Loss of symmetric cell division of apical neural progenitors drives DENND5A-related developmental and epileptic encephalopathy.

Developmental and epileptic encephalopathies (DEEs) are a heterogenous group of epilepsies in which altered brain development leads to developmental delay and seizures, with the epileptic activity further negatively impacting neurodevelopment. Identifying the underlying cause of DEEs is essential for progress toward precision therapies. Here we describe a group of individuals with biallelic variants in DENND5A and determine that variant type is correlated with disease severity. We demonstrate that DENND5A interacts with MUPP1 and PALS1, components of the Crumbs apical polarity complex, which is required for both neural progenitor cell identity and the ability of these stem cells to divide symmetrically. Induced pluripotent stem cells lacking DENND5A fail to undergo symmetric cell division during neural induction and have an inherent propensity to differentiate into neurons, and transgenic DENND5A mice, with phenotypes like the human syndrome, have an increased number of neurons in the adult subventricular zone. Disruption of symmetric cell division following loss of DENND5A results from misalignment of the mitotic spindle in apical neural progenitors. A subset of DENND5A is localized to centrosomes, which define the spindle poles during mitosis. Cells lacking DENND5A orient away from the proliferative apical domain surrounding the ventricles, biasing daughter cells towards a more fate-committed state and ultimately shortening the period of neurogenesis. This study provides a mechanism behind DENND5A-related DEE that may be generalizable to other developmental conditions and provides variant-specific clinical information for physicians and families.

IFT74 variants cause skeletal ciliopathy and motile cilia defects in mice and humans.

Motile and non-motile cilia play critical roles in mammalian development and health. These organelles are composed of a 1000 or more unique proteins, but their assembly depends entirely on proteins synthesized in the cell body and transported into the cilium by intraflagellar transport (IFT). In mammals, malfunction of non-motile cilia due to IFT dysfunction results in complex developmental phenotypes that affect most organs. In contrast, disruption of motile cilia function causes subfertility, disruption of the left-right body axis, and recurrent airway infections with progressive lung damage. In this work, we characterize allele specific phenotypes resulting from IFT74 dysfunction in human and mice. We identified two families carrying a deletion encompassing IFT74 exon 2, the first coding exon, resulting in a protein lacking the first 40 amino acids and two individuals carrying biallelic splice site mutations. Homozygous exon 2 deletion cases presented a ciliary chondrodysplasia with narrow thorax and progressive growth retardation along with a mucociliary clearance disorder phenotype with severely shorted cilia. Splice site variants resulted in a lethal skeletal chondrodysplasia phenotype. In mice, removal of the first 40 amino acids likewise results in a motile cilia phenotype but with little effect on primary cilia structure. Mice carrying this allele are born alive but are growth restricted and developed hydrocephaly in the first month of life. In contrast, a strong, likely null, allele of Ift74 in mouse completely blocks ciliary assembly and causes severe heart defects and midgestational lethality. In vitro studies suggest that the first 40 amino acids of IFT74 are dispensable for binding of other IFT subunits but are important for tubulin binding. Higher demands on tubulin transport in motile cilia compared to primary cilia resulting from increased mechanical stress and repair needs could account for the motile cilia phenotype observed in human and mice.

IFT74 variants cause skeletal ciliopathy and motile cilia defects in mice and humans.

Motile and non-motile cilia are critical to mammalian development and health. Assembly of these organelles depends on proteins synthesized in the cell body and transported into the cilium by intraflagellar transport (IFT). A series of human and mouse IFT74 variants were studied to understand the function of this IFT subunit. Humans missing exon 2, which codes for the first 40 residues, presented an unusual combination of ciliary chondrodysplasia and mucociliary clearance disorders while individuals carrying biallelic splice site variants developed a lethal skeletal chondrodysplasia. In mice, variants thought to remove all Ift74 function, completely block ciliary assembly and result in midgestational lethality. A mouse allele that removes the first 40 amino acids, analogous to the human exon 2 deletion, results in a motile cilia phenotype with mild skeletal abnormalities. In vitro studies suggest that the first 40 amino acids of IFT74 are dispensable for binding of other IFT subunits but are important for tubulin binding. Higher demands on tubulin transport in motile cilia compared to primary cilia could account for the motile cilia phenotype observed in human and mice.

