Moderate expansion of a normally biallelic trinucleotide repeat in spinocerebellar ataxia type 2

The gene for spinocerebellar ataxia type 2 (SCA2) has been mapped to 12q24.1. A 1.1-megabase contig in the candidate region was assembled in P1 artificial chromosome and bacterial artificial chromosome clones. Using this contig, we identified a CAG trinucleotide repeat with CAA interruptions that was expanded in patients with SCA2. In contrast to other unstable trinucleotide repeats, this CAG repeat was not highly polymorphic in normal individuals. In SCA2 patients, the repeat was perfect and expanded to 36-52 repeats. The most common disease allele contained (CAG)37, one of the shortest expansions seen in a CAG expansion syndrome. The repeat occurs in the 5'-coding region of SCA2 which is a member of a novel gene family.

Large expansion of the ATTCT pentanucleotide repeat in spinocerebellar ataxia type 10

Spinocerebellar ataxia type 10 (SCA10; MIM 603516; refs 1,2) is an autosomal dominant disorder characterized by cerebellar ataxia and seizures. The gene SCA10 maps to a 3.8-cM interval on human chromosome 22q13-qter (refs 1,2). Because several other SCA subtypes show trinucleotide repeat expansions, we examined microsatellites in this region. We found an expansion of a pentanucleotide (ATTCT) repeat in intron 9 of SCA10 in all patients in five Mexican SCA10 families. There was an inverse correlation between the expansion size, up to 22.5 kb larger than the normal allele, and the age of onset (r2=0.34, P=0.018). Analysis of 562 chromosomes from unaffected individuals of various ethnic origins (including 242 chromosomes from Mexican persons) showed a range of 10 to 22 ATTCT repeats with no evidence of expansions. Our data indicate that the new SCA10 intronic ATTCT pentanucleotide repeat in SCA10 patients is unstable and represents the largest microsatellite expansion found so far in the human genome.

Nuclear localization or inclusion body formation of ataxin-2 are not necessary for SCA2 pathogenesis in mouse or human

Instability of CAG DNA trinucleotide repeats is the mutational mechanism for several neurodegenerative diseases resulting in the expansion of a polyglutamine (polyQ) tract. Proteins with long polyQ tracts have an increased tendency to aggregate, often as truncated fragments forming ubiquitinated intranuclear inclusion bodies. We examined whether similar features define spinocerebellar ataxia type 2 (SCA2) pathogenesis using cultured cells, human brains and transgenic mouse lines. In SCA2 brains, we found cytoplasmic, but not nuclear, microaggregates. Mice expressing ataxin-2 with Q58 showed progressive functional deficits accompanied by loss of the Purkinje cell dendritic arbor and finally loss of Purkinje cells. Despite similar functional deficits and anatomical changes observed in ataxin-1[Q80] transgenic lines, ataxin-2[Q58] remained cytoplasmic without detectable ubiquitination.

A novel protein with RNA-binding motifs interacts with ataxin-2

Spinocerebellar ataxia type 2 (SCA2) is caused by expansion of a polyglutamine tract in ataxin-2, a protein of unknown function. Using the yeast two-hybrid system, we identified a novel protein, A2BP1 (ataxin-2 binding protein 1) which binds to the C-terminus of ataxin-2. Northern blot analysis showed that A2BP1 was predominantly expressed in muscle and brain. By immunocfluorescent staining, A2BP1 and ataxin-2 were both localized to the trans -Golgi network. Immunocytochemistry showed that A2BP1 was expressed in the cytoplasm of Purkinje cells and dentate neurons in a pattern similar to that seen for ataxin-2 labeling. Western blot analysis of subcellular fractions indicated enrichment of A2BP1 in the same fractions as ataxin-2. Sequence analysis of the A2BP1 cDNA revealed an RNP motif that is highly conserved among RNA-binding proteins. A2BP1 had striking homology with a human cDNA clone, P83A20, of unknown function and at least two copies of A2BP1 homologs are found in the Caenorhabditis elegans genome database. A2BP1 and related proteins appear to form a novel gene family sharing RNA-binding motifs.

