Quantitative Susceptibility Mapping Suggests Altered Brain Iron in Premanifest Huntington Disease

BACKGROUND AND PURPOSE

In patients with premanifest (nonsymptomatic) and advanced Huntington disease, changes in brain iron levels in the basal ganglia have been previously reported, especially in the striatum. Quantitative susceptibility mapping by using MR phase imaging allows in vivo measurements of tissue magnetic susceptibility, which has been shown to correlate well with iron levels in brain gray matter and is believed to be more specific than other imaging-based iron measures. The purpose of this study was to investigate the use of magnetic susceptibility as a biomarker of disease progression.

MATERIALS AND METHODS

Fifteen subjects with premanifest Huntington disease and 16 age-matched healthy controls were scanned at 7T. Magnetic susceptibility, effective relaxation, and tissue volume in deep gray matter structures were quantified and compared with genetic and clinical measures.

RESULTS

Subjects with premanifest Huntington disease showed significantly higher susceptibility values in the caudate nucleus, putamen, and globus pallidus, indicating increased iron levels in these structures. Significant decreases in magnetic susceptibility were found in the substantia nigra and hippocampus. In addition, significant volume loss (atrophy) and an increase effective relaxation were observed in the caudate nucleus and putamen. Susceptibility values in the caudate nucleus and putamen were found to be inversely correlated with structure volumes and directly correlated with the genetic burdens, represented by cytosine-adenine-guanine repeat age-product-scaled scores.

CONCLUSIONS

The significant magnetic susceptibility differences between subjects with premanifest Huntington disease and controls and their correlation with genetic burden scores indicate the potential use of magnetic susceptibility as a biomarker of disease progression in premanifest Huntington disease.

A comparison of nine scales to detect depression in Parkinson disease: which scale to use?

OBJECTIVE

The Methods of Optimal Depression Detection in Parkinson's Disease (MOOD-PD) study compared the psychometric properties of 9 depression scales to provide guidance on scale selection in Parkinson disease (PD).

METHODS

Patients with PD (n = 229) from community-based neurology practices completed 6 self-report scales (Beck Depression Inventory [BDI]-II, Center for Epidemiologic Studies Depression Rating Scale-Revised [CESD-R], 30-item Geriatric Depression Scale [GDS-30], Inventory of Depressive Symptoms-Patient [IDS-SR], Patient Health Questionnaire-9 [PHQ-9], and Unified Parkinson's Disease Rating Scale [UPDRS]-Part I) and were administered 3 clinician-rated scales (17-item Hamilton Depression Rating Scale [HAM-D-17], Inventory of Depressive Symptoms-Clinician [IDS-C], and Montgomery-Åsberg Depression Rating Scale [MADRS] and a psychiatric interview. DSM-IV-TR diagnoses were established by an expert panel blinded to the self-reported rating scale data. Receiver operating characteristic curves were used to estimate the area under the curve (AUC) of each scale.

RESULTS

All scales performed better than chance (AUC 0.75-0.85). Sensitivity ranged from 0.66 to 0.85 and specificity ranged from 0.60 to 0.88. The UPDRS Depression item had a smaller AUC than the BDI-II, HAM-D-17, IDS-C, and MADRS. The CESD-R also had a smaller AUC than the MADRS. The remaining AUCs were statistically similar.

CONCLUSIONS

The GDS-30 may be the most efficient depression screening scale to use in PD because of its brevity, favorable psychometric properties, and lack of copyright protection. However, all scales studied, except for the UPDRS Depression, are valid screening tools when PD-specific cutoff scores are used.

CAG repeat expansion in Huntington disease determines age at onset in a fully dominant fashion

OBJECTIVE

Age at onset of diagnostic motor manifestations in Huntington disease (HD) is strongly correlated with an expanded CAG trinucleotide repeat. The length of the normal CAG repeat allele has been reported also to influence age at onset, in interaction with the expanded allele. Due to profound implications for disease mechanism and modification, we tested whether the normal allele, interaction between the expanded and normal alleles, or presence of a second expanded allele affects age at onset of HD motor signs.

METHODS

We modeled natural log-transformed age at onset as a function of CAG repeat lengths of expanded and normal alleles and their interaction by linear regression.

RESULTS

An apparently significant effect of interaction on age at motor onset among 4,068 subjects was dependent on a single outlier data point. A rigorous statistical analysis with a well-behaved dataset that conformed to the fundamental assumptions of linear regression (e.g., constant variance and normally distributed error) revealed significance only for the expanded CAG repeat, with no effect of the normal CAG repeat. Ten subjects with 2 expanded alleles showed an age at motor onset consistent with the length of the larger expanded allele.

CONCLUSIONS

Normal allele CAG length, interaction between expanded and normal alleles, and presence of a second expanded allele do not influence age at onset of motor manifestations, indicating that the rate of HD pathogenesis leading to motor diagnosis is determined by a completely dominant action of the longest expanded allele and as yet unidentified genetic or environmental factors.

SP600125 suppresses Cdk1 and induces endoreplication directly from G2 phase, independent of JNK inhibition

Cell cycle controls ensure that DNA replication (S phase) follows mitosis resulting in two precise copies of the genome. A failure of the control mechanisms can result in multiple rounds of DNA replication without cell division. In endoreplication, cells with replicated genomes bypass mitosis, then replicate their DNA again, resulting in polyploidy. Endoreplication from G2 phase lacks all hallmarks of mitosis. Using synchronized cells, we show that the c-Jun N-terminal kinase (JNK) inhibitor, SP600125, prevents the entry of cells into mitosis and leads to endoreplication of DNA from G2 phase. We show that cells proceed from G2 phase to replicate their DNA in the absence of mitosis. This effect of SP600125 is independent of its suppression of JNK activity. Instead, the inhibitory effect of SP600125 on mitotic entry predominantly occurs upstream of Aurora A kinase and Polo-like kinase 1, resulting in a failure to remove the inhibitory phosphorylation of Cdk1. Importantly, our results directly show that the inhibition of Cdk1 activity and the persistence of Cdk2 activity in G2 cells induces endoreplication without mitosis. Furthermore, endoreplication from G2 phase is independent of p53 control.

