Development of a Weight-Band Dosing Approach for Vosoritide in Children with Achondroplasia Using a Population Pharmacokinetic Model.

BACKGROUND AND OBJECTIVE: Vosoritide is a recently approved therapy for achondroplasia, the most common form of disproportionate short stature, that has been shown to be well tolerated and effective in increasing linear growth. This study aimed to develop a population pharmacokinetic (PPK) model to characterize pharmacokinetics (PK) of vosoritide and establish a weight-band dosing regimen. METHODS: A PPK model was developed using data from five clinical trials in children with achondroplasia (aged 0.95-15 years) who received daily per-kg doses of vosoritide. The model was used to simulate expected exposures in children with a refined weight-band dosing regimen. Simulated exposure was compared with the observed exposure from the pivotal clinical trial to evaluate appropriateness of the weight-band dosing regimen. RESULTS: A one-compartment model with a change-point first-order absorption and first-order elimination accurately described PK of vosoritide in children with achondroplasia. Body weight was found to be a predictor of vosoritide's clearance and volume of distribution. Additionally, it was observed that dosing solution concentration and duration of treatment influenced bioavailability. The weight-band dosing regimen resulted in simulated exposures that were within the range demonstrated to be well tolerated and effective in the pivotal clinical trial and showed improved consistency in drug exposure across the achondroplasia population. CONCLUSIONS: The weight-band dosing regimen reduced the number of recommended dose levels by body weight and is expected to simplify dosing for children with achondroplasia and their caregivers. CLINICAL TRIAL REGISTRATION: NCT02055157, NCT02724228, NCT03197766, NCT03424018, and NCT03583697.

The clinical utility and diagnostic implementation of human subject cell transdifferentiation followed by RNA sequencing.

RNA sequencing (RNA-seq) has recently been used in translational research settings to facilitate diagnoses of Mendelian disorders. A significant obstacle for clinical laboratories in adopting RNA-seq is the low or absent expression of a significant number of disease-associated genes/transcripts in clinically accessible samples. As this is especially problematic in neurological diseases, we developed a clinical diagnostic approach that enhanced the detection and evaluation of tissue-specific genes/transcripts through fibroblast-to-neuron cell transdifferentiation. The approach is designed specifically to suit clinical implementation, emphasizing simplicity, cost effectiveness, turnaround time, and reproducibility. For clinical validation, we generated induced neurons (iNeurons) from 71 individuals with primary neurological phenotypes recruited to the Undiagnosed Diseases Network. The overall diagnostic yield was 25.4%. Over a quarter of the diagnostic findings benefited from transdifferentiation and could not be achieved by fibroblast RNA-seq alone. This iNeuron transcriptomic approach can be effectively integrated into diagnostic whole-transcriptome evaluation of individuals with genetic disorders.

Novel syndromic neurodevelopmental disorder caused by de novo deletion of CHASERR, a long noncoding RNA.

Genes encoding long non-coding RNAs (lncRNAs) comprise a large fraction of the human genome, yet haploinsufficiency of a lncRNA has not been shown to cause a Mendelian disease. CHASERR is a highly conserved human lncRNA adjacent to CHD2-a coding gene in which de novo loss-of-function variants cause developmental and epileptic encephalopathy. Here we report three unrelated individuals each harboring an ultra-rare heterozygous de novo deletion in the CHASERR locus. We report similarities in severe developmental delay, facial dysmorphisms, and cerebral dysmyelination in these individuals, distinguishing them from the phenotypic spectrum of CHD2 haploinsufficiency. We demonstrate reduced CHASERR mRNA expression and corresponding increased CHD2 mRNA and protein in whole blood and patient-derived cell lines-specifically increased expression of the CHD2 allele in cis with the CHASERR deletion, as predicted from a prior mouse model of Chaserr haploinsufficiency. We show for the first time that de novo structural variants facilitated by Alu-mediated non-allelic homologous recombination led to deletion of a non-coding element (the lncRNA CHASERR) to cause a rare syndromic neurodevelopmental disorder. We also demonstrate that CHD2 has bidirectional dosage sensitivity in human disease. This work highlights the need to carefully evaluate other lncRNAs, particularly those upstream of genes associated with Mendelian disorders.

Improving access to exome sequencing in a medically underserved population through the Texome Project.

