Clonal hematopoiesis as a pitfall in germline variant interpretation in the context of Mendelian disorders.

Clonal hematopoiesis because of somatic mutations in hematopoietic stem/progenitor cells is an age-related phenomenon and commonly observed when sequencing blood DNA in elderly individuals. Several genes that are implicated in clonal hematopoiesis are also associated with Mendelian disorders when mutated in the germline, potentially leading to variant misinterpretation. We performed a literature search to identify genes associated with age-related clonal hematopoiesis followed by an OMIM query to identify the subset of genes in which germline variants are associated with Mendelian disorders. We retrospectively screened for diagnostic cases in which the presence of age-related clonal hematopoiesis confounded exome sequencing data interpretation. We found 58 genes in which somatic mutations are implicated in clonal hematopoiesis, while germline variants in the same genes are associated with Mendelian (mostly neurodevelopmental) disorders. Using five selected cases of individuals with suspected monogenic disorders, we illustrate how clonal hematopoiesis in either variant databases or exome sequencing datasets poses a pitfall, potentially leading to variant misclassification and erroneous conclusions regarding gene-disease associations.

A Homozygous PTRHD1 Missense Variant (p.Arg122Gln) in an Individual with Intellectual Disability, Generalized Epilepsy, and Juvenile Parkinsonism.

Biallelic variants in PTRHD1 have been associated with autosomal recessive intellectual disability, spasticity, and juvenile parkinsonism, with few reported cases. Here, we present the clinical and genetic findings of a female of Austrian origin exhibiting infantile neurodevelopmental abnormalities, intellectual disability, and childhood-onset parkinsonian features, consistent with the established phenotypic spectrum. Notably, she developed genetic generalized epilepsy at age 4, persisting into adulthood. Using diagnostic exome sequencing, we identified a homozygous missense variant (c.365G > A, p.(Arg122Gln)) in PTRHD1 (NM_001013663). In summary, our findings not only support the existing link between biallelic PTRHD1 variants and parkinsonism with neurodevelopmental abnormalities but also suggest a potential extension of the phenotypic spectrum to include generalized epilepsy.

ARF1-related disorder: phenotypic and molecular spectrum.

PURPOSE: ARF1 was previously implicated in periventricular nodular heterotopia (PVNH) in only five individuals and systematic clinical characterisation was not available. The aim of this study is to provide a comprehensive description of the phenotypic and genotypic spectrum of ARF1-related neurodevelopmental disorder. METHODS: We collected detailed phenotypes of an international cohort of individuals (n=17) with ARF1 variants assembled through the GeneMatcher platform. Missense variants were structurally modelled, and the impact of several were functionally validated. RESULTS: De novo variants (10 missense, 1 frameshift, 1 splice altering resulting in 9 residues insertion) in ARF1 were identified among 17 unrelated individuals. Detailed phenotypes included intellectual disability (ID), microcephaly, seizures and PVNH. No specific facial characteristics were consistent across all cases, however microretrognathia was common. Various hearing and visual defects were recurrent, and interestingly, some inflammatory features were reported. MRI of the brain frequently showed abnormalities consistent with a neuronal migration disorder. CONCLUSION: We confirm the role of ARF1 in an autosomal dominant syndrome with a phenotypic spectrum including severe ID, microcephaly, seizures and PVNH due to impaired neuronal migration.

A de novo missense variant in GABRA4 alters receptor function in an epileptic and neurodevelopmental phenotype.

Variants in γ-aminobutyric acid A (GABAA ) receptor genes cause different forms of epilepsy and neurodevelopmental disorders. To date, GABRA4, encoding the α4-subunit, has not been associated with a monogenic condition. However, preclinical evidence points toward seizure susceptibility. Here, we report a de novo missense variant in GABRA4 (c.899C>T, p.Thr300Ile) in an individual with early-onset drug-resistant epilepsy and neurodevelopmental abnormalities. An electrophysiological characterization of the variant, which is located in the pore-forming domain, shows accelerated desensitization and a lack of seizure-protective neurosteroid function. In conclusion, our findings strongly suggest an association between de novo variation in GABRA4 and a neurodevelopmental disorder with epilepsy.

Short-term and sustained clinical response following thymectomy in patients with myasthenia gravis.

