SIL1 Mutations Research Articles

Genotype-phenotype correlation and adaptive proteome reorganization in Marinesco-Sjögren syndrome

Marinesco-Sjögren Syndrome (MSS) causes cerebellar ataxia, myopathy and congenital cataracts in people carrying SIL1 mutations. SIL1 is an ATP exchange factor for BiP, the major endoplasmic reticulum (ER) chaperone involved in protein folding. SIL1 loss influences BiP activity, leading to ER stress and the activation of unfolded protein response (UPR). Purkinje cells and skeletal muscle fibers are the most sensitive cells to prolonged pathologic UPR, but adverse effects are detectable in other cell types. Currently a clear genotype-phenotype correlation is missing, due to the variable symptomatology and to the discovery of new SIL1 variants. We decided to focus our attention on two recent works providing different strategies to shed light on the pathophysiology of MSS. In the first one several cellular biomarkers have been evaluated to distinguish between malignant and benign SIL1 mutations. The other study proposed a proteomic approach to clarify adaptative mechanisms of MSS fibroblasts in response to SIL1 loss. Further investigations are needed to better understand the pathogenesis of MSS and to simplify the diagnosis in patients.

Identification of novel mutations by targeted next-generation sequencing in Moroccan families clinically diagnosed with a neuromuscular disorder

The identification of underlying genes of genetic conditions has expanded greatly in the past decades, which has broadened the field of genes responsible for inherited neuromuscular diseases. We aimed to investigate mutations associated with neuromuscular disorders phenotypes in 2 Moroccan families. Next-generation sequencing combined with Sanger sequencing could assist with understanding the hereditary variety and underlying disease mechanisms in these disorders. Two novel homozygous mutations were described in this study. The SIL1 mutation is the first identified in the Moroccan population, the mutation was identified as the main cause of Marinesco-Sjogren syndrome in one patient. While the second mutation identified in the fatty acid 2-hydroxylase gene (FA2H) was associated with the Spastic paraplegia 35 in another patient, both transmitted in an autosomal recessive pattern. These conditions are extremely rare in the North African population and may be underdiagnosed due to overlapping clinical characteristics and heterogeneity of these diseases. We have reported in this studymutations associated with the diseases found in the patients. In addition, we have narrowed the phenotypic spectrum, as well as the diagnostic orientation of patients with neuromuscular disorders, who might have very similar symptoms to other disease groups.Keywords: Neuromuscular Disorders; Next-Generation Sequencing; Hereditary Spastic Paraplegia Type 35; North Africa; Marinesco-Sjogren syndrome.

Identification of novel mutations by targeted NGS in Moroccan families clinically diagnosed with a neuromuscular disorder

Background and aimsThe identification of underlying genes of genetic conditions has expanded greatly in the past decades, which has broadened the field of genes responsible for inherited neuromuscular diseases. We aimed to investigate mutations associated with neuromuscular disorders phenotypes in 2 Moroccan families. Material and methodsNext-generation sequencing combined with Sanger sequencing could assist with understanding the hereditary variety and underlying disease mechanisms in these disorders. ResultsTwo novel homozygous mutations were described in this study. The SIL1 mutation is the first identified in the Moroccan population, the mutation was identified as the main cause of Marinesco-Sjogren syndrome in one patient. While the second mutation identified in the fatty acid 2-hydroxylase gene (FA2H) was associated with the Spastic paraplegia 35 in another patient, both transmitted in an autosomal recessive pattern. Discussion and conclusionsThese conditions are extremely rare in the North African population and may be underdiagnosed due to overlapping clinical characteristics and heterogeneity of these diseases. We have reported in this study mutations associated with the diseases found in the patients. In addition, we have narrowed the phenotypic spectrum, as well as the diagnostic orientation of patients with neuromuscular disorders, who might have very similar symptoms to other disease groups.

INPP5K and SIL1 associated pathologies with overlapping clinical phenotypes converge through dysregulation of PHGDH.

