Homozygosity mapping of Marinesco-Sjögren syndrome to 5q31

Genotype-phenotype correlations in ocular manifestations of Marinesco-Sjögren syndrome: Case report and literature review

PURPOSE

This study aims to present a family with two children with MSS who presented with different ophthalmic features. We also aim to review MSS patients' ocular manifestations to provide a basis for future clinical trials and improve MSS patients' ophthalmologic care.

CASE DESCRIPTION

Both patients presented with global developmental delay, microcephaly, cerebellar ataxia, and myopathy. The older sibling had developed bilateral cataracts at the age of six. Her 2 years younger sister interestingly showed bilateral hyperopic refractive error without cataracts yet. Mendeliome sequencing unraveled a novel homozygous frameshift mutation in the SIL1 gene (SIL1, NM_022464.5, c.1042dupG, p.E348Gfs*4), causing MSS. A systematic literature review revealed that cataracts appear in 96% of MSS cases with a mean onset at 3.2 years. Additional frequent ocular features were strabismus (51.6%) and nystagmus (45.2%).

CONCLUSION

SIL1-related MSS is associated with marked clinical variability. Cataracts can develop later than neuromuscular features and cognitive signs. Since cataract is a relatively late finding, patients may refer to ophthalmologists for other reasons such as refractive errors, strabismus, or nystagmus. Molecular genetic testing for SIL1 is essential to facilitate early diagnosis in patients with suspected MSS.

Role of the HSP70 Co-Chaperone SIL1 in Health and Disease

Cell surface and secreted proteins provide essential functions for multicellular life. They enter the endoplasmic reticulum (ER) lumen co-translationally, where they mature and fold into their complex three-dimensional structures. The ER is populated with a host of molecular chaperones, associated co-factors, and enzymes that assist and stabilize folded states. Together, they ensure that nascent proteins mature properly or, if this process fails, target them for degradation. BiP, the ER HSP70 chaperone, interacts with unfolded client proteins in a nucleotide-dependent manner, which is tightly regulated by eight DnaJ-type proteins and two nucleotide exchange factors (NEFs), SIL1 and GRP170. Loss of SIL1′s function is the leading cause of Marinesco-Sjögren syndrome (MSS), an autosomal recessive, multisystem disorder. The development of animal models has provided insights into SIL1′s functions and MSS-associated pathologies. This review provides an in-depth update on the current understanding of the molecular mechanisms underlying SIL1′s NEF activity and its role in maintaining ER homeostasis and normal physiology. A precise understanding of the underlying molecular mechanisms associated with the loss of SIL1 may allow for the development of new pharmacological approaches to treat MSS.

Neuroimaging Findings in Pediatric Genetic Skeletal Disorders: A Review

Genetic skeletal disorders (GSDs) are a heterogeneous group characterized by an intrinsic abnormality in growth and (re-)modeling of cartilage and bone. A large subgroup of GSDs has additional involvement of other structures/organs beside the skeleton, such as the central nervous system (CNS). CNS abnormalities have an important role in long-term prognosis of children with GSDs and should consequently not be missed. Sensitive and specific identification of CNS lesions while evaluating a child with a GSD requires a detailed knowledge of the possible associated CNS abnormalities. Here, we provide a pattern-recognition approach for neuroimaging findings in GSDs guided by the obvious skeletal manifestations of GSD. In particular, we summarize which CNS findings should be ruled out with each GSD. The diseases (n = 180) are classified based on the skeletal involvement (1. abnormal metaphysis or epiphysis, 2. abnormal size/number of bones, 3. abnormal shape of bones and joints, and 4. abnormal dynamic or structural changes). For each disease, skeletal involvement was defined in accordance with Online Mendelian Inheritance in Man. Morphological CNS involvement has been described based on extensive literature search. Selected examples will be shown based on prevalence of the diseases and significance of the CNS involvement. CNS involvement is common in GSDs. A wide spectrum of morphological abnormalities is associated with GSDs. Early diagnosis of CNS involvement is important in the management of children with GSDs. This pattern-recognition approach aims to assist and guide physicians in the diagnostic work-up of CNS involvement in children with GSDs and their management.

