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Spinocerebellar disorders are a vast group of rare neurogenetic conditions, generally characterized by overlapping clinical symptoms including progressive cerebellar ataxia, spastic paraparesis, cognitive deficiencies, skeletal/muscular and ocular abnormalities. The objective of the present study is to identify the underlying genetic causes of the rare spinocerebellar disorders in the Pakistani population. Herein, nine consanguineous families presenting different spinocerebellar phenotypes have been investigated using whole exome sequencing. Sanger sequencing was performed for segregation analysis in all the available individuals of each family. The molecular analysis of these families identified six novel pathogenic/likely pathogenic variants; ZFYVE26: c.1093del, SACS: c.1201C>T, BICD2: c.2156A>T, ALS2: c.2171-3T>G, ALS2: c.3145T>A, and B4GALNT1: c.334_335dup, and three already reported pathogenic variants; FA2H: c.159_176del, APTX: c.689T>G, and SETX: c.5308_5311del. The clinical features of all patients in each family are concurrent with the already reported cases. Hence, the current study expands the mutation spectrum of rare spinocerebellar disorders and implies the usefulness of next-generation sequencing in combination with clinical investigation for better diagnosis of these overlapping phenotypes.

International audience; Bardet-Biedl syndrome (BBS) is a ciliopathy characterized by retinitis pigmentosa, obesity, polydactyly, cognitive impairment and renal failure. Pathogenic variants in 24 genes account for the molecular basis of >80% of cases. Toward saturated discovery of the mutational basis of the disorder, we carefully explored our cohorts and identified a hominid-specific SINE-R/VNTR/Alu type F (SVA-F) insertion in exon 13 of BBS1 in eight families. In six families, the repeat insertion was found in trans with c.1169 T > G, p.Met390Arg and in two families the insertion was found in addition to other recessive BBS loci. Whole genome sequencing, de novo assembly and SNP array analysis were performed to characterize the genomic event. This insertion is extremely rare in the general population (found in 8 alleles of 8 BBS cases but not in >10 800 control individuals from gnomAD-SV) and due to a founder effect. Its 2435 bp sequence contains hallmarks of LINE1 mediated retrotransposition. Functional studies with patient-derived cell lines confirmed that the BBS1 SVA-F is deleterious as evidenced by a significant depletion of both mRNA and protein levels. Such findings highlight the importance of dedicated bioinformatics pipelines to identify all types of variation.

In this paper I argue that it’s impossible for there to be a single universal theory of meaning for a language. First, I will consider some minimal expressiveness requirements a language must meet to be able to express semantic claims. Then I will argue that in order to have a single unified theory of meaning, these expressiveness requirements must be satisfied by a language which the semantic theory itself applies to. That is, we would need a language which can express its own meaning. It has been well-known since Tarski that theories of meaning whose central notion is truth can’t be expressed in a language which they apply to. Here, I develop Quine’s formulation of the Liar Paradox in grammatical terms and use this to extend Tarski’s result to all theories of meaning. This general version of the paradox can be formalised as a special case of the Lawvere Fixed-Point Theorem applied to a categorial grammar. Taken together with the initial arguments, I infer that a universal theory of meaning is impossible and conclude the paper with a brief discussion on what alternatives are available.

PurposeThe rationale behind the SUDden cardiac Death in the Young (SUDDY) cohort was to provide a complete nationwide, high-quality platform with integrated multisource data, for clinical and genetic research on sudden cardiac death (SCD) in the young, with the ultimate goal to predict and prevent SCD.ParticipantsThe cohort contains all SCD victims Findings to dateWe identified 903 individuals diagnosed with SCD (67% men, 33% women). The cases comprised 236 infants Future plansWe will explore the SUDDY cohort for symptoms and healthcare consumption, socioeconomic variables and family history of SCD. Furthermore, we will perform whole exome sequencing analysis on DNA of cases obtained from DBS or postmortem samples together with parental blood samples in search for gene variants associated with cardiac disease. The genetic analysis together with data compiled in the nationwide cohort is expected to improve current knowledge on the incidence, aetiology, clinical characteristics and family history of SCD.