Marinesco-Sjögren syndrome is a rare human disorder caused by biallelic mutations in SIL1 characterized by cataracts in infancy, myopathy and ataxia, symptoms which are also associated with a novel disorder caused by mutations in INPP5K. While these phenotypic similarities may suggest commonalties at a molecular level, an overlapping pathomechanism has not been established yet. In this study, we present six new INPP5K patients and expand the current mutational and phenotypical spectrum of the disease showing the clinical overlap between Marinesco-Sjögren syndrome and the INPP5K phenotype. We applied unbiased proteomic profiling on cells derived from Marinesco-Sjögren syndrome and INPP5K patients and identified alterations in d-3-PHGDH as a common molecular feature. d-3-PHGDH modulates the production of l-serine and mutations in this enzyme were previously associated with a neurological phenotype, which clinically overlaps with Marinesco-Sjögren syndrome and INPP5K disease. As l-serine administration represents a promising therapeutic strategy for d-3-PHGDH patients, we tested the effect of l-serine in generated sil1, phgdh and inpp5k a+b zebrafish models, which showed an improvement in their neuronal phenotype. Thus, our study defines a core phenotypical feature underpinning a key common molecular mechanism in three rare diseases and reveals a common and novel therapeutic target for these patients.

Identification of Cellular Pathogenicity Markers for SIL1 Mutations Linked to Marinesco-Sjögren Syndrome.

Background and objective: Recessive mutations in the SIL1 gene cause Marinesco-Sjögren syndrome (MSS), a rare neuropediatric disorder. MSS-patients typically present with congenital cataracts, intellectual disability, cerebellar ataxia and progressive vacuolar myopathy. However, atypical clinical presentations associated with SIL1 mutations have been described over the last years; compound heterozygosity of SIL1 missense mutations even resulted in a phenotype not fulfilling the clinical diagnostic criteria of MSS. Thus, a read-out system to evaluate reliably the pathogenicity of amino acid changes in SIL1 is needed. Here, we aim to provide suitable cellular biomarkers enabling the robust evaluation of pathogenicity of SIL1 mutations.Methods: Five SIL1 variants including one polymorphism (p.K132Q), three known pathogenic mutations (p.V231_I232del, p.G312R, and p.L457P) and one ambiguous missense variant (p.R92W) were studied along with the wild-type proteins in Hek293 in vitro models by cell biological assays, immunoprecipitation, immunoblotting, and immunofluorescence as well as electron microscopy. Moreover, the SIL1-interactomes were interrogated by tandem-affinity-purification and subsequent mass spectrometry.Results: Our combined studies confirmed the pathogenicity of p.V231_I232del, p.G312R, and p.L457P by showing instability of the proteins as well as tendency to form aggregates. This observation is in line with altered structure of the ER-Golgi system and vacuole formation upon expression of these pathogenic SIL1-mutants as well as the presence of oxidative or ER-stress. Reduced cellular fitness along with abnormal mitochondrial architecture could also be observed. Notably, both the polymorphic p.K132Q and the ambiguous p.R92W variants did not elicit such alterations. Study of the SIL1-interactome identified POC1A as a novel binding partner of wild-type SIL1; the interaction is disrupted upon the presence of pathogenic mutants but not influenced by the presence of benign variants. Disrupted SIL1-POC1A interaction is associated with centrosome disintegration.Conclusions: We developed a combination of cellular outcome measures to evaluate the pathogenicity of SIL1 variants in suitable in vitro models and demonstrated that the p. R92W missense variant is a polymorphism rather than a pathogenic mutation leading to MSS.

PERK inhibition delays neurodegeneration and improves motor function in a mouse model of Marinesco-Sjögren syndrome.

Marinesco-Sjögren syndrome (MSS) is a rare, early onset, autosomal recessive multisystem disorder characterized by cerebellar ataxia, cataracts and myopathy. Most MSS cases are caused by loss-of-function mutations in the gene encoding SIL1, a nucleotide exchange factor for the molecular chaperone BiP which is essential for correct protein folding in the endoplasmic reticulum. Woozy mice carrying a spontaneous Sil1 mutation recapitulate key pathological features of MSS, including cerebellar atrophy with degeneration of Purkinje cells and progressive myopathy. Because the PERK branch of the unfolded protein response is activated in degenerating neurons of woozy mice, and inhibiting PERK-mediated translational attenuation has shown protective effects in protein-misfolding neurodegenerative disease models, we tested the therapeutic efficacy of GSK2606414, a potent inhibitor of PERK. Mice were chronically treated with GSK2606414 starting from a presymptomatic stage, and the effects were evaluated on biochemical, histopathological and clinical readouts. GSK2606414 delayed Purkinje cell degeneration and the onset of motor deficits, prolonging the asymptomatic phase of the disease; it also reduced the skeletal muscle abnormalities and improved motor performance during the symptomatic phase. The protein but not the mRNA level of ORP150, a nucleotide exchange factor which can substitute for SIL1, was increased in the cerebellum of GSK2606414-treated woozy mice, suggesting that translational recovery promoted the synthesis of this alternative BiP co-factor. Targeting PERK signaling may have beneficial disease-modifying effects in carriers of SIL1 mutations.