The neuroimaging and clinical spectrum of neurofibromatosis 2

Neurofibromatosis 2 (NF2) is an autosomal dominant disease predisposing to multiple tumors of the central and peripheral nervous system. Bilateral vestibular schwannomas are the hallmark of the disease. To define the clinical spectrum of the disease, we performed gadolinium-enhanced magnetic resonance imaging of the brain and spine as well as neurological, dermatological, and ocular examinations in 48 patients with NF2 diagnosed with the National Institutes of Health diagnostic criteria. Patients were ascertained from patient workshops and publications and from referral as a result of vestibular schwannoma surgery. Vestibular schwannomas were found in 46 patients (96%, 43 bilateral and 3 unilateral), spinal tumors were found in 43 (90%), posterior subcapsular cataracts were found in 30 (63%), meningiomas were found in 28 (58%), and trigeminal schwannomas were found in 14 (29%). The presenting symptoms included hearing loss or tinnitus in 15 patients (31%), multiple or nonspecific symptoms in 15 (31%), skin tumors in 12 (25%), and ocular symptoms in 6 (13%). When the complete spine was imaged, spinal tumors were more common in patients with NF2 than has previously been reported. This is a noteworthy finding, because spinal tumors are a major cause of NF2 morbidity and mortality.

Learning deficits, but normal development and tumor predisposition, in mice lacking exon 23a of Nf1

Neurofibromatosis type 1 (NF1) is a commonly inherited autosomal dominant disorder. Previous studies indicated that mice homozygous for a null mutation in Nf1 exhibit mid-gestation lethality, whereas heterozygous mice have an increased predisposition to tumors and learning impairments. Here we show that mice lacking the alternatively spliced exon 23a, which modifies the GTPase-activating protein (GAP) domain of Nf1, are viable and physically normal, and do not have an increased tumor predisposition, but show specific learning impairments. Our findings have implications for the development of a treatment for the learning disabilities associated with NF1 and indicate that the GAP domain of NF1 modulates learning and memory.

Expression of ataxin-2 in brains from normal individuals and patients with Alzheimer's disease and spinocerebellar ataxia 2

Spinocerebellar ataxia type 2 (SCA2) is caused by expansion of a CAG trinucleotide repeat located in the coding region of the human SCA2 gene. The SCA2 gene product, ataxin-2, is a basic protein with two domains (Sm1 and Sm2) implicated in RNA splicing and protein interaction. However, the wild-type function of ataxin-2 is yet to be determined. To help clarify the function of ataxin-2, we produced antibodies to three antigenic peptides of ataxin-2 and analyzed the expression pattern of ataxin-2 in normal and SCA2 adult brains and cerebellum at different developmental stages. These studies revealed that (1) both wild-type and mutant forms of ataxin-2 were synthesized; (2) the wild-type ataxin-2 was localized in the cytoplasm in specific neuronal groups with strong labeling of Purkinje cells; (3) the level of ataxin-2 increased with age in Purkinje cells of normal individuals; and (4) ataxin-2-like immunoreactivity in SCA2 brain tissues was more intense than in normal brain tissues, and intranuclear ubiquitinated inclusions were not seen in SCA2 brain tissues.

Spinocerebellar ataxia type 6. Frequency of the mutation and genotype-phenotype correlations

Spinocerebellar ataxia type 6 (SCA6) is the most recently identified mutation causing autosomal-dominant cerebellar ataxia without retinal degeneration (ADCA). The SCA6 mutation is allelic with episodic ataxia type 2 (EA-2), but the two differ clinically because of the presence of progressive, rather than episodic, ataxia in SCA6. SCA6 accounts for 12% of families with ADCA in an ethnically heterogeneous population of patients. Clinical examination, quantitative eye movement testing, and imaging data show that the brainstem is normal in most patients with SCA6, especially within the first 10 years of symptoms. Most patients show progressive ataxia from the onset, but several patients show an episodic course resembling EA-2. Thus, SCA6 mutations not only account for patients with ADCA I and ADCA III phenotypes but also for some patients presenting with episodic features that are typical for EA-2. Interestingly, a compound heterozygote for the SCA6 expansion manifested an earlier onset and more rapid course than family members with the same larger expanded allele.