Background Oesophageal atresia (OA) is a life-threatening developmental defect characterized by a lost continuity between the upper and lower oesophagus. The most common form is a distal connection between the trachea and the oesophagus, i.e. a tracheoesophageal fistula (TEF). The condition may be part of a syndrome or occurs as an isolated feature. The recurrence risk in affected families is increased compared to the population-based incidence suggesting contributing genetic factors. Methods To gain insight into gene variants and genes associated with isolated OA we conducted whole genome sequencing on samples from three families with recurrent cases affected by congenital and isolated TEF. Results We identified a combination of single nucleotide variants (SNVs), splice site variants (SSV) and structural variants (SV) annotated to altogether 100 coding genes in the six affected individuals. Conclusion This study highlights rare SVs among candidate gene variants in our individuals with OA and provides a gene framework for further investigations of genetic factors behind this malformation.

Induced pluripotent stem cells (iPSCs) from patients are an attractive disease model to study tissues with poor accessibility such as the brain. Using this approach, we and others have shown that trisomy 21 results in genome-wide transcriptional dysregulations. The effects of loss of genes on chromosome 21 is much less characterized. Here, we use patient-derived neural cells from an individual with neurodevelopmental delay and a ring chromosome 21 with two deletions spanning 3.8 Mb at the terminal end of 21q22.3, containing 60 protein-coding genes. To investigate the molecular perturbations of the partial monosomy on neural cells, we established patient-derived iPSCs from fibroblasts retaining the ring chromosome 21, and we then induced iPSCs into neuroepithelial stem cells. RNA-Seq analysis of NESCs with the ring chromosome revealed downregulation of 18 genes within the deleted region together with global transcriptomic dysregulations when compared to euploid NESCs. Since the deletions on chromosome 21 represent a genetic "contrary" to trisomy of the corresponding region, we further compared the dysregulated transcriptomic profile in with that of two NESC lines with trisomy 21. The analysis revealed opposed expression changes for 23 genes on chromosome 21 as well as 149 non-chromosome 21 genes. Taken together, our results bring insights into the effects on the global and chromosome 21 specific gene expression from a partial monosomy of chromosome 21qter during early neuronal differentiation.

Heterozygous variants in POLR2A, encoding the largest subunit of RNA polymerase II, cause severe neurodevelopmental and multisystem abnormalities in humans. Using CRISPR/Cas9 we generated the human iPSC line KICRi002A-5 with a heterozygous truncating 4 bp insertion in exon 5 of the POLR2A gene. Analysis using qRT-PCR confirmed reduced POLR2A mRNA in KICRi002A-5 vs. the isogenic WT iPSC line. The edited iPSC line expressed pluripotency markers and exhibited differentiation capacity into the three germ layers. Assessment of genomic integrity revealed a normal karyotype and OFF-target editing was excluded. The iPSC line KICRi002A-5 provides a useful resource to study mechanisms underlying developmental defects caused by RBP1 insufficiency.

GPR56 gene is best known for its pivotal role in cerebral cortical development. Mutations in GPR56 give rise to cobblestone-like brain malformation, white matter changes and cerebellar dysplasia. This study aimed to identify causative variant in a consanguineous family having five individuals affected with developmental delay, mild to severe intellectual disability, speech impairment, strabismus and seizures. Whole exome sequencing was performed to identify mutation in affected individuals. Variants were filtered and further validated by Sanger sequencing and segregation analysis. A novel frameshift variant c.1601dupT leading to p.Ala535GlyfsTer17) was identified in GPR56 gene by whole exome sequencing and subsequent filtering. All five affected individuals were homozygous for the mutant allele while four asymptomatic individuals carried the variant in heterozygous state. Radiological findings of a representative patient presented features of GPR56-associated cobblestone like brain malformation. MRI findings suggested paucity of sulci, dilated ventricular system and brainstem atrophy. The microgyria were observed in a simplified gyral pattern (cobblestone). This single bp insertion, and the consequent frameshift, results in the truncation of GPR56 protein. This could result in a malformed cortex giving the brain a cobblestone like shape. Our study identified a 7th novel frameshift variant from Pakistani population in GPR56 gene, thus broadening mutation spectrum.