A novel trinucleotide repeat expansion at chromosome 3q26.2 identified by a CAG/CTG repeat expansion detection array

CAG/CTG repeat expansions cause at least 12 different neurological disorders, and additional disorders of this type probably exist. Using the repeat expansion detection (RED) assay, we identified an expanded CAG/CTG repeat in a 50-year-old woman with an autosomal dominant syndrome with prominent progressive sensory neuropathy. The expansion could not be accounted for by any of the CAG/CTG repeats known to undergo expansion. To identify the locus of the expansion, we created a PCR array to assess the repeat length of all repeats of eight or more CAG or CTG triplets in the human genome. The expansion was localized to a repeat contained in an intron of a Genscan-predicted gene, 185 nt downstream of a predicted exon that is conserved through mouse. The closest experimentally verified gene in the region (TNIK, encoding a serine/threonine kinase) occurs approximately 63 Kb downstream from the repeat. The length of the expansion in the proband is 98 triplets. This repeat is not expanded in the proband's cousin (the only other affected family member for whom DNA is currently available) and no expansions were detected in a set of 230 patients with movement disorders of unknown cause. An expanded allele containing 58 triplets was detected in a single control individual, and no other expansions were detected in a set of 255 controls. The normal repeat length ranges from 5 to 30 triplets, with 8 triplets the most common allele. Our results suggest that this new repeat expansion is probably not the direct cause of the phenotype in the proband. Whether the repeat contributes to the patient's phenotype, or is associated with another phenotype, remains to be determined.

The association of CAG repeat length with clinical progression in Huntington disease

OBJECTIVE

To determine whether the rate of clinical progression in Huntington disease (HD) is influenced by the size of the CAG expansion.

METHODS

The dataset consisted of 3,402 examinations of 512 subjects seen through the Baltimore Huntington's Disease Center. Subjects were seen for a mean of 6.64 visits, with mean follow-up of 6.74 years. Subjects were administered the Quantified Neurological Examination, with its subsets the Motor Impairment and Chorea Scores, the Mini-Mental State Examination, and the HD Activities of Daily Living (ADL) Scale.

RESULTS

In an analysis based on the Random Effects Model, CAG length was significantly associated with the rate of progression of all measures except chorea and ADL. There was a significant interaction term between CAG length and disease duration for all measures except chorea. Further graphical exploration of the data supported these linear models and suggested that subjects at the low end of the expanded CAG repeat range may experience a more benign late course.

CONCLUSIONS

CAG repeat length has a small effect on rate of progression that may be clinically important over time. Individuals with the shortest expansions appear to have the best prognosis. These effects of the CAG length may be relevant in the analysis of clinical trials.

The clinical and genetic spectrum of spinocerebellar ataxia 14

Spinocerebellar ataxia 14 (SCA14) is associated with missense mutations in the protein kinase C gamma gene (PRKCG), rather than a nucleotide repeat expansion. In this large-scale study of PRKCG in patients with ataxia, two new missense mutations, an in-frame deletion, and a possible splice site mutation were found and can now be added to the four previously described missense mutations. The genotype/phenotype correlations in these families are described.

Evidence of a common founder for SCA12 in the Indian population

Spinocerebellar ataxia type 12 (SCA12) is an autosomal dominant cerebellar ataxia associated with the expansion of an unstable CAG repeat in the 5' region of the PPP2R2B gene on chromosome 5q31-5q32. We found that it accounts for approximately 16% (20/124) of all the autosomal dominant ataxia cases diagnosed in AIIMS, a major tertiary referral centre in North India. The length of the expanded allele in this population ranges from 51-69 CAG triplets. Interestingly, all the affected families belong to an endogamous population, which originated in the state of Haryana, India. We identified four novel SNPs and a dinucleotide marker spanning approximately 137 kb downstream of CAG repeat in the PPP2R2B gene. Analysis of 20 Indian SCA12 families and ethnically matched normal unrelated individuals revealed one haplotype to be significantly associated with the affected alleles (P= 0.000), clearly indicating the presence of a common founder for SCA12 in the Indian population. This haplotype was not shared by the American pedigree with SCA12. Therefore, the SCA12 expansion appears to have originated at least twice.

A frameshift mutation in Disrupted in Schizophrenia 1 in an American family with schizophrenia and schizoaffective disorder

In a large Scottish pedigree, a balanced translocation t(1;11)(q42.1;q14.3) segregates with major mental illness, including schizophrenia, bipolar disorder, and recurrent major depression. The translocation is predicted to result in the loss of the C-terminal region of the protein product of Disrupted In SChizophrenia 1 (DISC1), a gene located on 1q42.1. Since this initial discovery, DISC1 has been functionally implicated in several processes, including neurodevelopment. Based on the genetic and functional evidence that DISC1 may be associated with schizophrenia, we sequenced portions of DISC1 in 28 unrelated probands with schizophrenia and six unrelated probands with schizoaffective disorder, ascertained as part of a large sibpair study. We detected a 4 bp deletion at the extreme 3' end of exon 12 in a proband with schizophrenia. The mutation was also present in a sib with schizophrenia, a sib with schizoaffective disorder, and the unaffected father, while the mutation was not detected in 424 control individuals. The mutation is predicted to cause a frameshift and encode a truncated protein with nine abnormal C-terminal amino acids. The truncated transcript is detectable, but at a reduced level, in lymphoblastoid cell lines from three of four mutation carriers. These findings are consistent with the possibility that mutations in the DISC1 gene can increase the risk for schizophrenia and related disorders.