PURPOSE: Genomic medicine can end diagnostic odysseys for patients with complex phenotypes; however, limitations in insurance coverage and other systemic barriers preclude individuals from accessing comprehensive genetics evaluation and testing. METHODS: The Texome Project is a 4-year study that reduces barriers to genomic testing for individuals from underserved and underrepresented populations. Participants with undiagnosed, rare diseases who have financial barriers to obtaining exome sequencing (ES) clinically are enrolled in the Texome Project. RESULTS: We highlight the Texome Project process and describe the outcomes of the first 60 ES results for study participants. Participants received a genetic evaluation, ES, and return of results at no cost. We summarize the psychosocial or medical implications of these genetic diagnoses. Thus far, ES provided molecular diagnoses for 18 out of 60 (30%) of Texome participants. Plus, in 11 out of 60 (18%) participants, a partial or probable diagnosis was identified. Overall, 5 participants had a change in medical management. CONCLUSION: To date, the Texome Project has recruited a racially, ethnically, and socioeconomically diverse cohort. The diagnostic rate and medical impact in this cohort support the need for expanded access to genetic testing and services. The Texome Project will continue reducing barriers to genomic care throughout the future study years.

Intrafamilial phenotypic heterogeneity in siblings with pseudohypoparathyroidism 1B due to maternal STX16 deletion.

OBJECTIVES: Pseudohypoparathyroidism (PHP1B) is most commonly caused by epigenetic defects resulting in loss of methylation at the GNAS locus, although deletions of STX16 leading to GNAS methylation abnormalities have been previously reported. The phenotype of this disorder is variable and can include hormonal resistances and severe infantile obesity with hyperphagia. A possible time relationship between the onset of obesity and endocrinopathies has been previously reported but remains unclear. Understanding of the condition's natural history is limited, partly due to a scarcity of literature, especially in children. CASE PRESENTATION: We report three siblings with autosomal dominant PHP1B caused by a deletion in STX16 who presented with early childhood onset PTH-resistance with normocalcemia with a progressive nature, accompanied by TSH-resistance and severe infantile obesity with hyperphagia in some, not all of the affected individuals. CONCLUSIONS: PHP1B from a STX16 deletion displays intrafamilial phenotypic variation. It is a novel cause of severe infantile obesity, which is not typically included in commercially available gene panels but must be considered in the genetic work-up. Finally, it does not seem to have a clear time relationship between the onset of obesity and hormonal resistance.

Vosoritide therapy in children with achondroplasia aged 3-59 months: a multinational, randomised, double-blind, placebo-controlled, phase 2 trial.

BACKGROUND: Vosoritide is a recombinant C-type natriuretic peptide analogue that increases annualised growth velocity in children with achondroplasia aged 5-18 years. We aimed to assess the safety and efficacy of vosoritide in infants and children younger than 5 years. METHODS: This double-blind, randomised, placebo-controlled, phase 2 trial was done in 16 hospitals across Australia, Japan, the UK, and the USA. Children younger than 60 months with a clinical diagnosis of achondroplasia confirmed by genetic testing and who had completed a baseline growth study or observation period were enrolled into one of three sequential cohorts based on age at screening: 24-59 months (cohort 1); 6-23 months (cohort 2); and 0-5 months (cohort 3). Each cohort included sentinels who received vosoritide to determine appropriate daily drug dose, with the remainder randomly assigned (1:1) within each age stratum (except in Japan, where participants were randomly assigned within each cohort) to receive daily subcutaneous injections of vosoritide (30·0 µg/kg for infants aged 0-23 months; 15·0 µg/kg for children aged 24-59 months) or placebo for 52 weeks. Participants, caregivers, investigators, and the sponsor were masked to treatment assignment. The first primary outcome was safety and tolerability, assessed in all participants who received at least one study dose. The second primary outcome was change in height Z score at 52 weeks from baseline, analysed in all randomly assigned participants. This trial is registered with EudraCT, 2016-003826-18, and ClinicalTrials.gov, NCT03583697. FINDINGS: Between May 13, 2018, and March 1, 2021, 75 participants were recruited (37 [49%] females). 11 were assigned as sentinels, whereas 32 were randomly assigned to receive vosoritide and 32 placebo. Two participants discontinued treatment and the study: one in the vosoritide group (death) and one in the placebo group (withdrawal). Adverse events occurred in all 75 (100%) participants (annual rate 204·5 adverse events per patient in the vosoritide group and 73·6 per patient in the placebo group), most of which were transient injection-site reactions and injection-site erythema. Serious adverse events occurred in three (7%) participants in the vosoritide group (decreased oxygen saturation, respiratory syncytial virus bronchiolitis and sudden infant death syndrome, and pneumonia) and six (19%) participants in the placebo group (petit mal epilepsy, autism, gastroenteritis, vomiting and parainfluenza virus infection, respiratory distress, and skull fracture and otitis media). The least-squares mean difference for change from baseline in height Z score between the vosoritide and placebo groups was 0·25 (95% CI -0·02 to 0·53). INTERPRETATION: Children with achondroplasia aged 3-59 months receiving vosoritide for 52 weeks had a mild adverse event profile and gain in the change in height Z score from baseline. FUNDING: BioMarin Pharmaceutical.