BACKGROUND AND PURPOSE: This study was undertaken to investigate short- and long-term outcome following thymectomy in patients with acetylcholine receptor antibody (AChR-Ab)-positive myasthenia gravis (MG). METHODS: Rates of clinical response (defined as minimal manifestation, pharmacological remission, or complete stable remission) lasting for at least 1 year were retrospectively analyzed using Cox proportional hazard models. The occurrence of relapses was recorded during follow-up. Clinical factors associated with achieving an initial or a sustained response were analyzed. RESULTS: Ninety-four patients with a median age of 33 years (interquartile range [IQR] = 22-51), 68% with nonthymomatous MG and 32% with thymoma-associated MG, were included. An initial clinical response was reached in 72% (68/94). Neither sex, age at onset, thymus histology, delay to surgery after disease onset, surgical approach, corticosteroid treatment, nor clinical severity before thymectomy was significantly associated with achieving this endpoint. During long-term follow-up (median = 89.5 months, IQR = 46-189.5), only half of the patients with an initial response (34/68) had a sustained response without relapses. No clinical factors predicted whether the response would become sustained. In patients without immunosuppressive treatment before thymectomy (n = 24), a high AChR-Ab reduction rate after thymectomy was associated with a higher likelihood of achieving an initial response (p = 0.03). CONCLUSIONS: Sustained long-term clinical response of MG patients after thymectomy is significantly lower than the initial response rates would suggest. The observation that none of the evaluated clinical factors was associated with a worse outcome supports the current clinical practice of patient selection for thymectomy. The relative decline of AChR-Abs after surgery appears to be a promising prognostic marker.

Clinico-genetic spectrum of limb-girdle muscular weakness in Austria: A multicentre cohort study.

BACKGROUND AND PURPOSE: Hereditary myopathies with limb-girdle muscular weakness (LGW) are a genetically heterogeneous group of disorders, in which molecular diagnosis remains challenging. Our aim was to present a detailed clinical and genetic characterization of a large cohort of patients with LGW. METHODS: This nationwide cohort study included patients with LGW suspected to be associated with hereditary myopathies. Parameters associated with specific genetic aetiologies were evaluated, and we further assessed how they predicted the detection of causative variants by conducting genetic analyses. RESULTS: Molecular diagnoses were identified in 62.0% (75/121) of the cohort, with a higher proportion of patients diagnosed by next-generation sequencing (NGS) than by single-gene testing (77.3% vs. 22.7% of solved cases). The median (interquartile range) time from onset to genetic diagnosis was 8.9 (3.7-19.9) and 17.8 (7.9-27.8) years for single-gene testing and NGS, respectively. The most common diagnoses were myopathies associated with variants in CAPN3 (n = 9), FKRP (n = 9), ANO5 (n = 8), DYSF (n = 8) and SGCA (n = 5), which together accounted for 32.2% of the cohort. Younger age at disease onset (p = 0.043), >10× elevated creatine kinase activity levels (p = 0.024) and myopathic electromyography findings (p = 0.007) were significantly associated with the detection of causative variants. CONCLUSIONS: Our findings suggest that an earlier use of NGS in patients with LGW is needed to avoid long diagnostic delays. We further present parameters predictive of a molecular diagnosis that may help to select patients for genetic analyses, especially in centres with limited access to sequencing.

Scoring Algorithm-Based Genomic Testing in Dystonia: A Prospective Validation Study.

BACKGROUND: Despite the established value of genomic testing strategies, practice guidelines for their use do not exist in many indications. OBJECTIVES: We sought to validate a recently introduced scoring algorithm for dystonia, predicting the diagnostic utility of whole-exome sequencing (WES) based on individual phenotypic aspects (age-at-onset, body distribution, presenting comorbidity). METHODS: We prospectively enrolled a set of 209 dystonia-affected families and obtained summary scores (0-5 points) according to the algorithm. Singleton (N = 146), duo (N = 11), and trio (N = 52) WES data were generated to identify genetic diagnoses. RESULTS: Diagnostic yield was highest (51%) among individuals with a summary score of 5, corresponding to a manifestation of early-onset segmental or generalized dystonia with coexisting non-movement disorder-related neurological symptoms. Sensitivity and specificity at the previously suggested threshold for implementation of WES (3 points) was 96% and 52%, with area under the curve of 0.81. CONCLUSIONS: The algorithm is a useful predictive tool and could be integrated into dystonia routine diagnostic protocols. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson Movement Disorder Society.