Combined measurements of mRNA and protein expression in single cells enable in-depth analysis of cellular states. We present SPARC, an approach that combines single-cell RNA-sequencing with proximity extension essays to simultaneously measure global mRNA and 89 intracellular proteins in individual cells. We show that mRNA expression fails to accurately reflect protein abundance at the time of measurement, although the direction of changes is in agreement during neuronal differentiation. Moreover, protein levels of transcription factors better predict their downstream effects than do their corresponding transcripts. Finally, we highlight that protein expression variation is overall lower than mRNA variation, but relative protein variation does not reflect the mRNA level. Our results demonstrate that mRNA and protein measurements in single cells provide different and complementary information regarding cell states. SPARC presents a state-of-the-art co-profiling method that overcomes current limitations in throughput and protein localization, including removing the need for cell fixation., Here, the authors present SPARC, a scalable approach for simultaneously measuring mRNA expression levels and targeted intracellular protein levels in single cells. They use SPARC to measure dynamic expression changes in human cells during neuronal differentiation and show that mRNA levels are poor predictors of protein abundances and activity in individual cells, indicating that the measurements are complementary.

Hereditary Spastic paraplegias (HSPs) are heterogeneous group of degenerative disorders characterized by progressive weakness and spasticity of the lower limbs, combined with additional neurological features. This study aimed to identify causative gene variants in two nonrelated consanguineous Pakistani families segregating HSP. Whole exome sequencing (WES) was performed on a total of five individuals from two families including four affected and one phenotypically normal individual. The variants were validated by Sanger sequencing and segregation analysis. In family A, a novel homozygous variant c.604G > A (p.Glu202Lys) was identified in the CYP2U1 gene with clinical symptoms of SPG56 in 3 siblings. Whereas, a previously reported variant c.5769delT (p.Ser1923Argfs*28) in the SPG11 gene was identified in family B manifesting clinical features of SPG11 in 3 affected individuals. Our combined findings add to the clinical and genetic variability associated with CYP2U1 and SPG11 variants highlighting the complexity of HSPs. These findings further emphasize the usefulness of WES as a powerful diagnostic tool.

Availability of numerous high-quality iPSC lines is needed to overcome donor-associated variability caused by genetic background effects. We generated two human iPSC lines from dermal fibroblasts of two healthy females using Sendai virus reprogramming. Quality assessment of the iPSC lines confirmed the expression of pluripotency markers, trilineage differentiation capacity and absence of exogenous expression of reprogramming factors. Both iPSC lines were genetically stable with a genotype that matched the fibroblast lines of donors. These iPSC lines add to available reference lines as a resource for disease modeling of polygenic and multifactorial diseases, for evaluation of differentiation protocols and toxicology screening. Svitlana Vasylovska and Jens Schuster contributed equally to the study.