Characterization of the Role for the N‐Terminal Domain on Sil1 Activities as a Nucleotide Exchange Factor and Reductase

The accumulation of reactive oxygen species (ROS) can lead to oxidative stress and play a role in human diseases such as cancer and neurodegenerative diseases. We are interested in studying how cells use ROS as signaling molecules to maintain a balanced redox environment. Using yeast as our model system, we have previously shown that the Hsp70 in the endoplasmic reticulum (ER), BiP, acts as a direct sensor of peroxide, a type of ROS produced during protein folding. BiP has two major domains that regulate its function as a chaperone: an ATPase domain and a substrate‐binding domain. Under ER oxidative stress, yeast BiP's conserved cysteine gets modified/oxidized by peroxide. Modification of BiP's cysteine causes a conformational change, which enhances BiP's ability to bind to substrates, leading to protection of cells under ER oxidative stress. When cells go back to non‐stress conditions, reversibility of BiP's cysteine modification is important for normal cellular function and survival. We have evidence that the protein Sil1, a known nucleotide exchange factor (NEF) of BiP, can remove the modification on BiP's cysteine. We have shown that in addition to acting as a NEF, Sil1 has an unexpected reductase activity that depends on two cysteines, Cys‐52 and Cys‐57, located at the N terminus. While the N‐terminal domain is required for Sil1 activity as a reductase, Sil1 is competent as a NEF even in the absence of the N‐terminal domain. Our goal is to further elucidate the molecular details relating to how the N‐terminal region of Sil1 impacts both Sil1 NEF and reductase activity by utilizing a variety of biochemical and biophysical approaches. Our preliminary data suggest that NEF activity is influenced by the presence of the N terminus. Our current data also suggest the N‐terminal domain may adopt multiple conformations, allowing for regulation of Sil1 NEF activity and potentially its activity as a reductase. Of note, mutations in the Sil1 gene have been found in over half of patients with Marinesco‐Sjögren Syndrome (MSS), a rare autosomal disease characterized by early onset cataracts, cerebellar ataxia, and delayed mental development. One such mutations maps near the N‐terminal domain, and we expect that characterization of full‐length Sil1 may also lend further insight into how mutations in Sil1 can cause MSS.Support or Funding InformationNSF GRFP and SUNY Diversity Fellowship

Loss of Sil1, an ER Co‐Chaperone, Causes an Age‐Dependent Collapse of Skeletal Muscle Proteostasis, Affecting Pathways Critical for Muscle Physiology

