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Biallelic variants in TSPOAP1, encoding the active-zone protein RIMBP1, cause autosomal recessive dystonia.

ABSTRACT: Dystonia is a debilitating hyperkinetic movement disorder, which can be transmitted as a monogenic trait. Here, we describe homozygous frameshift, nonsense, and missense variants in TSPOAP1, which encodes the active-zone RIM-binding protein 1 (RIMBP1), as a genetic cause of autosomal recessive dystonia in 7 subjects from 3 unrelated families. Subjects carrying loss-of-function variants presented with juvenile-onset progressive generalized dystonia, associated with intellectual disability and cerebellar atrophy. Conversely, subjects carrying a pathogenic missense variant (p.Gly1808Ser) presented with isolated adult-onset focal dystonia. In mice, complete loss of RIMBP1, known to reduce neurotransmission, led to motor abnormalities reminiscent of dystonia, decreased Purkinje cell dendritic arborization, and reduced numbers of cerebellar synapses. In vitro analysis of the p.Gly1808Ser variant showed larger spike-evoked calcium transients and enhanced neurotransmission, suggesting that RIMBP1-linked dystonia can be caused by either reduced or enhanced rates of spike-evoked release in relevant neural networks. Our findings establish a direct link between dysfunction of the presynaptic active zone and dystonia and highlight the critical role played by well-balanced neurotransmission in motor control and disease pathogenesis.

SUBMITTER: Mencacci NE

PROVIDER: S-EPMC8011894 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Biallelic variants in TMEM222 cause a new autosomal recessive neurodevelopmental disorder.

Project description:PurposeTo elucidate the novel molecular cause in families with a new autosomal recessive neurodevelopmental disorder.MethodsA combination of exome sequencing and gene matching tools was used to identify pathogenic variants in 17 individuals. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) and subcellular localization studies were used to characterize gene expression profile and localization.ResultsBiallelic variants in the TMEM222 gene were identified in 17 individuals from nine unrelated families, presenting with intellectual disability and variable other features, such as aggressive behavior, shy character, body tremors, decreased muscle mass in the lower extremities, and mild hypotonia. We found relatively high TMEM222 expression levels in the human brain, especially in the parietal and occipital cortex. Additionally, subcellular localization analysis in human neurons derived from induced pluripotent stem cells (iPSCs) revealed that TMEM222 localizes to early endosomes in the synapses of mature iPSC-derived neurons.ConclusionOur findings support a role for TMEM222 in brain development and function and adds variants in the gene TMEM222 as a novel underlying cause of an autosomal recessive neurodevelopmental disorder.

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Biallelic Pathogenic <i>GFRA1</i> Variants Cause Autosomal Recessive Bilateral Renal Agenesis.

Project description:BackgroundCongenital anomalies of the kidney and urinary tract (CAKUT) are one of the most common malformations identified in the fetal stage. Bilateral renal agenesis (BRA) represents the most severe and fatal form of CAKUT. Only three genes have been confirmed to have a causal role in humans (ITGA8, GREB1L, and FGF20).MethodsGenome sequencing within a diagnostic setting and combined data repository analysis identified a novel gene.ResultsTwo patients presented with BRA, detected during the prenatal period, without additional recognizable malformations. They had parental consanguinity and similarly affected, deceased siblings, suggesting autosomal recessive inheritance. Evaluation of homozygous regions in patient 1 identified a novel, nonsense variant in GFRA1 (NM_001348097.1:c.676C>T, p.[Arg226*]). We identified 184 patients in our repository with renal agenesis and analyzed their exome/genome data. Of these 184 samples, 36 were from patients who presented with isolated renal agenesis. Two of them had loss-of-function variants in GFRA1. The second patient was homozygous for a frameshift variant (NM_001348097.1:c.1294delA, p.[Thr432Profs*13]). The GFRA1 gene encodes a receptor on the Wolffian duct that regulates ureteric bud outgrowth in the development of a functional renal system, and has a putative role in the pathogenesis of Hirschsprung disease.ConclusionsThese findings strongly support the causal role of GFRA1-inactivating variants for an autosomal recessive, nonsyndromic form of BRA. This knowledge will enable early genetic diagnosis and better genetic counseling for families with BRA.