Onset and rate of striatal atrophy in preclinical Huntington disease

BACKGROUND

Huntington disease (HD) is characterized by striatal atrophy that begins long before the onset of motor symptoms.

OBJECTIVE

To determine when striatal atrophy begins, the extent and rate of atrophy before diagnosis of motor symptoms, and whether striatal atrophy can predict when symptom onset will occur.

METHODS

Caudate and putamen volumes were measured on MRI scans of 19 preclinical subjects with the HD gene expansion who were very far (9 to 20 years) from estimated onset, and on serial scans from 17 preclinical subjects, six of whom were diagnosed with HD within 5 years after the initial scan.

RESULTS

Striatal volumes were significantly smaller for the subjects who were very far from estimated onset than for age-matched control subjects. Statistical models fit to the longitudinal data suggest that rate of caudate atrophy becomes significant when subjects are approximately 11 years from estimated onset and rate of putamen atrophy becomes significant approximately 9 years prior to onset. In the six incident cases, caudate and putamen were approximately one-third to one-half of normal volume at diagnosis, and caudate volume alone was able to predict with 100% accuracy those subjects who would be diagnosed within 2 years of imaging.

CONCLUSIONS

Striatal atrophy begins many years prior to diagnosable HD, and assessment of atrophy on MRI may be very useful in both predicting HD onset and in tracking progression in future therapeutic trials in preclinical subjects.

Novel CAG/CTG repeat expansion mutations do not contribute to the genetic risk for most cases of bipolar disorder or schizophrenia

The possible presence of anticipation in bipolar affective disorder and schizophrenia has led to the hypothesis that repeat expansion mutations could contribute to the genetic etiology of these diseases. Using the repeat expansion detection (RED) assay, we have systematically examined genomic DNA from 100 unrelated probands with schizophrenia and 68 unrelated probands with bipolar affective disorder for the presence of CAG/CTG repeat expansions. Our results show that 28% of the probands with schizophrenia and 30% of probands with bipolar disorder have a CAG/CTG repeat in the expanded range, but that each expansion could be explained by one of three nonpathogenic repeat expansions known to exist in the general population. We conclude that novel CAG/CTG repeat expansions are not a common genetic risk factor for bipolar disorder or schizophrenia.

Why is SCA12 different from other SCAs?

Spinocerebellar ataxia type 12 (SCA12), now described in European-American and Asian (Indian) pedigrees, is unique among the SCAs from clinical, pathological, and molecular perspectives. Clinically, the distinguishing feature is early and prominent action tremor with variability in other signs. Pathologically, brain MRIs also suggest variability, with prominent cortical as well as cerebellar atrophy. Genetically, SCA12 is caused by a CAG repeat expansion that does not encode polyglutamine; we speculate that the mutation may affect expression of the gene PPP2R2B, which encodes a brain-specific regulatory subunit of the protein phosphatase PP2A.

Huntington's disease-like 2 can present as chorea-acanthocytosis

Three patients from a previously described family with autosomal dominant chorea-acanthocytosis were found to have the CTG trinucleotide repeat expansion mutation of the junctophilin-3 gene associated with Huntington's disease-like 2 (HDL2). One of six previously identified patients with HDL2 had acanthocytosis on peripheral blood smear, suggesting that HDL2 should be considered in the differential of chorea-acanthocytosis.

Interaction of normal and expanded CAG repeat sizes influences age at onset of Huntington disease

Huntington disease (HD) is a neurodegenerative disorder caused by the abnormal expansion of CAG repeats in the HD gene on chromosome 4p16.3. Past studies have shown that the size of expanded CAG repeat is inversely associated with age at onset (AO) of HD. It is not known whether the normal Huntington allele size influences the relation between the expanded repeat and AO of HD. Data collected from two independent cohorts were used to test the hypothesis that the unexpanded CAG repeat interacts with the expanded CAG repeat to influence AO of HD. In the New England Huntington Disease Center Without Walls (NEHD) cohort of 221 HD affected persons and in the HD-MAPS cohort of 533 HD affected persons, we found evidence supporting an interaction between the expanded and unexpanded CAG repeat sizes which influences AO of HD (P = 0.08 and 0.07, respectively). The association was statistically significant when both cohorts were combined (P = 0.012). The estimated heritability of the AO residual was 0.56 after adjustment for normal and expanded repeats and their interaction. An analysis of tertiles of repeats sizes revealed that the effect of the normal allele is seen among persons with large HD repeat sizes (47-83). These findings suggest that an increase in the size of the normal repeat may mitigate the expression of the disease among HD affected persons with large expanded CAG repeats.

Trinucleotide repeats in 202 families with ataxia: a small expanded (CAG)n allele at the SCA17 locus

BACKGROUND

Ten neurodegenerative disorders characterized by spinocerebellar ataxia (SCA) are known to be caused by trinucleotide repeat (TNR) expansions. However, in some instances the molecular diagnosis is considered indeterminate because of the overlap between normal and affected allele ranges. In addition, the mechanism that generates expanded alleles is not completely understood.

OBJECTIVE

To examine the clinical and molecular characteristics of a large group of Portuguese and Brazilian families with ataxia to improve knowledge of the molecular diagnosis of SCA.