Once-weekly TransCon CNP (navepegritide) in children with achondroplasia (ACcomplisH): a phase 2, multicentre, randomised, double-blind, placebo-controlled, dose-escalation trial.

Background: TransCon CNP (navepegritide) is an investigational prodrug of C-type natriuretic peptide (CNP) designed to allow for continuous CNP exposure with once-weekly dosing. This 52-week phase 2 (ACcomplisH) trial assessed the safety and efficacy of TransCon CNP in children with achondroplasia. Methods: ACcomplisH is a global, randomised, double-blind, placebo-controlled, dose-escalation trial. Study participants were recruited between June 10, 2020, and September 24, 2021. Eligible participants were prepubertal, aged 2-10 years, with genetically confirmed achondroplasia, and randomised 3:1 to once-weekly subcutaneous injections of TransCon CNP (6, 20, 50, or 100 µg CNP/kg/week) or placebo for 52 weeks. Primary objectives were safety and annualised growth velocity (AGV). ACcomplisH is registered with ClinicalTrials.gov (NCT04085523) and Eudra (CT 2019-002754-22). Findings: Forty-two participants received TransCon CNP at doses of 6 µg (n = 10; 7 female), 20 µg (n = 11; 3 female), 50 µg (n = 10; 3 female), or 100 µg (n = 11; 6 female) CNP/kg/week, with 15 receiving placebo (5 female). Treatment-emergent adverse events (TEAEs) were mild or moderate with no grade 3/4 events reported. There were 2 serious TEAEs that were assessed as not related to TransCon CNP. Eleven injection site reactions occurred in 8 participants receiving TransCon CNP and no symptomatic hypotension occurred. TransCon CNP demonstrated a dose-dependent improvement in AGV. At 52 weeks, TransCon CNP 100 µg CNP/kg/week significantly improved AGV vs placebo (least squares mean [95% CI] 5.42 [4.74-6.11] vs 4.35 [3.75-4.94] cm/year; p = 0.0218), and improved achondroplasia-specific height SDS from baseline (least squares mean [95% CI] 0.22 [0.02-0·41] vs -0·08 [-0.25 to 0.10]; p = 0.0283). All participants completed the randomised period and continued in the ongoing open-label extension period receiving TransCon CNP 100 µg CNP/kg/week. Interpretation: This phase 2 trial suggests that TransCon CNP is effective, safe, with low injection site reaction frequency, and may provide a novel, once-weekly treatment option for children with achondroplasia. These results support TransCon CNP at 100 µg CNP/kg/week in the ongoing pivotal trial. Funding: Ascendis Pharma, A/S.

Enabling endpoint development for interventional clinical trials in individuals with Angelman syndrome: a prospective, longitudinal, observational clinical study (FREESIAS).