International audience; Neurochondrin (NCDN) is a cytoplasmatic neural protein of importance for neural growth, glutamate receptor (mGluR) signaling, and synaptic plasticity. Conditional loss of Ncdn in mice neural tissue causes depressive-like behaviors, impaired spatial learning, and epileptic seizures. We report on NCDN missense variants in six affected individuals with variable degrees of developmental delay, intellectual disability (ID), and seizures. Three siblings were found homozygous for a NCDN missense variant, whereas another three unrelated individuals carried different de novo missense variants in NCDN. We assayed the missense variants for their capability to rescue impaired neurite formation in human neuroblastoma (SH-SY5Y) cells depleted of NCDN. Overexpression of wild-type NCDN rescued the neurite-phenotype in contrast to expression of NCDN containing the variants of affected individuals. Two missense variants, associated with severe neurodevelopmental features and epilepsy, were unable to restore mGluR5-induced ERK phosphorylation. Electrophysiological analysis of SH-SY5Y cells depleted of NCDN exhibited altered membrane potential and impaired action potentials at repolarization, suggesting NCDN to be required for normal biophysical properties. Using available transcriptome data from human fetal cortex, we show that NCDN is highly expressed in maturing excitatory neurons. In combination, our data provide evidence that bi-allelic and de novo variants in NCDN cause a clinically variable form of neurodevelopmental delay and epilepsy, highlighting a critical role for NCDN in human brain development.

Ataxias constitute a group of heterogeneous diseases with overlapping symptoms. The clinical investigation should primarily seek for treatable conditions such as neurometabolic disorders and autoimmune diseases. Rapid progression is often characteristic for paraneoplastic cerebellar degeneration, autoimmune diseases or multiple system atrophy (MSA). The rapid development of massive parallel DNA sequencing and its increased accessibility have enabled for improved diagnostic resolution of patients. A diagnosis based on the etiology is crucial for prognosis and treatment of ataxias. In hereditary forms, the identification of causative genetic factors is essential for family planning.

PAX6 gene mutations cause a variety of eye and central nervous system (CNS) abnormalities. Aniridia is often accompanied by CNS abnormalities such as pineal gland atrophy or hypoplasia, leading to disturbed circadian rhythm and sleep disorders. Less is known on the coincidence of narcolepsy in this patient group. We aimed to find out whether the circadian rhythm or sleep-wake structure was affected in patients with aniridia. Four members of a family segregating with congenital aniridia in two generations were included in the study. The patients were subjected to genetic testing for a PAX6 mutation, multiple sleep latency test, whole-brain magnetic resonance imaging (MRI), hypocretin-1 in cerebrospinal fluid, and Human Leukocyte Antigen DQ beta1*06:02. All four members were heterozygous for the pathogenic c.959-1G>A mutation in the PAX6 gene. Sleep disturbance was observed in all family members. The index patient was diagnosed with narcolepsy. MRI showed a hypoplastic pineal gland in all members. We describe the first case of a patient with PAX6 haploinsufficiency, aniridia and pineal gland hypoplasia diagnosed with narcolepsy type-1, suggesting a complex sleep disorder pathogenesis.

Background Down syndrome (DS) is characterized by neurodevelopmental abnormalities caused by partial or complete trisomy of human chromosome 21 (T21). Analysis of Down syndrome brain specimens has shown global epigenetic and transcriptional changes but their interplay during early neurogenesis remains largely unknown. We differentiated induced pluripotent stem cells (iPSCs) established from two DS patients with complete T21 and matched euploid donors into two distinct neural stages corresponding to early- and mid-gestational ages. Results Using the Illumina Infinium 450K array, we assessed the DNA methylation pattern of known CpG regions and promoters across the genome in trisomic neural iPSC derivatives, and we identified a total of 500 stably and differentially methylated CpGs that were annotated to CpG islands of 151 genes. The genes were enriched within the DNA binding category, uncovering 37 factors of importance for transcriptional regulation and chromatin structure. In particular, we observed regional epigenetic changes of the transcription factor genes ZNF69, ZNF700 and ZNF763 as well as the HOXA3, HOXB3 and HOXD3 genes. A similar clustering of differential methylation was found in the CpG islands of the HIST1 genes suggesting effects on chromatin remodeling. Conclusions The study shows that early established differential methylation in neural iPSC derivatives with T21 are associated with a set of genes relevant for DS brain development, providing a novel framework for further studies on epigenetic changes and transcriptional dysregulation during T21 neurogenesis.

