DySMA - an Instrument to Monitor Swallowing Function in Children with Spinal Muscular Atrophy ages 0 to 24 Months: Development, Consensus, and Pilot Testing.

Background: The manifestation of bulbar symptoms, especially swallowing, is important for evaluating disease-modifying therapies for spinal muscular atrophy (SMA). Due to the lack of instruments, the topic is still underrepresented in research. Objective: This study aimed to develop a tool to monitor swallowing development in children aged 0 to 24 months with SMA. Methods: The method was guided by the COSMIN guidelines and followed a multi-stage Delphi process. The first step was a rapid review of swallowing outcomes in children with SMA younger than 24 months. In the second step, online group interviews with experts (n = 7) on dysphagia in infants were conducted, followed by an anonymous online survey among experts in infants with SMA (n = 19). A predefined consensus threshold for nominal scaled voting was set at≥75 % and for 5-point Likert scale voting at 1.25 of the interquartile range. The third step was the pilot test of the instrument, performed with three groups (healthy controls n = 8; pre-symptomatic n = 6, symptomatic n = 6). Results: Based on the multi-level interprofessional consensus, the DySMA comprises two parts (history and examination), ten categories, with 36 items. Implementation and scoring are clearly articulated and easy to implement. The pilot test showed that swallowing development could be recorded in all groups. Conclusion: The DySMA is well suited for monitoring swallowing development in pre-symptomatic and symptomatic treated infants with SMA. It can be performed in a time-efficient and interprofessional manner. The resulting score is comparable to results from other instruments measuring other domains, e.g., motor function.

Biallelic loss-of-function variants of SLC12A9 cause lysosome dysfunction and a syndromic neurodevelopmental disorder.

PURPOSE: Pathogenic variants of FIG4 generate enlarged lysosomes and neurological and developmental disorders. To identify additional genes regulating lysosomal volume, we carried out a genome-wide activation screen to detect suppression of enlarged lysosomes in FIG4-/- cells. METHODS: The CRISPR-a gene activation screen utilized sgRNAs from the promoters of protein-coding genes. Fluorescence-activated cell sorting separated cells with correction of the enlarged lysosomes from uncorrected cells. Patient variants of SLC12A9 were identified by exome or genome sequencing and studied by segregation analysis and clinical characterization. RESULTS: Overexpression of SLC12A9, a solute co-transporter, corrected lysosomal swelling in FIG4-/- cells. SLC12A9 (NP_064631.2) colocalized with LAMP2 at the lysosome membrane. Biallelic variants of SLC12A9 were identified in 3 unrelated probands with neurodevelopmental disorders. Common features included intellectual disability, skeletal and brain structural abnormalities, congenital heart defects, and hypopigmented hair. Patient 1 was homozygous for nonsense variant p.(Arg615∗), patient 2 was compound heterozygous for p.(Ser109Lysfs∗20) and a large deletion, and proband 3 was compound heterozygous for p.(Glu290Glyfs∗36) and p.(Asn552Lys). Fibroblasts from proband 1 contained enlarged lysosomes that were corrected by wild-type SLC12A9 cDNA. Patient variant p.(Asn552Lys) failed to correct the lysosomal defect. CONCLUSION: Impaired function of SLC12A9 results in enlarged lysosomes and a recessive disorder with a recognizable neurodevelopmental phenotype.

Association between Tubulointerstitial Nephritis and Uveitis Syndrome and Small-Vessel CNS Vasculitis: A Case of Polyautoimmunity.

INTRODUCTION: We report a case study of two male pediatric patients presenting with anterior uveitis and elevated renal function parameters. Both were diagnosed with tubulointerstitial nephritis and uveitis syndrome and subsequently developed diffuse cerebral symptoms such as headache, fatigue, and diziness. METHODS: Magnetic resonance images (MRIs) of the brain showed T2-hyperintense lesions with and without gadolinium enhancement leading to brain biopsy and diagnosis of small-vessel central nervous system (CNS) vasculitis in both cases. Both patients were treated according to BrainWorks small-vessel vasculitis protocol and symptoms vanished over the course of treatment. Follow-up MRIs up to 12 months after initiation of therapy showed no signs of recurrence indicating a monophasic disease. CONCLUSION: Small-vessel CNS vasculitis can occur simultaneously to other autoimmune diseases (ADs) in the scope of polyautoimmunity. As clinical findings of CNS vasculitis are often unspecific, neurological symptoms in nonneurological ADs should be adressed thoroughly. Under suspicion of small-vessel CNS vasculitis brain biopsy is still the gold standard and only secure way of definitive diagnosis.

