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Retinitis pigmentosa (RP) is a clinically and genetically heterogeneous group of inherited retinal degenerations. The ortholog of Drosophila eyes shut/spacemaker, EYS on chromosome 6q12 is a major genetic cause of recessive RP worldwide, with prevalence of 5 to 30%. In this study, by using targeted NGS, MLPA and Sanger sequencing we uncovered the EYS gene as the second most common genetic cause of RP in northern Sweden accounting for at least 18%. The most frequent pathogenic variant was c.8648_8655del that in some patients was identified in cis with c.1155T>A, indicating Finnish ancestry. We also showed that two novel EYS variants, c.2992_2992+6delinsTG and c.3877+1G>A caused exon skipping in human embryonic kidney cells, HEK293T and in retinal pigment epithelium cells, ARPE-19 demonstrating that in vitro minigene assay is a straightforward tool for the analysis of intronic variants. We conclude, that whenever it is possible, functional testing is of great value for classification of intronic EYS variants and the following molecular testing of family members, their genetic counselling, and inclusion of RP patients to future treatment studies.

Background Hereditary myopathy with lactic acidosis (HML) is an autosomal recessive disease caused by an intron mutation in the iron‐sulfur cluster assembly (ISCU) gene. The mutation results in aberrant splicing, where part of the intron is retained in the final mRNA transcript, giving rise to a truncated nonfunctional ISCU protein. Using an ISCU mini‐gene system, we have previously shown that PTBP1 can act as a repressor of the mis‐splicing of ISCU, where overexpression of PTBP1 resulted in a decrease of the incorrect splicing. In this study, we wanted to, in more detail, analyze the role of PTBP1 in the regulation of endogenous ISCU mis‐splicing. Methods Overexpression and knockdown of PTBP1 was performed in myoblasts from two HML patients and a healthy control. Quantification of ISCU mis‐splicing was done by qRTPCR. Biotinylated ISCU RNA, representing wildtype and mutant intron sequence, was used in a pull‐down assay with nuclear extracts from myoblasts. Levels of PTBP1 in human cell lines and mice tissues were analyzed by qRTPCR and western blot. Results PTBP1 overexpression in HML patient myoblasts resulted in a substantial decrease of ISCU mis‐splicing while knockdown of PTBP1 resulted in a drastic increase. The effect could be observed in both patient and control myoblasts. We could also show that PTBP1 interacts with both the mutant and wild‐type ISCU intron sequence, but with a higher affinity to the mutant sequence. Furthermore, low levels of PTBP1 among examined mouse tissues correlated with high levels of incorrect splicing of ISCU. Conclusion Our results show that PTBP1 acts as a dominant repressor of ISCU mis‐splicing. We also show an inverse correlation between the levels of PTBP1 and ISCU mis‐splicing, suggesting that the high level of mis‐splicing in the skeletal muscle is primarily due to the low levels of PTBP1.

Inherited retinal dystrophies (IRDs) represent a group of progressive conditions affecting the retina. There is a great genetic heterogeneity causing IRDs, and to date, more than 260 genes are associated with IRDs. Stargardt disease, type 1 (STGD1) or macular degeneration with flecks, STGD1 represents a disease with early onset, central visual impairment, frequent appearance of yellowish flecks and mutations in the ATP-binding cassette subfamily A, member 4 (ABCA4) gene. A large number of intronic sequence variants in ABCA4 have been considered pathogenic although their functional effect was seldom demonstrated. In this study, we aimed to reveal how intronic variants present in patients with Stargardt from the same Swedish family affect splicing.The splicing of the ABCA4 gene was studied in human embryonic kidney cells, HEK293T, and in human retinal pigment epithelium cells, ARPE-19, using a minigene system containing variants c.4773+3AG and c.5461-10TC.We showed that both ABCA4 variants, c.4773+3AG and c.5461-10TC, cause aberrant splicing of the ABCA4 minigene resulting in exon skipping. We also demonstrated that splicing of ABCA4 has different outcomes depending on transfected cell type.Two intronic variants c.4773+3AG and c.5461-10TC, both predicted to affect splicing, are indeed disease-causing mutations due to skipping of exons 33, 34, 39 and 40 of ABCA4 gene. The experimental proof that ABCA4 mutations in STGD patients affect protein function is crucial for their inclusion to future clinical trials; therefore, functional testing of all ABCA4 intronic variants associated with Stargardt disease by minigene technology is desirable.