Lissencephaly comprises a spectrum of brain malformations due to impaired neuronal migration in the developing cerebral cortex. Classical lissencephaly is characterized by smooth cerebral surface and cortical thickening that result in seizures, severe neurological impairment and developmental delay. Mutations in the X-chromosomal gene DCX, encoding doublecortin, is the main cause of classical lissencephaly. Much of our knowledge about DCX-associated lissencephaly comes from post-mortem analyses of patient's brains, mainly since animal models with DCX mutations do not mimic the disease. In the absence of relevant animal models and patient brain specimens, we took advantage of induced pluripotent stem cell (iPSC) technology to model the disease. We established human iPSCs from two males with mutated DCX and classical lissencephaly including smooth brain and abnormal cortical morphology. The disease was recapitulated by differentiation of iPSC into neural cells followed by expression profiling and dissection of DCX-associated functions. Here we show that neural stem cells, with absent or reduced DCX protein expression, exhibit impaired migration, delayed differentiation and deficient neurite formation. Hence, the patient-derived iPSCs and neural stem cells provide a system to further unravel the functions of DCX in normal development and disease.

Spinocerebellar ataxias (SCA) comprise a heterogeneous group of inherited neurological disorders characterized by a range of symptoms from both cerebellar and extra cerebellar structures. We investigated the cause of autosomal recessive, congenital SCA in six affected family members from a large consanguineous family. Using whole-exome sequencing, we identified a homozygous ITPR1 missense variant [c.5360T>C; p.(L1787P)] segregating in all affected individuals. Heterozygous carriers were asymptomatic despite cerebellar hypoplasia. Variants in the ITPTR1 gene have previously been associated exclusively with autosomal dominant SCA15 and SCA29 with slow or no progression. The L1787 residue is highly conserved and the leucine to proline substitution has a predicted destabilizing effect on the protein structure. Additionally, the L1787P variant is located in a domain separated from previously described and dominant-acting missense variants consistent with a distinct effect on IP3R1 tetramer structure and function. Taken together, we show for the first time that a biallelic ITPR1 missense variant may cause an autosomal recessive and infantile onset SCA29, albeit with subclinical cerebellar hypoplasia in carriers. Our findings add to the genetic complexity of SCA29 and broaden the correlations between ITPR1 variants and their clinical expression.

We describe eight subjects from two consanguineous families segregating with autosomal recessive childhood onset spastic ataxia, peripheral neuropathy and intellectual disability. The degree of intellectual disability varied from mild to severe and all four affected individuals in one family developed aggressive behavior and epilepsy. Using exome sequencing, we identified two novel truncating mutations (c.2656CT (p.Gln886*)) and (c.4756_4760delAATCA (p.Asn1586Tyrfs*3)) in the SACS gene responsible for autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS). MRI revealed typical cerebellar and pontine changes associated with ARSACS as well as multiple supratentorial changes in both families as likely contributing factors to the cognitive symptoms. Intellectual disability and behavioral abnormalities have been reported in some cases of ARSACS but are not a part of the characteristic triad of symptoms that includes cerebellar ataxia, spasticity and peripheral neuropathy. Our combined findings bring further knowledge to the phenotypic spectrum, neurodegenerative changes and genetic variability associated with the SACS gene of clinical and diagnostic importance.

Combined measurements of mRNA and protein expression in single cells enables in-depth analysis of cellular states. We present single-cell protein and RNA co-profiling (SPARC), an approach to simultaneously measure global mRNA and large sets of intracellular protein in individual cells. Using SPARC, we show that mRNA expression fails to accurately reflect protein abundance at the time of measurement in human embryonic stem cells, although the direction of changes of mRNA and protein expression are in agreement during cellular differentiation. Moreover, protein levels of transcription factors better predict their downstream effects than do the corresponding transcripts. We further show that changes of the balance between protein and mRNA expression levels can be applied to infer expression kinetic trajectories, revealing future states of individual cells. Finally, we highlight that mRNA expression may be more varied among cells than levels of the corresponding proteins. Overall, our results demonstrate that mRNA and protein measurements in single cells provide different and complementary information regarding cell states. Accordingly, SPARC can offer valuable insights in gene expression programs of single cells.