High-sensitive cardiac troponin I (hs-cTnI) concentrations in newborns diagnosed with spinal muscular atrophy.

Background: Spinal muscular atrophy (SMA) is a genetic neurodegenerative disease leading to muscular weakness and premature death. Three therapeutic options are currently available including gene replacement therapy (GRT), which is potentially cardiotoxic. High-sensitive cardiac troponin I (hs-cTnI) is widely used to monitor potential cardiac contraindications or side effects of GRT, but reference data in healthy newborns are limited and lacking in neonates with SMA. The aim of this study is to determine the range of pre-therapeutic hs-cTnI concentrations in neonates with SMA and to provide guidance for the assessment of these values. Methods: Hs-cTnI levels, genetic and clinical data of 30 newborns (age range 2-26 days) with SMA were retrospectively collected from 6 German neuromuscular centers. In addition, hs-cTnI levels were measured in 16 neonates without SMA. Results: The median hs-cTnI concentration in neonates with SMA was 39.5 ng/L (range: 4-1205). In 16 newborns with SMA, hs-cTnI levels were above the test-specific upper reference limit (URL). Exploratory statistical analysis revealed no relevant correlation between hs-cTnI levels and gender, gestational age, mode of delivery, SMN2 copy number, symptoms of SMA or abnormal cardiac findings. Discussion: Our results suggest higher hs-cTnI plasma levels in newborns with and without SMA compared to assay-specific reference values generated in adults. Given the wide range of hs-cTnI values in neonates with SMA, hs-cTnI levels must be determined before treatment in each patient and post-treatment elevations should be interpreted in the context of the course rather than as individual values.

An autosomal-dominant childhood-onset disorder associated with pathogenic variants in VCP.

Valosin-containing protein (VCP) is an AAA+ ATPase that plays critical roles in multiple ubiquitin-dependent cellular processes. Dominant pathogenic variants in VCP are associated with adult-onset multisystem proteinopathy (MSP), which manifests as myopathy, bone disease, dementia, and/or motor neuron disease. Through GeneMatcher, we identified 13 unrelated individuals who harbor heterozygous VCP variants (12 de novo and 1 inherited) associated with a childhood-onset disorder characterized by developmental delay, intellectual disability, hypotonia, and macrocephaly. Trio exome sequencing or a multigene panel identified nine missense variants, two in-frame deletions, one frameshift, and one splicing variant. We performed in vitro functional studies and in silico modeling to investigate the impact of these variants on protein function. In contrast to MSP variants, most missense variants had decreased ATPase activity, and one caused hyperactivation. Other variants were predicted to cause haploinsufficiency, suggesting a loss-of-function mechanism. This cohort expands the spectrum of VCP-related disease to include neurodevelopmental disease presenting in childhood.

Natural History and Developmental Trajectories of Individuals With Disease-Causing Variants in STXBP1.

BACKGROUND AND OBJECTIVES: Pathogenic variants in STXBP1 are among the major genetic causes of neurodevelopmental disorders. Despite the increasing number of individuals diagnosed without a history of epilepsy, little is known about the natural history and developmental trajectories in this subgroup and endpoints for future therapeutic studies are limited to seizure control. METHODS: We performed a cross-sectional retrospective study using standardized questionnaires for clinicians and caregivers of individuals with STXBP1-related disorders capturing medical histories, genetic findings, and developmental outcomes. Motor and language function were assessed using Gross Motor Function Classification System (GMFCS) scores and a speech impairment score and were compared within and across clinically defined subgroups. RESULTS: We collected data of 71 individuals with STXBP1-related disorders, including 44 previously unreported individuals. Median age at inclusion was 5.3 years (interquartile range 3.5-9.3) with the oldest individual aged 43.8 years. Epilepsy was absent in 18/71 (25%) of individuals. The range of developmental outcomes was broad, including 2 individuals presenting with close to age-appropriate motor development. Twenty-nine of 61 individuals (48%) were able to walk unassisted, and 24/69 (35%) were able to speak single words. Individuals without epilepsy presented with a similar onset and spectrum of phenotypic features but had lower GMFCS scores (median 3 vs 4, p < 0.01) than individuals with epilepsy. Individuals with epileptic spasms were less likely to walk unassisted than individuals with other seizure types (6% vs 58%, p < 0.01). Individuals with early epilepsy onset had higher speech impairment scores (p = 0.02) than individuals with later epilepsy onset. DISCUSSION: We expand the spectrum of STXBP1-related disorders and provide clinical features and developmental trajectories in individuals with and without a history of epilepsy. Individuals with epilepsy, in particular epileptic spasms, and neonatal or early-onset presented with less favorable motor and language functional outcomes compared with individuals without epilepsy. These findings identify children at risk for severe disease and can serve as comparator for future interventional studies in STXBP1-related disorders.