PATIENTS AND METHODS

We have (1) assessed repeat sizes at all known TNR loci implicated in SCA; (2) determined frequency distributions of normal alleles and expansions; and (3) looked at genotype-phenotype correlations in 202 unrelated Portuguese and Brazilian patients with SCA. Molecular analysis of TNR expansions was performed using polymerase chain reaction amplification.

RESULTS

Patients from 110 unrelated families with SCA showed TNR expansions at 1 of the loci studied. Dominantly transmitted cases had (CAG)(n) expansions at the Machado-Joseph disease gene (MJD1) (63%), at SCA2 (3%), the gene for dentatorubropallidoluysian atrophy (DRPLA) (2%), SCA6 (1%), or SCA7 (1%) loci, or (CTG)(n) expansions at the SCA8 (2%) gene, whereas (GAA)(n) expansions in the Freidreich ataxia gene (FRDA) were found in 64% of families with recessive ataxia. Isolated patients also had TNR expansions at the MJD1 (6%), SCA8 (6%), or FRDA (8%) genes; in addition, an expanded allele at the TATA-binding protein gene (TBP), with 43 CAGs, was present in a patient with ataxia and mental deterioration. Associations between frequencies of SCA2 and SCA6 and a frequency of large normal alleles were found in Portuguese and Brazilian individuals, respectively. Interestingly, no association between the frequencies of DRPLA and large normal alleles was found in the Portuguese group.

CONCLUSIONS

Our results show that (1) a significant number of isolated cases of ataxia are due to TNR expansions; (2) expanded DRPLA alleles in Portuguese families may have evolved from an ancestral haplotype; and (3) small (CAG)(n) expansions at the TBP gene may cause SCA17.

CAG/CTG repeat expansions at the Huntington's disease-like 2 locus are rare in Huntington's disease patients

The authors report a large series of patients with Huntington disease (HD)-like phenotype without CAG repeat expansions in the IT15 gene that were screened for the newly identified CAG/CTG expansion in the gene encoding junctophilin-3. Normal alleles in controls had from 8 to 28 repeats. A single patient of North African origin with typical HD carried an allele with 50 uninterrupted repeats, representing approximately 2% of the non-IT15 HD patients tested. Therefore, further genetic heterogeneity is expected in HD.

A disorder similar to Huntington's disease is associated with a novel CAG repeat expansion

Huntington's disease (HD) is an autosomal dominant disorder characterized by abnormalities of movement, cognition, and emotion and selective atrophy of the striatum and cerebral cortex. While the etiology of HD is known to be a CAG trinucleotide repeat expansion, the pathways by which this mutation causes HD pathology remain unclear. We now report a large pedigree with an autosomal dominant disorder that is clinically similar to HD and that arises from a different CAG expansion mutation. The disorder is characterized by onset in the fourth decade, involuntary movements and abnormalities of voluntary movement, psychiatric symptoms, weight loss, dementia, and a relentless course with death about 20 years after disease onset. Brain magnetic resonance imaging scans and an autopsy revealed marked striatal atrophy and moderate cortical atrophy, with striatal neurodegeneration in a dorsal to ventral gradient and occasional intranuclear inclusions. All tested affected individuals, and no tested unaffecteds, have a CAG trinucleotide repeat expansion of 50 to 60 triplets, as determined by the repeat expansion detection assay. Tests for the HD expansion, for all other known CAG expansion mutations, and for linkage to chromosomes 20p and 4p were negative, indicating that this mutation is novel. Cloning the causative CAG expansion mutation for this new disease, which we have termed Huntington's disease-like 2, may yield valuable insight into the pathogenesis of HD and related disorders.

A repeat expansion in the gene encoding junctophilin-3 is associated with Huntington disease-like 2

We recently described a disorder termed Huntington disease-like 2 (HDL2) that completely segregates with an unidentified CAG/CTG expansion in a large pedigree (W). We now report the cloning of this expansion and its localization to a variably spliced exon of JPH3 (encoding junctophilin-3), a gene involved in the formation of junctional membrane structures.

Neither p21WAF1 nor 14-3-3sigma prevents G2 progression to mitotic catastrophe in human colon carcinoma cells after DNA damage, but p21WAF1 induces stable G1 arrest in resulting tetraploid cells

p21WAF1 and 14-3-3sigma, which are both transcriptional products of p53, have been reported to play a role in the G2 DNA damage checkpoint in mammalian cells. Human colon carcinoma cells, isogenic except for the presence or absence of either p21WAF1 or 14-3-3sigma (T. A. Chan et al., Genes Dev., 14: 1584-1588, 2000), are useful models for analysis of the role of these proteins in checkpoint control. Here, we have examined mitotic behavior within a single cell cycle after DNA damage in these cell lines. Our results show that p21WAF1, but not 14-3-3sigma, imposes a significant G2 delay after DNA damage. After G2 delay, we found that all isogenic cells, including those competent for both p21WAF1 and 14-3-3sigma, adapt to the DNA damage checkpoint and progress into mitosis, where they undergo incomplete chromosome segregation and reenter G1 with a tetraploid DNA content. Strikingly, our results show that p21WAF1, but not 14-3-3sigma, activates a checkpoint in response to DNA damage that prevents continued cycling of the tetraploid cells that result from a mitotic catastrophe characterized by failure to complete cell division. These results demonstrate that a tetraploid DNA content is not a reliable criterion to establish that arrest occurs in G2. Also, the DNA damage checkpoint mediated by p53-dependent induction of p21WAF1 assures neither G2 arrest nor DNA repair sufficient to enable accurate chromosome segregation in human colon carcinoma cells. We conclude that p21WAF1, but not 14-3-3sigma, has a unique role in the induction of G1 arrest in tetraploid cells that results from mitotic catastrophe after DNA damage.

