD groups. We found significant differences in thyroid function, however, between GH-treated and non-GH-treated groups. The mean TSH was lower (2.25 ± 1.17 uIU/M, range 0.03-4.92 uIU/M versus 2.80 ± 1.44 uIU/M, range 0.55-5.33 uIU/M respectively, p = 0.046), and the free T4 levels were significantly higher (1.13 ± 0.70 and 1.03 ± 0.11 ng/dL, respectively, p = 0.05) in the GH-treated individuals compared to non-GH-treated individuals. In this cohort of subjects with PWS, we identified two previously diagnosed individuals with hypothyroidism and two individuals with subclinical hypothyroidism (4/52, 7.6%), three of whom were not receiving GH treatment. We did not find any significant differences in thyroid function between molecular subtypes; however, we found that euthyroid status (lower TSH levels and higher free T4 levels) was significantly higher in individuals who were treated with GH compared to the untreated group. We recommend that individuals with PWS should be screened regularly for thyroid deficiency and start treatment early with GH in view of the potentially lower incidence of thyroid deficiency.

Angelman syndrome (AS) is an autosomal dominant neurodevelopmental genetic disease with maternal imprint, which is associated with the presence of the abnormal chromosome 15q11-q13, and the loss of maternal specific expression of ubiquitin-protein ligase E3A (UBE3A). The expression levels of UBE3A depend on the parental origin and exhibit tissue specificity. In normal brain tissues, the maternal UBE3A gene is actively expressed, whereas the paternal UBE3A gene is not. In total, ~85% of pediatric patients with AS present with epilepsy within their 3rd year of life. This condition is usually difficult to control with medical treatment. An 8-year-old female visited the Affiliated Hospital of Jining Medical University due to frequent epilepsy. Her clinical manifestations included specific facial features, moderate mental retardation and frequent seizures. It was interesting to note that her 15-year-old sister exhibited similar clinical manifestations to those of AS. The results of the electroencephalogram and the imaging examinations were also in line with the characteristics of AS. In order to further clarify the diagnosis, all the suspected genes in her sister and in their parents were sequenced. The multiplex ligation-dependent probe amplification project of the Angel/chubby and copy number variation (CNV) sequencing were assessed concomitantly to identify the pathogenic genes responsible for the development of AS. The latter occurs due to the missense mutation c.1146T>G, which results in asparagine replacement by lysine at position 382 (p.Asn382Lys) in exon 7. This amino acid change affects the normal expression of UBE3A; the mutation is a novel mutation, which, to the best of our knowledge, has not been previously reported. Relevant large fragments of mutations and methylation abnormalities were not found in the associated genes. The data further revealed absence of 25-bp repeat mutations at the shear mutation site of exon 1 of the small nuclear ribonucleoprotein polypeptide N gene in the subjects examined. No suspected CNV was found following analysis.

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are genomic imprinting disorders that are mainly caused by a deletion on 15q11-q13, the uniparental disomy of chromosome 15, or an imprinting defect. We evaluated the utility of methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) as a diagnostic tool and for demonstrating the relationship between molecular mechanisms and clinical presentation. We performed MS-MLPA using DNA samples from 93 subjects (45 PWS, 24 AS, and 24 non-PWS/AS controls) who had previously undergone MS-PCR for the diagnosis of PWS/AS. We compared the results of both assays, and patients' clinical phenotypes were reviewed retrospectively. MS-MLPA showed a 100% concordance rate with MS-PCR. Among the 45 PWS patients, 26 (57.8%) had a deletion of 15q11-q13, and the others (42.2%) had uniparental disomy 15 or an imprinting defect. Among the 24 AS patients, 16 (66.7%) had a deletion of 15q11-q13, 7 AS patients (29.2%) had uniparental disomy 15 or an imprinting defect, and one AS patient (4.2%) showed an imprinting center deletion. MS-MLPA has clinical utility for the diagnosis of PWS/AS, and it is superior to MS-PCR in that it can identify the molecular mechanism underlying the disease.