Comprehensive In Vivo Interrogation Reveals Phenotypic Impact of Human Enhancer Variants.

Establishing causal links between non-coding variants and human phenotypes is an increasing challenge. Here, we introduce a high-throughput mouse reporter assay for assessing the pathogenic potential of human enhancer variants in vivo and examine nearly a thousand variants in an enhancer repeatedly linked to polydactyly. We show that 71% of all rare non-coding variants previously proposed as causal lead to reporter gene expression in a pattern consistent with their pathogenic role. Variants observed to alter enhancer activity were further confirmed to cause polydactyly in knockin mice. We also used combinatorial and single-nucleotide mutagenesis to evaluate the in vivo impact of mutations affecting all positions of the enhancer and identified additional functional substitutions, including potentially pathogenic variants hitherto not observed in humans. Our results uncover the functional consequences of hundreds of mutations in a phenotype-associated enhancer and establish a widely applicable strategy for systematic in vivo evaluation of human enhancer variants.

COL11A2 as a candidate gene for vertebral malformations and congenital scoliosis.

Human vertebral malformations (VMs) have an estimated incidence of 1/2000 and are associated with significant health problems including congenital scoliosis (CS) and recurrent organ system malformation syndromes such as VACTERL (vertebral anomalies; anal abnormalities; cardiac abnormalities; tracheo-esophageal fistula; renal anomalies; limb anomalies). The genetic cause for the vast majority of VMs are unknown. In a CS/VM patient cohort, three COL11A2 variants (R130W, R1407L and R1413H) were identified in two patients with cervical VM. A third patient with a T9 hemivertebra and the R130W variant was identified from a separate study. These substitutions are predicted to be damaging to protein function, and R130 and R1407 residues are conserved in zebrafish Col11a2. To determine the role for COL11A2 in vertebral development, CRISPR/Cas9 was used to create a nonsense mutation (col11a2L642*) as well as a full gene locus deletion (col11a2del) in zebrafish. Both col11a2L642*/L642* and col11a2del/del mutant zebrafish exhibit vertebral fusions in the caudal spine, which form due to mineralization across intervertebral segments. To determine the functional consequence of VM-associated variants, we assayed their ability to suppress col11a2del VM phenotypes following transgenic expression within the developing spine. While wildtype col11a2 expression suppresses fusions in col11a2del/+ and col11a2del/del backgrounds, patient missense variant-bearing col11a2 failed to rescue the loss-of-function phenotype in these animals. These results highlight an essential role for COL11A2 in vertebral development and support a pathogenic role for two missense variants in CS.

Survey of the Landscape of Society Practice Guidelines for Genetic Testing of Neurodevelopmental Disorders.

Genetic testing of patients with neurodevelopmental disabilities (NDDs) is critical for diagnosis, medical management, and access to precision therapies. Because genetic testing approaches evolve rapidly, professional society practice guidelines serve an essential role in guiding clinical care; however, several challenges exist regarding the creation and equitable implementation of these guidelines. In this scoping review, we assessed the current state of United States professional societies' guidelines pertaining to genetic testing for unexplained global developmental delay, intellectual disability, autism spectrum disorder, and cerebral palsy. We describe several identified shortcomings and argue the need for a unified, frequently updated, and easily-accessible cross-specialty society guideline. ANN NEUROL 2024;96:900-913.

Exome sequencing of 1190 non-syndromic clubfoot cases reveals HOXD12 as a novel disease gene.

BACKGROUND: Clubfoot, presenting as a rigid inward and downward turning of the foot, is one of the most common congenital musculoskeletal anomalies. The aetiology of clubfoot is poorly understood and variants in known clubfoot disease genes account for only a small portion of the heritability. METHODS: Exome sequence data were generated from 1190 non-syndromic clubfoot cases and their family members from multiple ethnicities. Ultra-rare variant burden analysis was performed comparing 857 unrelated clubfoot cases with European ancestry with two independent ethnicity-matched control groups (1043 in-house and 56 885 gnomAD controls). Additional variants in prioritised genes were identified in a larger cohort, including probands with non-European ancestry. Segregation analysis was performed in multiplex families when available. RESULTS: Rare variants in 29 genes were enriched in clubfoot cases, including PITX1 (a known clubfoot disease gene), HOXD12, COL12A1, COL9A3 and LMX1B. In addition, rare variants in posterior HOX genes (HOX9-13) were enriched overall in clubfoot cases. In total, variants in these genes were present in 8.4% (100/1190) of clubfoot cases with both European and non-European ancestry. Among these, 3 are de novo and 22 show variable penetrance, including 4 HOXD12 variants that segregate with clubfoot. CONCLUSION: We report HOXD12 as a novel clubfoot disease gene and demonstrate a phenotypic expansion of known disease genes (myopathy gene COL12A1, Ehlers-Danlos syndrome gene COL9A3 and nail-patella syndrome gene LMX1B) to include isolated clubfoot.