Clinical Validation of Genome Reference Consortium Human Build 38 in a Laboratory Utilizing Next-Generation Sequencing Technologies.

BACKGROUND: Laboratories utilizing next-generation sequencing align sequence data to a standardized human reference genome (HRG). Several updated versions, or builds, have been released since the original HRG in 2001, including the Genome Reference Consortium Human Build 38 (GRCh38) in 2013. However, most clinical laboratories still use GRCh37, which was released in 2009. We report our laboratory's clinical validation of GRCh38. METHODS: Migration to GRCh38 was validated by comparing the coordinates (lifting over) of 9443 internally curated variants from GRCh37 to GRCh38, globally comparing protein coding sequence variants aligned with GRCh37 vs GRCh38 from 917 exomes, assessing genes with known discrepancies, comparing coverage differences, and establishing the analytic sensitivity and specificity of variant detection using Genome in a Bottle data. RESULTS: Eight discrepancies, due to strand swap or reference base, were observed. Three clinically relevant variants had the GRCh37 alternate allele as the reference allele in GRCh38. A comparison of 88 295 calls between builds identified 8 disease-associated genes with sequence differences: ABO, BNC2, KIZ, NEFL, NR2E3, PTPRQ, SHANK2, and SRD5A2. Discrepancies in coding regions in GRCh37 were resolved in GRCh38. CONCLUSIONS: There were a small number of clinically significant changes between the 2 genome builds. GRCh38 provided improved detection of nucleotide changes due to the resolution of discrepancies present in GRCh37. Implementation of GRCh38 results in more accurate and consistent reporting.

Phenotypic expansion and variable expressivity in individuals with JARID2-related intellectual disability: A case series.

Loss of function variants in JARID2 were recently reported in 16 patients with a neurodevelopmental disorder characterized by delays, intellectual and learning disability, autism, behavioral abnormalities, and dysmorphic features. Most cases were de novo, with only one variant inherited from an affected parent. Here, we present seven additional individuals from five families with pathogenic or likely pathogenic JARID2 variants, confirming this gene-disease association and highlighting palatal abnormalities and heart defects as part of the phenotype. In addition, we report inheritance of JARID2 variants from mildly affected parents, demonstrating the variable expressivity of the disease. We also note the high prevalence of intragenic JARID2 copy number variants, emphasizing the importance of exon-level analysis.

Delayed diagnosis of holocarboxylase synthetase deficiency in three patients with prominent skin findings.

Holocarboxylase deficiency (HLCSD) is caused by biallelic pathogenic variants in HLCS and is associated with poor feeding, emesis, lethargy, seizures, life-threatening metabolic acidosis, and hyperammonemia. Skin involvement in HLCSD is typically described as scaly, erythrodermic, seborrhea-like, or ichthyosiform, but there is a paucity of reports. We report three patients, including two siblings, with HLCSD and significant cutaneous manifestations including ichthyosiform dermatitis and a presentation with features of annular pustular psoriasis. In this report, we show that persistent, unexplained rash, even in the absence of other clinical findings, should warrant consideration and potential workup for HLCSD.

Factors Affecting Migration to GRCh38 in Laboratories Performing Clinical Next-Generation Sequencing.