SCA12: an unusual mutation leads to an unusual spinocerebellar ataxia

Spinocerebellar ataxia type 12 (SCA12) is an autosomal dominant neurodegenerative disorder which has been described in pedigrees of German American and Indian descent. The phenotype typically begins with tremor in the fourth decade, progressing to include ataxia and other cerebellar and cortical signs. SCA12 is associated with an expansion of a CAG repeat in the 5' region of the gene PPP2R2B which encodes a brain-specific regulatory subunit of the protein phosphatase PP2A. The repeat size ranges from 55 to 78 triplets in the mutant allele of affected individuals, and from 9 to 28 triplets in normal alleles. It is possible that an expansion mutation in PPP2R2B may influence PPP2R2B expression, perhaps altering the activity of PP2A, an enzyme implicated in multiple cellular functions, including cell cycle regulation, tau phosphorylation, and apoptosis.

Tetraploid state induces p53-dependent arrest of nontransformed mammalian cells in G1

A "spindle assembly" checkpoint has been described that arrests cells in G1 following inappropriate exit from mitosis in the presence of microtubule inhibitors. We have here addressed the question of whether the resulting tetraploid state itself, rather than failure of spindle function or induction of spindle damage, acts as a checkpoint to arrest cells in G1. Dihydrocytochalasin B induces cleavage failure in cells where spindle function and chromatid segregation are both normal. Notably, we show here that nontransformed REF-52 cells arrest indefinitely in tetraploid G1 following cleavage failure. The spindle assembly checkpoint and the tetraploidization checkpoint that we describe here are likely to be equivalent. Both involve arrest in G1 with inactive cdk2 kinase, hypophosphorylated retinoblastoma protein, and elevated levels of p21(WAF1) and cyclin E. Furthermore, both require p53. We show that failure to arrest in G1 following tetraploidization rapidly results in aneuploidy. Similar tetraploid G1 arrest results have been obtained with mouse NIH3T3 and human IMR-90 cells. Thus, we propose that a general checkpoint control acts in G1 to recognize tetraploid cells and induce their arrest and thereby prevents the propagation of errors of late mitosis and the generation of aneuploidy. As such, the tetraploidy checkpoint may be a critical activity of p53 in its role of ensuring genomic integrity.

A disorder similar to Huntington's disease is associated with a novel CAG repeat expansion

Huntington's disease (HD) is an autosomal dominant disorder characterized by abnormalities of movement, cognition, and emotion and selective atrophy of the striatum and cerebral cortex. While the etiology of HD is known to be a CAG trinucleotide repeat expansion, the pathways by which this mutation causes HD pathology remain unclear. We now report a large pedigree with an autosomal dominant disorder that is clinically similar to HD and that arises from a different CAG expansion mutation. The disorder is characterized by onset in the fourth decade, involuntary movements and abnormalities of voluntary movement, psychiatric symptoms, weight loss, dementia, and a relentless course with death about 20 years after disease onset. Brain magnetic resonance imaging scans and an autopsy revealed marked striatal atrophy and moderate cortical atrophy, with striatal neurodegeneration in a dorsal to ventral gradient and occasional intranuclear inclusions. All tested affected individuals, and no tested unaffecteds, have a CAG trinucleotide repeat expansion of 50 to 60 triplets, as determined by the repeat expansion detection assay. Tests for the HD expansion, for all other known CAG expansion mutations, and for linkage to chromosomes 20p and 4p were negative, indicating that this mutation is novel. Cloning the causative CAG expansion mutation for this new disease, which we have termed Huntington's disease-like 2, may yield valuable insight into the pathogenesis of HD and related disorders.

Familial influence on age of onset among siblings with Huntington disease

In order to provide data relevant to a search for modifying genes for age of onset in Huntington disease, we examined the relationship between CAG number and age of onset in a total of 370 individuals from 165 siblingships, in two cohorts of siblings with Huntington disease: an American group of 144 individuals from 64 siblingships, and a Canadian population of 255 individuals from 113 siblingships. Using a logarithmic model to regress the age of onset on the number of CAG triplets, we found that CAG number alone accounted for 65%-71% of the variance in age of onset. The siblingship an individual belonged to accounted for 11%-19% of additional variance. This adds to the previous evidence that there are familial modifiers of the age of onset, independent of the CAG number. Such modifiers may consist of additional genes, which could be the target of a linkage study. A linkage study is feasible with the cooperation of a number of major centers and may be made more efficient by concentrating on sibling pairs that are highly discordant for age of onset.

Tubulin detyrosination is a frequent occurrence in breast cancers of poor prognosis

Tubulin, the dimeric subunit of microtubules, is a major cell protein that is centrally involved in cell division. Tubulin is subject to specific enzymatic posttranslational modifications including cyclic tyrosine removal and addition at the COOH terminus of the alpha-subunit. Tubulin is normally extensively tyrosinated in cycling cells. However, we have previously shown that detyrosinated tubulin accumulates in cancer cells during tumor progression in nude mice. Tubulin detyrosination, resulting from suppression of tubulin tyrosine ligase and the resulting unbalanced activity of tubulin-carboxypeptidase, apparently represents a strong selective advantage for cancer cells. We have now analyzed the occurrence and significance of tubulin detyrosination in human breast tumors. We studied a total of 134 breast cancer tumors from patients with or without known complications over a follow-up period of 31 +/- 10 months. The mean age of the patients at the time of diagnosis was 57 years. For each patient, detailed data concerning the histology and extension of the tumor were available. Tumor cells containing detyrosinated tubulin were visualized by immunohistochemical staining of paraffin-embedded tissue sections. Cancer cells with detyrosinated tubulin were observed in 53% of the tumors and were predominant in 19.4% of the tumors. Tubulin detyrosination correlated to a high degree of significance (P < 0.001) with a high Scarf-Bloom-Richardson (SBR) grade, a known marker of tumor aggressiveness. Among SBR grade 1 tumors, 3.8% were strongly positive for tubulin detyrosination compared with 65.4% of the SBR grade 3 tumors. The SBR component showing the strongest correlation with tubulin detyrosination was the mitotic score. In the entire patient population, neither the SBR grade nor the detyrosination index had significant prognostic value (P = 0.11, P = 0.27, respectively), whereas a combined index was significantly correlated with the clinical outcome (P = 0.02). A preliminary subgroup analysis indicated that tubulin detyrosination may define high- and low- risk groups in breast cancer tumors with an SBR grade of 2. Our study shows that tubulin detyrosination is a frequent occurrence in breast cancer, easy to detect, and linked to tumor aggressiveness.

