Angelman syndrome is a rare neurodevelopmental disorder caused by the loss of function of the maternally inherited UBE3A gene within the chr15q11-q13 region. This gene is subjected to a tissue-specific form of genomic imprinting leading to the silencing of the paternal allele in neurons. Angelman syndrome can result from various (epi)genetic mechanisms, with paternal uniparental disomy of chromosome 15 (patUPD15) being one of the rarest and least studied due to the absence of suitable models. To address this gap, we generated three independent induced pluripotent stem cell (iPSC) lines from individuals with Angelman syndrome caused by patUPD15, alongside genetically matched unaffected familial controls. Peripheral blood mononuclear cells (PBMCs) were reprogrammed into iPSCs using a non-integrative Sendai virus-based approach expressing the Yamanaka factors. All iPSC lines underwent rigorous quality control, confirming stem cell identity, trilineage differentiation potential, and genetic and epigenetic integrity. This newly established iPSC toolkit provides a powerful platform to investigate the molecular underpinnings of Angelman syndrome caused by patUPD15, paving the way for future translational research and therapeutic development tailored for this understudied form of the disorder.

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.

Uniparental disomy (UPD) constitutes an unconventional mode of inheritance that disrupts the typical biparental genetic contribution and may result in phenotypic abnormalities. This report centers on a patient diagnosed with Bartter syndrome Type 1, attributed to a homozygous pathogenic variant in SLC12A1 unmasked by mosaic paternal UPD of chromosome 15. We hypothesize that this pattern (or constellation) emerged from a trisomy rescue event, resulting in two distinct cell lines. Concurrently, the unmasking of a pathogenic paternal SLC12A1 variant by trisomy rescue resulted in the manifestation of Bartter syndrome Type 1. The maternally derived ring chromosome 15 and its impact on nondisjunction and UPD elucidate a unique etiology of Bartter syndrome. Furthermore, the presence of a pathogenic paternal SLC12A1 variant underscores the pivotal role of trisomic rescue and paternal UPD in unveiling a recessive variant.

Angelman syndrome (AS) is a rare genetic disorder due to lack of UBE3A function on chromosome 15q11.2q13 caused by a deletion, uniparental paternal disomy (UPD), imprinting center disorder (ICD), or pathological variant of the UBE3A gene. AS is characterized by developmental delay, epilepsy, and lack of speech. Although fractures are observed frequently in our clinical practice, there are few studies on bone health in AS. The aim of this study is to investigate bone health in children with AS. In this prospective cohort study, we describe bone health in 91 children with AS visiting the ENCORE Expertise Center for AS between April 2010 and December 2021. Bone health was assessed with the bone health index (BHI) in standard deviation score (SDS) measured by digital radiogrammetry of the left hand using BoneXpert software. Risk factors analyzed were age, sex, genetic subtype, epilepsy, anti-seizure medication use, mobility, body mass index (BMI), and onset of puberty. Children with AS had a mean BHI of -1.77 SDS (SD 1.4). A significantly lower BHI was found in children with a deletion (-2.24 SDS) versus non-deletion (-1.02 SDS). Other factors associated with reduced BHI-SDS were inability to walk and late onset of puberty. Children with a history of one or more fractures (22%) had a significantly lower BHI than children without fractures (-2.60 vs -1.56 SDS). Longitudinal analysis showed a significant decrease in BHI-SDS with age in all genetic subtypes.  Conclusions: Children with AS have a reduced bone health. Risk factors are deletion genotype, no independent walking, and late onset of puberty. Bone health decreased significantly with age. What is Known: • Children with neurological disorders often have a low bone health and higher risk of fractures. • Little is known about bone health in children with Angelman syndrome (AS). What is New: • Children with AS showed a reduced bone health and this was significantly associated with having a deletion, not being able to walk independently, and late onset of puberty. • Longitudinal analysis showed a significant decrease in bone health as children got older.

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.