Bi-allelic loss-of-function variants in genes that encode subunits of the adaptor protein complex 4 (AP-4) lead to prototypical yet poorly understood forms of childhood-onset and complex hereditary spastic paraplegia: SPG47 (AP4B1), SPG50 (AP4M1), SPG51 (AP4E1) and SPG52 (AP4S1). Here, we report a detailed cross-sectional analysis of clinical, imaging and molecular data of 156 patients from 101 families. Enrolled patients were of diverse ethnic backgrounds and covered a wide age range (1.0–49.3 years). While the mean age at symptom onset was 0.8 ± 0.6 years [standard deviation (SD), range 0.2–5.0], the mean age at diagnosis was 10.2 ± 8.5 years (SD, range 0.1–46.3). We define a set of core features: early-onset developmental delay with delayed motor milestones and significant speech delay (50% non-verbal); intellectual disability in the moderate to severe range; mild hypotonia in infancy followed by spastic diplegia (mean age: 8.4 ± 5.1 years, SD) and later tetraplegia (mean age: 16.1 ± 9.8 years, SD); postnatal microcephaly (83%); foot deformities (69%); and epilepsy (66%) that is intractable in a subset. At last follow-up, 36% ambulated with assistance (mean age: 8.9 ± 6.4 years, SD) and 54% were wheelchair-dependent (mean age: 13.4 ± 9.8 years, SD). Episodes of stereotypic laughing, possibly consistent with a pseudobulbar affect, were found in 56% of patients. Key features on neuroimaging include a thin corpus callosum (90%), ventriculomegaly (65%) often with colpocephaly, and periventricular white-matter signal abnormalities (68%). Iron deposition and polymicrogyria were found in a subset of patients. AP4B1-associated SPG47 and AP4M1-associated SPG50 accounted for the majority of cases. About two-thirds of patients were born to consanguineous parents, and 82% carried homozygous variants. Over 70 unique variants were present, the majority of which are frameshift or nonsense mutations. To track disease progression across the age spectrum, we defined the relationship between disease severity as measured by several rating scales and disease duration. We found that the presence of epilepsy, which manifested before the age of 3 years in the majority of patients, was associated with worse motor outcomes. Exploring genotype-phenotype correlations, we found that disease severity and major phenotypes were equally distributed among the four subtypes, establishing that SPG47, SPG50, SPG51 and SPG52 share a common phenotype, an ‘AP-4 deficiency syndrome’. By delineating the core clinical, imaging, and molecular features of AP-4-associated hereditary spastic paraplegia across the age spectrum our results will facilitate early diagnosis, enable counselling and anticipatory guidance of affected families and help define endpoints for future interventional trials.

Dravet syndrome (DS) is an early onset refractory epilepsy typically caused by de novo heterozygous variants in SCN1A encoding the a-subunit of the neuronal sodium channel Na(v)1.1. The syndrome is characterized by age related progression of seizures, cognitive decline and movement disorders. We hypothesized that the distinct neurodevelopmental features in DS are caused by the disruption of molecular pathways in Na(v)1.1 haploinsufficient cells resulting in perturbed neural differentiation and maturation. Here, we established DS-patient and control induced pluripotent stem cell derived neural progenitor cells (iPSC NPC) and GABAergic interneuronal (iPSC GABA) cells. The DS-patient iPSC GABA cells showed a shift in sodium current activation and a perturbed response to induced oxidative stress. Transcriptome analysis revealed specific dysregulations of genes for chromatin structure, mitotic progression, neural plasticity and excitability in DS-patient iPSC NPCs and DS-patient iPSC GABA cells versus controls. The transcription factors FOXM1 and E2F1, positive regulators of the disrupted pathways for histone modification and cell cycle regulation, were markedly up-regulated in DS-iPSC GABA lines. Our study highlights transcriptional changes and disrupted pathways of chromatin remodeling in Na(v)1.1 haploinsufficient GABAergic cells, providing a molecular framework that overlaps with that of neurodevelopmental disorders and other epilepsies. De tre första författarna delar förstaförfattarskapet.