Mammalian mad2 and bub1/bubR1 recognize distinct spindle-attachment and kinetochore-tension checkpoints

Metaphase checkpoint controls sense abnormalities of chromosome alignment during mitosis and prevent progression to anaphase until proper alignment has been attained. A number of proteins, including mad2, bub1, and bubR1, have been implicated in the metaphase checkpoint control in mammalian cells. Metaphase checkpoints have been shown, in various systems, to read loss of either spindle tension or microtubule attachment at the kinetochore. Characteristically, HeLa cells arrest in metaphase in response to low levels of microtubule inhibitors that leave an intact spindle and a metaphase plate. Here we show that the arrest induced by nanomolar vinblastine correlates with loss of tension at the kinetochore, and that in response the checkpoint proteins bub1 and bubR1 are recruited to the kinetochore but mad2 is not. mad2 remains competent to respond and is recruited at higher drug doses that disrupt spindle association with the kinetochores. Further, although mad2 forms a complex with cdc20, it does not associate with bub1 or bubR1. We conclude that mammalian bub1/bubR1 and mad2 operate as elements of distinct pathways sensing tension and attachment, respectively.

The Gln-Ala repeat transcriptional activator CA150 interacts with huntingtin: Neuropathologic and genetic evidence for a role in Huntington's disease pathogenesis

Huntington's disease (HD) is a neurodegenerative disease caused by polyglutamine expansion in the protein huntingtin (htt). Pathogenesis in HD appears to involve the formation of ubiquitinated neuronal intranuclear inclusions containing N-terminal mutated htt, abnormal protein interactions, and the aggregate sequestration of a variety of proteins (noticeably, transcription factors). To identify novel htt-interacting proteins in a simple model system, we used a yeast two-hybrid screen with a Caenorhabditis elegans activation domain library. We found a predicted WW domain protein (ZK1127.9) that interacts with N-terminal fragments of htt in two-hybrid tests. A human homologue of ZK1127.9 is CA150, a transcriptional coactivator with a N-terminal insertion that contains an imperfect (Gln-Ala)(38) tract encoded by a polymorphic repeat DNA. CA150 interacted in vitro with full-length htt from lymphoblastoid cells. The expression of CA150, measured immunohistochemically, was markedly increased in human HD brain tissue compared with normal age-matched human brain tissue, and CA150 showed aggregate formation with partial colocalization to ubiquitin-positive aggregates. In 432 HD patients, the CA150 repeat length explains a small, but statistically significant, amount of the variability in the onset age. Our data suggest that abnormal expression of CA150, mediated by interaction with polyglutamine-expanded htt, may alter transcription and have a role in HD pathogenesis.

SCA-12: Tremor with cerebellar and cortical atrophy is associated with a CAG repeat expansion

OBJECTIVE

To characterize the clinical and neuroradiologic features of a new spinocerebellar ataxia, SCA-12, in the index family.

BACKGROUND

The authors recently linked SCA-12 to a novel CAG repeat expansion on chromosome 5q31-33 that is located within the 5' region of PPP2R2B, a gene encoding a brain-specific regulatory subunit of protein phosphatase 2A.

METHODS

Neurologic features of the proband and nine symptomatic relatives in the first SCA-12 family were compiled and, in some individuals, related to changes found on brain MRI or CT.

RESULTS

SCA-12 typically presented in the 4th decade of life with action tremor of the head or arms (present in 10/10 of the affected individuals). Hyperreflexia (8/10) was a common feature, and cerebellar signs (8/10), including ataxia, dysmetria, and dysarthria, developed gradually but were less prominent and disabling than cerebellar dysfunction in other SCA. Subtle parkinsonian features (9/10) and dementia (2/10) were observed in later stages of SCA-12, and psychiatric symptoms, including depression, anxiety, or delusions, were present in some affected family members (4/10). Two individuals studied had nondisabling neurologic signs neonatally, including nystagmus and lower extremity dystonia. Brain images of affected individuals revealed cerebral and cerebellar atrophy.

CONCLUSIONS

SCA-12 is a slowly progressive, autosomal dominant, neurodegenerative disorder that differs from other SCA in that it typically presents with action tremor in patients in their mid 30s and usually includes hyperreflexia and subtle parkinsonian signs. Cerebellar dysfunction, including gait ataxia, is relatively nondisabling, and cognitive or psychiatric disorders may occur. Neuroradiologic studies reveal atrophy of the cerebellum and cerebral cortex.

SCA12 is a rare locus for autosomal dominant cerebellar ataxia: a study of an Indian family

Spinocerebellar ataxia 12 (SCA12) is an autosomal dominant cerebellar ataxia (ADCA) described in a single family with a CAG repeat expansion in the PPP2R2B gene. We screened 247 index cases, including 145 families with ADCA, for this expansion. An expanded repeat ranging from 55 to 61 triplets was detected in 6 affected and 3 unaffected individuals at risk in a single family from India. The association of the PPP2R2B CAG repeat expansion with disease in this new family provides additional evidence that the mutation is causative.