Rare and de novo coding variants in chromodomain genes in Chiari I malformation.

Chiari I malformation (CM1), the displacement of the cerebellum through the foramen magnum into the spinal canal, is one of the most common pediatric neurological conditions. Individuals with CM1 can present with neurological symptoms, including severe headaches and sensory or motor deficits, often as a consequence of brainstem compression or syringomyelia (SM). We conducted whole-exome sequencing (WES) on 668 CM1 probands and 232 family members and performed gene-burden and de novo enrichment analyses. A significant enrichment of rare and de novo non-synonymous variants in chromodomain (CHD) genes was observed among individuals with CM1 (combined p = 2.4 × 10-10), including 3 de novo loss-of-function variants in CHD8 (LOF enrichment p = 1.9 × 10-10) and a significant burden of rare transmitted variants in CHD3 (p = 1.8 × 10-6). Overall, individuals with CM1 were found to have significantly increased head circumference (p = 2.6 × 10-9), with many harboring CHD rare variants having macrocephaly. Finally, haploinsufficiency for chd8 in zebrafish led to macrocephaly and posterior hindbrain displacement reminiscent of CM1. These results implicate chromodomain genes and excessive brain growth in CM1 pathogenesis.

Clinical variants paired with phenotype: A rich resource for brain gene curation.

PURPOSE: Clinically ascertained variants are under-utilized in neurodevelopmental disorder research. We established the Brain Gene Registry (BGR) to coregister clinically identified variants in putative brain genes with participant phenotypes. Here, we report 179 genetic variants in the first 179 BGR registrants and analyze the proportion that were novel to ClinVar at the time of entry and those that were absent in other disease databases. METHODS: From 10 academically affiliated institutions, 179 individuals with 179 variants were enrolled into the BGR. Variants were cross-referenced for previous presence in ClinVar and for presence in 6 other genetic databases. RESULTS: Of 179 variants in 76 genes, 76 (42.5%) were novel to ClinVar, and 62 (34.6%) were absent from all databases analyzed. Of the 103 variants present in ClinVar, 37 (35.9%) were uncertain (ClinVar aggregate classification of variant of uncertain significance or conflicting classifications). For 5 variants, the aggregate ClinVar classification was inconsistent with the interpretation from the BGR site-provided classification. CONCLUSION: A significant proportion of clinical variants that are novel or uncertain are not shared, limiting the evidence base for new gene-disease relationships. Registration of paired clinical genetic test results with phenotype has the potential to advance knowledge of the relationships between genes and neurodevelopmental disorders.

Genetic association and characterization of FSTL5 in isolated clubfoot.

Talipes equinovarus (clubfoot, TEV) is a congenital rotational foot deformity occurring in 1 per 1000 births with increased prevalence in males compared with females. The genetic etiology of isolated clubfoot (iTEV) remains unclear. Using a genome-wide association study, we identified a locus within FSTL5, encoding follistatin-like 5, significantly associated with iTEV. FSTL5 is an uncharacterized gene whose potential role in embryonic and postnatal development was previously unstudied. Utilizing multiple model systems, we found that Fstl5 was expressed during later stages of embryonic hindlimb development, and, in mice, expression was restricted to the condensing cartilage anlage destined to form the limb skeleton. In the postnatal growth plate, Fstl5 was specifically expressed in prehypertrophic chondrocytes. As Fstl5 knockout rats displayed no gross malformations, we engineered a conditional transgenic mouse line (Fstl5LSL) to overexpress Fstl5 in skeletal osteochondroprogenitors. We observed that hindlimbs were slightly shorter and that bone mineral density was reduced in adult male, but not female, Prrx1-cre;Fstl5LSL mice compared with control. No overt clubfoot-like deformity was observed in Prrx1-cre;Fstl5LSL mice, suggesting FSTL5 may function in other cell types to contribute to iTEV pathogenesis. Interrogating published mouse embryonic single-cell expression data showed that Fstl5 was expressed in cell lineage subclusters whose transcriptomes were associated with neural system development. Moreover, our results suggest that lineage-specific expression of the Fstl genes correlates with their divergent roles as modulators of transforming growth factor beta and bone morphogenetic protein signaling. Results from this study associate FSTL5 with iTEV and suggest a potential sexually dimorphic role for Fstl5 in vivo.