ObjectiveDecipher molecular mechanism(s) underlying the myopathy associated with Marinesco‐Sjögren syndrome.BackgroundMarinesco‐Sjögren syndrome (MSS) is an autosomal recessive, multisystem disorder clinically characterized by cerebellar ataxia, bilateral cataracts, and progressive myopathy. MSS is attributed to loss‐of‐function mutations in Sil1, a nucleotide exchange factor for the ER resident Hsp70 molecular chaperone‐BiP.MethodsUsing a combination of an inverted screen test, histopathology, electron microscopy, LC‐MS/MS‐based proteomics, real‐time PCR, and western blotting, we investigated the effects of Sil1 disruption in skeletal muscles of the MSS mouse model (Sil1Gt).ResultsSil1Gt mice exhibited progressive loss of skeletal muscle mass and strength beginning around six months of age. Histopathological and ultrastructural investigations confirmed a multifocal, myogenic myopathy which predominantly affected fast myofibers and phenocopied the MSS‐myopathy. Electron microscopy (EM) revealed a severe swelling of sarcoplasmic reticular triads, autophagic vesicles, electron‐dense material suggestive of protein aggregates, and disruption of the overall cytoarchitecture.Quantitative proteomic profiling performed on quadriceps from six‐month‐old Sil1Gt and wild‐type mice identified that 490 proteins were significantly altered, including secretory pathway proteins, as well as proteins residing in all major cellular organelles. Importantly, multiple pathways critical to muscle physiology were strikingly affected.To validate these changes in protein expression and to determine their onset and progression, we performed western blotting and mRNA expression analyses on quadriceps derived from mice ranging from 1–18 months of age. Prior to the onset of muscle weakness, we detected increased levels of BiP and the lectin chaperones, accompanied by activation of the unfolded protein response, which became profound after six months. We observed robust increases in markers of autophagy, lysosomal biogenesis, and cytoskeletal remodeling. Conversely, components of glucose metabolism and pentose phosphate pathways were dramatically decreased. Interestingly, while levels of Insulin and Igf1 receptors ‐which are synthesized in the ER‐ were decreased, there was a progressive increase in the insulin‐regulated glucose transporter, Glut4. These changes were accompanied by increased levels of both total and phospho‐Akt, similar to data observed in murine skeletal muscles with genetic ablation of both the Insulin and Igf1 receptors.ConclusionThese findings provide evidence for extensive cellular perturbations upon loss of Sil1 in murine skeletal muscles due to a wide‐spread proteostasis collapse, offering critical insights into pathomechanisms underlying the MSS‐myopathy.

P.98 - Pediatric presentation of Marinesco–Sjögren syndrome with a novel SIL1 mutation in two siblings

P.98 - Pediatric presentation of Marinesco–Sjögren syndrome with a novel SIL1 mutation in two siblings

Novel SIL1 mutations cause cerebellar ataxia and atrophy in a French-Canadian family.

Two French-Canadian sibs with cerebellar ataxia and dysarthria were seen in our neurogenetics clinic. The older brother had global developmental delay and spastic paraplegia. Brain MRIs from these two affected individuals showed moderate to severe cerebellar atrophy. To identify the genetic basis for their disease, we conducted a whole exome sequencing (WES) investigation using genomic DNA prepared from the affected sibs and their healthy father. We identified two mutations in the SIL1 gene, which is reported to cause Marinesco-Sjögren syndrome. This study emphasizes how the diagnosis of patients with ataxic gait and cerebellar atrophy may benefit from WES to identify the genetic cause of their condition.

Hierarchical Functional Specificity of Cytosolic Heat Shock Protein 70 (Hsp70) Nucleotide Exchange Factors in Yeast

Heat shock protein 70 (Hsp70) molecular chaperones play critical roles in protein homeostasis. In the budding yeast Saccharomyces cerevisiae, cytosolic Hsp70 interacts with up to three types of nucleotide exchange factors (NEFs) homologous to human counterparts: Sse1/Sse2 (Heat shock protein 110 (Hsp110)), Fes1 (HspBP1), and Snl1 (Bag-1). All three NEFs stimulate ADP release; however, it is unclear why multiple distinct families have been maintained throughout eukaryotic evolution. In this study we investigate NEF roles in Hsp70 cell biology using an isogenic combinatorial collection of NEF deletion mutants. Utilizing well characterized model substrates, we find that Sse1 participates in most Hsp70-mediated processes and is of particular importance in protein biogenesis and degradation, whereas Fes1 contributes to a minimal extent. Surprisingly, disaggregation and resolubilization of thermally denatured firefly luciferase occurred independently of NEF activity. Simultaneous deletion of SSE1 and FES1 resulted in constitutive activation of heat shock protein expression mediated by the transcription factor Hsf1, suggesting that these two factors are important for modulating stress response. Fes1 was found to interact in vivo preferentially with the Ssa family of cytosolic Hsp70 and not the co-translational Ssb homolog, consistent with the lack of cold sensitivity and protein biogenesis phenotypes for fes1Δ cells. No significant consequence could be attributed to deletion of the minor Hsp110 SSE2 or the Bag homolog SNL1. Together, these lines of investigation provide a comparative analysis of NEF function in yeast that implies Hsp110 is the principal NEF for cytosolic Hsp70, making it an ideal candidate for therapeutic intervention in human protein folding disorders.