Down syndrome (DS) is caused by trisomy for chromosome 21 (T21). We generated two induced pluripotent stem cell (iPSC) lines from skin fibroblasts of two males with DS using Sendai virus delivery of OCT4, SOX2, KLF4, and c-MYC. Characterization of the two iPSC lines, UUIGPi013-A and UUIPGi014-A, showed that they are genetically stable with a 47,XY,+21 karyotype. Both lines displayed expression of pluripotency markers and trilineage differentiation capacity. These two iPSC lines provide a useful resource for DS modeling and pharmacological interventions.

Megacystis Microcolon Intestinal Hypoperistalsis Syndrome (MMIHS) is a rare congenital disorder, in which heterozygous missense variants in the Enteric Smooth Muscle actin gamma-2 (ACTG2) gene have been recently identified. To investigate the mechanism by which ACTG2 variants lead to MMIHS, we screened a cohort of eleven MMIHS patients, eight sporadic and three familial cases, and performed immunohistochemistry, molecular modeling and molecular dynamics (MD) simulations, and in vitro assays. In all sporadic cases, a heterozygous missense variant in ACTG2 was identified. ACTG2 expression was detected in all intestinal layers where smooth muscle cells are present in different stages of human development. No histopathological abnormalities were found in the patients. Using molecular modeling and MD simulations, we predicted that ACTG2 variants lead to significant changes to the protein function. This was confirmed by in vitro studies, which showed that the identified variants not only impair ACTG2 polymerization, but also contribute to reduced cell contractility. Taken together, our results confirm the involvement of ACTG2 in sporadic MMIHS, and bring new insights to MMIHS pathogenesis.

Vestibular disorders comprise a heterogeneous group of diseases with transient or permanent loss of vestibular function. Vestibulopathy is in most cases associated with migraine, Meniere disease, hereditary ataxias, or sensorineural hearing loss. We identified two brothers and their first cousin affected by hearing loss and episodic vertigo. The brothers were homozygous STRC nonsense variant [c.4027 C > T, p.(Q1343*)], whereas their first cousin was compound heterozygous for the STRC nonsense variant and a 97 kb deletion spanning the entire STRC gene. Clinical investigations confirmed pathological vestibular responses in addition to a characteristic DFNB16 hearing loss. The STRC gene encodes Stereocilin in the cochlea and in the vestibular organ where it ensheathes the kinocilium of the otolithic membranes. Stereocilin is associated with the gel overlaying the vestibular kinocilia, suggesting a role for the protein in sensing balance and spatial orientation. Our findings support such a function for Stereocilin in the vestibular organ and expand the phenotype associated with DFNB16.

Biallelic and pathogenic variants in the RTTN gene, encoding the centrosomal protein Rotatin, are associated with variable degrees of neurodevelopmental abnormalities, microcephaly, and extracranial malformations. To date, no reported case has reached their third decade. Herein, we report on a consanguineous family with three adult members, age 43, 57, and 60 years respectively, with primary microcephaly, developmental delay, primordial dwarfism, and brachydactyly segregating a homozygous splice site variant NM_173630.3:c.5648-5T>A in RTTN. The variant RTTN allele results in a nonhypomorphic skipping of exon 42 and a frameshift [(NP_775901.3:p.Ala1883Glyfs*6)]. Brain MRI of one affected individual showed markedly reduced volume of cerebral lobes and enlarged sulci but without signs of neural migration defects. Our assessment of three adult cases with a biallelic RTTN variant shows that a predicted shortened Rotatin, lacking the C-terminal end, are associated with stationary clinical features into the seventh decade. Furthermore, our report adds brachydactyly to the phenotypic spectrum in this pleiotropic entity.