High resolution deletion analysis of constitutional DNA from neurofibromatosis type 2 (NF2) patients using microarray-CGH

Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder whose hallmark is bilateral vestibular schwannoma. It displays a pronounced clinical heterogeneity with mild to severe forms. The NF2 tumor suppressor (merlin/schwannomin) has been cloned and extensively analyzed for mutations in patients with different clinical variants of the disease. Correlation between the type of the NF2 gene mutation and the patient phenotype has been suggested to exist. However, several independent studies have shown that a fraction of NF2 patients with various phenotypes have constitutional deletions that partly or entirely remove one copy of the NF2 gene. The purpose of this study was to examine a 7 Mb interval in the vicinity of the NF2 gene in a large series of NF2 patients in order to determine the frequency and extent of deletions. A total of 116 NF2 patients were analyzed using high-resolution array-comparative genomic hybridization (CGH) on an array covering at least 90% of this region of 22q around the NF2 locus. Deletions, which remove one copy of the entire gene or are predicted to truncate the schwannomin protein, were detected in 8 severe, 10 moderate and 6 mild patients. This result does not support the correlation between the type of mutation affecting the NF2 gene and the disease phenotype. This work also demonstrates the general usefulness of the array-CGH methodology for rapid and comprehensive detection of small (down to 40 kb) heterozygous and/or homozygous deletions occurring in constitutional or tumor-derived DNA.

Neurofibromatosis 2 tumour suppressor schwannomin interacts with betaII-spectrin

NF2 is the most commonly mutated gene in benign tumours of the human nervous system. The NF2 protein, called schwannomin or merlin, is absent in virtually all schwannomas, and many meningiomas and ependymomas. Using the yeast two-hybrid system, we identified betaII-spectrin (also known as fodrin) as a schwannomin-binding protein. Interaction occurred between the carboxy-terminal domain of schwannomin isoform 2 and the ankyrin-binding region of betaII-spectrin. Isoform 1 of schwannomin, in contrast, interacted weakly with betaII-spectrin, presumably because of its strong self-interaction. Thus, alternative splicing of NF2 may regulate betaII-spectrin binding. Schwannomin co-immunoprecipitated with betaII-spectrin at physiological concentrations. The two proteins interacted in vitro and co-localized in several target tissues and in STS26T cells. Three naturally occurring NF2 missense mutations showed reduced, but not absent, betaII-spectrin binding, suggesting an explanation for the milder phenotypes seen in patients with missense mutations. STS26T cells treated with NF2 antisense oligonucleotides showed alterations of the actin cytoskeleton. Schwannomin itself lacks the actin binding sites found in ezrin, radixin and moesin, suggesting that signalling to the actin cytoskeleton occurs via actin-binding sites on betaII-spectrin. Thus, schwannomin is a tumour suppressor directly involved in actin-cytoskeleton organization, which suggests that alterations in the cytoskeleton are an early event in the pathogenesis of some tumour types.

Oculomotor phenotypes in autosomal dominant ataxias

OBJECTIVE

To quantify the oculomotor features of the common spinocerebellar ataxia (SCA) syndromes.

SETTING

University ataxia clinic.

PATIENTS

Twenty probands with documented SCA mutations.

METHODS

Electro-oculographic recordings of saccadic, smooth pursuit, optokinetic, vestibular, and visual-vestibular eye movements.

RESULTS

Distinct phenotype and genotype patterns were identified with modest overlap between patterns. Slowing of saccade peak velocities occurred only in SCA1 and SCA2, being present in 100% of patients with SCA2. Impaired vestibulo-ocular reflex gain occurred with SCA3 only. Patients with SCA6 had prominent deficits in smooth tracking but normal saccade velocities and vestibuloocular reflex gain.

CONCLUSIONS

The oculomotor findings are consistent with pure cerebellar involvement in SCA6, pontine involvement in SCA1 and SCA2, and vestibular nerve or nuclei involvement in SCA3. These phenotypes can be useful for clinical diagnosis and for investigating the mechanism of system specificity with the SCA syndromes.

Consensus paper: pathological mechanisms underlying neurodegeneration in spinocerebellar ataxias