Hereditary myopathy with lactic acidosis (HML) is an autosomal recessive disease caused by an intronic one-base mutation in the iron-sulfur cluster assembly (ISCU) gene, resulting in aberrant splicing. The incorrectly spliced transcripts contain a 100 or 86 bp intron sequence encoding a non-functional ISCU protein, which leads to defects in several Fe-S containing proteins in the respiratory chain and the TCA cycle. The symptoms in HML are restricted to skeletal muscle, and it has been proposed that this effect is due to higher levels of incorrectly spliced ISCU in skeletal muscle compared with other energy-demanding tissues. In this study, we confirm that skeletal muscle contains the highest levels of incorrect ISCU splice variants compared with heart, brain, liver and kidney using a transgenic mouse model expressing human HML mutated ISCU. We also show that incorrect splicing occurs to a significantly higher extent in the slow-twitch soleus muscle compared with the gastrocnemius and quadriceps. The splicing factor serine/arginine-rich splicing factor 3 (SRSF3) was identified as a potential candidate for the slow fiber specific regulation of ISCU splicing since this factor was expressed at higher levels in the soleus compared to the gastrocnemius and quadriceps. We identified an interaction between SRSF3 and the ISCU transcript, and by overexpressing SRSF3 in human myoblasts we observed increased levels of incorrectly spliced ISCU, while knockdown of SRSF3 resulted in decreased levels. We therefore suggest that SRSF3 may participate in the regulation of the incorrect splicing of mutant ISCU and may, at least partially, explain the muscle-specific symptoms of HML.

We have previously identified a homozygous missense (R221W) mutation in the NGFB gene in patients with loss of deep pain perception. NGF is important not only for the survival of sensory neurons but also for the sympathetic neurons and cholinergic neurons of the basal forebrain; however, it is the sensory neurons that are mainly affected in patients with mutant NGFB. In this report, we describe the effects of the mutation on the function of NGF protein and the molecular mechanisms that may underlie the pain insensitivity phenotype in these patients. We show that the mutant NGF has lost its ability to mediate differentiation of PC12 cells into a neuron-like phenotype. We also show that the inability of PC12 cells to differentiate is due to a markedly reduced secretion of mature R221W NGF. The R221W NGF is found mainly as proNGF, in contrast to wild-type NGF which is predominantly in the mature form in both undifferentiated and differentiated PC12 cells. The reduction in numbers of sensory fibers observed in the patients is therefore probably due to loss of trophic support as a result of drastically reduced secretion of NGF from the target organs. Taken together, these data show a clear decrease in the availability of mutant mature NGF and also an accumulation of proNGF in both neuronal and non-neuronal cells. The differential loss of NGF-dependent neurons in these patients, mainly affecting sensory neurons, may depend on differences in the roles of mature NGF and proNGF in different cells and tissues.

We describe the mapping and identification of the gene for hereditary myopathy with lactic acidosis (HML). HML is characterized by low physical performance, resulting in physical exertion that causes early exhaustion, dyspnoea and palpitations. Using an autosomal recessive mode of inheritance, we mapped the trait to chromosome 12q23.3-24.11, with a maximum lod score of 5.26. The 1.6-Mb disease-critical region contained one obvious candidate gene-ISCU-specifying a protein involved in iron-sulphur cluster assembly. IscU is produced in two isoforms; one cytosolic and one mitochondrial, coded for by different splice variants of the ISCU gene. Mutational analysis of all exon and intron sequences as well as 1000 bp of the promoter of the ISCU gene revealed one intron mutation that was specific for the disease haplotype. The mutation is located in a region with homology to the interferon-stimulated response element (ISRE), but we could not see any effect of the mutation on expression levels in vitro or in vivo. We did, however, observe a drastic difference in the splicing pattern between patients and controls. In controls the mRNA was, as expected, mainly in the mitochondrial form, while in the patients a larger mRNA transcript was predominant. Sequencing of the product revealed that the mutation activates cryptic splice sites in intron 5 resulting in aberrant mRNA containing 100 bp of the intron. To conclude, our data strongly suggest that an intron mutation in the ISCU gene, leading to incorrectly spliced mRNA, is the cause of myopathy with lactic acidosis in this family.