The most recent build of the human reference genome, GRCh38, was released in 2013. However, many laboratories performing next-generation sequencing (NGS) continue to align to GRCh37. Our aim was to assess the number of clinical diagnostic laboratories that have migrated to GRCh38 and discern factors impeding migration for those still using GRCh37. A brief, five-question survey was electronically administered to 71 clinical laboratories offering constitutional NGS-based testing and analyzed categorically. Twenty-eight responses meeting inclusion criteria were collected from 24 academic and four commercial diagnostic laboratories. Most of these (14; 50%) reported volumes of <500 NGS-based tests in 2019. Only two respondents (7%) had already migrated entirely to GRCh38; most laboratories (15; 54%) had no plans to migrate. The two prevailing reasons for not yet migrating were as follows: laboratories did not feel the benefits outweighed the time and monetary costs (14; 50%); and laboratories had insufficient staff to facilitate the migration (12; 43%). These data, although limited, suggest most clinical molecular laboratories are reluctant to migrate to GRCh38, and there appear to be multiple obstacles to overcome before GRCh38 is widely adopted.

Nager syndrome in patient lacking acrofacial dysostosis: Expanding the phenotypic spectrum of SF3B4-related disease.

Nager syndrome epitomizes the acrofacial dysostoses, which are characterized by craniofacial and limb defects. The craniofacial defects include midfacial retrusion, downslanting palpebral fissures, prominent nasal bridge, and micrognathia. Limb malformations typically include hypoplasia or aplasia of radial elements including the thumb. Nager syndrome is caused by haploinsufficiency of SF3B4, encoding a spliceosomal protein called SAP49. Here, we report a patient with a loss of function variant in SF3B4 without acrofacial dysostosis or limb defects, whose reason for referral was developmental and growth delay. This patient is evidence of a broader phenotypic spectrum associated with SF3B4 variants than previously appreciated.

Variants in CHRNB2 and CHRNA4 Identified in Patients with Insular Epilepsy.

PURPOSE: Our purpose was to determine the role of CHRNA4 and CHRNB2 in insular epilepsy. METHOD: We identified two patients with drug-resistant predominantly sleep-related hypermotor seizures, one harboring a heterozygous missense variant (c.77C>T; p. Thr26Met) in the CHRNB2 gene and the other a heterozygous missense variant (c.1079G>A; p. Arg360Gln) in the CHRNA4 gene. The patients underwent electrophysiological and neuroimaging studies, and we performed functional characterization of the p. Thr26Met (c.77C>T) in the CHRNB2 gene. RESULTS: We localized the epileptic foci to the left insula in the first case (now seizure-free following epilepsy surgery) and to both insulae in the second case. Based on tools predicting the possible impact of amino acid substitutions on the structure and function of proteins (sorting intolerant from tolerant and PolyPhen-2), variants identified in this report could be deleterious. Functional expression in human cell lines of α4ß2 (wild-type), α4ß2-Thr26Met (homozygote), and α4ß2/ß2-Thr26Met (heterozygote) nicotinic acetylcholine receptors revealed that the mutant subunit led to significantly higher whole-cell nicotinic currents. This feature was observed in both homo- and heterozygous conditions and was not accompanied by major alterations of the current reversal potential or the shape of the concentration-response relation. CONCLUSIONS: This study suggests that variants in CHRNB2 and CHRNA4, initially linked to autosomal dominant nocturnal frontal lobe epilepsy, are also found in patients with predominantly sleep-related insular epilepsy. Although the reported variants should be considered of unknown clinical significance for the moment, identification of additional similar cases and further functional studies could eventually strengthen this association.

Deficient histone H3 propionylation by BRPF1-KAT6 complexes in neurodevelopmental disorders and cancer.