BACKGROUND: Angelman syndrome (AS) is a rare neurodevelopmental disorder characterized by the absence of a functional UBE3A gene, which causes developmental, behavioral, and medical challenges. While currently untreatable, comprehensive data could help identify appropriate endpoints assessing meaningful improvements in clinical trials. Herein are reported the results from the FREESIAS study assessing the feasibility and utility of in-clinic and at-home measures of key AS symptoms. METHODS: Fifty-five individuals with AS (aged < 5 years: n = 16, 5-12 years: n = 27, ≥ 18 years: n = 12; deletion genotype: n = 40, nondeletion genotype: n = 15) and 20 typically developing children (aged 1-12 years) were enrolled across six USA sites. Several clinical outcome assessments and digital health technologies were tested, together with overnight 19-lead electroencephalography (EEG) and additional polysomnography (PSG) sensors. Participants were assessed at baseline (Clinic Visit 1), 12 months later (Clinic Visit 2), and during intermittent home visits. RESULTS: The participants achieved high completion rates for the clinical outcome assessments (adherence: 89-100% [Clinic Visit 1]; 76-91% [Clinic Visit 2]) and varied feasibility of and adherence to digital health technologies. The coronavirus disease 2019 (COVID-19) pandemic impacted participants' uptake of and/or adherence to some measures. It also potentially impacted the at-home PSG/EEG recordings, which were otherwise feasible. Participants achieved Bayley-III results comparable to the available natural history data, showing similar scores between individuals aged ≥ 18 and 5-12 years. Also, participants without a deletion generally scored higher on most clinical outcome assessments than participants with a deletion. Furthermore, the observed AS EEG phenotype of excess delta-band power was consistent with prior reports. CONCLUSIONS: Although feasible clinical outcome assessments and digital health technologies are reported herein, further improved assessments of meaningful AS change are needed. Despite the COVID-19 pandemic, remote assessments facilitated high adherence levels and the results suggested that at-home PSG/EEG might be a feasible alternative to the in-clinic EEG assessments. Taken altogether, the combination of in-clinic/at-home clinical outcome assessments, digital health technologies, and PSG/EEG may improve protocol adherence, reduce patient burden, and optimize study outcomes in AS and other rare disease populations.

Rare variants in PPFIA3 cause delayed development, intellectual disability, autism, and epilepsy.

PPFIA3 encodes the Protein-Tyrosine Phosphatase, Receptor-Type, F Polypeptide-Interacting Protein Alpha-3 (PPFIA3), which is a member of the LAR protein-tyrosine phosphatase-interacting protein (liprin) family involved in synaptic vesicle transport and presynaptic active zone assembly. The protein structure and function are well conserved in both invertebrates and vertebrates, but human diseases related to PPFIA3 dysfunction are not yet known. Here, we report 14 individuals with rare mono-allelic PPFIA3 variants presenting with features including developmental delay, intellectual disability, hypotonia, autism, and epilepsy. To determine the pathogenicity of PPFIA3 variants in vivo , we generated transgenic fruit flies expressing either human PPFIA3 wildtype (WT) or variant protein using GAL4-UAS targeted gene expression systems. Ubiquitous expression with Actin-GAL4 showed that the PPFIA3 variants had variable penetrance of pupal lethality, eclosion defects, and anatomical leg defects. Neuronal expression with elav-GAL4 showed that the PPFIA3 variants had seizure-like behaviors, motor defects, and bouton loss at the 3 rd instar larval neuromuscular junction (NMJ). Altogether, in the fly overexpression assays, we found that the PPFIA3 variants in the N-terminal coiled coil domain exhibited stronger phenotypes compared to those in the C-terminal region. In the loss-of-function fly assay, we show that the homozygous loss of fly Liprin- α leads to embryonic lethality. This lethality is partially rescued by the expression of human PPFIA3 WT, suggesting human PPFIA3 protein function is partially conserved in the fly. However, the PPFIA3 variants failed to rescue lethality. Altogether, the human and fruit fly data reveal that the rare PPFIA3 variants are dominant negative loss-of-function alleles that perturb multiple developmental processes and synapse formation.

YWHAE loss of function causes a rare neurodevelopmental disease with brain abnormalities in human and mouse.

PURPOSE: Miller-Dieker syndrome is caused by a multiple gene deletion, including PAFAH1B1 and YWHAE. Although deletion of PAFAH1B1 causes lissencephaly unambiguously, deletion of YWHAE alone has not clearly been linked to a human disorder. METHODS: Cases with YWHAE variants were collected through international data sharing networks. To address the specific impact of YWHAE loss of function, we phenotyped a mouse knockout of Ywhae. RESULTS: We report a series of 10 individuals with heterozygous loss-of-function YWHAE variants (3 single-nucleotide variants and 7 deletions <1 Mb encompassing YWHAE but not PAFAH1B1), including 8 new cases and 2 follow-ups, added with 5 cases (copy number variants) from literature review. Although, until now, only 1 intragenic deletion has been described in YWHAE, we report 4 new variants specifically in YWHAE (3 splice variants and 1 intragenic deletion). The most frequent manifestations are developmental delay, delayed speech, seizures, and brain malformations, including corpus callosum hypoplasia, delayed myelination, and ventricular dilatation. Individuals with variants affecting YWHAE alone have milder features than those with larger deletions. Neuroanatomical studies in Ywhae-/- mice revealed brain structural defects, including thin cerebral cortex, corpus callosum dysgenesis, and hydrocephalus paralleling those seen in humans. CONCLUSION: This study further demonstrates that YWHAE loss-of-function variants cause a neurodevelopmental disease with brain abnormalities.

