SIL1 Research Articles

Unveiling a rare co-occurrence: Marinesco-Sjogren syndrome and Griscelli syndrome type 3 with novel mutations in a child presenting with cataract – A unique case report

This case report describes a child with the coexistence of Marinesco-Sjögren syndrome (MSS) and Griscelli syndrome type 3 (GS3). A 9-year-old female with developmental delay and silvery hair had bilateral cataract and esotropia. Isolated finding of silvery hair was found in family members. Light microscopy features of the hair shaft were typical of Griscelli syndrome. Confirmation of GS3 was done by genetic sequencing, which also revealed SIL1 gene mutation, seen in MSS. This case underscores the intricacy of clinical findings and highlights the importance of genetic analysis in achieving an accurate diagnosis.

Sil1-deficient fibroblasts generate an aberrant extracellular matrix leading to tendon disorganisation in Marinesco-Sjögren syndrome

BackgroundMarinesco-Sjögren syndrome (MSS) is an autosomal recessive neuromuscular disorder that arises in early childhood and is characterized by congenital cataracts, myopathy associated with muscle weakness, and degeneration of Purkinje neurons leading to ataxia. About 60% of MSS patients have loss-of-function mutations in the SIL1 gene. Sil1 is an endoplasmic reticulum (ER) protein required for the release of ADP from the master chaperone Bip, which in turn will release the folded proteins. The expression of non-functional Sil1 leads to the accumulation of unfolded proteins in the ER and this triggers the unfolded protein response (UPR). A dysfunctional UPR could be a key element in the pathogenesis of MSS, although our knowledge of the molecular pathology of MSS is still incomplete.MethodsRNA-Seq transcriptomics was analysed using the String database and the Ingenuity Pathway Analysis platform. Fluorescence confocal microscopy was used to study the remodelling of the extracellular matrix (ECM). Transmission electron microscopy (TEM) was used to reveal the morphology of the ECM in vitro and in mouse tendon.ResultsOur transcriptomic analysis, performed on patient-derived fibroblasts, revealed 664 differentially expressed (DE) transcripts. Enrichment analysis of DE genes confirmed that the patient fibroblasts have a membrane trafficking issue. Furthermore, this analysis indicated that the extracellular space/ECM and the cell adhesion machinery, which together account for around 300 transcripts, could be affected in MSS. Functional assays showed that patient fibroblasts have a reduced capacity of ECM remodelling, reduced motility, and slower spreading during adhesion to Petri dishes. TEM micrographs of negative-stained ECM samples from these fibroblasts show differences of filaments in terms of morphology and size. Finally, structural analysis of the myotendinous junction of the soleus muscle and surrounding regions of the Achilles tendon revealed a disorganization of collagen fibres in the mouse model of MSS (woozy).ConclusionsECM alterations can affect the proper functioning of several organs, including those damaged in MSS such as the central nervous system, skeletal muscle, bone and lens. On this basis, we propose that aberrant ECM is a key pathological feature of MSS and may help explain most of its clinical manifestations.

Exome sequencing revealed variants in SGCA and SIL1 genes underlying limb girdle muscular dystrophy and Marinesco-Sjögren syndrome patients.

Inherited neuromuscular (NMD) and neurodegenerative diseases (NDD) belong to two distinct categories that disturb different components of the nervous system, leading to a variety of different symptoms and clinical manifestations. Both NMD and NDD are a heterogeneous group of genetic conditions. Genetic variations in the SGCA and SIL1 genes have been implicated in causing Limb Girdle Muscular Dystrophy (LGMD), a type of neuromuscular disorder, and Marinesco-Sjögren Syndrome (MSS) which is a neurodegenerative disorder. In the present study, we have investigated four patients presenting LGMD and five patients with MSS features. After collecting detailed clinical and family history, necessary laboratory investigations, including estimation of a skeletal muscle marker enzyme serum creatine kinase (CK), nerve conduction study (NCS), electromyography (EMG), echocardiography (Echo), Magnetic resonance imaging (MRI -brain), CT-brain and X-rays were performed. Whole exome followed by Sanger sequencing was employed to search for the disease-causing variants. Physical examination in LGMD patients revealed poor muscle tone and facing difficulty in straightening up from the floor. Clinical history revealed frequent falls and strenuousness in climbing stairs. They started toe-walking in early childhood. Laboratory investigations confirmed elevated CK levels and abnormal NCS and EMG. The MSS patients showed abnormalities in gate and jerking movement, abnormal speech, and strabismus with cataract. MRI-brain showed cerebral atrophy in some MSS patients with elevated CK levels. Whole exome sequencing revealed a nonsense variant [c.C574T, p.(Arg192*)] in the SGCA gene and a frameshift [c.936dupG, p.(Leu313AlaFs*39)] in the SIL1 gene in LGMD and MSS patients, respectively. Our study emphasizes the significance of integrating clinical and genetic analyses for precise diagnosis and tailored management strategies in inherited NMD and NDD disorders. To the best of our knowledge, this is the first study documenting SGCA and SIL1 recurrent variants in subcontinent populations with few rare clinical features. The recurrent mutations expanding the global understanding of the mutation's geographic and ethnic distribution and contributing valuable epidemiological data. The study will facilitate genetic counseling for families experiencing similar clinical features, both within Pakistani populations and in other regions.