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Biallelic SUN5 Mutations Cause Autosomal-Recessive Acephalic Spermatozoa Syndrome.

Project description:Acephalic spermatozoa syndrome is a rare and severe form of teratozoospermia characterized by a predominance of headless spermatozoa in the ejaculate. Family clustering and consanguinity suggest a genetic origin; however, causative mutations have yet to be identified. We performed whole-exome sequencing in two unrelated infertile men and subsequent variant filtering identified one homozygous (c.824C>T [p.Thr275Met]) and one compound heterozygous (c.1006C>T [p.Arg356Cys] and c.485T>A [p.Met162Lys]) SUN5 (also named TSARG4) variants. Sanger sequencing of SUN5 in 15 additional unrelated infertile men revealed four compound heterozygous (c.381delA [p.Val128Serfs∗7] and c.824C>T [p.Thr275Met]; c.381delA [p.Val128Serfs∗7] and c.781G>A [p.Val261Met]; c.216G>A [p.Trp72∗] and c.1043A>T [p.Asn348Ile]; c.425+1G>A/c.1043A>T [p.Asn348Ile]) and two homozygous (c.851C>G [p.Ser284∗]; c.350G>A [p.Gly114Arg]) variants in six individuals. These 10 SUN5 variants were found in 8 of 17 unrelated men, explaining the genetic defect in 47.06% of the affected individuals in our cohort. These variants were absent in 100 fertile population-matched control individuals. SUN5 variants lead to absent, significantly reduced, or truncated SUN5, and certain variants altered SUN5 distribution in the head-tail junction of the sperm. In summary, these results demonstrate that biallelic SUN5 mutations cause male infertility due to autosomal-recessive acephalic spermatozoa syndrome.

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Mutations in HPCA cause autosomal-recessive primary isolated dystonia.

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Autosomal recessive Noonan syndrome associated with biallelic LZTR1 variants.

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Project description:Primary familial brain calcification (PFBC) is characterized by calcium deposition in the brain, causing progressive movement disorders, psychiatric symptoms, and cognitive decline. PFBC is a heterogeneous disorder currently linked to variants in six different genes, but most patients remain genetically undiagnosed. Here, we identify biallelic NAA60 variants in ten individuals from seven families with autosomal recessive PFBC. The NAA60 variants lead to loss-of-function with lack of protein N-terminal (Nt)-acetylation activity. We show that the phosphate importer SLC20A2 is a substrate of NAA60 in vitro. In cells, loss of NAA60 caused reduced surface levels of SLC20A2 and a reduction in extracellular phosphate uptake. This study establishes NAA60 as a causal gene for PFBC, provides a possible biochemical explanation of its disease-causing mechanisms and underscores NAA60-mediated Nt-acetylation of transmembrane proteins as a fundamental process for healthy neurobiological functioning.

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Biallelic truncating mutations in FMN2, encoding the actin-regulatory protein Formin 2, cause nonsyndromic autosomal-recessive intellectual disability.

Project description:Dendritic spines represent the major site of neuronal activity in the brain; they serve as the receiving point for neurotransmitters and undergo rapid activity-dependent morphological changes that correlate with learning and memory. Using a combination of homozygosity mapping and next-generation sequencing in two consanguineous families affected by nonsyndromic autosomal-recessive intellectual disability, we identified truncating mutations in formin 2 (FMN2), encoding a protein that belongs to the formin family of actin cytoskeleton nucleation factors and is highly expressed in the maturing brain. We found that FMN2 localizes to punctae along dendrites and that germline inactivation of mouse Fmn2 resulted in animals with decreased spine density; such mice were previously demonstrated to have a conditioned fear-learning defect. Furthermore, patient neural cells derived from induced pluripotent stem cells showed correlated decreased synaptic density. Thus, FMN2 mutations link intellectual disability either directly or indirectly to the regulation of actin-mediated synaptic spine density.

| S-EPMC4259997 | biostudies-literature

Biallelic sequence and structural variants in RAX2 are a novel cause for autosomal recessive inherited retinal disease.