De novo variants in FRMD5 are associated with developmental delay, intellectual disability, ataxia, and abnormalities of eye movement.

Proteins containing the FERM (four-point-one, ezrin, radixin, and moesin) domain link the plasma membrane with cytoskeletal structures at specific cellular locations and have been implicated in the localization of cell-membrane-associated proteins and/or phosphoinositides. FERM domain-containing protein 5 (FRMD5) localizes at cell adherens junctions and stabilizes cell-cell contacts. To date, variants in FRMD5 have not been associated with a Mendelian disease in OMIM. Here, we describe eight probands with rare heterozygous missense variants in FRMD5 who present with developmental delay, intellectual disability, ataxia, seizures, and abnormalities of eye movement. The variants are de novo in all for whom parental testing was available (six out of eight probands), and human genetic datasets suggest that FRMD5 is intolerant to loss of function (LoF). We found that the fly ortholog of FRMD5, CG5022 (dFrmd), is expressed in the larval and adult central nervous systems where it is present in neurons but not in glia. dFrmd LoF mutant flies are viable but are extremely sensitive to heat shock, which induces severe seizures. The mutants also exhibit defective responses to light. The human FRMD5 reference (Ref) cDNA rescues the fly dFrmd LoF phenotypes. In contrast, all the FRMD5 variants tested in this study (c.340T>C, c.1051A>G, c.1053C>G, c.1054T>C, c.1045A>C, and c.1637A>G) behave as partial LoF variants. In addition, our results indicate that two variants that were tested have dominant-negative effects. In summary, the evidence supports that the observed variants in FRMD5 cause neurological symptoms in humans.

Exome sequencing efficacy and phenotypic expansions involving esophageal atresia/tracheoesophageal fistula plus.

Esophageal atresia/tracheoesophageal fistula (EA/TEF) is a life-threatening birth defect that often occurs with other major birth defects (EA/TEF+). Despite advances in genetic testing, a molecular diagnosis can only be made in a minority of EA/TEF+ cases. Here, we analyzed clinical exome sequencing data and data from the DECIPHER database to determine the efficacy of exome sequencing in cases of EA/TEF+ and to identify phenotypic expansions involving EA/TEF. Among 67 individuals with EA/TEF+ referred for clinical exome sequencing, a definitive or probable diagnosis was made in 11 cases for an efficacy rate of 16% (11/67). This efficacy rate is significantly lower than that reported for other major birth defects, suggesting that polygenic, multifactorial, epigenetic, and/or environmental factors may play a particularly important role in EA/TEF pathogenesis. Our cohort included individuals with pathogenic or likely pathogenic variants that affect TCF4 and its downstream target NRXN1, and FANCA, FANCB, and FANCC, which are associated with Fanconi anemia. These cases, previously published case reports, and comparisons to other EA/TEF genes made using a machine learning algorithm, provide evidence in support of a potential pathogenic role for these genes in the development of EA/TEF.

Growth parameters in children with achondroplasia: A 7-year, prospective, multinational, observational study.

PURPOSE: This study was undertaken to collect baseline growth parameters in children with achondroplasia who might enroll in interventional trials of vosoritide, and to establish a historical control. METHODS: In this prospective, observational study, participants (≤17 years) underwent a detailed medical history and physical examination and were followed every 3 months until they finished participating in the study by enrolling in an interventional trial or withdrawing. RESULTS: A total of 363 children were enrolled (28 centers, 8 countries). Mean (SD) follow up was 20.4 (15.0) months. In participants <1 year, mean annualized growth velocity (AGV) was 11.6 cm/year for girls and 14.6 cm/year for boys. By age 1 year, mean AGV decreased to 7.4 cm/year in girls and 7.1 cm/year in boys. By age 10 years, mean AGV decreased to 3.6 cm/year for both sexes. Mean height z-score in participants <1 year was -2.5 for girls and -3.2 for boys and decreased up to the age 5 years (-5.3 for girls; -4.6 for boys). Girls and boys had a disproportionate upper-to-lower body segment ratio. Mean ratio was highest in participants aged <1 year (2.9 for girls; 2.8 for boys) and decreased gradually to approximately 2 in both sexes from 4 years of age onward. CONCLUSION: This study represents one of the largest datasets of prospectively collected medical and longitudinal growth data in children with achondroplasia. It serves as a robust historical control to measure therapeutic interventions against and to further delineate the natural history of this condition.