Migraine is a complex, multifactorial disorder for which several loci have been identified in the human genome. We have previously reported linkage to a 10 Mb-region on chromosome 6p12.2-p21.1 in one large Swedish pedigree involving migraine with and without aura. To further investigate this candidate region, a dense set of single nucleotide polymorphic (SNP) markers was used for fine-mapping, decreasing the critical region to 8.5 Mb. Within this region, EFHC1 was recently identified as the disease gene for juvenile myoclonic epilepsy. Migraine and epilepsy has been suggested to share disease mechanisms and therefore EFHC1 is an excellent candidate gene for migraine in this family. Mutation analysis of the gene revealed a disease-segregating polymorphism in the promoter. Association analysis of the polymorphism in a case-control material did not support a role for this gene in migraine pathology. We therefore analyzed five additional candidate genes in the disease-critical region, including MEP1A, RHAG, IL17, SLC25A27 and TNFRSF21. In two of these genes, MEP1A and RHAG, we identified two novel polymorphisms associated with the disease haplotype. The combination of these polymorphisms could not be found in any control individuals, suggesting that they might be involved in genetic predisposition to migraine in this family.

Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disease primarily affecting the cerebellum, brainstem and retina. The disease is caused by a polyglutamine expansion in ataxin-7, a protein with largely unknown function. To improve our knowledge of the expression and function of wild-type and expanded ataxin-7, we looked for alternative SCA7 transcripts in mice. We identified a murine SCA7 isoform (SCA7b) containing an uncharacterized exon homologous to the newly identified human exon 12b. Northern blot analysis revealed three exon 12b containing transcripts with molecular sizes of 7.5, 4.4 and 3.0 kb in mice. This contrasted with the situation in humans, where only one exon 12b-containing transcript was observed. Furthermore, Northern blot of the human 4.4 kb SCA7b isoform predominantly showed expression in the brain, while expression of both the murine 7.5-kb and the 4.4-kb transcripts were observed in several tissues including brain, heart, liver, kidney and testis. Quantitative real-time RT-PCR analysis revealed that in muscle and heart SCA7b is the predominant SCA7 isoform, while in brain equal levels of SCA7a and SCA7b was observed. Insertion of exon 12b into the murine SCA7 ORF resulted in a frame-shift that gave rise to an alternative ataxin-7 protein (ataxin-7b). The novel 58-amino acid C-terminus in ataxin-7b directed the protein to a more cytoplasmic location.

Identification of genes associated with pain insensitivity syndromes can increase the understanding of the pathways involved in pain and contribute to the understanding of how sensory pathways relate to other neurological functions. In this report we describe the mapping and identification of the gene responsible for loss of deep pain perception in a large family from northern Sweden. The loss of pain perception in this family is characterized by impairment in the sensing of deep pain and temperature but with normal mental abilities and with most other neurological responses intact. A severe reduction of unmyelinated nerve fibers and a moderate loss of thin myelinated nerve fibers are observed in the patients. Thus the cases in this study fall into the class of patients with loss of pain perception with underlying peripheral neuropathy. Clinically they best fit into HSAN V. Using a model of recessive inheritance we identified an 8.3 Mb region on chromosome 1p11.2-p13.2 shared by the affected individuals in the family. Analysis of functional candidate genes in the disease critical region revealed a mutation in the coding region of the nerve growth-factor beta (NGFB) gene specific for the disease haplotype. This NGF mutation seems to separate the effects of NGF involved in development of central nervous system functions such as mental abilities, from those involved in peripheral pain pathways. This mutation could therefore potentially provide an important tool to study different roles of NGF, and of pain control.