Marinesco-Sjögren Syndrome in an Emirati Child with a Novel Mutation in SIL1 Affecting the 5' Untranslated Region

OBJECTIVE

The aim of this study was to report clinical and molecular findings in an Emirati child with Marinesco-Sjögren syndrome born to consanguineous parents.

CLINICAL PRESENTATION AND INTERVENTION

The child presented with developmental delay, ataxia, bilateral cataracts, and dysmorphic craniofacial features, along with cerebellar atrophy. Sequencing of the SIL1 gene revealed a novel homozygous large indel mutation that was predicted to abrogate part of the 5' untranslated region (UTR) and the first 30 amino acids of the protein.

CONCLUSION

This was a case of mutation in SIL1 that affected the 5' UTR, translation initiation site and the endoplasmic reticulum-targeting signal sequence. Further studies will be needed on the functional delineation of the mutation.

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.

Molecular and clinical study of a cohort of 110 Algerian patients with autosomal recessive ataxia

BACKGROUND

Autosomal recessive cerebellar ataxias (ARCA) are a complex group of neurodegenerative disorders with great genetic and phenotypic heterogeneity, over 30 genes/loci have been associated with more than 20 different clinical forms of ARCA. Genetic heterogeneity combined with highly variable clinical expression of the cerebellar symptoms and overlapping features complicate furthermore the etiological diagnosis of ARCA. The determination of the most frequent mutations and corresponding ataxias, as well as particular features specific to a population, are mandatory to facilitate and speed up the diagnosis process, especially when an appropriate treatment is available.

METHODS

We explored 166 patients (115 families) refered to the neurology units of Algiers central hospitals (Algeria) with a cerebellar ataxia phenotype segregating as an autosomal recessive pattern of inheritance. Genomic DNA was extracted from peripheral blood samples and mutational screening was performed by PCR and direct sequencing or by targeted genomic capture and massive parallel sequencing of 57 genes associated with inherited cerebellar ataxia phenotypes.

RESULTS

In this work we report the clinical and molecular results obtained on a large cohort of Algerian patients (110 patients/76 families) with genetically determined autosomal recessive ataxia, representing 9 different types of ARCA and 23 different mutations, including 6 novel ones. The five most common ARCA in this cohort were Friedreich ataxia, ataxia with isolated vitamin E deficiency, ataxia with oculomotor apraxia type 2, autosomal recessive spastic ataxia of Charlevoix-Saguenay and ataxia with oculomotor apraxia type 1.

CONCLUSION

We report here a large cohort of patients with genetically determined autosomal recessive ataxia and the first study of the genetic context of ARCA in Algeria. This study showed that in Algerian patients, the two most common types of ataxia (Friedreich ataxia and ataxia with isolated vitamin E deficiency) coexist with forms that may be less common or underdiagnosed. To refine the genotype/phenotype correlation in rare and heteregeneous diseases as autosomal recessive ataxias, more extensive epidemiological investigations and reports are necessary as well as more accurate and detailed clinical characterizations. The use of standardized clinical and molecular protocols would thus enable a better knowledge of the different forms of ARCA.

SIL1, a causative cochaperone gene of Marinesco-Söjgren 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.

Molecular diagnosis of autosomal recessive cerebellar ataxia in the whole exome/genome sequencing era

Autosomal recessive cerebellar ataxias (ARCA) are a clinically and genetically heterogeneous group of rare neurodegenerative disorders characterized by autosomal recessive inheritance and an early age of onset. Progressive ataxia is usually the prominent symptom and is often associated with other neurological or additional features. ARCA classification still remains controversial even though different approaches have been proposed over the years. Furthermore, ARCA molecular diagnosis has been a challenge due to phenotypic overlap and increased genetic heterogeneity observed within this group of disorders. Friedreich’s ataxia and ataxia telangiectasia have been reported as the most frequent and well-studied forms of ARCA. Significant progress in understanding the genetic etiologies of the ARCA has been achieved during the last 15 years. The methodological revolution that has been observed in genetics over the last few years has contributed significantly to the molecular diagnosis of rare diseases including the ARCAs. Development of high throughput technologies has resulted in the identification of new ARCA genes and novel mutations in known ARCA genes. Therefore, an improvement in the molecular diagnosis of ARCA is expected. Moreover, based on the fact that many patients still remain undiagnosed, additional forms of ataxia are expected to be identified. We hereby review the current knowledge on the ARCAs, focused on the genetic findings of the most common forms that were molecularly characterized before the whole exome/genome era, as well as the most recently described forms that have been elucidated with the use of these novel technologies. The significant contribution of whole-exome sequencing or whole-genome sequencing in the molecular diagnosis of ARCAs is discussed.