Rodzinne występowanie zespołu Marinesco – Sjögrena (opis przypadku występowania rzadkiego zespołu u rodzeństwa)

Marinesco-Sjögren syndrome (MSS) is a rare malformation syndrome inherited in an autosomal recessive manner. The most typical features are cerebellar ataxia with cerebellar atrophy, dysarthria, nystagmus, early-onset cataract, myopathy, hypotonia and muscle weakness. Additional symptoms often include psychomotor delay, hypergonadotropic hypogonadism and short stature. We present a case of a 6-year-old boy admitted to the Department due to psychomotor developmental retardation for completion of further diagnostics. Initial diagnostics led to a preliminary diagnosis of Marinesco-Sjögren syndrome, ultimately confirmed by genetic testing. When the patient’s younger brother was born, he presented with similar symptoms. Knowledge of his older sibling’s diagnosis aided in immediately using single- -gene testing to confirm the presence of two mutated copies of the SIL1 gene. This finding allowed to establish a proper diagnosis in the younger brother, leading to immediate multi-specialist intervention.

LGMD like presentation of marinesco sjogren syndrome: Atypical presentation of rare disease

Marinesco-sjogren syndrome is a rare, autosomal recessive disorder. Mutation in SIL-1 gene account for majority of cases. It commonly presents with cerebellar ataxia, congenital cataracts, myopathy and mental retardation. Skeletal abnormalities including short stature, dysarthria, nystagmus and hypergonadotropic hypogonadism are also occasionally observed. Myopathic presentation without ataxia is rare. We are reporting this rare LGMD like presentation of genetically proven marinesco sjogren syndrome as it is probably the first case report after thorough review of literature

Development and Initial Characterization of Cellular Models for COG Complex-Related CDG-II Diseases.

Conserved Oligomeric Golgi (COG) is an octameric protein complex that orchestrates intra-Golgi trafficking of glycosylation enzymes. Over a hundred individuals with 31 different COG mutations have been identified until now. The cellular phenotypes and clinical presentations of COG-CDGs are heterogeneous, and patients primarily represent neurological, skeletal, and hepatic abnormalities. The establishment of a cellular COG disease model will benefit the molecular study of the disease, explaining the detailed sequence of the interplay between the COG complex and the trafficking machinery. Moreover, patient fibroblasts are not a good representative of all the organ systems and cell types that are affected by COG mutations. We developed and characterized cellular models for human COG4 mutations, specifically in RPE1 and HEK293T cell lines. Using a combination of CRISPR/Cas9 and lentiviral transduction technologies, both myc-tagged wild-type and mutant (G516R and R729W) COG4 proteins were expressed under the endogenous COG4 promoter. Constructed isogenic cell lines were comprehensively characterized using biochemical, microscopy (superresolution and electron), and proteomics approaches. The analysis revealed similar stability and localization of COG complex subunits, wild-type cell growth, and normal Golgi morphology in all three cell lines. Importantly, COG4-G516R cells demonstrated increased HPA-647 binding to the plasma membrane glycoconjugates, while COG4-R729W cells revealed high GNL-647 binding, indicating specific defects in O- and N-glycosylation. Both mutant cell lines express an elevated level of heparin sulfate proteoglycans. Moreover, a quantitative mass-spectrometry analysis of proteins secreted by COG-deficient cell lines revealed abnormal secretion of SIL1 and ERGIC-53 proteins by COG4-G516R cells. Interestingly, the clinical phenotype of patients with congenital mutations in the SIL1 gene (Marinesco-Sjogren syndrome) overlaps with the phenotype of COG4-G516R patients (Saul-Wilson syndrome). Our work is the first compressive study involving the creation of different COG mutations in different cell lines other than the patient’s fibroblast. It may help to address the underlying cause of the phenotypic defects leading to the discovery of a proper treatment guideline for COG-CDGs.

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.