We have identified a large family in the northern part of Sweden with multiple cases of autoimmune diseases, namely type 1 diabetes (T1D), Graves' disease (GD) and Hashimoto's thyroiditis (HT). The family members affected by any of these diseases share a region of 2.4 Mb that comprises among others the CTLA4 gene. We determined that all affected members of the family shared the HLA susceptibility haplotype (DR4-DQA1*0301-DQB1*0302). Analysis of genetic interaction conditioning for HLA haplotype provided strong evidence that the critical region which includes the CTLA4 gene acts together with the HLA locus on the etiology of disease (lodscore 4.20 (theta=0.0). The study of this family allowed us to: (1) reinforce a number of reports on linkage and association of the CTLA4 region to T1D and AITD; (2) demonstrate that a single haplotypic variant in this region constitutes an etiological factor to disease susceptibility in T1D, GD and HT; (3) reveal a strong genetic interaction of the CTLA4 and HLA loci in the genetic architecture of autoimmune disease; (4) emphasise the value of large pedigrees drawn from isolated populations as tools to single out the effect of individual loci in the etiology of complex diseases.

Migraine is the most common type of chronic episodic headache. To find novel susceptibility genes for familial migraine with and without aura, a genomewide screen was performed in a large family from northern Sweden. Evidence of linkage was obtained on chromosome 6p12.2-p21.1, with a maximum two-point lod score of 5.41 for marker D6S452. The patients with migraine shared a common haplotype of 10 Mb between markers D6S1650 and D6S1960.

Spinocerebellar ataxia 7 (SCA7) is a neurodegenerative disease caused by the expansion of a CAG repeat encoding a polyglutamine tract in the protein ataxin-7. We developed antibodies directed against two different parts of the ataxin-7 protein and studied its distribution in brain and peripheral tissue from healthy subjects. Normal ataxin-7 was widely expressed in brain, retina and peripheral tissues, including striated muscle, testis and thyroid gland. In the brain, expression of ataxin-7 was not limited to areas in which neurones degenerate, and the level of expression was not related to the severity of neuronal loss. Immunoreactivity was low in some vulnerable populations of neurones, such as Purkinje cells. In neurones, ataxin-7 was found in the cell bodies and in processes. Nuclear labelling was also observed in some neurones, but was not related to the distribution of intranuclear inclusions observed in an SCA7 patient. In this patient, the proportion of neurones with nuclear labelling was higher, on average, in regions with neuronal loss. Double immunolabelling coupled with confocal microscopy showed that ataxin-7 colocalized with BiP, a marker of the endoplasmic reticulum, but not with markers of mitochondria or the trans-Golgi network.

Spinocerebellar ataxia 7 (SCA7) is a neurodegenerative disorder characterized by degeneration of the cerebellum, brainstem and retina. The gene responsible for SCA7, located on chromosome 3p, recently was cloned and shown to contain a CAG repeat in the coding region of the gene, that is expanded in SCA7 patients of French origin. We examined the SCA7 repeat region in four Swedish SCA7 families as well as in 57 healthy controls. All Swedish SCA7 patients exhibited expanded CAG repeats with a strong negative correlation between repeat size and age of onset. The repeat length in SCA7 patients ranged from 40 to200 repeats. The largest expansion was observed in a juvenile case with an age of onset of 3 months, and represents the longest polyglutamine stretch ever reported. In patients with 59 repeats or more, visual impairment was the most common initial symptom observed, while ataxia predominates in patients with59 repeats. Two of the Swedish SCA7 families analysed in this study were shown to be related genealogically. The other two SCA7 families could not be traced back to a common ancestor. All four families shared the same allele on the disease chromosome at a locus closely linked to SCA7, suggesting the possibility of a founder effect in the Swedish population.