CNS Manifestations in Mucolipidosis Type II-A Retrospective Analysis of Longitudinal Data on Neurocognitive Development and Neuroimaging in Eleven Patients.

Mucolipidosis type II (MLII), an ultra-rare lysosomal storage disorder, manifests as a fatal multi-systemic disease. Mental inhibition and progressive neurodegeneration are commonly reported disease manifestations. Nevertheless, longitudinal data on neurocognitive testing and neuroimaging lack in current literature. This study aimed to provide details on central nervous system manifestations in MLII. All MLII patients with at least one standardized developmental assessment performed between 2005 and 2022 were included by retrospective chart review. A multiple mixed linear regression model was applied. Eleven patients with a median age of 34.0 months (range 1.6-159.6) underwent 32 neurocognitive and 28 adaptive behaviour assessments as well as 14 brain magnetic resonance imagings. The scales used were mainly BSID-III (42%) and VABS-II (47%). Neurocognitive testing (per patient: mean 2.9, standard deviation (SD) 2.0) performed over 0-52.1 months (median 12.1) revealed profound impairment with a mean developmental quotient of 36.7% (SD 20.4) at last assessment. The patients showed sustained development; on average, they gained 0.28 age-equivalent score points per month (confidence interval 0.17-0.38). Apart from common (63%) cervical spinal stenosis, neuroimaging revealed unspecific, non-progressive abnormalities (i.e., mild brain atrophy, white matter lesions). In summary, MLII is associated with profound developmental impairment, but not with neurodegeneration and neurocognitive decline.

Experiences of Health Care and Psychosocial Needs in Parents of Children with Spinal Muscular Atrophy.

Spinal muscular atrophy (SMA) is a neurodegenerative disorder that is characterized by progressive weakness, respiratory insufficiency, and dysphagia. Due to symptom burden and disease progress, its care management and impact on daily life can severely burden the families of affected children. The objectives of this study are (1) to explore the health care experiences and (2) to investigate the psychosocial needs of the parents of children with SMA. In total, 29 parents of patients with SMA participated in our study. All children received supportive therapy (e.g., physiotherapy) and most were dependent on medical equipment. Parents perceived the health care positively regarding team quality, communication and access to medical care. An assessment of the impact of the child's health on the family (e.g., stressors, burden, consequences) is not routinely integrated into care. On average, parents reported low to medium levels of psychosocial needs. Due to the complex health care needs of SMA patients, the health care experiences of parents can provide relevant information on care delivery. To enhance the inclusion of psychosocial and emotional issues, as well as family impact, into routine health care, health care providers should be sensitive towards parental needs for consistency in the health care team and emotional aspects and, if applicable, address them proactively.

Single substitution in H3.3G34 alters DNMT3A recruitment to cause progressive neurodegeneration.

Germline histone H3.3 amino acid substitutions, including H3.3G34R/V, cause severe neurodevelopmental syndromes. To understand how these mutations impact brain development, we generated H3.3G34R/V/W knock-in mice and identified strikingly distinct developmental defects for each mutation. H3.3G34R-mutants exhibited progressive microcephaly and neurodegeneration, with abnormal accumulation of disease-associated microglia and concurrent neuronal depletion. G34R severely decreased H3K36me2 on the mutant H3.3 tail, impairing recruitment of DNA methyltransferase DNMT3A and its redistribution on chromatin. These changes were concurrent with sustained expression of complement and other innate immune genes possibly through loss of non-CG (CH) methylation and silencing of neuronal gene promoters through aberrant CG methylation. Complement expression in G34R brains may lead to neuroinflammation possibly accounting for progressive neurodegeneration. Our study reveals that H3.3G34-substitutions have differential impact on the epigenome, which underlie the diverse phenotypes observed, and uncovers potential roles for H3K36me2 and DNMT3A-dependent CH-methylation in modulating synaptic pruning and neuroinflammation in post-natal brains.