Intensive scientific research devoted in the recent years to understand the molecular mechanisms or neurodegeneration in spinocerebellar ataxias (SCAs) are identifying new pathways and targets providing new insights and a better understanding of the molecular pathogenesis in these diseases. In this consensus manuscript, the authors discuss their current views on the identified molecular processes causing or modulating the neurodegenerative phenotype in spinocerebellar ataxias with the common opinion of translating the new knowledge acquired into candidate targets for therapy. The following topics are discussed: transcription dysregulation, protein aggregation, autophagy, ion channels, the role of mitochondria, RNA toxicity, modulators of neurodegeneration and current therapeutic approaches. Overall point of consensus includes the common vision of neurodegeneration in SCAs as a multifactorial, progressive and reversible process, at least in early stages. Specific points of consensus include the role of the dysregulation of protein folding, transcription, bioenergetics, calcium handling and eventual cell death with apoptotic features of neurons during SCA disease progression. Unresolved questions include how the dysregulation of these pathways triggers the onset of symptoms and mediates disease progression since this understanding may allow effective treatments of SCAs within the window of reversibility to prevent early neuronal damage. Common opinions also include the need for clinical detection of early neuronal dysfunction, for more basic research to decipher the early neurodegenerative process in SCAs in order to give rise to new concepts for treatment strategies and for the translation of the results to preclinical studies and, thereafter, in clinical practice.

Spinal tumors in patients with neurofibromatosis type 2: MR imaging study of frequency, multiplicity, and variety

OBJECTIVE

Neurofibromatosis type 2 (NF2) is a rare autosomal dominant disorder leading to various tumors of the CNS, with vestibular schwannomas being the hallmark of the disease. We have observed multiple asymptomatic spinal lesions in patients who have a single symptomatic spinal tumor. Accordingly, we studied the frequency, multiplicity, and variety of spinal tumors in all patients with NF2 to determine what is characteristic of the disease.

SUBJECTS AND METHODS

MR images of the entire spinal canal were made in 73 patients aged 4-69 years with NF2. The number, location, morphology, signal characteristics, and contrast medium uptake of the spinal tumors as seen on MR images were recorded and analyzed. Histopathologic proof of 22 spinal tumors was obtained in 19 patients.

RESULTS

Spinal tumors were found on MR images in 89% of the patients studied. No location in any part of the spine was preferred. MR imaging showed intramedullary tumors in 24 patients (33%) (three ependymomas pathologically proven). Extradural and intradural extramedullary tumors were found on MR imaging in the cervical spine of 36 patients, the thoracic spine of 40 patients, and the lumbar spine of 49 patients. These tumors were meningiomas, schwannomas, or neurofibromas, three categories that could not be differentiated on the basis of the neuroradiologic findings, with ten schwannomas, seven meningiomas, and two neurofibromas pathologically proven. Extradural extramedullary tumors were found on MR imaging in the cervical spine of 12 patients, the thoracic spine of five patients, and the lumbar spine of 18 patients. A syrinx associated with a tumor was found in two patients. In 19 patients the variety of tumor types was confirmed by histologic examination.

CONCLUSION

Patients with NF2 frequently have spinal tumors, which are often multiple and of various histologic types. The presence of multiple and different pathologic types of spinal tumors is highly suggestive of NF2.

Spinocerebellar ataxia type 2. Genotype and phenotype in German kindreds

BACKGROUND

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant cerebellar ataxia (ADCA) for which the disease-causing mutation has recently been characterized as an expanded CAG trinucleotide repeat. We investigated 64 families of German ancestry with ADCA and 55 patients with sporadic ataxia for the SCA2 mutation.

RESULTS

Expanded alleles were found in 6 of the 64 families and in 1 patient with sporadic ataxia. This patient had a de novo mutation from an intermediate paternal allele. Length of repeats in 21 patients with SCA2 ranged from 36 to 52 CAG motifs and was inversely correlated with age at onset and progression of the disease. Expanded alleles were unstable during meiosis; paternal transmission especially caused significant anticipation of onset up to 26 years earlier. The SCA2 phenotype differed from those of SCA1 and SCA3 with higher frequencies of slowed ocular movements, postural and action tremor, myoclonus, and hyporeflexia. However, no single feature was sufficient to permit a specific clinical diagnosis.

CONCLUSIONS

Spinocerebellar ataxia type 2 accounts for about 10% of German families with ADCA but may also be present in sporadic ataxia due to de novo mutations. Clinical features are highly variable among and even within families. However, the size of the expanded repeat influences the phenotype and is relevant for course and prognosis of the disease.

Familial multisystem degeneration with parkinsonism associated with the 11778 mitochondrial DNA mutation

OBJECTIVE

To investigate a family with maternally inherited, adult-onset multisystem degeneration including prominent parkinsonism to determine whether clinical features can result from a mitochondrial DNA (mtDNA) mutation. The parkinsonism was levodopa responsive and was associated with the loss of pigmented neurons in the substantia nigra in at least one patient.