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

BACKGROUND

Marinesco-Sjögren syndrome is an autosomal recessive cerebellar ataxia, characterised by cerebellar ataxia, myopathy, cataracts and intellectual disability, due to mutations in the SIL1 gene.

METHODS

The 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.

RESULTS

The 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.

CONCLUSIONS

Because 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.

Other autosomal recessive and childhood ataxias

The label of "early-onset cerebellar ataxia with retained tendon reflexes" (EOCA) has been created to differentiate it from Friedreich ataxia (FRDA) patients with preserved knee jerks and absence of cardiomyopathy, optic atrophy, and diabetes mellitus. However, EOCA is a heterogeneous syndrome and several FRDA patients present with an EOCA-like phenotype. Cerebellar ataxia with hypogonadism is another heterogeneous syndrome for which no locus has been mapped yet. Two peculiar ataxic syndromes have been identified in genetically isolated populations: autosomal recessive ataxia of Charlevoix-Saguenay (ARSACS) in Quebec and infantile-onset spinocerebellar ataxia (IOSCA) in Finland. Both conditions present usually within the second year of life. ARSACS is characterized by marked spasticity and IOSCA by a complex phenotype which includes, besides ataxia, epilepsy, optic atrophy, ophthalmoplegia, hearing loss, and areflexia. The responsible genes are SACS, encoding sacsin, a protein which may act as a chaperone, and C10orf2, encoding Twinkle, a mitochondrial DNA-specific helicase. Marinesco-Sjögren syndrome, clinically characterized by cerebellar ataxia, cataracts, myopathy, and mental retardation, is genetically heterogeneous. One gene, SIL1, encodes a nucleotide exchange factor for the heat-shock protein 70 chaperone HSPA5. Five conditions account for most cases of progressive myoclonic ataxia: Unverricht-Lundborg disease, Lafora disease, myoclonic epilepsy with ragged-red fibers, neuronal ceroid lipofuscinoses, and sialidoses.

[Autosomal recessive cerebellar ataxias]

INTRODUCTION

Autosomal recessive cerebellar ataxias (ARCA) are heterogeneous and complex inherited neurodegenerative diseases that may affect the cerebellum and/or the spinocerebellar tract, the posterior column of the spinal cord and the peripheral nerves. Cerebellar ataxia is frequently proeminent and mostly associated with several neurological or extra-neurological signs, leading to a major disability before the age of 30.

STATE OF ART

Friedreich's ataxia (FRDA) is clearly the most frequent ARCA and several rarer entities have been described during the past fifteen years such as ataxia with oculomotor apraxia type 1 (AOA1) and type 2 (AOA2), ataxia with vitamin E deficiency (AVED) and autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS). The ACAR are characterized by both allelic and non-allelic genetic heterogeneity. They may be divided into three groups: spino-cerebellar ataxia with pure sensory neuropathy; cerebellar ataxia with sensori-motor axonal neuropathy; pure cerebellar ataxia (i.e. ataxia of purely cerebellar origin that may be associated with other symptoms). Common physiological pathways are involved in several ARCA, such as DNA repair deficiency (AOA1, ataxia telangiectasia [AT]…), RNA termination disorder (AOA2), mitochondrial defect (FRDA, sensory ataxic neuropathy with dysarthria and ophthalmoplegia [Sando]…), lipoprotein assembly defects (AVED, abetalipoproteinemia [ABL]), chaperon protein disorders (ARSACS, Marinesco-Sjögren syndrome [MSS]) or peroxysomal diseases (Refsum disease [RD]).

PERSPECTIVES

New nanotechnology methods and high throughput gene analysis as well as bioinformatics should lead to the identification of several new ARCAs in the next few years despite the rarity of these entities. However, the challenge of the next decades will be the discovery of efficient treatments for these disabling neurodegenerative disorders.