Distinct epilepsy phenotypes and response to drugs in KCNA1 gain- and loss-of function variants.

A wide phenotypic spectrum of neurological diseases is associated with KCNA1 (Kv1.1) variants. To investigate the molecular basis of such a heterogeneous clinical presentation and identify the possible correlation with in vitro phenotypes, we compared the functional consequences of three heterozygous de novo variants (p.P403S, p.P405L, and p.P405S) in Kv1.1 pore region found in four patients with severe developmental and epileptic encephalopathy (DEE), with those of a de novo variant in the voltage sensor (p.A261T) identified in two patients with mild, carbamazepine-responsive, focal epilepsy. Patch-clamp electrophysiology was used to investigate the functional properties of mutant Kv1.1 subunits, both expressed as homomers and heteromers with wild-type Kv1.1 subunits. KCNA1 pore mutations markedly decreased (p. P405S) or fully suppressed (p. P403S, p. P405L) Kv1.1-mediated currents, exerting loss-of-function (LoF) effects. By contrast, channels carrying the p.A261T variant exhibited a hyperpolarizing shift of the activation process, consistent with a gain-of-function (GoF) effect. The present results unveil a novel correlation between in vitro phenotype (GoF vs LoF) and clinical course (mild vs severe) in KCNA1-related phenotypes. The excellent clinical response to carbamazepine observed in the patients carrying the A261T variant suggests an exquisite sensitivity of KCNA1 GoF to sodium channel inhibition that should be further explored.

Whole Exome Sequencing in Individuals with Idiopathic Clubfoot Reveals a Recurrent Filamin B (FLNB) Deletion.

BACKGROUND: Clubfoot, a congenital deformity that presents as a rigid, inward turning of the foot, affects approximately 1 in 1000 infants and occurs as an isolated birth defect in 80% of patients. Despite its high level of heritability, few causative genes have been identified, and mutations in known genes are only responsible for a small portion of clubfoot heritability. QUESTIONS/PURPOSES: (1) Are any rare gene variants enriched (that is, shared) in unrelated patients with isolated clubfoot? (2) Are there other rare variants in the identified gene (Filamin B) in these patients with clubfoot? METHODS: Whole-exome sequence data were generated from a discovery cohort of 183 unrelated probands with clubfoot and 2492 controls. Variants were filtered with minor allele frequency < 0.02 to identify rare variants as well as small insertions and deletions (indels) resulting in missense variants, nonsense or premature truncation, or in-frame deletions. A candidate deletion was then genotyped in another cohort of 974 unrelated patients with clubfoot (a replication cohort). Other rare variants in the candidate gene were also investigated. A segregation analysis was performed in multigenerational families of individuals with clubfoot to see if the genotypes segregate with phenotypes. Single-variant association analysis was performed using the Fisher two-tailed exact test (exact p values are presented to give an indication of the magnitude of the association). RESULTS: There were no recurrent variants in the known genes causing clubfoot in this study. A three-base pair in-frame codon deletion of Filamin B (FLNB) (p.E1792del, rs1470699812) was identified in 1.6% (3 of 183) of probands with clubfoot in the discovery cohort compared with 0% of controls (0 of 2492) (odds ratio infinity (inf) [95% CI 5.64 to inf]; p = 3.18 x 10-5) and 0.0016% of gnomAD controls (2 of 125,709) (OR 1.01 x 103 [95% CI 117.42 to 1.64 x 104]; p = 3.13 x 10-8). By screening a replication cohort (n = 974 patients), we found two probands with the identical FLNB deletion. In total, the deletion was identified in 0.43% (5 of 1157) of probands with clubfoot compared with 0% of controls and 0.0016% of gnomAD controls (OR 268.5 [95% CI 43.68 to 2.88 x 103]; p = 1.43 x 10-9). The recurrent FLNB p.E1792del variant segregated with clubfoot, with incomplete penetrance in two families. Affected individuals were more likely to be male and have bilateral clubfoot. Although most patients had isolated clubfoot, features consistent with Larsen syndrome, including upper extremity abnormalities such as elbow and thumb hypermobility and wide, flat thumbs, were noted in affected members of one family. We identified 19 additional rare FLNB missense variants located throughout the gene in patients with clubfoot. One of these missense variants, FLNB p.G2397D, exhibited incomplete penetrance in one family. CONCLUSION: A recurrent FLNB E1792 deletion was identified in 0.43% of 1157 isolated patients with clubfoot. Given the absence of any recurrent variants in our discovery phase (n = 183) for any of the known genes causing clubfoot, our findings support that novel and rare missense variants in FLNB in patients with clubfoot, although rare, may be among the most commonly known genetic causes of clubfoot. Patients with FLNB variants often have isolated clubfoot, but they and their family members may be at an increased risk of having additional clinical features consistent with Larsen syndrome. CLINICAL RELEVANCE: Identification of FLNB variants may be useful for determining clubfoot recurrence risk and comorbidities.