BACKGROUND

Mitochondrial dysfunction is hypothesized to play a role in late-onset neurodegenerative diseases including PD and AD. Mitochondrial genetic mutations are hypothesized to account for these defects, but attempts to identify specific mtDNA mutations have been inconclusive.

METHODS

Clinical examinations, DNA sequencing, and restriction digestion and biochemical analyses were performed.

RESULTS

Maternal relatives harbor a G-to-A missense mutation, heteroplasmic in some patients, at nucleotide position 11778 of the mitochondrial ND4 gene of complex I that converts a highly conserved arginine to a histidine. Sequencing of the entire mitochondrial genome in an affected family member reveals no other mutations likely to be pathogenic. This mutation has been identified previously only in families with Leber's hereditary optic neuropathy-a disorder also linked to complex I dysfunction but usually limited clinically to optic atrophy.

CONCLUSIONS

These data reveal previously unsuspected clinical heterogeneity of the G11778A mutation, and suggest that an inherited mtDNA mutation can contribute to the development of adult-onset parkinsonism and multisystem degeneration.

Ocular abnormalities in neurofibromatosis 2

PURPOSE

To evaluate the ocular abnormalities in patients with clinically diagnosed neurofibromatosis 2 and asymptomatic gene carriers.

METHODS

Probands were ascertained through a surgical otolaryngology practice. In a cross-sectional study, we examined 49 patients with neurofibromatosis 2, 30 offspring of patients, and, as a comparison group, 18 parents and siblings of patients with sporadic neurofibromatosis 2. The examination included a complete neuro-ophthalmic assessment, physical examination, and, for patients and first-degree relatives at risk, cranial and spinal magnetic resonance imaging with gadolinium enhancement, if not previously performed.

RESULTS

The most common ocular abnormalities were posterior subcapsular or capsular, cortical, or mixed lens opacities in 33 (67%) of 49 patients with neurofibromatosis 2 and retinal hamartomas in 11 (22%). We used segregation analysis to determine the mutation carrier status of six at-risk offspring who were 30 years old or younger in two multigeneration families. Three asymptomatic mutation carriers had cataracts, whereas those who were predicted not to carry the mutation did not have cataracts. Asymptomatic mutation carriers may have developmental abnormalities of the eye that are detectable in childhood or adolescence, a finding that may assist in early diagnosis of the disease.

CONCLUSIONS

A variety of ocular abnormalities are present in neurofibromatosis 2, including cataracts, retinal hamartomas, and ocular motor deficits. Many of these are developmental or acquired early in life and may assist in presymptomatic diagnosis. For screening at-risk relatives of patients with neurofibromatosis 2, the types of cataract that are most suggestive of neurofibromatosis 2 are plaque-like posterior subcapsular or capsular cataract and cortical cataract with onset under the age of 30 years.

Screening for germ-line mutations in the NF2 gene

Neurofibromatosis type 2 (NF2) is a monogenic dominantly inherited disease that predisposes to the development of tumors of the nervous system, particularly meningiomas and schwannomas. The gene which, when altered, causes NF2, is localized on chromosome 22 and has recently been identified. The NF2 gene is also the site of somatic mutation in tumors, suggesting that it might have a tumor suppressor activity. We here report a screening method for the detection of point mutations in NF2 which takes advantage of denaturing gradient gel electrophoresis (DGGE). This method efficiently screens 95% of the coding sequence and 90% of intron/exon junctions. When applied to 91 unrelated NF2 patients, it enabled the identification of 32 germ-line mutations. Since mutations are found in only one third of the patients, it is expected that mutations or deletions affecting the promoter and/or intronic regions of the NF2 gene occur frequently. The characterized mutations are preferentially located within the 5' half of the gene. Most of them are predicted to lead to the synthesis of a truncated protein. A search for genotype/phenotype correlations showed that, at least in this series of patients, mild manifestations of the disease were associated with mutations which preserve the C-terminal end of the protein.