Retrospective Pediatric Cohort Study Validates NEOS Score and Demonstrates Applicability in Children With Anti-NMDAR Encephalitis.

BACKGROUND AND OBJECTIVES: Anti-N-methyl-D-aspartate receptor encephalitis (NMDARE) is the most common form of autoimmune encephalitis in children and adults. Although our understanding of the disease mechanisms has progressed, little is known about estimating patient outcomes. Therefore, the NEOS (anti-NMDAR Encephalitis One-Year Functional Status) score was introduced as a tool to predict disease progression in NMDARE. Developed in a mixed-age cohort, it currently remains unclear whether NEOS can be optimized for pediatric NMDARE. METHODS: This retrospective observational study aimed to validate NEOS in a large pediatric-only cohort of 59 patients (median age of 8 years). We reconstructed the original score, adapted it, evaluated additional variables, and assessed its predictive power (median follow-up of 20 months). Generalized linear regression models were used to examine predictability of binary outcomes based on the modified Rankin Scale (mRS). In addition, neuropsychological test results were investigated as alternative cognitive outcome. RESULTS: The NEOS score reliably predicted poor clinical outcome (mRS ≥3) in children in the first year after diagnosis (p = 0.0014) and beyond (p = 0.036, 16 months after diagnosis). A score adapted to the pediatric cohort by adjusting the cutoffs of the 5 NEOS components did not improve predictive power. In addition to these 5 variables, further patient characteristics such as the "Herpes simplex virus encephalitis (HSE) status" and "age at disease onset" influenced predictability and could potentially be useful to define risk groups. NEOS also predicted cognitive outcome with higher scores associated with deficits of executive function (p = 0.048) and memory (p = 0.043). DISCUSSION: Our data support the applicability of the NEOS score in children with NMDARE. Although not yet validated in prospective studies, NEOS also predicted cognitive impairment in our cohort. Consequently, the score could help identify patients at risk of poor overall clinical outcome and poor cognitive outcome and thus aid in selecting not only optimized initial therapies for these patients but also cognitive rehabilitation to improve long-term outcomes.

INPP4A-related genetic and phenotypic spectrum and functional relevance of subcellular targeting of INPP4A isoforms.

Type I inositol polyphosphate-4-phosphatase (INPP4A) belongs to the group of phosphoinositide phosphatases controlling proliferation, apoptosis, and endosome function by hydrolyzing phosphatidylinositol 3,4-bisphosphate. INPP4A produces multiple transcripts encoding shorter and longer INPP4A isoforms with hydrophilic or hydrophobic C-terminus. Biallelic INPP4A truncating variants cause a spectrum of neurodevelopmental disorders ranging from moderate intellectual disability to postnatal microcephaly with developmental and epileptic encephalopathy and (ponto)cerebellar hypoplasia. We report a girl with the novel homozygous INPP4A variant NM_001134224.2:c.2840del/p.(Gly947Glufs*12) (isoform d). She presented with postnatal microcephaly, global developmental delay, visual impairment, myoclonic seizures, and pontocerebellar hypoplasia and died at the age of 27 months. The level of mutant INPP4A mRNAs in proband-derived leukocytes was comparable to controls suggesting production of C-terminally altered INPP4A isoforms. We transiently expressed eGFP-tagged INPP4A isoform a (NM_004027.3) wildtype and p.(Gly908Glufs*12) mutant [p.(Gly947Glufs*12) according to NM_001134224.2] as well as INPP4A isoform b (NM_001566.2) wildtype and p.(Asp915Alafs*2) mutant, previously reported in family members with moderate intellectual disability, in HeLa cells and determined their subcellular distributions. While INPP4A isoform a was preferentially found in perinuclear clusters co-localizing with the GTPase Rab5, isoform b showed a net-like distribution, possibly localizing near and/or on microtubules. Quantification of intracellular localization patterns of the two INPP4A mutants revealed significant differences compared with the respective wildtype and similarity with each other. Our data suggests an important non-redundant function of INPP4A isoforms with hydrophobic or hydrophilic C-terminus in the brain.