A nationwide survey on Marinesco-Sjögren syndrome in Japan.

BackgroundMarinesco-Sjögren syndrome (MSS) is an autosomal recessive multisystem disorder characterized by the tetralogy of cerebellar ataxia, congenital cataracts, intellectual disability, and progressive muscle weakness due to myopathy. MSS is extremely rare, and its clinical, pathological, and genetic features are not yet fully understood.MethodsWe conducted a nationwide, questionnaire-based survey on MSS in Japan and carefully reviewed the medical records of 36 patients suspected of having this disease. In addition, pathological examinations of muscles, sequence and haplotype analysis in SIL1 were performed.ResultsThe patients had been examined between the ages of 2 and 52 years. Delayed psychomotor development and cataracts from early childhood were observed in all patients, whereas no life-threatening events were observed. Mutations in SIL1 were identified in 24 of the 27 patients tested, and 43 of the 48 chromosomes possessed the SIL1 c.936dupG (p.Leu313fs) mutation. The haplotype analysis revealed that 31 of the 32 chromosomes (96.9%) with the c.936dupG mutation had the same haplotype.ConclusionsThe results of haplotype analysis suggested the presence of a founder effect. The clinical features of patients without SIL1 mutations were indistinguishable from those with SIL1 mutations, suggesting the genetic heterogeneity of MSS.

Whole-exome sequence analysis of ataxia telangiectasia-like phenotype

A number of diseases exhibit neurodegeneration with/without additional symptoms such as immunodeficiency, increased cancer risk, and microcephalus. Ataxia telangiectasia and Nijmegen breakage syndrome, for example, develop as a result of mutations in genes involved in the DNA damage response. However, such diseases can be difficult to diagnose as they are only rarely encountered by physicians. To overcome this challenge, nine patients with symptoms that resemble those of ataxia telangiectasia, including neurodegeneration, hypogammaglobulinemia, telangiectasia, and/or elevated serum α-fetoprotein, were subjected to whole-exome sequencing (WES) to identify the causative mutations. Molecular diagnosis was achieved in two patients: one displayed CD40 ligand (CD40LG) deficiency, while a second showed a homozygous SIL1 mutation, which has been linked to Marinesco-Sjögren syndrome (MSS). Typical features of CD40LG deficiency and MSS are distinct from the symptoms usually seen in ataxia telangiectasia. These dissociations between phenotype and genotype make it difficult to achieve molecular diagnosis of orphan diseases. Whole-exome sequencing analyses will assist in the molecular diagnosis of such cases and allow the identification of genotypes that would not be expected from the phenotype.

Marinesco-Sjogren Syndrome and SIL1 Mutations

Investigators from Aachen University, Germany, and multiple centers in Europe, UK, USA, Turkey and Argentina, report the results of SIL1 mutation analysis in 62 patients presenting with early-onset ataxia, cataracts and myopathy, the characteristic Marinesco-Sjogren syndrome triad.

SIL1 , a causative cochaperone gene of M arinesco‐ S jögren syndrome, plays an essential role in establishing the architecture of the developing cerebral cortex

Marinesco-Sjögren syndrome (MSS) is a rare autosomal recessively inherited disorder with mental retardation (MR). Recently, mutations in the SIL1 gene, encoding a co-chaperone which regulates the chaperone HSPA5, were identified as a major cause of MSS. We here examined the pathophysiological significance of SIL1 mutations in abnormal corticogenesis of MSS. SIL1-silencing caused neuronal migration delay during corticogenesis ex vivo. While RNAi-resistant SIL1 rescued the defects, three MSS-causing SIL1 mutants tested did not. These mutants had lower affinities to HSPA5 in vitro, and SIL1-HSPA5 interaction as well as HSPA5 function was found to be crucial for neuronal migration ex vivo. Furthermore time-lapse imaging revealed morphological disorganization associated with abnormal migration of SIL1-deficient neurons. These results suggest that the mutations prevent SIL1 from interacting with and regulating HSPA5, leading to abnormal neuronal morphology and migration. Consistent with this, when SIL1 was silenced in cortical neurons in one hemisphere, axonal growth in the contralateral hemisphere was delayed. Taken together, abnormal neuronal migration and interhemispheric axon development may contribute to MR in MSS.Subject Categories Genetics; Gene Therapy & Genetic Disease;