Rare and de novo duplications containing SHOX in clubfoot.

INTRODUCTION: Congenital clubfoot is a common birth defect that affects at least 0.1% of all births. Nearly 25% cases are familial and the remaining are sporadic in inheritance. Copy number variants (CNVs) involving transcriptional regulators of limb development, including PITX1 and TBX4, have previously been shown to cause familial clubfoot, but much of the heritability remains unexplained. METHODS: Exome sequence data from 816 unrelated clubfoot cases and 2645 in-house controls were analysed using coverage data to identify rare CNVs. The precise size and location of duplications were then determined using high-density Affymetrix Cytoscan chromosomal microarray (CMA). Segregation in families and de novo status were determined using qantitative PCR. RESULTS: Chromosome Xp22.33 duplications involving SHOX were identified in 1.1% of cases (9/816) compared with 0.07% of in-house controls (2/2645) (p=7.98×10-5, OR=14.57) and 0.27% (38/13592) of Atherosclerosis Risk in Communities/the Wellcome Trust Case Control Consortium 2 controls (p=0.001, OR=3.97). CMA validation confirmed an overlapping 180.28 kb duplicated region that included SHOX exons as well as downstream non-coding regions. In four of six sporadic cases where DNA was available for unaffected parents, the duplication was de novo. The probability of four de novo mutations in SHOX by chance in a cohort of 450 sporadic clubfoot cases is 5.4×10-10. CONCLUSIONS: Microduplications of the pseudoautosomal chromosome Xp22.33 region (PAR1) containing SHOX and downstream enhancer elements occur in ~1% of patients with clubfoot. SHOX and regulatory regions have previously been implicated in skeletal dysplasia as well as idiopathic short stature, but have not yet been reported in clubfoot. SHOX duplications likely contribute to clubfoot pathogenesis by altering early limb development.

Mutations in Kinesin family member 6 reveal specific role in ependymal cell ciliogenesis and human neurological development.

Cerebrospinal fluid flow is crucial for neurodevelopment and homeostasis of the ventricular system of the brain, with localized flow being established by the polarized beating of the ependymal cell (EC) cilia. Here, we report a homozygous one base-pair deletion, c.1193delT (p.Leu398Glnfs*2), in the Kinesin Family Member 6 (KIF6) gene in a child displaying neurodevelopmental defects and intellectual disability. To test the pathogenicity of this novel human KIF6 mutation we engineered an analogous C-terminal truncating mutation in mouse. These mutant mice display severe, postnatal-onset hydrocephalus. We generated a Kif6-LacZ transgenic mouse strain and report expression specifically and uniquely within the ependymal cells (ECs) of the brain, without labeling other multiciliated mouse tissues. Analysis of Kif6 mutant mice with scanning electron microscopy (SEM) and immunofluorescence (IF) revealed specific defects in the formation of EC cilia, without obvious effect of cilia of other multiciliated tissues. Dilation of the ventricular system and defects in the formation of EC cilia were also observed in adult kif6 mutant zebrafish. Finally, we report Kif6-GFP localization at the axoneme and basal bodies of multi-ciliated cells (MCCs) of the mucociliary Xenopus epidermis. Overall, this work describes the first clinically-defined KIF6 homozygous null mutation in human and defines KIF6 as a conserved mediator of neurological development with a specific role for EC ciliogenesis in vertebrates.