Flexible endoscopic evaluation of swallowing in children with type 1 spinal muscular atrophy.

PURPOSE: This study aimed to report on implementing flexible endoscopic evaluation of swallowing (FEES) in infants and toddlers with type 1 spinal muscular atrophy (SMA). In addition, a comparison of FEES results and clinical scores was carried out. METHODS: A prospective pilot study was conducted including ten symptomatic children with SMA type 1 (two SMN2 copies). They started treatment with one of the three currently approved therapies for SMA at a median age of 3.8 months (range 0.7-8.9). FEES was performed according to a standard protocol using Penetration-Aspiration Scale (PAS) and Murray Secretion Scale as a primary outcome. The Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP-INTEND) for motor function, Neuromuscular Disease Swallowing Status Scale (NdSSS), Oral and Swallowing Abilities Tool (OrSAT), and single clinical swallowing-related parameters were also assessed. RESULTS: Distinct swallowing disorders were already evident in eight children at inclusion. The most common findings from FEES were pharyngeal secretion pooling, penetration, and aspiration of saliva and food as well as delayed initiation of swallowing. Despite an average increase in motor function, no comparable improvement was found in swallowing function. None of the surveyed clinical scores showed a significant dependence on PAS in a mixed linear model. CONCLUSIONS: Valuable information regarding the status of dysphagia can be gathered endoscopically, particularly concerning secretion management and when oral intake is limited. Currently available clinical tools for children with type 1 may represent a change in nutritional status but are not yet mature enough to conclude swallowing ability. Further development is still required.

Health-Related Quality of Life and mental health of families with children and adolescents affected by rare diseases and high disease burden: the perspective of affected children and their siblings.

BACKGROUND: Advances in genetic and pharmaceutical technology and pediatric care have enabled treatment options for an increasing number of rare diseases in affected children. However, as current treatment options are primarily of palliative nature, the Health-Related Quality of Life (HRQoL) and mental health of this impaired population and their siblings are of increasing importance. Among children and adolescents with rare diseases, those who are technology-dependent carry a high disease burden and are selected as the target population in our study. In a cross-sectional observational design, the children's HRQoL was assessed with the DISABKIDS (DCGM-37) as well as KIDSCREEN-27, while mental health was assessed with the Strengths and Difficulties Questionnaire (SDQ) by both the affected children, their parents, and siblings. RESULTS: Results of the study sample were compared to normative data. Affected children scored significantly lower than the norm on almost all HRQoL subscales as reported by parent and child. From the parental perspective, more mental health subscales were significantly impaired compared to the child's perspective. Siblings showed no impairment in HRQoL as well as significantly fewer behavioral problems and higher prosocial behavior regarding their mental health compared to the norm. CONCLUSION: Children and adolescents with rare diseases seem particularly impaired in social and emotional aspects of HRQoL and mental health. Interventions may focus primarily on promoting social skills, fostering prosocial behavior and peer relationships.

Variant-specific effects define the phenotypic spectrum of HNRNPH2-associated neurodevelopmental disorders in males.