Spinocerebellar ataxia 7 (SCA7) is caused by the expansion of an unstable CAG repeat in the first exon of the SCA7 gene. We have analyzed the SCA7 mutation in 19 families and one isolated case of various geographical origins, presenting with autosomal dominant cerebellar ataxia with progressive macular dystrophy. The SCA7 CAG repeat was expanded in 77 patients and in 11 at-risk individuals, with alleles containing from 37 to 130 repeats, demonstrating that SCA7 is genetically homogeneous. Repeats on normal alleles contained from 7 to 35 CAGs. There was a strong negative correlation (r = -0.84) between the age at onset and the size of the CAG repeat expansion in SCA7 patients. Larger expansions were associated with earlier onset, a more severe and rapid clinical course, and a higher frequency of decreased vision, ophthalmoplegia, extensor plantar response and scoliosis. The frequency of other clinical signs such as dysphagia and sphincter disturbances increased with disease duration. The mutation was highly unstable during transmission, with a mean increase of 10 +/- 16 CAG repeats, which was significantly greater in paternal (15 +/- 20) than in maternal (5 +/- 5) transmissions. This correlated well with the marked anticipation (19 +/- 13 years) observed in the families. Gonadal mosaicism, observed in the sperm of a patient, was particularly important, with expanded alleles ranging from 42 to >155 CAG repeats. The degree of instability during transmission, resulting mostly in expansions, is greater than in the seven other neurodegenerative disorders caused by polyglutamine expansions.

A gene (DYT1) for early onset idiopathic torsion dystonia was mapped to chromosome 9q34 in non-Jewish and Jewish families. The DYT1 gene region has been excluded in other families with adult onset and cervical or cranial onset idiopathic torsion dystonia from the United States, Great Britain, and France. The role of DYT1 in a Swedish family with adult onset idiopathic torsion dystonia in four generations was examined. The disease seems to be inherited in an autosomal dominant mode with reduced penetrance in this family. There were 10 affected family members, with a mean age of onset of 27 (range 18 to 50) years. The disease showed variable expression, with focal, multifocal, and generalised forms of dystonia in different family members. Genetic analysis excluded the chromosomal region containing the DYT1 locus as being responsible for dystonia in this family.

Hereditary myopathy with lactic acidosis (HML) is caused by an intron mutation in the iron-sulfur cluster assembly gene ISCU, which leads to the activation of cryptic splice sites and the retention of part of intron 4. This incorrect splicing is more pronounced in muscle than in other tissues, resulting in a muscle-specific phenotype. In this study, we identified five nuclear factors that interact with the sequence harboring the mutation and analyzed their effect on the splicing of the ISCU gene. The identification revealed three splicing factors, SFRS14, RBM39, and PTBP1, and two additional RNA binding factors, matrin 3 (MATR3) and IGF2BP1. IGF2BP1 showed a preference for the mutant sequence, whereas the other factors showed similar affinity for both sequences. PTBP1 was found to repress the defective splicing of ISCU, resulting in a drastic loss of mutant transcripts. In contrast, IGF2BP1 and RBM39 shifted the splicing ratio toward the incorrect splice form.

Hereditary myopathy with lactic acidosis (HML) is caused by an intron mutation in the iron-sulphur cluster assembly gene (ISCU) leading to incorporation of intron sequence into the mRNA. This results in a deficiency of Fe-S cluster proteins, affecting the TCA cycle and the respiratory chain. The proteins involved in the Fe-S machinery are evolutionary conserved and shown to be fundamental in all organisms examined. ISCU is expressed at high levels in numerous tissues in mammals, including high metabolic tissues like the heart, suggesting that a drastic mutation in the ISCU gene would be damaging to all energy-demanding organs. In spite of this, the symptoms in patients with HML are restricted to skeletal muscle, and it has been proposed that splicing events may contribute to the muscle specificity. In this study we confirm that a striking difference in the splicing pattern of mutant ISCU exists between different tissues. The highest level of incorrectly spliced ISCU mRNA was found in skeletal muscle, while the normal splice form predominated in patient heart. The splicing differences were also reflected at a functional level, where loss of Fe-S cluster carrying enzymes and accumulation of iron were present in muscle, but absent in other tissues. We also show that complete loss of ISCU in mice results in early embryonic death. The mice data confirm a fundamental role for ISCU in mammals and further support tissue-specific splicing as the major mechanism limiting the phenotype to skeletal muscle in HML.