Myopathy in Marinesco–Sjögren syndrome links endoplasmic reticulum chaperone dysfunction to nuclear envelope pathology

Marinesco-Sjögren syndrome (MSS) features cerebellar ataxia, mental retardation, cataracts, and progressive vacuolar myopathy with peculiar myonuclear alterations. Most MSS patients carry homozygous or compound heterozygous SIL1 mutations. SIL1 is a nucleotide exchange factor for the endoplasmic reticulum resident chaperone BiP which controls a plethora of essential processes in the endoplasmic reticulum. In this study we made use of the spontaneous Sil1 mouse mutant woozy to explore pathomechanisms leading to Sil1 deficiency-related skeletal muscle pathology. We found severe, progressive myopathy characterized by alterations of the sarcoplasmic reticulum, accumulation of autophagic vacuoles, mitochondrial changes, and prominent myonuclear pathology including nuclear envelope and nuclear lamina alterations. These abnormalities were remarkably similar to the myopathy in human patients with MSS. In particular, the presence of perinuclear membranous structures which have been reported as an ultrastructural hallmark of MSS-related myopathy could be confirmed in woozy muscles. We found that these structures are derived from the nuclear envelope and nuclear lamina and associate with proliferations of the sarcoplasmic reticulum. In line with impaired function of BiP secondary to loss of its nucleotide exchange factor Sil1, we observed activation of the unfolded protein response and the endoplasmic-reticulum-associated protein degradation-pathway. Despite initiation of the autophagy-lysosomal system, autophagic clearance was found ineffective which is in agreement with the formation of autophagic vacuoles. This report identifies woozy muscle as a faithful phenocopy of the MSS myopathy. Moreover, we provide a link between two well-established disease mechanisms in skeletal muscle, dysfunction of chaperones and nuclear envelope pathology.

SIL1 mutations and clinical spectrum in patients with Marinesco-Sjögren syndrome

Marinesco-Sjögren syndrome is a rare autosomal recessive multisystem disorder featuring cerebellar ataxia, early-onset cataracts, chronic myopathy, variable intellectual disability and delayed motor development. More recently, mutations in the SIL1 gene, which encodes an endoplasmic reticulum resident co-chaperone, were identified as the main cause of Marinesco-Sjögren syndrome. Here we describe the results of SIL1 mutation analysis in 62 patients presenting with early-onset ataxia, cataracts and myopathy or combinations of at least two of these. We obtained a mutation detection rate of 60% (15/25) among patients with the characteristic Marinesco-Sjögren syndrome triad (ataxia, cataracts, myopathy) whereas the detection rate in the group of patients with more variable phenotypic presentation was below 3% (1/37). We report 16 unrelated families with a total of 19 different SIL1 mutations. Among these mutations are 15 previously unreported changes, including single- and multi-exon deletions. Based on data from our screening cohort and data compiled from the literature we found that SIL1 mutations are invariably associated with the combination of a cerebellar syndrome and chronic myopathy. Cataracts were observed in all patients beyond the age of 7 years, but might be missing in infants. Six patients with SIL1 mutations had no intellectual disability, extending the known wide range of cognitive capabilities in Marinesco-Sjögren syndrome to include normal intelligence. Modestly constant features were somatic growth retardation, skeletal abnormalities and pyramidal tract signs. Examination of mutant SIL1 expression in cultured patient lymphoblasts suggested that SIL1 mutations result in severely reduced SIL1 protein levels irrespective of the type and position of mutations. Our data broaden the SIL1 mutation spectrum and confirm that SIL1 is the major Marinesco-Sjögren syndrome gene. SIL1 patients usually present with the characteristic triad but cataracts might be missing in young children. As cognitive impairment is not obligatory, patients without intellectual disability but a Marinesco-Sjögren syndrome-compatible phenotype should receive SIL1 mutation analysis. Despite allelic heterogeneity and many families with private mutations, the phenotype related to SIL1 mutations is relatively homogenous. Based on SIL1 expression studies we speculate that this may arise from a uniform effect of different mutations on protein expression.