Lysine acetyltransferase 6A (KAT6A) and its paralog KAT6B form stoichiometric complexes with bromodomain- and PHD finger-containing protein 1 (BRPF1) for acetylation of histone H3 at lysine 23 (H3K23). We report that these complexes also catalyze H3K23 propionylation in vitro and in vivo. Immunofluorescence microscopy and ATAC-See revealed the association of this modification with active chromatin. Brpf1 deletion obliterates the acylation in mouse embryos and fibroblasts. Moreover, we identify BRPF1 variants in 12 previously unidentified cases of syndromic intellectual disability and demonstrate that these cases and known BRPF1 variants impair H3K23 propionylation. Cardiac anomalies are present in a subset of the cases. H3K23 acylation is also impaired by cancer-derived somatic BRPF1 mutations. Valproate, vorinostat, propionate and butyrate promote H3K23 acylation. These results reveal the dual functionality of BRPF1-KAT6 complexes, shed light on mechanisms underlying related developmental disorders and various cancers, and suggest mutation-based therapy for medical conditions with deficient histone acylation.

Autosomal-dominant adult neuronal ceroid lipofuscinosis caused by duplication in DNAJC5 initially missed by Sanger and whole-exome sequencing.

Adult-onset neuronal ceroid lipofuscinoses (ANCL, Kufs disease) are rare hereditary neuropsychiatric disorders characterized by intralysosomal accumulation of ceroid in tissues. The ceroid accumulation primarily affects the brain, leading to neuronal loss and progressive neurodegeneration. Although several causative genes have been identified (DNAJC5, CLN6, CTSF, GRN, CLN1, CLN5, ATP13A2), the genetic underpinnings of ANCL in some families remain unknown. Here we report one family with autosomal dominant (AD) Kufs disease caused by a 30 bp in-frame duplication in DNAJC5, encoding the cysteine-string protein alpha (CSPα). This variant leads to a duplication of the central core motif of the cysteine-string domain of CSPα and affects palmitoylation-dependent CSPα sorting in cultured neuronal cells similarly to two previously described CSPα variants, p.(Leu115Arg) and p.(Leu116del). Interestingly, the duplication was not detected initially by standard Sanger sequencing due to a preferential PCR amplification of the shorter wild-type allele and allelic dropout of the mutated DNAJC5 allele. It was also missed by subsequent whole-exome sequencing (WES). Its identification was facilitated by reanalysis of original WES data and modification of the PCR and Sanger sequencing protocols. Independently occurring variants in the genomic sequence of DNAJC5 encoding the cysteine-string domain of CSPα suggest that this region may be more prone to DNA replication errors and that insertions or duplications within this domain should be considered in unsolved ANCL cases.

Haploinsufficiency of the Notch Ligand DLL1 Causes Variable Neurodevelopmental Disorders.

Notch signaling is an established developmental pathway for brain morphogenesis. Given that Delta-like 1 (DLL1) is a ligand for the Notch receptor and that a few individuals with developmental delay, intellectual disability, and brain malformations have microdeletions encompassing DLL1, we hypothesized that insufficiency of DLL1 causes a human neurodevelopmental disorder. We performed exome sequencing in individuals with neurodevelopmental disorders. The cohort was identified using known Matchmaker Exchange nodes such as GeneMatcher. This method identified 15 individuals from 12 unrelated families with heterozygous pathogenic DLL1 variants (nonsense, missense, splice site, and one whole gene deletion). The most common features in our cohort were intellectual disability, autism spectrum disorder, seizures, variable brain malformations, muscular hypotonia, and scoliosis. We did not identify an obvious genotype-phenotype correlation. Analysis of one splice site variant showed an in-frame insertion of 12 bp. In conclusion, heterozygous DLL1 pathogenic variants cause a variable neurodevelopmental phenotype and multi-systemic features. The clinical and molecular data support haploinsufficiency as a mechanism for the pathogenesis of this DLL1-related disorder and affirm the importance of DLL1 in human brain development.

De Novo and Inherited Pathogenic Variants in KDM3B Cause Intellectual Disability, Short Stature, and Facial Dysmorphism.