The primary dystonias are a genetically heterogeneous group of disorders that can be subdivided in pure dystonias, dystonia-plus syndromes, and paroxymal dystonia. Four pure autosomal dominant dystonia loci have been mapped to date, DYT1, 6, 7, and 13, with varying penetrance. We report the mapping of a novel locus for a late-onset form of pure torsion dystonia in a family from northern Sweden. The disease is inherited in an autosomal dominant manner with a penetrance that may be as high as 90%. The torsion dystonia locus in this family was mapped to chromosome 2q14.3-q21.3 using an Illumina linkage panel. We also confirmed the linkage, using ten tightly linked microsatellite markers in the region, giving a maximum LOD score of 5.59 for marker D2S1260. The disease-critical region is 3.6-8.9 Mb depending on the disease status of one individual carrying a centromeric recombination. Mutational analysis was performed on 22 genes in the disease-critical region, including all known and hypothetical genes in the smaller, 3.6-Mb region, but no disease-specific mutations were identified. Copy number variation analysis of the region did not reveal any deletions or duplications. In order to increase the chances of finding the disease gene, fine-mapping may be necessary to decrease the region of interest. This report will hopefully result in the identification of additional dystonia families with linkage to the same locus, and thereby, refinement of the disease critical region.

To evaluate pallidal DBS in a non-DYT1 form of hereditary dystonia. We present the results of pallidal DBS in a family with non-DYT1 dystonia where DYT5 to 17 was excluded. The dystonia is following an autosomal dominant pattern. Ten members had definite dystonia and five had dystonia with minor symptoms. Four patients received bilateral pallidal DBS. Mean age was 47 years. The patients were evaluated before surgery, and "on" stimulation after a mean of 2.5 years (range 1-3) using the Burke-Fahn-Marsden scale (BFM). Mean BFM score decreased by 79 % on stimulation, from 42.5 +/- 24 to 9 +/- 6.5 at the last evaluation. Cervical involvement improved by 89%. The 2 patients with oromandibular dystonia and blepharospasm demonstrated a reduction of 95% regarding these symptoms. The present study confirms the effectiveness of pallidal DBS in a new family with hereditary primary segmental and generalized dystonia.

A family with neurological findings similar to hereditary sensory and autonomic neuropathy type V having a point mutation in the nerve growth factor beta (NGFB) gene was recently described. The homozygous genotype gives disabling symptoms. The purpose of the present study was to evaluate the symptoms in heterozygous patients.26 patients heterozygous for the NGFB mutation (12 men, mean age 50 (13-90) years) were examined clinically and answered a health status questionnaire, including the Michigan Neuropathy Screening Instrument (MNSI). 28 relatives (15 men, mean age 44 (15-86) years) without the mutation served as controls in the clinical examination part. 23 of the heterozygotes were examined neurophysiologically and six heterozygous patients underwent a sural nerve biopsy.The heterozygous phenotype ranged from eight patients with Charcot arthropathy starting in adult age and associated with variable symptoms of neuropathy but without complete insensitivity to pain, anhidrosis or mental retardation, to 10 symptom free patients. There was no difference in MNSI between the young heterozygous cases (55 years old) and the controls. Six of 23 heterozygous patients had impaired cutaneous thermal perception and 11 of 23 had signs of carpal tunnel syndrome. Sural nerve biopsies showed a moderate reduction of both small myelinated (Adelta) and unmyelinated (C) fibres. No apparent correlation of small fibre reduction to symptoms was found.The NGFB mutation in its heterozygous form results in a milder disease than in homozygotes, with a variable clinical picture, ranging from asymptomatic cases to those with Charcot arthropathy appearing in adult age. Particularly age, but perhaps lifestyle factors also, may influence the development of clinical polyneuropathy.