Phenotype–genotype correlations in patients with Marinesco–Sjögren syndrome

Marinesco-Sjögren syndrome (MSS; MIM 248800) is an autosomal recessive disorder characterized by congenital cerebellar ataxia, early cataracts, developmental delay, myopathy and short stature. Alterations in the gene SIL1 cause MSS in some patients with typical findings. In this study, molecular investigations including sequencing of the SIL1 gene, western blotting and microscopic investigations in fibroblast cultures were carried out in a cohort of 15 patients from 14 unrelated families, including the large, inbred family reported by Superneau et al., having the clinical features of MSS to provide insights into the pathophysiology of the disorder. A total of seven different mutations were found in eight of the patients from seven families. The mutations caused loss of the BIP-associated protein (BAP) protein in four patients by western blot. Novel clinical features such as dental abnormalities, iris coloboma, eczema and hormonal abnormalities were noticed in some patients, but there was no clear way to distinguish those with and without SIL1 mutations. Cultured fibroblasts contained numerous cytoplasmic inclusion bodies, similar to those identified in the brain of the whoozy mouse in five unrelated patients, three with and two without SIL1 mutations, suggesting some SIL1 negative patients share a common cellular pathogenesis with those who are SIL1 positive.

Marinesco-Sjögren syndrome due to SIL1 mutations with a comment on the clinical phenotype

BackgroundMarinesco-Sjögren syndrome is an autosomal recessive cerebellar ataxia, characterised by cerebellar ataxia, myopathy, cataracts and intellectual disability, due to mutations in the SIL1 gene. MethodsThe clinical features and two novel SIL1 mutations of four Dutch patients with Marinesco-Sjögren syndrome are described and compared to the literature on genetically proven Marinesco-Sjögren patients. ResultsThe core phenotype of this syndrome appears homogeneous, but: [1] cataract can develop later than the motor and cognitive signs; [2] myopathy is an early feature that seems progressive during the course of the disease; [3] serum creatine kinase is normal or only mildly elevated; [4] peripheral neuropathy is absent; and [5] a variable degree of intellectual disability is present in most Marinesco-Sjögren patients. ConclusionsBecause the late appearance of some hallmarks and the uncertainty as to whether incomplete phenotypes occur, SIL1 mutation analysis is helpful early in the diagnostic work-up of children with suspected inherited ataxias.

G.P.127 A nation-wide survey for Marinesco-Sjögren syndrome

Abstract Marinesco–Sjogren syndrome (MSS) is an autosomal recessive multisystem disorder typically featuring a tetralogy of cerebellar ataxia, congenital cataracts, progressive muscle weakness due to myopathy, and delayed psychomotor development. MSS is a rare disease and its prevalence in Japan and detailed natural history of the disease are unclear. The purpose was to elucidate the clinical, pathological, and genetical features of Japanese patients with MSS. We conducted a nation-wide questionnaire survey in Japan, and the medical records were carefully reviewed. Mutation screening of the SIL1 gene was performed by direct sequencing. Haplotype analysis was also done. The nation-wide questionnaires were sent to a total of 5452 Japanese neurologists and pediatric neurologists. We received information on 38 possible MSS patients. Mutations in SIL1 were identified in 21 of 26 patients examined (10 men and 11 women, aged from 1 to 52 years). A homozygous c.937dupG (p.L313fs) mutation in exon 9 was common and found in 19 patients, however the founder effect was not confirmed by the haplotype analysis. All 21 patients with SIL1 mutations showed cerebellar manifestation, marked atrophy of the cerebellum, on brain MRI, mild to severe mental retardation. Bilateral cataracts appeared and progressed rapidly at age 3.4 ± 1.1 years. All patients with SIL1 mutation showed delayed developmental milestones. Serum creatine kinase levels were elevated (411.7 ± 484.1 U/L). Muscle biopsy was done in 13 patients and all showed fibers with rimmed vacuoles (RVs). On the other hand, three patients without SIL1 mutation had a tetralogy of MSS, but muscle biopsies revealed myopathic changes with no RVs. The patients with SIL1 mutations had clinical features of a tetralogy of MSS. Presence of RVs on muscle biopsy was helpful for the diagnosis. A c.937dupG mutation was common in Japanese MSS patients, but the founder effect was not confirmed.