By using exome sequencing and a gene matching approach, we identified de novo and inherited pathogenic variants in KDM3B in 14 unrelated individuals and three affected parents with varying degrees of intellectual disability (ID) or developmental delay (DD) and short stature. The individuals share additional phenotypic features that include feeding difficulties in infancy, joint hypermobility, and characteristic facial features such as a wide mouth, a pointed chin, long ears, and a low columella. Notably, two individuals developed cancer, acute myeloid leukemia and Hodgkin lymphoma, in childhood. KDM3B encodes for a histone demethylase and is involved in H3K9 demethylation, a crucial part of chromatin modification required for transcriptional regulation. We identified missense and truncating variants, suggesting that KDM3B haploinsufficiency is the underlying mechanism for this syndrome. By using a hybrid facial-recognition model, we show that individuals with a pathogenic variant in KDM3B have a facial gestalt, and that they show significant facial similarity compared to control individuals with ID. In conclusion, pathogenic variants in KDM3B cause a syndrome characterized by ID, short stature, and facial dysmorphism.

On the verge of diagnosis: Detection, reporting, and investigation of de novo variants in novel genes identified by clinical sequencing.

The variable evidence supporting gene-disease associations contributes to the difficulty of accurate variant reporting in a clinical setting. An evidence-based scoring system for evaluating the clinical validity of gene-disease associations, proposed by ClinGen, considers experimental as well as genetic evidence. De novo variants are heavily weighted, given the overall rarity in the genome and their contribution to human disease, however they are reported as "genes of unknown significance" in our center when there is insufficient evidence for the gene-disease assertion. We report a collection of 21 de novo variants in genes of unknown clinical significance ascertained via clinical testing, of which eight of 21 (38%) are predicted to cause loss of function. These genes were subjected to ClinGen scoring to assess the strength of gene-disease relationships. Using a cutoff for moderate high or strong, 10 of 21 genes now have sufficient evidence to qualify as likely pathogenic or pathogenic variants. Sharing such cases with phenotypic data is imperative to strengthen available genetic evidence to ultimately upgrade clinical validity classifications and facilitate accurate molecular diagnosis.

Dual Molecular Effects of Dominant RORA Mutations Cause Two Variants of Syndromic Intellectual Disability with Either Autism or Cerebellar Ataxia.

RORα, the RAR-related orphan nuclear receptor alpha, is essential for cerebellar development. The spontaneous mutant mouse staggerer, with an ataxic gait caused by neurodegeneration of cerebellar Purkinje cells, was discovered two decades ago to result from homozygous intragenic Rora deletions. However, RORA mutations were hitherto undocumented in humans. Through a multi-centric collaboration, we identified three copy-number variant deletions (two de novo and one dominantly inherited in three generations), one de novo disrupting duplication, and nine de novo point mutations (three truncating, one canonical splice site, and five missense mutations) involving RORA in 16 individuals from 13 families with variable neurodevelopmental delay and intellectual disability (ID)-associated autistic features, cerebellar ataxia, and epilepsy. Consistent with the human and mouse data, disruption of the D. rerio ortholog, roraa, causes significant reduction in the size of the developing cerebellum. Systematic in vivo complementation studies showed that, whereas wild-type human RORA mRNA could complement the cerebellar pathology, missense variants had two distinct pathogenic mechanisms of either haploinsufficiency or a dominant toxic effect according to their localization in the ligand-binding or DNA-binding domains, respectively. This dichotomous direction of effect is likely relevant to the phenotype in humans: individuals with loss-of-function variants leading to haploinsufficiency show ID with autistic features, while individuals with de novo dominant toxic variants present with ID, ataxia, and cerebellar atrophy. Our combined genetic and functional data highlight the complex mutational landscape at the human RORA locus and suggest that dual mutational effects likely determine phenotypic outcome.

Global characterization of copy number variants in epilepsy patients from whole genome sequencing.