Congenital insensitivity to pain is a rare hereditary sensory neuropathy.We present 6 patients from a family with a mutation in the nerve growth factor beta gene (NGFB).3 patients were homozygous with a mutilating arthropathy starting early in life, and 3 patients were presumably heterozygous with a milder course starting in adulthood. All patients had normal mental abilities. In addition to absence of deep pain, the patients had impaired temperature sensation, but no autonomic deficiency. Sural nerve biopsies showed a moderate loss of A-delta fibres and a severe reduction in C fibers. Clinically, the disorder most often affected the lower extremities, with an insidious progressive joint swelling or a painless fracture, but the spine could also be involved with gross and unstable spondylolisthesis. Fracture healing was uneventful, but the arthropathy was progressive, eventually resulting in gross deformity and instability. When treating patients with congenital disorders such as this one, it is important to consider the slowly progressive nature of the disorder, and the orthopedic operations should therefore be planned from a long-term standpoint. Arthrodesis, limb lengthening and spinal decompression or fusion are the only elective procedures that seem reasonable. Fitting of orthosis for joint protection is also demanding. To delay the development of neuropathic arthropathy, patient education is essential but difficult in the very young.The different expression between homo- and heterozygous subjects and the central role of nerve growth factor make this disease an interesting model system for studies of disease mechanisms and the molecular background to pain.

Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disease caused by the expansion of a polyglutamine tract in the protein ataxin-7, a protein of unknown function. In order to analyze the expression pattern of wild type ataxin-7 in detail, the murine SCA7 gene homolog was cloned and the expression pattern in mice analyzed. The SCA7 mouse and human gene exhibit a high degree of identity at both DNA (88.2%) and protein (88.7%) level. The CAG repeat region, known to be polymorphic in man, is conserved in mouse but contained only five repeats in all mouse strains analyzed. The arrestin homology domain and the nuclear localization signal found in human ataxin-7 is also conserved in the murine homolog. Expression of ataxin-7 was detected during mouse embryonic development and in all adult mouse tissues examined by northern and western blots. In brain, immunohistological staining revealed an ataxin-7 expression pattern similar to that in human, with ataxin-7 expression in cerebellum, several brainstem nuclei, cerebral cortex and hippocampus. Our data show high conservation of ataxin-7 both structurally and at the level of expression, suggesting a conserved role for the protein in mice and humans.

Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder primarily affecting the cerebellum, brain stem and retina. The disease is caused by an expanded polyglutamine tract in the protein ataxin-7. In this study we analyzed the expression pattern of ataxin-7 in CNS and non-CNS tissue from three SCA7 patients and age-matched controls. SCA7 is a rare autosomal dominant disorder, limiting the number of patients available for analysis. We therefore compiled data on ataxin-7 expression from all SCA7 patients (n=5) and controls (n=7) published to date, and compared with the results obtained in this study. Expression of ataxin-7 was found in neurons throughout the CNS and was highly abundant in Purkinje cells of the cerebellum, in regions of the hippocampus and in cerebral cortex. Ataxin-7 expression was not restricted to regions of pathology, and there were no apparent regional differences in ataxin-7 expression patterns between patients and controls. The subcellular distribution of ataxin-7 was primarily nuclear in all brain regions studied. In cerebellar Purkinje cells, however, differences in subcellular distribution of ataxin-7 were observed between patients and controls of different ages. Here we provide an increased understanding of the distribution of ataxin-7, and the possible implication of subcellular localization of this protein on disease pathology is discussed.

Spinocerebellar ataxia type 7 (SCA7) is a neuro-degenerative disorder characterised by progressive cerebellar ataxia and macular degeneration. SCA7 is one of the least common genetically verified autosomal dominant cerebellar ataxias (ADCAs) in the world (4.5 to 11.6%), but in Sweden and Finland SCA7 is the most commonly identified form of ADCA. In an inventory of hereditary ataxias in Scandinavia (Sweden, Norway, Denmark and Finland) we identified 15 SCA7 families, eight in Sweden and seven in Finland, while no cases of SCA7 could be found in Norway or Denmark. We examined whether the relatively high frequency of SCA7 families in Sweden and Finland was the result of a common founder effect. Only two out of 15 families could be connected genealogically. However, an extensive haplotype analysis over a 10.2 cM region surrounding the SCA7 gene locus showed that all 15 families studied shared a common haplotype over at least 1.9 cM. This strongly suggests that all Scandinavian SCA7 families originate from a common founder pre-mutation.