The TGF-b/SOX4 axis and ROS-driven autophagy co-mediate CD39 expression in regulatory T-cells.

The ectonucleotidase CD39 on human regulatory T-cells (Treg) is an important immune regulator which is dysregulated in autoimmune diseases and cancer immunosuppression. We here define that CD39 expression on Treg is independent of the Treg-specific transcription factors FOXP3 and HELIOS and promoted by canonical TGF-b- and mTOR-signaling. Furthermore, the TGF-b mediated upregulation of CD39 is counteracted by reactive oxygen species (ROS)-driven autophagy. In line, CD39+ peripheral blood Treg constitute a distinct lineage with low autophagic flux and absent ROS production. Patients with rare genetic defects in autophagy show supraphysiological levels of CD39+ Treg, validating our observations in vivo. These biological processes rely on a distinct transcriptional program with CD39+ Treg expressing low levels of two genes with putative involvement in autophagy, NEFL and PLAC8. Furthermore, the TGF-b downstream transcription factor SOX4 is selectively upregulated in CD39+ Treg. Overexpression of SOX4 in Treg strongly increases CD39 expression, while Crispr/Cas9-mediated knockout of SOX4 in Treg has the opposing effect. Thus, we identify a crucial role of SOX4 in immune regulation and provide new insights involving the interplay of tolerogenic cues and autophagy in Treg.

Diagnostic exome sequencing in non-acquired focal epilepsies highlights a major role of GATOR1 complex genes.

BACKGROUND: The genetic architecture of non-acquired focal epilepsies (NAFEs) becomes increasingly unravelled using genome-wide sequencing datasets. However, it remains to be determined how this emerging knowledge can be translated into a diagnostic setting. To bridge this gap, we assessed the diagnostic outcomes of exome sequencing (ES) in NAFE. METHODS: 112 deeply phenotyped patients with NAFE were included in the study. Diagnostic ES was performed, followed by a screen to detect variants of uncertain significance (VUSs) in 15 well-established focal epilepsy genes. Explorative gene prioritisation was used to identify possible novel candidate aetiologies with so far limited evidence for NAFE. RESULTS: ES identified pathogenic or likely pathogenic (ie, diagnostic) variants in 13/112 patients (12%) in the genes DEPDC5, NPRL3, GABRG2, SCN1A, PCDH19 and STX1B. Two pathogenic variants were microdeletions involving NPRL3 and PCDH19. Nine of the 13 diagnostic variants (69%) were found in genes of the GATOR1 complex, a potentially druggable target involved in the mammalian target of rapamycin (mTOR) signalling pathway. In addition, 17 VUSs in focal epilepsy genes and 6 rare variants in candidate genes (MTOR, KCNA2, RBFOX1 and SCN3A) were detected. Five patients with reported variants had double hits in different genes, suggesting a possible (oligogenic) role of multiple rare variants. CONCLUSION: This study underscores the molecular heterogeneity of NAFE with GATOR1 complex genes representing the by far most relevant genetic aetiology known to date. Although the diagnostic yield is lower compared with severe early-onset epilepsies, the high rate of VUSs and candidate variants suggests a further increase in future years.

Testing association of rare genetic variants with resistance to three common antiseizure medications.

OBJECTIVE: Drug resistance is a major concern in the treatment of individuals with epilepsy. No genetic markers for resistance to individual antiseizure medication (ASM) have yet been identified. We aimed to identify the role of rare genetic variants in drug resistance for three common ASMs: levetiracetam (LEV), lamotrigine (LTG), and valproic acid (VPA). METHODS: A cohort of 1622 individuals of European descent with epilepsy was deeply phenotyped and underwent whole exome sequencing (WES), comprising 575 taking LEV, 826 LTG, and 782 VPA. We performed gene- and gene set-based collapsing analyses comparing responders and nonresponders to the three drugs to determine the burden of different categories of rare genetic variants. RESULTS: We observed a marginally significant enrichment of rare missense, truncating, and splice region variants in individuals who were resistant to VPA compared to VPA responders for genes involved in VPA pharmacokinetics. We also found a borderline significant enrichment of truncating and splice region variants in the synaptic vesicle glycoprotein (SV2) gene family in nonresponders compared to responders to LEV. We did not see any significant enrichment using a gene-based approach. SIGNIFICANCE: In our pharmacogenetic study, we identified a slightly increased burden of damaging variants in gene groups related to drug kinetics or targeting in individuals presenting with drug resistance to VPA or LEV. Such variants could thus determine a genetic contribution to drug resistance.