CONCLUSION

Clinicians should be aware of the more frequent ARCAs, especially FRDA, in addition to ARCAs for which treatment is available (FRDA, AVED, ABL and RD for instance).

Molecular diagnosis of known recessive ataxias by homozygosity mapping with SNP arrays

The diagnosis of rare inherited diseases is becoming more and more complex as an increasing number of clinical conditions appear to be genetically heterogeneous. Multigenic inheritance also applies to the autosomal recessive progressive cerebellar ataxias (ARCAs), for which 14 genes have been identified and more are expected to be discovered. We used homozygosity mapping as a guide for identification of the defective locus in patients with ARCA born from consanguineous parents. Patients from 97 families were analyzed with GeneChip Mapping 10K or 50K SNP Affymetrix microarrays. We identified six families homozygous for regions containing the autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) gene, two families homozygous for the ataxia-telangiectasia gene (ATM), two families homozygous for the ataxia with oculomotor apraxia type 1 (AOA1) gene, and one family homozygous for the AOA type 2 (AOA2) gene. Upon direct gene testing, we were able to identify a disease-related mutation in all families but one of the two kindred homozygous at the ATM locus. Although linkage analyses pointed to a single locus on chromosome 11q22.1-q23.1 for this family, clinical features, normal levels of serum alpha-foetoprotein as well as absence of mutations in the ATM gene rather suggest the existence of an additional ARCA-related gene in that interval. While the use of homozygosity mapping was very effective at pointing to the correct gene, it also suggests that the majority of patients harbor mutations either in the genes of the rare forms of ARCA or in genes yet to be identified.

Autosomal recessive ataxias: 20 types, and counting

More than 140 years after the first description of Friedreich ataxia, autosomal recessive ataxias have become one of the more complex fields in Neurogenetics. Currently this group of diseases contains more than 20 clinical entities and an even larger number of associated genes. Some disorders are very rare, restricted to isolated populations, and others are found worldwide. An expressive number of recessive ataxias are treatable, and responsibility for an accurate diagnosis is high. The purpose of this review is to update the practitioner on clinical and pathophysiological aspects of these disorders and to present an algorithm to guide the diagnosis.

Marinesco-Sjögren syndrome with atrophy of the brain stem tegmentum and dysplastic cytoarchitecture in the cerebral cortex

Marinesco-Sjögren syndrome (MSS) is a progressive multisystem disease with autosomal recessive inheritance characterized by cataracts, mental retardation, and cerebellar ataxia. Recently, two causative genes for MSS, SIL1 and SARA2, have been identified. On the other hand, the histopathologic features of the CNS in this syndrome have not yet been clarified in detail. We report here the features of an autopsy case of MSS with progressive myopathy, in which atrophy of the cerebellum and brain stem tegmentum, retinal degeneration, and dysplastic cytoarchitecture in the cerebral cortex were evident. An elder brother of the patient showed quite similar symptoms, implying an autosomal recessive mode of inheritance. However, we detected no mutations in the available genes. This case appears to represent an unusual example of MSS manifesting widespread developmental anomaly and neuronal degeneration in the CNS.

ADCK3, an ancestral kinase, is mutated in a form of recessive ataxia associated with coenzyme Q10 deficiency

Muscle coenzyme Q(10) (CoQ(10) or ubiquinone) deficiency has been identified in more than 20 patients with presumed autosomal-recessive ataxia. However, mutations in genes required for CoQ(10) biosynthetic pathway have been identified only in patients with infantile-onset multisystemic diseases or isolated nephropathy. Our SNP-based genome-wide scan in a large consanguineous family revealed a locus for autosomal-recessive ataxia at chromosome 1q41. The causative mutation is a homozygous splice-site mutation in the aarF-domain-containing kinase 3 gene (ADCK3). Five additional mutations in ADCK3 were found in three patients with sporadic ataxia, including one known to have CoQ(10) deficiency in muscle. All of the patients have childhood-onset cerebellar ataxia with slow progression, and three of six have mildly elevated lactate levels. ADCK3 is a mitochondrial protein homologous to the yeast COQ8 and the bacterial UbiB proteins, which are required for CoQ biosynthesis. Three out of four patients tested showed a low endogenous pool of CoQ(10) in their fibroblasts or lymphoblasts, and two out of three patients showed impaired ubiquinone synthesis, strongly suggesting that ADCK3 is also involved in CoQ(10) biosynthesis. The deleterious nature of the three identified missense changes was confirmed by the introduction of them at the corresponding positions of the yeast COQ8 gene. Finally, a phylogenetic analysis shows that ADCK3 belongs to the family of atypical kinases, which includes phosphoinositide and choline kinases, suggesting that ADCK3 plays an indirect regulatory role in ubiquinone biosynthesis possibly as part of a feedback loop that regulates ATP production.