Phenotypic and genetic spectrum of ATP6V1A encephalopathy: a disorder of lysosomal homeostasis.

Vacuolar-type H+-ATPase (V-ATPase) is a multimeric complex present in a variety of cellular membranes that acts as an ATP-dependent proton pump and plays a key role in pH homeostasis and intracellular signalling pathways. In humans, 22 autosomal genes encode for a redundant set of subunits allowing the composition of diverse V-ATPase complexes with specific properties and expression. Sixteen subunits have been linked to human disease. Here we describe 26 patients harbouring 20 distinct pathogenic de novo missense ATP6V1A variants, mainly clustering within the ATP synthase α/ß family-nucleotide-binding domain. At a mean age of 7 years (extremes: 6 weeks, youngest deceased patient to 22 years, oldest patient) clinical pictures included early lethal encephalopathies with rapidly progressive massive brain atrophy, severe developmental epileptic encephalopathies and static intellectual disability with epilepsy. The first clinical manifestation was early hypotonia, in 70%; 81% developed epilepsy, manifested as developmental epileptic encephalopathies in 58% of the cohort and with infantile spasms in 62%; 63% of developmental epileptic encephalopathies failed to achieve any developmental, communicative or motor skills. Less severe outcomes were observed in 23% of patients who, at a mean age of 10 years and 6 months, exhibited moderate intellectual disability, with independent walking and variable epilepsy. None of the patients developed communicative language. Microcephaly (38%) and amelogenesis imperfecta/enamel dysplasia (42%) were additional clinical features. Brain MRI demonstrated hypomyelination and generalized atrophy in 68%. Atrophy was progressive in all eight individuals undergoing repeated MRIs. Fibroblasts of two patients with developmental epileptic encephalopathies showed decreased LAMP1 expression, Lysotracker staining and increased organelle pH, consistent with lysosomal impairment and loss of V-ATPase function. Fibroblasts of two patients with milder disease, exhibited a different phenotype with increased Lysotracker staining, decreased organelle pH and no significant modification in LAMP1 expression. Quantification of substrates for lysosomal enzymes in cellular extracts from four patients revealed discrete accumulation. Transmission electron microscopy of fibroblasts of four patients with variable severity and of induced pluripotent stem cell-derived neurons from two patients with developmental epileptic encephalopathies showed electron-dense inclusions, lipid droplets, osmiophilic material and lamellated membrane structures resembling phospholipids. Quantitative assessment in induced pluripotent stem cell-derived neurons identified significantly smaller lysosomes. ATP6V1A-related encephalopathy represents a new paradigm among lysosomal disorders. It results from a dysfunctional endo-lysosomal membrane protein causing altered pH homeostasis. Its pathophysiology implies intracellular accumulation of substrates whose composition remains unclear, and a combination of developmental brain abnormalities and neurodegenerative changes established during prenatal and early postanal development, whose severity is variably determined by specific pathogenic variants.

A novel, de novo intronic variant in POGZ causes White-Sutton syndrome.

White-Sutton syndrome (WHSUS), which is caused by heterozygous pathogenic variants in POGZ, is characterized by a spectrum of intellectual disabilities and global developmental delay with or without features of autism spectrum disorder. Additional features may include hypotonia, behavioral abnormalities, ophthalmic abnormalities, hearing loss, sleep apnea, microcephaly, dysmorphic facial features, and rarely, congenital diaphragmatic hernia (CDH). We present a 6-year-old female with features of WHSUS, including CDH, but with nondiagnostic clinical trio exome sequencing. Exome sequencing reanalysis revealed a heterozygous, de novo, intronic variant in POGZ (NM_015100.3:c.2546-20T>A). RNA sequencing revealed that this intronic variant leads to skipping of exon 18. This exon skipping event results in a frameshift with a predicted premature stop codon in the last exon and escape from nonsense-mediated mRNA decay (NMD). To our knowledge, this case is the first case of WHSUS caused by a de novo, intronic variant that is not near a canonical splice site within POGZ. These findings emphasize the limitations of standard clinical exome filtering algorithms and the importance of research reanalysis of exome data together with RNA sequencing to confirm a suspected diagnosis of WHSUS. As the sixth reported case of CDH with heterozygous pathogenic variants in POGZ and features consistent with WHSUS, this report supports the conclusion that WHSUS should be considered in the differential diagnosis for patients with syndromic CDH.