SIL1 deficiency causes degenerative changes of peripheral nerves and neuromuscular junctions in fish, mice and human

BackgroundMarinesco-Sjögren Syndrome (MSS) is a rare neuromuscular condition caused by recessive mutations in the SIL1 gene resulting in the absence of functional SIL1 protein, a co-chaperone for the major ER chaperone, BiP. As BiP is decisive for proper protein processing, loss of SIL1 results in the accumulation of misshaped proteins. This accumulation likely damages and destroys cells in vulnerable tissues, leading to congenital cataracts, cerebellar ataxia, vacuolar myopathy and other MSS phenotypes. Whether the peripheral nervous system (PNS) is affected in MSS has not been conclusively shown. MethodsTo study PNS vulnerability in MSS, intramuscular nerves fibres from MSS patients and from SIL1-deficient mice (woozy) as well as sciatic nerves and neuromuscular junctions (NMJ) from these mice have been investigated via transmission electron microscopic and immunofluorescence studies accompanied by transcript studies and unbiased proteomic profiling. In addition, PNS and NMJ integrity were analyzed via immunofluorescence studies in an MSS-zebrafish model which has been generated for that purpose. ResultsElectron microscopy revealed morphological changes indicative of impaired autophagy and mitochondrial maintenance in distal axons and in Schwann cells. Moreover, changes of the morphology of NMJs as well as of transcripts encoding proteins important for NMJ function were detected in woozy mice. These findings were in line with a grossly abnormal structure of NMJs in SIL1-deficient zebrafish embryos. Proteome profiling of sciatic nerve specimens from woozy mice revealed altered levels of proteins implicated in neuronal maintenance suggesting the activation of compensatory mechanisms. ConclusionTaken together, our combined data expand the spectrum of tissues affected by SIL1-loss and suggest that impaired neuromuscular transmission might be part of MSS pathophysiology.

PERK inhibition attenuates the abnormalities of the secretory pathway and the increased apoptotic rate induced by SIL1 knockdown in HeLa cells

Loss-of-function mutations in the SIL1 gene are linked to Marinesco-Sjögren syndrome (MSS), a rare multisystem disease of infancy characterized by cerebellar and skeletal muscle degeneration. SIL1 is a ubiquitous adenine nucleotide exchange factor for the endoplasmic reticulum (ER) chaperone BiP. The complexity of mechanisms by which loss of SIL1 causes MSS is not yet fully understood. We used HeLa cells to test the hypothesis that impaired protein folding in the ER due to loss of SIL1 could affect secretory trafficking, impairing the transport of cargoes essential for the function of MSS vulnerable cells. Immunofluorescence and ultrastructural analysis of SIL1-knocked-down cells detected ER chaperone aggregation, enlargement of the Golgi complex, increased autophagic vacuoles, and mitochondrial swelling. SIL1-interefered cells also had delayed ER-to-plasma membrane transport with retention of Na+/K+-ATPase and procollagen-I in the ER and Golgi, and increased apoptosis. The PERK pathway of the unfolded protein response was activated in SIL1-interfered cells, and the PERK inhibitor GSK2606414 attenuated the morphological and functional alterations of the secretory pathway, and significantly reduced cell death. These results indicate that loss of SIL1 is associated with alterations of secretory transport, and suggest that inhibiting PERK signalling may alleviate the cellular pathology of SIL1-related MSS.

Genetically proven marinesco sjogren syndrome from India: Rare combination of ataxia, myopathy and cataracts

Background: Marinesco-sjogren syndrome is a rare, autosomal recessive disorder characterized by cerebellar ataxia, myopathy, congenital cataracts and mental retardation. The syndrome has been mapped to chromosome 5q31, with mutations in the SIL-1 gene.

Longitudinal analysis of motor symptoms and histopathology in woozy mice, a model of cerebellar ataxia.

Woozy (wz) mice develop ataxia and carry a mutation in the Sil1 gene. Homozygous wz mice have been characterized histopathologically, but no details of their motor function have been reported. In the present study, to comprehensively understand the relationship between symptomatic progression and pathological feature, we evaluated motor function and neurodegeneration with age from presymptomatic to terminal stages. We evaluated the motor function of homozygous and heterozygous wz mice aged from 5 to 71 weeks. Motor function was evaluated using the rotarod test, the footprint test, and the parallel rod floor test. Furthermore, we carried out a histopathological analysis of the mice at several ages. Impairment of motor function in homozygous wz mice began at around 11 weeks of age and became markedly worse until around 14 weeks. Heterozygous wz mice did not show motor dysfunction until 71 weeks of age. Features of cerebellar ataxia were evaluated using the footprint test and the parallel rod floor test. In addition to the observation of ubiquitin-positive aggregates at 6 weeks of age, Purkinje cell loss at 9 weeks of age and cerebellar atrophy were confirmed by histopathology. Apart from the cerebellar changes, we detected no other pathology that could contribute toward ataxia. In heterozygous wz mice, only minimal formation of ubiquitin-positive aggregates was observed. Homozygous wz mice showed adult-onset ataxia with progressive neurodegeneration of the cerebellum. Homozygous wz mice might be useful as an animal model of diseases showing adult-onset ataxia because of cerebellar neurodegeneration.