Novel SIL1 mutations and exclusion of functional candidate genes in Marinesco-Sjögren syndrome

Marinesco-Sjögren syndrome (MSS) is a rare autosomal recessively inherited neurodegenerative disorder characterized by cerebellar ataxia, cataracts, mental retardation, and progressive myopathy. Recently, mutations in the SIL1 gene, which encodes an endoplasmic reticulum (ER) resident cochaperone, were identified as a major cause of MSS. We here report four novel mutations in SIL1, including the first missense substitution p.Leu457Pro described in MSS. In addition, we excluded three functional candidate genes, HSPA5, HYOU1, and AARS, as causative genes in SIL1 mutation-negative patients. To understand the mechanisms of disturbed SIL1 function, we studied the subcellular localization of the missense mutant Leu457Pro protein in COS-1 cells. Moreover, we studied a mutant protein lacking the putative C-terminal ER retrieval signal. In contrast to the wild-type protein's localization to ER and Golgi apparatus, both mutant proteins formed aggregates within the ER depending on the expression level. These data imply that aggregation of mutant proteins may contribute to MSS pathogenesis. The genetic background of a subgroup of patients with MSS remains uncovered.

Autosomal recessive cerebellar ataxias

Autosomal recessive cerebellar ataxias (ARCA) are a heterogeneous group of rare neurological disorders involving both central and peripheral nervous system, and in some case other systems and organs, and characterized by degeneration or abnormal development of cerebellum and spinal cord, autosomal recessive inheritance and, in most cases, early onset occurring before the age of 20 years. This group encompasses a large number of rare diseases, the most frequent in Caucasian population being Friedreich ataxia (estimated prevalence 2–4/100,000), ataxia-telangiectasia (1–2.5/100,000) and early onset cerebellar ataxia with retained tendon reflexes (1/100,000). Other forms ARCA are much less common. Based on clinicogenetic criteria, five main types ARCA can be distinguished: congenital ataxias (developmental disorder), ataxias associated with metabolic disorders, ataxias with a DNA repair defect, degenerative ataxias, and ataxia associated with other features. These diseases are due to mutations in specific genes, some of which have been identified, such as frataxin in Friedreich ataxia, α-tocopherol transfer protein in ataxia with vitamin E deficiency (AVED), aprataxin in ataxia with oculomotor apraxia (AOA1), and senataxin in ataxia with oculomotor apraxia (AOA2). Clinical diagnosis is confirmed by ancillary tests such as neuroimaging (magnetic resonance imaging, scanning), electrophysiological examination, and mutation analysis when the causative gene is identified. Correct clinical and genetic diagnosis is important for appropriate genetic counseling and prognosis and, in some instances, pharmacological treatment. Due to autosomal recessive inheritance, previous familial history of affected individuals is unlikely. For most ARCA there is no specific drug treatment except for coenzyme Q10 deficiency and abetalipoproteinemia.