Autosomal dominant cerebellar ataxia with progressive macular degeneration is caused by a CAG/glutamine repeat expansion in the SCA7 gene/protein. Neuronal intranuclear inclusions were detected in the brain of an early onset SCA7 case with the 1C2 antibody directed against an expanded polyglutamine domain. Nuclear inclusions were most frequent in the inferior olivary complex, a site of severe neuronal loss in SCA7. They were also observed in other brain regions, including the cerebral cortex, not considered to be affected in the disease. Using confocal microscopy we showed that some inclusions were ubiquitinated, but to varying degrees, ranging from

The autosomal dominant cerebellar ataxias (ADCA) are a group of neurodegenerative disorders with ataxia and dysarthria as early and dominant signs. In ADCA type II, retinal degeneration causes severe visual impairment. ADCA type II has recently been mapped to chromosome 3p by three independent groups. In the family with ADCA type II studied here, the disease has been mapped to chromosome 3p12-p21.1. Histochemical examination of muscle biopsies in 5 cases showed slight neurogenic atrophy and irregular lobulated appearance or focal decreases of enzyme activity when staining for NADH dehydrogenase, succinic dehydrogenase and cytochrome oxidase. Ragged-red fibres were scarce. Electron microscopic examination showed uneven distribution of mitochondria with large fibre areas devoid of mitochondria and/or large subsarcolemmal accumulations of small rounded mitochondria, and frequent autophagic vacuoles. These vacuoles contained remnants of multiple small rounded organelles, possibly mitochondria, and had a remarkably consistent ultrastructural appearance. Biochemical investigation of mitochondrial function showed reduced activity of complex IV and slightly reduced activity of complex I in the respiratory chain in a severely affected child while no abnormalities were found in his affected uncle.

International audience; Expanded CAG repeat sequences have been identified in the coding region of genes mutated in several neurodegenerative disorders, including spinocerebellar ataxia type 1 and Machado-Joseph disease. In all disorders described to date the CAG expansion codes for an elongated polyglutamine chain. An increased polyglutamine chain size leads to a more severe disease, thus correlating with the genetic anticipation seen in repeat expansion disorders. Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant spinocerebellar ataxia with anticipation and a progressive degeneration of the cerebellar cortex. Using repeat expansion detection (RED), a method in which a thermostable ligase is used to detect repeat expansions directly from genomic DNA, we have analyzed 8 SCA7 families for the presence of CAG repeat expansions. RED products of 150-240 bp were found in all affected individuals and found to cosegregate with the disease (P < 0.000001, n = 66), indicating strongly that a CAG expansion is the cause of SCA7. On the basis of a previously established correlation between RED product sizes and actual repeat sizes in Machado-Joseph disease, we were able to estimate the average expansion size in SCA7 to be 64 CAG copies.

We present linkage analysis on a large Swedish five-generation family of 15 affected individuals with autosomal dominant cerebellar ataxia (ADCA) associated with retinal degeneration and anticipation. Common clinical signs in this family include ataxia, dysarthria and severely impaired vision with the phenotype ADCA type II. Different subtypes of ADCA have proven difficult to classify clinically due to extensive phenotypic variability within and between families. Genetic analysis of a number of ADCA type I families shows that heterogeneity exists also genetically. During the last few years several types of ADCA type I have been localized and to date six genetically distinct forms have been identified including SCA1 (6p), SCA2 (12q), SCA3 and Machado-Joseph disease (MJD) (14q), SCA4 (16q), and finally SCA5 (11). We performed a genome-wide search of the Swedish ADCA type II family using a total of 270 microsatellite markers. Positive lod scores were obtained with a number of microsatellite markers located on chromosome 3p12-p21.1. Three markers gave lod scores over 3 with a maximum lod score of 4.53 achieved with the marker D3S1600. The ADCA type II gene could be restricted to a region of 32 cM by the markers D3S1547 and D3S1274.