Mutations of the neurofibromatosis type 2 gene and lack of the gene product in vestibular schwannomas

Schwannomas are common tumors of the nervous system and are frequently found in patients with neurofibromatosis (NF) 2. Although loss of heterozygosity in NF2 tumors suggests that the NF2 gene functions as a tumor suppressor gene, the NF2 gene shows amino acid sequence homology to structural proteins in one of which dominantly acting mutations have been described. We performed a mutational analysis in 30 vestibular schwannomas and examined the effect of mutations on the NF2 protein. We detected 18 mutations in 30 vestibular schwannomas of which seven contained loss or mutation of both NF2 alleles. Most mutations were predicted to result in a truncated protein. Mutational hot spots were not identified. Immunocytochemical studies using antibodies to the NF2 protein showed complete absence of staining in tumor Schwann cells, whereas staining was observed in normal vestibular nerve. These data indicate that loss of NF2 protein function is a necessary step in schwannoma pathogenesis and that the NF2 gene functions as a recessive tumor suppressor gene.

Mapping of a new autosomal dominant spinocerebellar ataxia to chromosome 22

The autosomal dominant cerebellar ataxias (ADCAs) are a clinically and genetically heterogeneous group of disorders. The clinical symptoms include cerebellar dysfunction and associated signs from dysfunction in other parts of the nervous system. So far, five spinocerebellar ataxia (SCA) genes have been identified: SCA1, SCA2, SCA3, SCA6, and SCA7. Loci for SCA4 and SCA5 have been mapped. However, approximately one-third of SCAs have remained unassigned. We have identified a Mexican American pedigree that segregates a new form of ataxia clinically characterized by gait and limb ataxia, dysarthria, and nystagmus. Two individuals have seizures. After excluding all known genetic loci for linkage, we performed a genomewide search and identified linkage to a 15-cM region on chromosome 22q13. A maximum LOD score of 4.3 (recombination fraction 0) was obtained for D22S928 and D22S1161. This distinct form of ataxia has been designated "SCA10." Anticipation was observed in the available parent-child pairs, suggesting that trinucleotide-repeat expansion may be the mutagenic mechanism.

Neurofibromatosis 2 in the pediatric age group

Bilateral acoustic neurofibromatosis or neurofibromatosis 2 (NF2) is an autosomal dominant disease predisposing to the formation of multiple tumors in the central and peripheral nervous system. Vestibular schwannomas (VSs) are considered to be the hallmark of the disease, but other tumors and ocular findings occur as well. In patients that do not carry the NF2 mutation, VSs usually occur in the fifth or sixth decade of life. VSs in patients with NF2 are often bilateral and become symptomatic in the third or fourth decade of life. In order to define the early manifestations of NF2, we examined nine children who either had one parent with NF2 or had multiple skin or spinal tumors suggestive of NF2. In addition to neurological, dermatological, and ocular examinations, all patients were studied by gadolinium-enhanced magnetic resonance imaging of the brain and spine. None of the children exhibited symptoms or signs due to VSs. However, VSs were detected during the neuroradiological work-up in six children. Seven children developed symptoms or signs due to skin or spinal tumors. Slit lamp examination detected cataracts in four patients as young as 10 years of age. The diagnosis of NF2 in the pediatric age group requires a high degree of suspicion and should be considered in children with multiple central nervous system or skin tumors without cafe-au-lait spots or Lisch nodules. Because VSs are unlikely to produce the signs seen at the time of admission, careful examination of the skin and eyes is necessary and should be followed by gadolinium-enhanced magnetic resonance imaging of the brain and spine. First-degree relatives need to be examined as well.

Cellular distribution of torsin A and torsin B in normal human brain

BACKGROUND

Early-onset torsion dystonia is a hyperkinetic movement disorder caused by a deletion of 1 glutamic acid residue in torsin A protein, a novel member of the AAA family of adenosine triphosphatases. No mutation has been found so far in the closely related torsin B protein. Little is known about the molecular basis of the disease, and the cellular functions of torsin proteins remain to be investigated.

OBJECTIVE

To study the regional, cellular, and subcellular distribution of the torsin A and torsin B proteins.

METHODS

Expression of torsin proteins in the central nervous system was analyzed by Western blot analysis and immunohistochemistry in human postmortem brain tissues.

RESULTS

We generated polyclonal antipeptide antibodies directed against human torsin A and torsin B proteins. In Western blot analysis of normal human brain homogenates, the antibodies specifically recognized 38-kd endogenous torsin A and 62-kd endogenous torsin B. Absorption controls showed that labeling was blocked by cognate peptide used for immunization. Immunolocalization studies revealed that torsin A and torsin B were widely expressed throughout the human central nervous system. Both proteins displayed cytoplasmic distribution, although torsin B localization in some neurons was perinuclear. Strong labeling of neuronal processes was detected for both proteins.