Genome-wide meta-analysis and replication studies in multiple ethnicities identify novel adolescent idiopathic scoliosis susceptibility loci.

Adolescent idiopathic scoliosis (AIS) is the most common musculoskeletal disorder of childhood development. The genetic architecture of AIS is complex, and the great majority of risk factors are undiscovered. To identify new AIS susceptibility loci, we conducted the first genome-wide meta-analysis of AIS genome-wide association studies, including 7956 cases and 88 459 controls from 3 ancestral groups. Three novel loci that surpassed genome-wide significance were uncovered in intragenic regions of the CDH13 (P-value_rs4513093 = 1.7E-15), ABO (P-value_ rs687621 = 7.3E-10) and SOX6 (P-value_rs1455114 = 2.98E-08) genes. Restricting the analysis to females improved the associations at multiple loci, most notably with variants within CDH13 despite the reduction in sample size. Genome-wide gene-functional enrichment analysis identified significant perturbation of pathways involving cartilage and connective tissue development. Expression of both SOX6 and CDH13 was detected in cartilage chondrocytes and chromatin immunoprecipitation sequencing experiments in that tissue revealed multiple HeK27ac-positive peaks overlapping associated loci. Our results further define the genetic architecture of AIS and highlight the importance of vertebral cartilage development in its pathogenesis.

Distal chromosome 16p11.2 duplications containing SH2B1 in patients with scoliosis.

INTRODUCTION: Adolescent idiopathic scoliosis (AIS) is a common musculoskeletal disorder with strong evidence for a genetic contribution. CNVs play an important role in congenital scoliosis, but their role in idiopathic scoliosis has been largely unexplored. METHODS: Exome sequence data from 1197 AIS cases and 1664 in-house controls was analysed using coverage data to identify rare CNVs. CNV calls were filtered to include only highly confident CNVs with >10 average reads per region and mean log-ratio of coverage consistent with single-copy duplication or deletion. The frequency of 55 common recurrent CNVs was determined and correlated with clinical characteristics. RESULTS: Distal chromosome 16p11.2 microduplications containing the gene SH2B1 were found in 0.7% of AIS cases (8/1197). We replicated this finding in two additional AIS cohorts (8/1097 and 2/433), resulting in 0.7% (18/2727) of all AIS cases harbouring a chromosome 16p11.2 microduplication, compared with 0.06% of local controls (1/1664) and 0.04% of published controls (8/19584) (p=2.28×10-11, OR=16.15). Furthermore, examination of electronic health records of 92 455 patients from the Geisinger health system showed scoliosis in 30% (20/66) patients with chromosome 16p11.2 microduplications containing SH2B1 compared with 7.6% (10/132) of controls (p=5.6×10-4, OR=3.9). CONCLUSIONS: Recurrent distal chromosome 16p11.2 duplications explain nearly 1% of AIS. Distal chromosome 16p11.2 duplications may contribute to scoliosis pathogenesis by directly impairing growth or by altering expression of nearby genes, such as TBX6. Individuals with distal chromosome 16p11.2 microduplications should be screened for scoliosis to facilitate early treatment.

Massively parallel single-nucleotide mutagenesis using reversibly terminated inosine.

Large-scale mutagenesis of target DNA sequences allows researchers to comprehensively assess the effects of single-nucleotide changes. Here we demonstrate the construction of a systematic allelic series (SAS) using massively parallel single-nucleotide mutagenesis with reversibly terminated deoxyinosine triphosphates (rtITP). We created a mutational library containing every possible single-nucleotide mutation surrounding the active site of the TEM-1 ß-lactamase gene. When combined with high-throughput functional assays, SAS mutational libraries can expedite the functional assessment of genetic variation.

Missense variants in the chromatin remodeler CHD1 are associated with neurodevelopmental disability.

BACKGROUND: The list of Mendelian disorders of the epigenetic machinery has expanded rapidly during the last 5 years. A few missense variants in the chromatin remodeler CHD1 have been found in several large-scale sequencing efforts focused on uncovering the genetic aetiology of autism. OBJECTIVES: To explore whether variants in CHD1 are associated with a human phenotype. METHODS: We used GeneMatcher to identify other physicians caring for patients with variants in CHD1. We also explored the epigenetic consequences of one of these variants in cultured fibroblasts. RESULTS: Here we describe six CHD1 heterozygous missense variants in a cohort of patients with autism, speech apraxia, developmental delay and facial dysmorphic features. Importantly, three of these variants occurred de novo. We also report on a subject with a de novo deletion covering a large fraction of the CHD1 gene without any obvious neurological phenotype. Finally, we demonstrate increased levels of the closed chromatin modification H3K27me3 in fibroblasts from a subject carrying a de novo variant in CHD1. CONCLUSIONS: Our results suggest that variants in CHD1 can lead to diverse phenotypic outcomes; however, the neurodevelopmental phenotype appears to be limited to patients with missense variants, which is compatible with a dominant negative mechanism of disease.