Epilepsy will affect nearly 3% of people at some point during their lifetime. Previous copy number variants (CNVs) studies of epilepsy have used array-based technology and were restricted to the detection of large or exonic events. In contrast, whole-genome sequencing (WGS) has the potential to more comprehensively profile CNVs but existing analytic methods suffer from limited accuracy. We show that this is in part due to the non-uniformity of read coverage, even after intra-sample normalization. To improve on this, we developed PopSV, an algorithm that uses multiple samples to control for technical variation and enables the robust detection of CNVs. Using WGS and PopSV, we performed a comprehensive characterization of CNVs in 198 individuals affected with epilepsy and 301 controls. For both large and small variants, we found an enrichment of rare exonic events in epilepsy patients, especially in genes with predicted loss-of-function intolerance. Notably, this genome-wide survey also revealed an enrichment of rare non-coding CNVs near previously known epilepsy genes. This enrichment was strongest for non-coding CNVs located within 100 Kbp of an epilepsy gene and in regions associated with changes in the gene expression, such as expression QTLs or DNase I hypersensitive sites. Finally, we report on 21 potentially damaging events that could be associated with known or new candidate epilepsy genes. Our results suggest that comprehensive sequence-based profiling of CNVs could help explain a larger fraction of epilepsy cases.

Novel heterozygous pathogenic variants in CHUK in a patient with AEC-like phenotype, immune deficiencies and 1q21.1 microdeletion syndrome: a case report.

BACKGROUND: Ectodermal dysplasias (ED) are a group of diseases that affects the development or function of the teeth, hair, nails and exocrine and sebaceous glands. One type of ED, ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC or Hay-Wells syndrome), is an autosomal dominant disease characterized by the presence of skin erosions affecting the palms, soles and scalp. Other clinical manifestations include ankyloblepharon filiforme adnatum, cleft lip, cleft palate, craniofacial abnormalities and ectodermal defects such as sparse wiry hair, nail changes, dental changes, and subjective hypohydrosis. CASE PRESENTATION: We describe a patient presenting clinical features reminiscent of AEC syndrome in addition to recurrent infections suggestive of immune deficiency. Genetic testing for TP63, IRF6 and RIPK4 was negative. Microarray analysis revealed a 2 MB deletion on chromosome 1 (1q21.1q21.2). Clinical exome sequencing uncovered compound heterozygous variants in CHUK; a maternally-inherited frameshift variant (c.1365del, p.Arg457Aspfs*6) and a de novo missense variant (c.1388C > A, p.Thr463Lys) on the paternal allele. CONCLUSIONS: To our knowledge, this is the fourth family reported with CHUK-deficiency and the second patient with immune abnormalities. This is the first case of CHUK-deficiency with compound heterozygous pathogenic variants, including one variant that arose de novo. In comparison to cases found in the literature, this patient demonstrates a less severe phenotype than previously described.

High Rate of Recurrent De Novo Mutations in Developmental and Epileptic Encephalopathies.

Developmental and epileptic encephalopathy (DEE) is a group of conditions characterized by the co-occurrence of epilepsy and intellectual disability (ID), typically with developmental plateauing or regression associated with frequent epileptiform activity. The cause of DEE remains unknown in the majority of cases. We performed whole-genome sequencing (WGS) in 197 individuals with unexplained DEE and pharmaco-resistant seizures and in their unaffected parents. We focused our attention on de novo mutations (DNMs) and identified candidate genes containing such variants. We sought to identify additional subjects with DNMs in these genes by performing targeted sequencing in another series of individuals with DEE and by mining various sequencing datasets. We also performed meta-analyses to document enrichment of DNMs in candidate genes by leveraging our WGS dataset with those of several DEE and ID series. By combining these strategies, we were able to provide a causal link between DEE and the following genes: NTRK2, GABRB2, CLTC, DHDDS, NUS1, RAB11A, GABBR2, and SNAP25. Overall, we established a molecular diagnosis in 63/197 (32%) individuals in our WGS series. The main cause of DEE in these individuals was de novo point mutations (53/63 solved cases), followed by inherited mutations (6/63 solved cases) and de novo CNVs (4/63 solved cases). De novo missense variants explained a larger proportion of individuals in our series than in other series that were primarily ascertained because of ID. Moreover, these DNMs were more frequently recurrent than those identified in ID series. These observations indicate that the genetic landscape of DEE might be different from that of ID without epilepsy.