Rare Human Missense Variants can affect the Function of Disease-Relevant Proteins by Loss and Gain of Peroxisomal Targeting Motifs.

Single nucleotide variants (SNVs) resulting in amino acid substitutions (i.e., missense variants) can affect protein localization by changing or creating new targeting signals. Here, we studied the potential of naturally occurring SNVs from the Genome Aggregation Database (gnomAD) to result in the loss of an existing peroxisomal targeting signal 1 (PTS1) or gain of a novel PTS1 leading to mistargeting of cytosolic proteins to peroxisomes. Filtering down from 32,985 SNVs resulting in missense mutations within the C-terminal tripeptide of 23,064 human proteins, based on gene annotation data and computational prediction, we selected six SNVs for experimental testing of loss of function (LoF) of the PTS1 motif and five SNVs in cytosolic proteins for gain in PTS1-mediated peroxisome import (GoF). Experimental verification by immunofluorescence microscopy for subcellular localization and FRET affinity measurements for interaction with the receptor PEX5 demonstrated that five of the six predicted LoF SNVs resulted in loss of the PTS1 motif while three of five predicted GoF SNVs resulted in de novo PTS1 generation. Overall, we showed that a complementary approach incorporating bioinformatics methods and experimental testing was successful in identifying SNVs capable of altering peroxisome protein import, which may have implications in human disease.

Next-generation sequencing and comprehensive data reassessment in 263 adult patients with neuromuscular disorders: insights into the gray zone of molecular diagnoses.

BACKGROUND: Neuromuscular disorders (NMDs) are heterogeneous conditions with a considerable fraction attributed to monogenic defects. Despite the advancements in genomic medicine, many patients remain without a diagnosis. Here, we investigate whether a comprehensive reassessment strategy improves the diagnostic outcomes. METHODS: We analyzed 263 patients with NMD phenotypes that underwent diagnostic exome or genome sequencing at our tertiary referral center between 2015 and 2023. We applied a comprehensive reassessment encompassing variant reclassification, re-phenotyping and NGS data reanalysis. Multivariable logistic regression was performed to identify predictive factors associated with a molecular diagnosis. RESULTS: Initially, a molecular diagnosis was identified in 53 cases (20%), while an additional 23 (9%) had findings of uncertain significance. Following comprehensive reassessment, the diagnostic yield increased to 23%, revealing 44 distinct monogenic etiologies. Reasons for newly obtained molecular diagnoses were variant reclassifications in 7 and NGS data reanalysis in 3 cases including one recently described disease-gene association (DNAJB4). Male sex reduced the odds of receiving a molecular diagnosis (OR 0.42; 95%CI 0.21-0.82), while a positive family history (OR 5.46; 95%CI 2.60-11.76) and a myopathy phenotype (OR 2.72; 95%CI 1.11-7.14) increased the likelihood. 7% were resolved through targeted genetic testing or classified as acquired etiologies. CONCLUSION: Our findings reinforce the use of NGS in NMDs of suspected monogenic origin. We show that a comprehensive reassessment enhances diagnostic accuracy. However, one needs to be aware that genetic diagnoses are often made with uncertainty and can even be downgraded based on new evidence.

De novo variants in GABRA4 are associated with a neurological phenotype including developmental delay, behavioral abnormalities and epilepsy.