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

Characterization of Zebrafish Models of Marinesco-Sjögren Syndrome.

SIL1 is a nucleotide exchange factor for the endoplasmic reticulum chaperone, BiP. Mutations in the SIL1 gene cause Marinesco-Sjögren syndrome (MSS), an autosomal recessive disease characterized by cerebellar ataxia, mental retardation, congenital cataracts, and myopathy. To create novel zebrafish models of MSS for therapeutic drug screening, we analyzed phenotypes in sil1 knock down fish by two different antisense oligo morpholinos. Both sil1 morphants had abnormal formation of muscle fibers and irregularity of the myosepta. Moreover, they showed smaller-sized eyes and loss of purkinje cells in cerebellar area compared to controls. Immunoblotting analysis revealed increased protein amounts of BiP, lipidated LC3, and caspase 3. These data supported that the sil1 morphants can represent mimicking phenotypes of human MSS. The sil1 morphants phenocopy the human MSS disease pathology and are a good animal model for therapeutic studies.

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.

Search for cryptic subtelomeric aberrations in patients with non-classical Marinesco-Sjögren phenotype

Marinesco-Sjogren syndrome (MSS) is a multiorgan disorder firstly described in 1931 by Gheorge Marinescu. During the last seven decades, research into the clinical picture of MSS has led to the description of varying MSS and since 2005, it is known that mutations within the SIL1 gene cause MSS in a part of these patients. Among these “SIL1-related MSS cases”, “classical and non-classical phenotypes” are distinguished. All “SIL1-related MSS cases” show at least an ataxia due to cerebellar atrophy, congenital or infantile cataracts and a progressive myopathy as well as mental impairment (“classical MSS phenotype”). Additional clinical features are for example in some cases short stature, hypogonadism, scoliosis, nystagmus and strabismus (“non-classical MSS phenotype”). However, the primary pathology has remained unknown in MSS cases. As the clinical features detected in “classical MSS phenotype” and “non-classical MSS phenotype” may also be associated with cryptic subtelomeric rearrangements and as a frequent localization of for example cataract-related genes/loci within these regions is proven, we performed subtelomere screening in a series of 23 patients with “non-SIL1-related non-classical MSS phenotypes” presenting with at least three features like early cataracts, mental retardation, brain malformations, muscular hypotonia, growth retardation and skeletal abnormalities. Karyotype and the SIL1 coding sequence were normal in all cases. Subtelomere screening by multiplex ligation-dependent probe amplification did not identify any subtelomeric imbalances. Therefore, a causative role of these regions in manifesting non-SIL1-related non-classical MSS phenotypes seems to be unlikely.

PP05.12 – 2659: Congenital cataract with facial dysmorphism and neuropathy (CCFDN): Clinical presentation and genetic correlation

Objective Congenital cataracts and peripheral nerve disease are described in a heterogeneous group of disorders. Other clinical features and genetic testing can guide the differential diagnosis. We present the clinical features and genetic correlation of a patient with congenital cataracts, peripheral neuropathy and associated choreoathetosis. Methods Case description providing the results of complementary tests. Results Previously known patient from Romania since she was 9 months old, presented to our hospital with bilateral congenital cataracts, which were operated in her country of origin. She showed signs of motor and intellectual development delay (she sat well unsupported at 24 months and started walking at 4 yo), ataxic gait and choreiform movements that increased when standing or with purposeful movements. Additionally, she presented bilateral atrophy of short extensor muscles of the toes, valgus feet, absent osteotendinous reflexes, obesity and slight facial dysmorphism (rounded face and microphthalmia). MRI and EEG were normal. Motor conduction studies showed slowing into the demyelinating range, with no sensory component. Molecular study ruled out mutation in the SIL1 gene (Marinesco-Sjogren syndrome) but showed a homozygous mutation in the CTDP1 gene (c.863+389C>T), thus confirming the suspected diagnosis. Conclusion CCFDN is a rare autosomal recessive disorder that is prevalent among Gypsies from central Europe. A patient showing abnormalities of the eye (bilateral congenital cataracts, microcornea, microphthalmia, micropupils), motor and intellectual development delay and ataxic gait should be considered for the molecular study of CTDP1 gene. Occasionally patients may associate mild dysmorphic facial features and cerebellar dysfunction. Choreoathetosis may be prominent and interferes with daily activities. The differential diagnosis should include Marinesco-Sjogren syndrome and disorders involving demyelinating peripheral neuropathy.

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;

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.