PRUNE1 c.933G>A synonymous variant induces exon 7 skipping, disrupts the DHHA2 domain, and leads to an atypical NMIHBA syndrome presentation: Case report and review of the literature.

Prune exopolyphosphatase-1 (PRUNE1) encodes a member of the aspartic acid-histidine-histidine (DHH) phosphodiesterase superfamily that regulates cell migration and proliferation during brain development. In 2015, biallelic PRUNE1 loss-of-function variants were identified to cause the neurodevelopmental disorder with microcephaly, hypotonia, and variable brain abnormalities (NMIHBA, OMIM#617481). NMIHBA is characterized by the namesake features and structural brain anomalies including thinning of the corpus callosum, cerebral and cerebellar atrophy, and delayed myelination. To date, 47 individuals have been reported in the literature, but the phenotypic spectrum of PRUNE1-related disorders and their causative variants remains to be characterized fully. Here, we report a novel homozygous PRUNE1 NM_021222.2:c.933G>A synonymous variant identified in a 6-year-old boy with intellectual and developmental disabilities, hypotonia, and spastic diplegia, but with the absence of microcephaly, brain anomalies, or seizures. Fibroblast RNA sequencing revealed that the PRUNE1 NM_021222.1:c.933G>A variant resulted in an in-frame skipping of the penultimate exon 7, removing 53 amino acids from an important protein domain. This case represents the first synonymous variant and the third pathogenic variant known to date affecting the DHH-associated domain (DHHA2 domain). These findings extend the genotypic and phenotypic spectrums in PRUNE1-related disorders and highlight the importance of considering synonymous splice site variants in atypical presentations.

A multidisciplinary approach and consensus statement to establish standards of care for Angelman syndrome.

BACKGROUND: Angelman syndrome (AS) is a rare neurogenetic disorder present in approximately 1/12,000 individuals and characterized by developmental delay, cognitive impairment, motor dysfunction, seizures, gastrointestinal concerns, and abnormal electroencephalographic background. AS is caused by absent expression of the paternally imprinted gene UBE3A in the central nervous system. Disparities in the management of AS are a major problem in preparing for precision therapies and occur even in patients with access to experts and recognized clinics. AS patients receive care based on collective provider experience due to limited evidence-based literature. We present a consensus statement and comprehensive literature review that proposes a standard of care practices for the management of AS at a critical time when therapeutics to alter the natural history of the disease are on the horizon. METHODS: We compiled the key recognized clinical features of AS based on consensus from a team of specialists managing patients with AS. Working groups were established to address each focus area with committees comprised of providers who manage >5 individuals. Committees developed management guidelines for their area of expertise. These were compiled into a final document to provide a framework for standardizing management. Evidence from the medical literature was also comprehensively reviewed. RESULTS: Areas covered by working groups in the consensus document include genetics, developmental medicine, psychology, general health concerns, neurology (including movement disorders), sleep, psychiatry, orthopedics, ophthalmology, communication, early intervention and therapies, and caregiver health. Working groups created frameworks, including flowcharts and tables, to help with quick access for providers. Data from the literature were incorporated to ensure providers had review of experiential versus evidence-based care guidelines. CONCLUSION: Standards of care in the management of AS are keys to ensure optimal care at a critical time when new disease-modifying therapies are emerging. This document is a framework for providers of all familiarity levels.

Delineation of a novel neurodevelopmental syndrome associated with PAX5 haploinsufficiency.