Nine out of 19 genes encoding GABAA receptor subunits have been linked to monogenic syndromes characterized by seizures and developmental disorders. Previously, we reported the de novo variant p.(Thr300Ile) in GABRA4 in a patient with epilepsy and neurodevelopmental abnormalities. However, no new cases have been reported since then. Through an international collaboration, we collected molecular and phenotype data of individuals carrying de novo variants in GABRA4. Patients and their parents were investigated either by exome or genome sequencing, followed by targeted Sanger sequencing in some cases. All variants within the transmembrane domain, including the previously reported p.(Thr300Ile) variant, were characterized in silico and analyzed by molecular dynamics (MD) simulation studies. We identified three novel de novo missense variants in GABRA4 (NM_000809.4): c.797 C > T, p.(Pro266Leu), c.899 C > A, p.(Thr300Asn), and c.634 G > A, p.(Val212Ile). The p.(Thr300Asn) variant impacts the same codon as the previously reported variant p.(Thr300Ile) and likely arose post-zygotically as evidenced by sequencing oral mucosal cells. Overlapping phenotypes among affected individuals included developmental delay (4/4), epileptiform EEG abnormalities (3/4), attention deficits (3/4), seizures (2/4), autistic features (2/4) and structural brain abnormalities (2/4). MD simulations of the three variants within the transmembrane domain of the receptor indicate that sub-microsecond scale dynamics differ between wild-type and mutated subunits. Taken together, our findings further corroborate an association between GABRA4 and a neurological phenotype including variable neurodevelopmental, behavioral and epileptic abnormalities.

Molecular and Phenotypic Characterization of the RORB-Related Disorder.

BACKGROUND AND OBJECTIVES: Heterozygous variants in RAR-related orphan receptor B (RORB) have recently been associated with susceptibility to idiopathic generalized epilepsy. However, few reports have been published so far describing pathogenic variants of this gene in patients with epilepsy and intellectual disability (ID). In this study, we aimed to delineate the epilepsy phenotype associated with RORB pathogenic variants and to provide arguments in favor of the pathogenicity of variants. METHODS: Through an international collaboration, we analyzed seizure characteristics, EEG data, and genotypes of a cohort of patients with heterozygous variants in RORB. To gain insight into disease mechanisms, we performed ex vivo cortical electroporation in mouse embryos of 5 selected variants, 2 truncating and 3 missense, and evaluated on expression and quantified changes in axonal morphology. RESULTS: We identified 35 patients (17 male, median age 10 years, range 2.5-23 years) carrying 32 different heterozygous variants in RORB, including 28 single-nucleotide variants or small insertions/deletions (12 missense, 12 frameshift or nonsense, 2 splice-site variants, and 2 in-frame deletions), and 4 microdeletions; de novo in 18 patients and inherited in 10. Seizures were reported in 31/35 (89%) patients, with a median age at onset of 3 years (range 4 months-12 years). Absence seizures occurred in 25 patients with epilepsy (81%). Nineteen patients experienced a single seizure type: absences, myoclonic absences, or absences with eyelid myoclonia and focal seizures. Nine patients had absence seizures combined with other generalized seizure types. One patient had presented with absences associated with photosensitive occipital seizures. Three other patients had generalized tonic-clonic seizures without absences. ID of variable degree was observed in 85% of the patients. Expression studies in cultured neurons showed shorter axons for the 5 tested variants, both truncating and missense variants, supporting an impaired protein function. DISCUSSION: In most patients, the phenotype of the RORB-related disorder associates absence seizures with mild-to-moderate ID. In silico and in vitro evaluation of the variants in our cohort, including axonal morphogenetic experiments in cultured neurons, supports their pathogenicity, showing a hypomorphic effect.

The clinical and molecular landscape of congenital myasthenic syndromes in Austria: a nationwide study.

BACKGROUND: Congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders caused by genetic defects resulting in impaired neuromuscular transmission. Although effective treatments are available, CMS is probably underdiagnosed, and systematic clinico-genetic investigations are warranted. METHODS: We used a nationwide approach to collect Austrian patients with genetically confirmed CMS. We provide a clinical and molecular characterization of this cohort and aimed to ascertain the current frequency of CMS in Austria. RESULTS: Twenty-eight cases with genetically confirmed CMS were identified, corresponding to an overall prevalence of 3.1 per million (95% CI 2.0-4.3) in Austria. The most frequent genetic etiology was CHRNE (n = 13), accounting for 46.4% of the cohort. Within this subgroup, the variant c.1327del, p.(Glu443Lysfs*64) was detected in nine individuals. Moreover, causative variants were found in DOK7 (n = 4), RAPSN (n = 3), COLQ (n = 2), GMPPB (n = 2), CHAT (n = 1), COL13A1 (n = 1), MUSK (n = 1) and AGRN (n = 1). Clinical onset within the first year of life was reported in one half of the patients. Across all subtypes, the most common symptoms were ptosis (85.7%), lower limb (67.9%), upper limb (60.7%) and facial weakness (60.7%). The majority of patients (96.4%) received specific treatment, including acetylcholinesterase inhibitors in 20, adrenergic agonists in 11 and 3,4-diaminopyridine in nine patients. CONCLUSIONS: Our study presents the first systematic characterization of individuals with CMS in Austria, providing prevalence estimates and genotype-phenotype correlations that may help to improve the diagnostic approach and patient management.