Organization of the human synphilin-1 gene, a candidate for Parkinson's disease

We have recently identified a protein we called synphilin-1, which interacts in vivo with alpha-synuclein. Mutations in alpha-synuclein cause familial Parkinson's disease (PD). Alpha-synuclein protein is present in the pathologic lesions of familial and sporadic PD, and diffuse Lewy body disease, indicating an important pathogenic role for alpha-synuclein. Here we describe the structure of the human synphilin-1 gene (SNCAIP). The open reading frame of this gene is contained within ten exons. We have designed primers to amplify each SNCAIP exon, so these primers can now be used to screen for mutations or polymorphisms in patients with Parkinson's disease or related diseases. We found a highly polymorphic GT repeat within intron 5 of SNCAIP, suitable for linkage analysis of families with PD. We have mapped SNCAIP locus to Chromosome (Chr) 5q23.1-23.3 near markers WI-4673 and AFMB352XH5. In addition, using immunohistochemistry in human postmortem brain tissue, we found that synphilin-1 protein is present in neuropil, similar to alpha-synuclein protein. Because of its association with alpha-synuclein, synphilin-1 may be a candidate for involvement in Parkinson's disease or other related disorders.

Human huntingtin-associated protein (HAP-1) gene: genomic organisation and an intragenic polymorphism

The huntingtin-associated protein (HAP-1) interacts with the Huntington disease gene product, huntingtin. It is predominantly expressed in the brain and shows an increased affinity for mutant huntingtin. We have sequenced an 18,656bp genomic region encompassing the entire human HAP-1 gene and determined its genomic organisation, with 11 exons spanning 12.1kb. We have also found an intragenic polymorphism within intron 6 of HAP-1. We have recently shown that HAP-1 maps to a region of the genome which has been implicated in a variety of neurological conditions, including progressive supranuclear palsy (PSP), a late-onset atypical parkinsonian disorder. The detailed characterisation of the genomic organisation of HAP-1 and the presence of an intragenic polymorphism will be helpful in evaluating its role in different disorders, using candidate gene approaches.

Crystal structure of human survivin reveals a bow tie-shaped dimer with two unusual alpha-helical extensions

Survivin is a mitotic spindle-associated protein involved in linking mitotic spindle function to activation of apoptosis in mammalian cells. The structure of the full-length human survivin has been determined by X-ray crystallography to 2.7 A. Strikingly, the structure forms a very unusual bow tie-shaped dimer. It does not dimerize through a C-terminal coiled-coil, contrary to sequence analysis prediction. The C-terminal helices contain hydrophobic clusters with the potential for protein-protein interactions. The unusual shape and dimensions of survivin suggest it serves an adaptor function through its alpha-helical extensions.

Allelic distribution of CTG18.1 in Caucasian populations: association studies in bipolar disorder, schizophrenia, and ataxia

CTG18.1 is a highly polymorphic and unstable CTG repeat within an intron of the SEF2-1 gene. We tested the CTG18.1 repeat length in affective disorder, schizophrenia, and nonspecific ataxia; these diseases all have shown clinical evidence for anticipation. There was no difference in the allele frequencies comparing the controls and disease groups. The most common allele contains 11 CAGs (35%) followed by alleles with 14-17 CAGs (35%). There was no difference in the distribution of the alleles in the cases vs controls for ataxia (P = 0.11), affective disorders (P = 0.21), or schizophrenia (P = 0.26). The frequency of unstable CTG18.1 alleles was approximately 3% in a population of N. European descent and is not related to the phenotypes tested.

A retrospective look at long-term adolescent recovery: clinicians talk to researchers

The purpose of the present article is to identify factors associated with long-term recovery for adolescents. A group of 14 young adults were given semistructured in-depth (one to two hour) interviews. The subjects had been in recovery for two to 16 years. Length of stay in treatment, involvement with self-help groups, psychotropic medication, family support, peer support, spirituality, and other factors were identified as helpful for long-term recovery. A major limitation of this inquiry is that it does not meet minimum standards for research. It is hoped, however, that this inquiry can inform directions for further research.

Trinucleotide repeat expansion and neuropsychiatric disease

Trinucleotide, or triplet, repeats consist of 3 nucleotides consecutively repeated (e.g., CCG CCG CCG CCG CCG) within a region of DNA, a not uncommon motif in the genome of humans and other species. In 1991, a new type of genetic mutation was discovered, known as a dynamic or expansion mutation, in which the number of triplets in a repeat increases and the length becomes unstable. During the past decade, nearly 20 diseases-including Huntington disease, 2 forms of the fragile X syndrome, and myotonic dystrophy-caused by trinucleotide repeat expansions have been identified. The unstable nature of the expanded repeat leads to remarkable patterns of inheritance in these diseases, distinctly at odds with traditional notions of mendelian genetics. We review the clinical and genetic features of these disorders, with a particular emphasis on their psychiatric manifestations. We also critically examine the hypothesis that expansion mutations may have an etiologic role in psychiatric diseases such as bipolar disorder, schizophrenia, and autism.