CONCLUSIONS

Torsin A and torsin B have similar distribution in the central nervous system, although their subcellular localization is not identical. Strong expression in neuronal processes points to a potential role for torsin proteins in synaptic functioning.

Carbon monoxide poisoning with features of Gilles de la Tourette's syndrome

A previously healthy 58-year-old man had severe carbon monoxide poisoning. Following a comatose state, tics of the head, coprolalia, fits of shouting, and abnormal vocal utterances developed. In addition to the signs of diffuse encephalopathy, he had some of the features associated with idiopathic Gilles de la Tourette's syndrome. The computed tomographic scan showed ventricular enlargement and low-density areas in the basal ganglia.

CAG repeat length in RAI1 is associated with age at onset variability in spinocerebellar ataxia type 2 (SCA2)

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant disorder caused by the expansion of a polymorphic (CAG)(n) tract, which is translated into an expanded polyglutamine tract in the ataxin-2 protein. Although repeat length and age at disease onset are inversely related, approximately 50% of the age at onset variance in SCA2 remains unexplained. Other familial factors have been proposed to account for at least part of this remaining variance in the polyglutamine dis-orders. The ability of polyglutamine tracts to interact with each other, as well as the presence of intra-nuclear inclusions in other polyglutamine disorders, led us to hypothesize that other CAG-containing proteins may interact with expanded ataxin-2 and affect the rate of protein accumulation, and thus influence age at onset. To test this hypothesis, we used step-wise multiple linear regression to examine 10 CAG-containing genes for possible influences on SCA2 age at onset. One locus, RAI1, contributed an additional 4.1% of the variance in SCA2 age at onset after accounting for the effect of the SCA2 expanded repeat. This locus was further studied in SCA3/Machado-Joseph disease (MJD), but did not have an effect on SCA3/MJD age at onset. This result implicates RAI1 as a possible contributor to SCA2 neurodegeneration and raises the possibility that other CAG-containing proteins may play a role in the pathogenesis of other polyglutamine disorders.

Analysis of the dynamic mutation in the SCA7 gene shows marked parental effects on CAG repeat transmission

The gene for spinocerebellar ataxia 7 (SCA7) includes a transcribed, translated CAG tract that is expanded in SCA7 patients. We have determined expansions in 73 individuals from 17 SCA7 kindreds and compared them with repeat lengths of 180 unaffected individuals. Subjects with abnormal expansions comprise 59 clinically affected individuals and 14 at-risk currently unaffected individuals predicted to carry the mutation by haplotype analysis. For expanded alleles, CAG repeat length correlates with disease progression and severity and correlates inversely with age of onset. Increased repeat lengths are seen in generational transmission of the disease allele, consistent with the pattern of clinical anticipation seen in these kindreds. Repeat lengths in expanded alleles show somatic mosaicism in leukocyte DNA, suggesting that these alleles are unstable within individuals as well as between generations. Although dynamic repeat expansions from paternal transmissions are greater than those from maternal transmissions, maternal transmission of disease is more common, suggesting germline or embryonic effects of the repeat expansion.

Differential expression and tissue distribution of type I and type II neurofibromins during mouse fetal development

Mutations in the NF1 gene may cause developmental abnormalities and the formation of a variety of tumors of neural crest origin in humans. The NF1 gene codes for a large protein, neurofibromin (nf), which is structurally and functionally related to yeast and human ras-GTPase-activating proteins (ras-GAPs). Recently, two transcripts coding for type I and type II nf with different ras-GAP activity have been identified. Since ras proteins do not appear to be significantly regulated during mouse development, we examined if differential expression of neurofibromins may provide evidence for a role of nfs in regulating ras-mediated cell proliferation and differentiation. Nfs were expressed as early as E8. At E11 a marked increase of NF1 transcripts occurred and was associated with expression of nfs in all tissues. Type I and type II nfs each showed a different time course of expression and tissue localization, with type II nf present mainly from E8 through E10, although in the heart type II nf was present at E12. In some tissues such as heart and dorsal root ganglia rapid increases and decreases of nfs were detected related to differentiation of these tissues. These results are consistent with a role of nfs in regulating ras-mediated cell proliferation and differentiation during development and support distinct functional roles for type I and type II nfs.