Bain type of X-linked syndromic intellectual developmental disorder, caused by pathogenic missense variants in HRNRPH2, was initially described in six female individuals affected by moderate-to-severe neurodevelopmental delay. Although it was initially postulated that the condition would not be compatible with life in males, several affected male individuals harboring pathogenic variants in HNRNPH2 have since been documented. However, functional in-vitro analyses of identified variants have not been performed and, therefore, possible genotype-phenotype correlations remain elusive. Here, we present eight male individuals, including a pair of monozygotic twins, harboring pathogenic or likely pathogenic HNRNPH2 variants. Notably, we present the first individuals harboring nonsense or frameshift variants who, similarly to an individual harboring a de novo p.(Arg29Cys) variant within the first quasi-RNA-recognition motif (qRRM), displayed mild developmental delay, and developed mostly autistic features and/or psychiatric co-morbidities. Additionally, we present two individuals harboring a recurrent de novo p.(Arg114Trp), within the second qRRM, who had a severe neurodevelopmental delay with seizures. Functional characterization of the three most common HNRNPH2 missense variants revealed dysfunctional nucleocytoplasmic shuttling of proteins harboring the p.(Arg206Gln) and p.(Pro209Leu) variants, located within the nuclear localization signal, whereas proteins with p.(Arg114Trp) showed reduced interaction with members of the large assembly of splicing regulators (LASR). Moreover, RNA-sequencing of primary fibroblasts of the individual harboring the p.(Arg114Trp) revealed substantial alterations in the regulation of alternative splicing along with global transcriptome changes. Thus, we further expand the clinical and variant spectrum in HNRNPH2-associated disease in males and provide novel molecular insights suggesting the disorder to be a spliceopathy on the molecular level.

Gene replacement therapy with onasemnogene abeparvovec in children with spinal muscular atrophy aged 24 months or younger and bodyweight up to 15 kg: an observational cohort study.

BACKGROUND: Given the novelty of gene replacement therapy with onasemnogene abeparvovec in spinal muscular atrophy, efficacy and safety data are limited, especially for children older than 24 months, those weighing more than 8·5 kg, and those who have received nusinersen. We aimed to provide real-world data on motor function and safety after gene replacement therapy in different patient subgroups. METHODS: We did a protocol-based, multicentre prospective observational study between Sept 21, 2019, and April 20, 2021, in 18 paediatric neuromuscular centres in Germany and Austria. All children with spinal muscular atrophy types 1 and 2 receiving onasemnogene abeparvovec were included in our cohort, and there were no specific exclusion criteria. Motor function was assessed at the time of gene replacement therapy and 6 months afterwards, using the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND) and Hammersmith Functional Motor Scale-Expanded (HFMSE) scores. Additionally, in children pretreated with nusinersen, motor function was assessed before and after treatment switch. Off-target adverse events were analysed with a focus on liver function, thrombocytopaenia, and potential cardiotoxicity. FINDINGS: 76 children (58 pretreated with nusinersen and 18 who were nusinersen naive) with spinal muscular atrophy were treated with onasemnogene abeparvovec at a mean age of 16·8 months (range 0·8-59·0, IQR 9-23) and a mean weight of 9·1 kg (range 4·0-15·0, IQR 7·4-10·6). In 60 patients with available data, 49 had a significant improvement on the CHOP-INTEND score (≥4 points) and HFMSE score (≥3 points). Mean CHOP INTEND scores increased significantly in the 6 months after therapy in children younger than 8 months (n=16; mean change 13·8 [SD 8·5]; p<0·0001) and children aged between 8 and 24 months (n=34; 7·7 [SD 5·2]; p<0·0001), but not in children older than 24 months (n=6; 2·5 [SD 5·2]; p=1·00). In the 45 children pretreated with nusinersen and had available data, CHOP INTEND score increased by 8·8 points (p=0·0003) at 6 months after gene replacement therapy. No acute complications occurred during infusion of onasemnogene abeparvovec, but 56 (74%) patients had treatment-related side-effects. Serious adverse events occurred in eight (11%) children. Liver enzyme elevation significantly increased with age and weight at treatment. Six (8%) patients developed acute liver dysfunction. Other adverse events included pyrexia (n=47 [62%]), vomiting or loss of appetite (41 [54%]), and thrombocytopenia (n=59 [78%]). Prednisolone treatment was significantly prolonged with a mean duration of 15·7 weeks (IQR 9-19), mainly due to liver enzyme elevation. Cardiac adverse events were rare; only two patients had abnormal echocardiogram and echocardiography findings. INTERPRETATION: This study provides class IV evidence that children with spinal muscular atrophy aged 24 months or younger and patients pretreated with nusinersen significantly benefit from gene replacement therapy, but adverse events can be severe and need to be closely monitored. FUNDING: None. TRANSLATION: For the German translation of the abstract see Supplementary Materials section.

Dominant KPNA3 Mutations Cause Infantile-Onset Hereditary Spastic Paraplegia.