A polygenic burden of rare variants across extracellular matrix genes among individuals with adolescent idiopathic scoliosis.

Adolescent idiopathic scoliosis (AIS) is a complex inherited spinal deformity whose etiology has been elusive. While common genetic variants are associated with AIS, they explain only a small portion of disease risk. To explore the role of rare variants in AIS susceptibility, exome sequence data of 391 severe AIS cases and 843 controls of European ancestry were analyzed using a pathway burden analysis in which variants are first collapsed at the gene level then by Gene Ontology terms. Novel non-synonymous/splice-site variants in extracellular matrix genes were significantly enriched in AIS cases compared with controls (P = 6 × 10(-9), OR = 1.7, CI = 1.4-2.0). Specifically, novel variants in musculoskeletal collagen genes were present in 32% (126/391) of AIS cases compared with 17% (146/843) of in-house controls and 18% (780/4300) of EVS controls (P = 1 × 10(-9), OR = 1.9, CI = 1.6-2.4). Targeted resequencing of six collagen genes replicated this association in combined 919 AIS cases (P = 3 × 10(-12), OR = 2.2, CI = 1.8-2.7) and revealed a highly significant single-gene association with COL11A2 (P = 6 × 10(-9), OR = 3.8, CI = 2.6-7.2). Importantly, AIS cases harbor mainly non-glycine missense mutations and lack the clinical features of monogenic musculoskeletal collagenopathies. Overall, our study reveals a complex genetic architecture of AIS in which a polygenic burden of rare variants across extracellular matrix genes contributes strongly to risk.

De novo mutations in SIK1 cause a spectrum of developmental epilepsies.

Developmental epilepsies are age-dependent seizure disorders for which genetic causes have been increasingly identified. Here we report six unrelated individuals with mutations in salt-inducible kinase 1 (SIK1) in a series of 101 persons with early myoclonic encephalopathy, Ohtahara syndrome, and infantile spasms. Individuals with SIK1 mutations had short survival in cases with neonatal epilepsy onset, and an autism plus developmental syndrome after infantile spasms in others. All six mutations occurred outside the kinase domain of SIK1 and each of the mutants displayed autophosphorylation and kinase activity toward HDAC5. Three mutations generated truncated forms of SIK1 that were resistant to degradation and also showed changes in sub-cellular localization compared to wild-type SIK1. We also report the human neuropathologic examination of SIK1-related developmental epilepsy, with normal neuronal morphology and lamination but abnormal SIK1 protein cellular localization. Therefore, these results expand the genetic etiologies of developmental epilepsies by demonstrating SIK1 mutations as a cause of severe developmental epilepsy.

De novo KCNA1 variants in the PVP motif cause infantile epileptic encephalopathy and cognitive impairment similar to recurrent KCNA2 variants.

Derangements in voltage-gated potassium channel function are responsible for a range of paroxysmal neurologic disorders. Pathogenic variants in the KCNA1 gene, which encodes the voltage-gated potassium channel Kv1.1, are responsible for Episodic Ataxia Type 1 (EA1). Patients with EA1 have an increased incidence of epilepsy, but KCNA1 variants have not been described in epileptic encephalopathy. Here, we describe four patients with infantile-onset epilepsy and cognitive impairment who harbor de novo KCNA1 variants located within the Kv-specific Pro-Val-Pro (PVP) motif which is essential for channel gating. The first two patients have KCNA1 variants resulting in (p.Pro405Ser) and (p.Pro405Leu), respectively, and a set of identical twins has a variant affecting a nearby residue (p.Pro403Ser). Notably, recurrent de novo variants in the paralogous PVP motif of KCNA2 have previously been shown to abolish channel function and also cause early-onset epileptic encephalopathy. Importantly, this report extends the range of phenotypes associated with KCNA1 variants to include epileptic encephalopathy when the PVP motif is involved.