Congenital cataracts-facial dysmorphism-neuropathy

Congenital Cataracts Facial Dysmorphism Neuropathy (CCFDN) syndrome is a complex developmental disorder of autosomal recessive inheritance. To date, CCFDN has been found to occur exclusively in patients of Roma (Gypsy) ethnicity; over 100 patients have been diagnosed. Developmental abnormalities include congenital cataracts and microcorneae, primary hypomyelination of the peripheral nervous system, impaired physical growth, delayed early motor and intellectual development, mild facial dysmorphism and hypogonadism. Para-infectious rhabdomyolysis is a serious complication reported in an increasing number of patients. During general anaesthesia, patients with CCFDN require careful monitoring as they have an elevated risk of complications. CCFDN is a genetically homogeneous condition in which all patients are homozygous for the same ancestral mutation in the CTDP1 gene. Diagnosis is clinical and is supported by electrophysiological and brain imaging studies. The major differential diagnosis is Marinesco-Sjögren syndrome. The definitive diagnosis is molecular, based on homozygosity for the CTDP1 mutation. CTDP1 maps to 18qter and encodes a protein phosphatase whose only known substrate is the phosphorylated serine residues of the carboxy-terminal domain of the largest subunit of RNA polymerase II, indicating that CCFDN affects basic cellular processes of gene expression and developmental regulation. Families benefit from genetic counselling and predictive testing. Management includes surgical treatment of the cataracts, and rehabilitation and corrective orthopaedic surgery for the peripheral neuropathy. Thus, the most disabling manifestations, though not curable, are manageable, and allow an acceptable quality of life and everyday living. Current data indicate that patients survive well into adulthood.

Cataracts, ataxia, short stature, and mental retardation in a Chinese family mapped to Xpter-q13.1

Six males in a Chinese family affected by congenital cataracts, cerebellar ataxia, short stature, and mental retardation, which were tentatively named CASM syndrome. Eight female carriers in the family had cataracts alone. Linkage analysis demonstrated that the disease is transmitted through X-linked inheritance, either by setting the syndrome in males as an X-linked recessive trait, or by setting cataracts in the family as an X-linked dominant trait. The gene responsible for the syndrome is mapped to Xpter-Xq13.1, with the highest lod score of 3.91 for DXS1226, DXS991, and DXS1213 at theta = 0. Haplotype analysis identified that the allele harboring the disease gene co-segregated with all female carriers as well as affected males in the family. Clinically and genetically, the disease in this family is different from any known disease. Major features of CASM syndrome that distinguish it from other diseases are X-linked inheritance and cataracts in carrier females.

Mutations in SIL1 cause Marinesco-Sjögren syndrome, a cerebellar ataxia with cataract and myopathy

SIL1 (also called BAP) acts as a nucleotide exchange factor for the Hsp70 chaperone BiP (also called GRP78), which is a key regulator of the main functions of the endoplasmic reticulum. We found nine distinct mutations that would disrupt the SIL1 protein in individuals with Marinesco-Sjögren syndrome, an autosomal recessive cerebellar ataxia complicated by cataracts, developmental delay and myopathy. Identification of SIL1 mutations implicates Marinesco-Sjögren syndrome as a disease of endoplasmic reticulum dysfunction and suggests a role for this organelle in multisystem disorders.

The gene disrupted in Marinesco-Sjögren syndrome encodes SIL1, an HSPA5 cochaperone

We identified the gene underlying Marinesco-Sjögren syndrome, which is characterized by cerebellar ataxia, progressive myopathy and cataracts. We identified four disease-associated, predicted loss-of-function mutations in SIL1, which encodes a nucleotide exchange factor for the heat-shock protein 70 (HSP70) chaperone HSPA5. These data, together with the similar spatial and temporal patterns of tissue expression of Sil1 and Hspa5, suggest that disturbed SIL1-HSPA5 interaction and protein folding is the primary pathology in Marinesco-Sjögren syndrome.

Congenital cataract facial dysmorphism neuropathy syndrome: a clinically recognizable entity

Congenital cataracts facial dysmorphism neuropathy syndrome is a recently delineated autosomal recessive condition exclusively found in the Gypsy population. Congenital cataracts facial dysmorphism neuropathy syndrome is caused by a homozygous mutation in the CTDP1 gene, leading to disruption of the ribonucleic acid transcription machinery. This report presents a young Gypsy female affected by this rare disorder. Electromyography and sural nerve histology were in accordance with a hypomyelinating neuropathy. After clinical recognition of congenital cataracts facial dysmorphism neuropathy syndrome some years ago, we recently demonstrated the presence of the homozygous IVS6+389C-->T mutation in the CTDP1 gene in this family.