OBJECTIVE: Hereditary spastic paraplegia (HSP) is a highly heterogeneous neurologic disorder characterized by lower-extremity spasticity. Here, we set out to determine the genetic basis of an autosomal dominant, pure, and infantile-onset form of HSP in a cohort of 8 patients with a uniform clinical presentation. METHODS: Trio whole-exome sequencing was used in 5 index patients with infantile-onset pure HSP to determine the genetic cause of disease. The functional impact of identified genetic variants was verified using bioinformatics and complementary cellular and biochemical assays. RESULTS: Distinct heterozygous KPNA3 missense variants were found to segregate with the clinical phenotype in 8 patients; in 4 of them KPNA3 variants had occurred de novo. Mutant karyopherin-α3 proteins exhibited a variable pattern of altered expression level, subcellular distribution, and protein interaction. INTERPRETATION: Our genetic findings implicate heterozygous variants in KPNA3 as a novel cause for autosomal dominant, early-onset, and pure HSP. Mutant karyopherin-α3 proteins display varying deficits in molecular and cellular functions, thus, for the first time, implicating dysfunctional nucleocytoplasmic shuttling as a novel pathomechanism causing HSP. ANN NEUROL 2021;90:738-750.

Prevalence and clinical prediction of mitochondrial disorders in a large neuropediatric cohort.

Neurological symptoms are frequent and often a leading feature of childhood-onset mitochondrial disorders (MD) but the exact incidence of MD in unselected neuropediatric patients is unknown. Their early detection is desirable due to a potentially rapid clinical decline and the availability of management options. In 491 children with neurological symptoms, a comprehensive diagnostic work-up including exome sequencing was performed. The success rate in terms of a molecular genetic diagnosis within our cohort was 51%. Disease-causing variants in a mitochondria-associated gene were detected in 12% of solved cases. In order to facilitate the clinical identification of MDs within neuropediatric cohorts, we have created an easy-to-use bedside-tool, the MDC-NP. In our cohort, the MDC-NP predicted disease conditions related to MDs with a sensitivity of 0.83, and a specificity of 0.96.

ANK3 related neurodevelopmental disorders: expanding the spectrum of heterozygous loss-of-function variants.

ANK3 encodes multiple isoforms of ankyrin-G, resulting in variegated tissue expression and function, especially regarding its role in neuronal development. Based on the zygosity, location, and type, ANK3 variants result in different neurodevelopmental phenotypes. Autism spectrum disorder has been associated with heterozygous missense variants in ANK3, whereas a more severe neurodevelopmental phenotype is caused by isoform-dependent, autosomal-dominant, or autosomal-recessive loss-of-function variants. Here, we present four individuals affected by a variable neurodevelopmental phenotype harboring a heterozygous frameshift or nonsense variant affecting all ANK3 transcripts. Thus, we provide further evidence of an isoform-based phenotypic continuum underlying ANK3-associated pathologies and expand its phenotypic spectrum.

Whole-Exome Sequencing in Critically Ill Neonates and Infants: Diagnostic Yield and Predictability of Monogenic Diagnosis.

INTRODUCTION: Monogenic diseases play an important role in critically ill neonates and infants treated in the intensive care unit. This study aimed to determine the diagnostic yield of whole-exome sequencing (WES) for monogenic diseases and identify phenotypes more likely associated with a genetic etiology. METHODS: From March 2017 to 2020, a comprehensive diagnostic workup including WES in a single academic center was performed in 61 unrelated, critically ill neonates and infants with an unknown underlying disease within the first year of life. We conducted 59 trio-WES, 1 duo-WES, and 1 single-WES analyses. Symptoms were classified according to the Human Phenotype Ontology. RESULTS: The overall molecular genetic diagnostic rate within our cohort was 46% (28/61) and 50% (15/30) in the subgroup of preterm neonates. Identifying the genetic cause of disease facilitates individualized management in the majority of patients. A positive or negative predictive power of specific clinical features for a genetic diagnosis could not be observed. CONCLUSION: WES is a powerful noninvasive diagnostic tool in critically ill neonates and infants with a high diagnostic rate. We recommend initiating WES as early as possible due to the impact on management and family counseling. Recommendations regarding the clinical utility of WES in critically ill neonates and infants should not be based on the phenotype alone. Here, we present a clinical workflow for the application of WES for critically ill neonates and infants in an interdisciplinary setting.