PAX5 is a transcription factor associated with abnormal posterior midbrain and cerebellum development in mice. PAX5 is highly loss-of-function intolerant and missense constrained, and has been identified as a candidate gene for autism spectrum disorder (ASD). We describe 16 individuals from 12 families who carry deletions involving PAX5 and surrounding genes, de novo frameshift variants that are likely to trigger nonsense-mediated mRNA decay, a rare stop-gain variant, or missense variants that affect conserved amino acid residues. Four of these individuals were published previously but without detailed clinical descriptions. All these individuals have been diagnosed with one or more neurodevelopmental phenotypes including delayed developmental milestones (DD), intellectual disability (ID), and/or ASD. Seizures were documented in four individuals. No recurrent patterns of brain magnetic resonance imaging (MRI) findings, structural birth defects, or dysmorphic features were observed. Our findings suggest that PAX5 haploinsufficiency causes a neurodevelopmental disorder whose cardinal features include DD, variable ID, and/or ASD.

Anxiety in Angelman Syndrome.

Angelman Syndrome (AS) is a neurodevelopmental disorder most commonly caused by the impaired expression of the maternal UBE3A gene on chromosome 15. Though anxiety has been identified as a frequently present characteristic in AS, there are limited studies examining anxiety in this population. Studies of anxiety in other neurodevelopmental disorders have found disorder specific symptoms of anxiety and age specific displays of anxiety symptoms. However, there is a consistent challenge in identifying anxiety in people with neurodevelopmental disorders given the lack of measurement instruments specifically designed for this population. Given the limited information about AS and anxiety, the aims of the current project were to (a) examine symptoms of anxiety in children with AS and (b) determine the correlates of anxiety in children with AS. Participants included 42 adult caregivers of youth with AS in the AS Natural History study who completed the Developmental Behavior Checklist (DBC). The results found that 26% of the sample demonstrated elevated symptoms of anxiety and established a relationship between elevated anxiety in youth with AS and higher levels of irritability, hyperactivity, self-absorbed behaviors, and disruptive/antisocial behaviors. Findings from this research provide a foundation for tailoring evidence-based assessments and treatments for youth with AS and anxiety.

Pharmacokinetics and Exposure-Response of Vosoritide in Children with Achondroplasia.

BACKGROUND AND OBJECTIVE: Vosoritide, an analog of C-type natriuretic peptide, has been developed for the treatment of children with achondroplasia. The pharmacokinetics of vosoritide and relationships between plasma exposure and efficacy, biomarkers, and safety endpoints were evaluated in a phase II, open-label, dose-escalation study (N = 35 patients aged 5-14 years who received daily subcutaneous injections for 24 months) and a phase III, double-blind, placebo-controlled study (N = 60 patients aged 5-18 years randomized to receive daily subcutaneous injections for 52 weeks). METHODS: Pharmacokinetic parameters for both studies were obtained from non-compartmental analysis. Potential correlations between vosoritide exposure and changes in annualized growth velocity, collagen type X marker (CXM; a biomarker of endochondral ossification), cyclic guanosine monophosphate (cGMP; a biomarker of pharmacological activity), heart rate, and systolic and diastolic blood pressures were then evaluated. RESULTS: The exposure-response relationships for changes in both annualized growth velocity and the CXM biomarker saturated at 15 µg/kg, while systemic pharmacological activity, as measured by urinary cGMP, was near maximal or saturated at exposures obtained at the highest dose studied (i.e. 30 µg/kg). This suggested that the additional bioactivity was likely in tissues not related to endochondral bone formation. In the phase III study, following subcutaneous administration at the recommended dose of 15 µg/kg to patients with achondroplasia aged 5-18 years, vosoritide was rapidly absorbed with a median time to maximal plasma concentration (Cmax) of 15 minutes, and cleared with a mean half-life of 27.9 minutes after 52 weeks of treatment. Vosoritide exposure (Cmax and area under the concentration-time curve [AUC]) was consistent across visits. No evidence of accumulation with once-daily dosing was observed. Total anti-vosoritide antibody (TAb) responses were detected in the serum of 25 of 60 (42%) treated patients in the phase III study, with no apparent impact of TAb development noted on annualized growth velocity or vosoritide exposure. Across the exposure range obtained with 15 µg/kg in the phase III study, no meaningful correlations between vosoritide plasma exposure and changes in annualized growth velocity or CXM, or changes from predose heart rate, and systolic or diastolic blood pressures were observed. CONCLUSIONS: The results support the recommended dose of vosoritide 15 µg/kg for once-daily subcutaneous administration in patients with achondroplasia aged ≥ 5 years whose epiphyses are not closed. CLINICAL TRIALS REGISTRATION: NCT02055157, NCT03197766, and NCT01603095.