Myopathy is a prominent feature in Marinesco-Sjögren syndrome: A muscle computed tomography study

BACKGROUND

Marinesco-Sjögren syndrome (MSS) is an autosomal recessive multiorgan disorder showing clinical and genetic heterogeneity. The key features of MSS include cerebellar ataxia, early bilateral cataracts, delayed motor development, and varying degrees of mental retardation. Patients with a subtype of MSS with myoglobinuria and neuropathy have been linked to chromosome 18qter, and recently a locus for classical MSS has been localized on chromosome 5q31.

OBJECTIVES

To determine the importance of myopathy in this disorder apart from the CNS based disability and to establish the pattern of muscle involvement and degree of its severity.

METHODS

Muscle computed tomography (CT) investigations were carried out in nine Finnish MSS patients homozygous for markers around the MSS locus on chromosome 5q31.

RESULTS

Patients with severe clinical disability showed severe and generalized muscle degeneration. Muscle CT findings in patients with relatively severe clinical picture were characterized by severe involvement of the posterior thoracic and pelvic muscles, and almost all thigh muscles. In the legs the peronei and posterior compartment muscles were severely degenerated. The group of patients with moderate severity of disease showed the same pattern of involved muscle, albeit with lower degree of muscle degeneration.

CONCLUSIONS

Patients with MSS linked to chromosome 5q31 have a severe progressive myopathy, the extent of which may remain largely unrecognized because of the CNS involvement.

Identification and functional consequences of a novel MRE11 mutation affecting 10 Saudi Arabian patients with the ataxia telangiectasia-like disorder

Ten new patients with ataxia telangiectasia-like disorder (ATLD) from three unrelated Saudi Arabian families have been identified aged 5-37 representing the largest cohort of ATLD patients ever identified. They presented with an early-onset, slowly progressive, ataxia plus ocular apraxia phenotype with an absence of tumor development, even in the oldest patient. Extra-neurological features such as telangiectasia, raised alpha-fetoprotein and reduced immunoglobulin levels were absent. No translocations were found in the two investigated patients, and the presence of microcephaly was noted in four out of eight ascertained patients. All patients are homozygous for a novel missense mutation (630G-->C, W210C) of the MRE11 gene. The cellular consequences of this amino acid change, localized in the nuclease domain of the Mre11 protein, have been determined in fibroblast cultures established from two individuals. They showed high constitutive levels of Mre11 and Rad50 proteins compared with cells from normal individuals but a very low level of the Nbs1 protein. After exposure to ionizing radiation, a dose-dependent defect in ataxia telangiectasia mutated (ATM)-serine 1981, p53-serine 15 and Chk2 phosphorylation, and p53 stabilization were noted, together with a failure to form Mre11 foci and enhanced radiation sensitivity. Formation of gammaH2AX foci was similar to that seen in normal fibroblasts under the experimental conditions examined. These results emphasize the importance of functional interactions among the three proteins of the Mre11-Rad50-Nbs1 complex and lend support to a role of this complex as a sensor of DNA double-strand breaks, acting upstream of ATM.

Marinesco-Sjögren syndrome in a male with mild dysmorphism

Marinesco-Sjogren syndrome (MSS) is a rare, autosomal recessive disorder comprising cataracts, cerebellar ataxia caused by cerebellar hypoplasia, mild to moderate mental retardation, neuromuscular weakness, short stature, hypergonadotrophic hypogonadism, and skeletal anomalies. The syndrome was recently mapped to chromosome 5q31, but there is evidence for genetic heterogeneity, and no gene has been identified. We report a 5-year-old male with cataracts, ataxia, a progressive cerebellar atrophy, developmental delay, seizures, hypotonia, and a sensorimotor neuropathy consistent with many cases of MSS. He also had mild craniofacial dysmorphism consisting of hypertrichosis and synophrys, deep-set eyes with epicanthic folds, a flat philtrum, a high palate, short thumbs, and a wide sandal gap between the first and second toes. Skeletal findings included an increased kyphosis. We reviewed the literature on MSS to determine if craniofacial dysmorphism and the presence of neuropathy and/or myopathy would prove to be diagnostically useful in this phenotypically heterogeneous condition. The majority of cases of MSS do not have craniofacial dysmorphism, but other cases have been reported with features such as ptosis or a myopathic facies that are likely to reflect the underlying myopathic or neuromuscular processes in MSS.