Diagnosis and misdiagnosis of adult neuronal ceroid lipofuscinosis (Kufs disease).

OBJECTIVE: To critically re-evaluate cases diagnosed as adult neuronal ceroid lipofuscinosis (ANCL) in order to aid clinicopathologic diagnosis as a route to further gene discovery. METHODS: Through establishment of an international consortium we pooled 47 unsolved cases regarded by referring centers as ANCL. Clinical and neuropathologic experts within the Consortium established diagnostic criteria for ANCL based on the literature to assess each case. A panel of 3 neuropathologists independently reviewed source pathologic data. Cases were given a final clinicopathologic classification of definite ANCL, probable ANCL, possible ANCL, or not ANCL. RESULTS: Of the 47 cases, only 16 fulfilled the Consortium's criteria of ANCL (5 definite, 2 probable, 9 possible). Definitive alternate diagnoses were made in 10, including Huntington disease, early-onset Alzheimer disease, Niemann-Pick disease, neuroserpinopathy, prion disease, and neurodegeneration with brain iron accumulation. Six cases had features suggesting an alternate diagnosis, but no specific condition was identified; in 15, the data were inadequate for classification. Misinterpretation of normal lipofuscin as abnormal storage material was the commonest cause of misdiagnosis. CONCLUSIONS: Diagnosis of ANCL remains challenging; expert pathologic analysis and recent molecular genetic advances revealed misdiagnoses in >1/3 of cases. We now have a refined group of cases that will facilitate identification of new causative genes.

Expanding the clinical phenotype associated with ELOVL4 mutation: study of a large French-Canadian family with autosomal dominant spinocerebellar ataxia and erythrokeratodermia.

IMPORTANCE: The autosomal dominant spinocerebellar ataxias (SCAs) are a complex group of neurodegenerative disorders with significant genetic heterogeneity. Despite the identification of 20 SCA genes, the cause of the disorder in a significant proportion of families with SCA remains unexplained. In 1972, a French-Canadian family segregating a combination of SCA and erythrokeratodermia variabilis (EKV) in an autosomal dominant fashion was described. OBJECTIVE: To map and identify the causative gene in this large family with SCA and EKV using a combination of linkage analysis and whole-exome sequencing. DESIGN, SETTING, AND PARTICIPANTS: A total of 32 individuals from the family have undergone complete neurologic and dermatologic examinations. MAIN OUTCOMES AND MEASURES: Mutations in ELOVL4 have been reported in families with macular degeneration. Recently, homozygous mutations were found in patients with ichthyosis, spastic paraplegia, and severe neurodevelopmental defects. In the present study, we report on a heterozygote mutation in ELOVL4 in affected individuals from the family with SCA and EKV. The mutation segregates with a milder phenotype consisting of early-onset patches of erythema and hyperkeratosis, as well as SCA manifesting in the fourth or fifth decade of life. RESULTS: We describe the mapping and the identification of a c.504G>C transversion in ELOVL4 resulting in the p.L168F substitution. We also provide clinical characterization of the phenotypes in 19 mutation carriers. CONCLUSIONS AND RELEVANCE: We report, to our knowledge, the first mutation in ELOVL4 that is associated with SCA and EKV. This gene encodes a member of the elongase family, which is responsible for the elongation of very long-chain fatty acids (at least 26 carbons). These fatty acids participate in a wide variety of physiological functions, including skin barrier formation and peroxisome ß-oxidation. Overall, these results provide additional insight into the pathogenesis of these complex neurodegenerative disorders.