Increased apoptosis of Huntington disease lymphoblasts associated with repeat length-dependent mitochondrial depolarization

Huntington disease (HD) is a genetically dominant condition caused by expanded CAG repeats coding for glutamine in the HD gene product huntingtin. Although HD symptoms reflect preferential neuronal death in specific brain regions, huntingtin is expressed in almost all tissues, so abnormalities outside the brain might be expected. Although involvement of nuclei and mitochondria in HD pathophysiology has been suggested, specific intracellular defects that might elicit cell death have been unclear. Mitochondria dysfunction is reported in HD brains; mitochondria are organelles that regulates apoptotic cell death. We now report that lymphoblasts derived from HD patients showed increased stress-induced apoptotic cell death associated with caspase-3 activation. When subjected to stress, HD lymphoblasts also manifested a considerable increase in mitochondrial depolarization correlated with increased glutamine repeats.

Mitogen-activated protein kinase kinase activity is required for the G(2)/M transition of the cell cycle in mammalian fibroblasts

The mitogen-activated protein kinase (MAPK) cascade is required for mitogenesis in somatic mammalian cells and is activated by a wide variety of oncogenic stimuli. Specific roles for this signaling module in growth were dissected by inhibiting MAPK kinase 1 (MAPKK1) activity in highly synchronized NIH 3T3 cells. In addition to the known role of this kinase in cell-cycle entry from G(0), the level of MAPKK activity was observed to affect the kinetics of progression through both the G(1) and G(2) phases of the cell cycle in NIH 3T3 cells. Ectopic expression of dominant-negative forms of MAPKK1, which was previously shown to inhibit G(0)/G(1) progression, was found to also delay progression of cells through G(2). In addition, treatment of cells with the specific MAPKK inhibitor PD 98059 during a synchronous S phase arrested the cells in the following G(2) phase. These data demonstrate a novel role for the MAPK cascade in progression from G(2) into mitosis in NIH 3T3 cells.

Complex Complexes: Report of an NIDDK Workshop on Coactivators and Corepressors, Bethesda, USA, 15-16 December 1998

Exciting new observations about receptor-interacting and nuclear accessory proteins and their ability to regulate gene expression have provided insight into hormonal regulation of gene expression. The goal of a recent NIDDK workshop was to discuss how diverse signaling pathways could converge on target genes and provide regulatory input to either activate or repress transcription.

Nuclear accumulation of truncated atrophin-1 fragments in a transgenic mouse model of DRPLA

Dentatorubral and pallidoluysian atrophy (DRPLA) is a member of a family of progressive neurodegenerative diseases caused by polyglutamine repeat expansion. Transgenic mice expressing full-length human atrophin-1 with 65 consecutive glutamines exhibit ataxia, tremors, abnormal movements, seizures, and premature death. These mice accumulate atrophin-1 immunoreactivity and inclusion bodies in the nuclei of multiple populations of neurons. Subcellular fractionation revealed 120 kDa nuclear fragments of mutant atrophin-1, whose abundance increased with age and phenotypic severity. Brains of DRPLA patients contained apparently identical 120 kDa nuclear fragments. By contrast, mice overexpressing atrophin-1 with 26 glutamines were phenotypically normal and did not accumulate the 120 kDa fragments. We conclude that the evolution of neuropathology in DRPLA involves proteolytic processing of mutant atrophin-1 and nuclear accumulation of truncated fragments.

Polyglutamine pathogenesis

An increasing number of neurodegenerative disorders have been found to be caused by expanding CAG triplet repeats that code for polyglutamine. Huntington's disease (HD) is the most common of these disorders and dentatorubral-pallidoluysian atrophy (DRPLA) is very similar to HD, but is caused by mutation in a different gene, making them good models to study. In this review, we will concentrate on the roles of protein aggregation, nuclear localization and proteolytic processing in disease pathogenesis. In cell model studies of HD, we have found that truncated N-terminal portions of huntingtin (the HD gene product) with expanded repeats form more aggregates than longer or full length huntingtin polypeptides. These shorter fragments are also more prone to aggregate in the nucleus and cause more cell toxicity. Further experiments with huntingtin constructs harbouring exogenous nuclear import and nuclear export signals have implicated the nucleus in direct cell toxicity. We have made mouse models of HD and DRPLA using an N-terminal truncation of huntingtin (N171) and full-length atrophin-1 (the DRPLA gene product), respectively. In both models, diffuse neuronal nuclear staining and nuclear inclusion bodies are observed in animals expressing the expanded glutamine repeat protein, further implicating the nucleus as a primary site of neuronal dysfunction. Neuritic pathology is also observed in the HD mice. In the DRPLA mouse model, we have found that truncated fragments of atrophin-1 containing the glutamine repeat accumulate in the nucleus, suggesting that proteolysis may be critical for disease progression. Taken together, these data lead towards a model whereby proteolytic processing, nuclear localization and protein aggregation all contribute to pathogenesis.

Synphilin-1 associates with alpha-synuclein and promotes the formation of cytosolic inclusions

Parkinson disease (PD) is a neurodegenerative disease characterized by tremor, bradykinesia, rigidity and postural instability. Post-mortem examination shows loss of neurons and Lewy bodies, which are cytoplasmic eosinophilic inclusions, in the substantia nigra and other brain regions. A few families have PD caused by mutations (A53T or A30P) in the gene SNCA (encoding alpha-synuclein). Alpha-synuclein is present in Lewy bodies of patients with sporadic PD, suggesting that alpha-synuclein may be involved in the pathogenesis of PD. It is unknown how alpha-synuclein contributes to the cellular and biochemical mechanisms of PD, and its normal functions and biochemical properties are poorly understood. To determine the protein-interaction partners of alpha-synuclein, we performed a yeast two-hybrid screen. We identified a novel interacting protein, which we term synphilin-1 (encoded by the gene SNCAIP). We found that alpha-synuclein interacts in vivo with synphilin-1 in neurons. Co-transfection of both proteins (but not control proteins) in HEK 293 cells yields cytoplasmic eosinophilic inclusions.