Project description:PURPOSE:RAX2 encodes a homeobox-containing transcription factor, in which four monoallelic pathogenic variants have been described in autosomal dominant cone-dominated retinal disease. METHODS:Exome sequencing in a European cohort with inherited retinal disease (IRD) (n?=?2086) was combined with protein structure modeling of RAX2 missense variants, bioinformatics analysis of deletion breakpoints, haplotyping of RAX2 variant c.335dup, and clinical assessment of biallelic RAX2-positive cases and carrier family members. RESULTS:Biallelic RAX2 sequence and structural variants were found in five unrelated European index cases, displaying nonsyndromic autosomal recessive retinitis pigmentosa (ARRP) with an age of onset ranging from childhood to the mid-40s (average mid-30s). Protein structure modeling points to loss of function of the novel recessive missense variants and to a dominant-negative effect of the reported dominant RAX2 alleles. Structural variants were fine-mapped to disentangle their underlying mechanisms. Haplotyping of c.335dup in two cases suggests a common ancestry. CONCLUSION:This study supports a role for RAX2 as a novel disease gene for recessive IRD, broadening the mutation spectrum from sequence to structural variants and revealing a founder effect. The identification of biallelic RAX2 pathogenic variants in five unrelated families shows that RAX2 loss of function may be a nonnegligible cause of IRD in unsolved ARRP cases.

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Two Compound Heterozygous Variants in <i>SNX14</i> Cause Stereotypies and Dystonia in Autosomal Recessive Spinocerebellar Ataxia 20.

Project description:Autosomal Recessive Spinocerebellar Ataxia 20, SCAR20, is a rare condition characterized by intellectual disability, lack of speech, ataxia, coarse facies and macrocephaly, caused by SNX14 variants. While all cases described are due to homozygous variants that generally result in loss of protein, so far there are no other cases of reported compound heterozygous variants. Here we describe the first non-consanguineous SCAR20 family, the second Portuguese, with two siblings presenting similar clinical features caused by compound heterozygous SNX14 variants: NM_001350532.1:c.1195C>T, p.(Arg399*) combined with a novel complex genomic rearrangement. Quantitative PCR (Q-PCR), long-range PCR and sequencing was used to elucidate the region and mechanisms involved in the latter: two deletions, an inversion and an AG insertion: NM_001350532.1:c.[612+3028_698-2759del;698-2758_698-516inv;698-515_1171+1366delinsAG]. In silico analyses of these variants are in agreement with causality, enabling a genotype-phenotype correlation in both patients. Clinical phenotype includes dystonia and stereotypies never associated with SCAR20. Overall, this study allowed to extend the knowledge of the phenotypic and mutational spectrum of SCAR20, and to validate the role of Sorting nexin-14 in a well-defined neurodevelopmental syndrome, which can lead to cognitive impairment. We also highlight the value of an accurate clinical evaluation and deep phenotyping to disclose the molecular defect underlying highly heterogeneous condition such as intellectual disability.

| S-EPMC7543990 | biostudies-literature

Novel biallelic variants in COL7A1 cause recessive dystrophic epidermolysis bullosa.

Project description:BackgroundAutosomal recessive dystrophic epidermolysis bullosa (RDEB) is an incurable and severe inherited skin disorder characterized by recurrent blistering at the sublamina densa beneath the cutaneous basement membrane. It is caused by biallelic loss-of-function mutation in the gene encoding type VII collagen (COL7A1). This study aimed to identify the causative variants of a Chinese RDEB patient and further provide prenatal diagnosis for the ongoing risk pregnancy of the proband's mother.MethodsClinical exome sequencing (CES) has been performed and an in-house pipeline was used to conduct a phenotype-driven data analysis. A minigene assay was used to verify the pathogenicity of a novel splice site variant in the COL7A1.ResultsHere we report two compound heterozygous variants in COL7A1, c.3867delT (p.G1290Efs*35) and c.5532+4_5532+5delAG, identified in a RDEB patient by CES. The minigene assay confirmed that thec.5532+4_5532+5delAGchange was a noncanonic splice site variant leading to in an in-frame deletion of exon 64. Prenatal diagnosis indicated that the present pregnancy of the patient's mother was not affected.ConclusionOur study expands the mutation spectrum of COL7A1 and demonstrated that CES and minigene assays were efficient tools for RDEB molecular diagnoses.

| S-EPMC7434731 | biostudies-literature

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