A de novo truncating variant in CSDE1 in an adult-onset neuropsychiatric phenotype without intellectual disability.

Variants in CSDE1, a gene encoding a constrained RNA-binding protein, have recently been associated with a spectrum of neurodevelopmental conditions encompassing autism, seizures and ocular abnormalities. According to previously reported individuals, pathogenic variants in CSDE1 are typically associated with developmental delay and intellectual disability. Here, we report one individual with normal neurodevelopment and adult-onset neuropsychiatric features (i.e., acute psychosis) due to the novel de novo truncating variant c.2272C>T, p.(Gln758*) in CSDE1 (NM_001242891.1). Neuropsychological assessment confirmed deficits regarding verbal fluency, semantic memory, executive function and processing speed. Overall, our findings expand the phenotypic spectrum of CSDE1-related disorder towards the mild end.

Estimation of patent foramen ovale size using transcranial Doppler ultrasound in patients with ischemic stroke.

BACKGROUND AND PURPOSE: Patent foramen ovale (PFO)is associated with cryptogenic stroke, especially in young adults. Transcranial Doppler (TCD) ultrasound is used as a screening tool before transesophageal echocardiography (TEE). However, the use of Valsalva maneuver (VM) to identify a right-to-left-shunt underlies interindividual variability. Here, we aimed to assess whether a pressure-controlled standardization of VM is useful to estimate PFO size. METHODS: We included patients aged 18-80 years with a PFO according to TEE. Subjects underwent TCD with microembolic signals (MES) counted under four pressure conditions (i.e., at rest, 15 mbar, 40 mbar, and maximum expiratory pressure). Findings were correlated with TEE-based PFO size. The predictive value of TCD at rest and VM-based TCD for PFO size estimation was assessed by stepwise multivariate linear regression models and multiple cross-tab-analyses. RESULTS: We screened 203 subjects after a cerebrovascular event, of which 78 (48 males [61.5%], median age 55 years [22-80]) with PFO were included. We found an association between MES count and expiratory pressure (p < .001). Predefined MES count categories at TCD pressure conditions correlated significantly with PFO size measured by TEE. We propose a PFO size estimation model based on TCD at rest and under VM, which classified PFO size correctly in 64.1% with the highest accuracy for small PFOs. CONCLUSION: Our data provide evidence that TCD with step-wise barometric standardization allows an estimation of PFO size with good accuracy. Though TCD will not replace TEE in future, this might be of clinical value in circumstances where TEE cannot be easily performed.

Connectome Analysis in an Individual with SETD1B -Related Neurodevelopmental Disorder and Epilepsy.

OBJECTIVE: Causative variants in SETD1B , encoding a lysine-specific methyltransferase, have recently been associated with a neurodevelopmental phenotype encompassing intellectual disability, autistic features, pronounced language delay, and epilepsy. It has been noted that long-term and deep phenotype data are needed to further delineate this rare condition. METHODS: In this study, we provide an in-depth clinical characterization with long-term follow-up and trio exome sequencing findings to describe one additional individual affected by SETD1B -related disorder. The diagnostic workup was complemented by a functional magnetic resonance imaging (fMRI) study. RESULTS: We report a 24-year-old male individual with an early-onset neurodevelopmental disorder with epilepsy due to the de novo missense variant c.5699A>G, p.(Tyr1900Cys) in SETD1B (NM_015048.1). He exhibited delayed speech development, autism spectrum disorder, and early-onset epilepsy with absence and generalized tonic-clonic seizures. Despite profoundly impaired communication skills, ongoing improvements regarding language production have been noted in adulthood. fMRI findings demonstrate abnormal language activation and resting-state connectivity structure. CONCLUSION: Our report expands the previously delineated phenotype of SETD1B -related disorder and provides novel insights into underlying disease mechanisms.