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.

Review of the 2012 Epizootic Hemorrhagic Disease Outbreak in Domestic Ruminants in the United States.

An unusually large number of cases of Epizootic hemorrhagic disease (EHD) were observed in United States cattle and white-tailed deer in the summer and fall of 2012. USDA APHIS Veterinary Services area offices were asked to report on foreign animal disease investigations and state diagnostic laboratory submissions which resulted in a diagnosis of EHD based on positive PCR results. EHD was reported in the following species: cattle (129 herds), captive white-tailed deer (65 herds), bison (8 herds), yak (6 herds), elk (1 herd), and sheep (1 flock). A majority of the cases in cattle and bison were found in Nebraska, South Dakota, and Iowa. The majority of cases in captive white-tailed deer were found in Ohio, Iowa, Michigan, and Missouri. The most common clinical sign observed in the cattle and bison herds was oral lesions. The major observation in captive white-tailed deer herds was death. Average within-herd morbidity was 7% in cattle and bison herds, and 46% in captive white-tailed deer herds. The average within-herd mortality in captive white-tailed deer herds was 42%.

Dual serotoninergic projections to forebrain in the rat: morphologically distinct 5-HT axon terminals exhibit differential vulnerability to neurotoxic amphetamine derivatives.

The cerebral cortex of the rat and other mammals is innervated by two morphologically distinct classes of serotoninergic (5-HT) axon terminals: fine axons with minute varicosities and beaded axons characterized by large, spherical varicosities. Fine and beaded 5-HT axons exhibit different regional and laminar distributions in forebrain and arise from separate brainstem nuclei, the dorsal and median raphe nuclei, respectively. The present neuroanatomic study, based on immunocytochemical methods to visualize 5-HT axons, demonstrates that the two axon types differ markedly in their vulnerability to the neurotoxic amphetamine derivatives, methylenedioxyamphetamine (MDA), and p-chloroamphetamine (PCA). While both drugs cause extensive degeneration of fine 5-HT axons throughout forebrain, beaded 5-HT axons are consistently spared. Fine 5-HT axons, which richly innervate most regions of dorsal forebrain in control rats, are rarely seen 2 weeks after treatment with MDA or PCA; this loss of fine axons reflects a marked denervation that persists for months after drug administration. The serotoninergic axon terminals remaining after MDA or PCA administration are almost entirely of the beaded type and appear to be unaffected by both drugs. Over a wide range of doses (2.5-40 mg/kg PCA) and survival times (2 weeks to 2 months), these spared 5-HT axons with large, spherical varicosities cannot be distinguished from the normal, beaded 5-HT axons in control rats by morphologic criteria. Moreover, beaded 5-HT axons exhibit a highly characteristic regional distribution which is the same in control as in MDA- and PCA-treated rats: these axons innervate specific zones or layers within parietal and occipital cortex, hippocampus, cingulate cortex, entorhinal cortex, and the olfactory bulb, among other forebrain areas, and they form a dense plexus lining the ventricular system. Taken together, the results of this study demonstrate that fine 5-HT axons are highly vulnerable to the neurotoxic effects of the amphetamine derivatives MDA and PCA, while beaded 5-HT axons are markedly resistant. These findings are consistent with the hypothesis that there are two anatomically and functionally distinct sets of serotoninergic neurons projecting to forebrain. While both of these neuronal systems utilize 5-HT as a neurotransmitter, they differ in several features: 1) origin from separate nuclei in the brainstem (the dorsal and median raphe), 2) two types of morphologically distinct axon terminals, 3) markedly different distribution and innervation patterns in forebrain, and 4) dissimilar pharmacological properties. The results further suggest that psychotropic amphetamine derivatives have a selective action upon fine serotoninergic axons that arise from the dorsal raphe nucleus.

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.

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.

Administration of a non-NMDA antagonist, GYKI 52466, increases excitotoxic Purkinje cell degeneration caused by ibogaine.

Ibogaine is a tremorigenic hallucinogen that has been proposed for clinical use in treating addiction. We previously reported that ibogaine, administered systemically, produces degeneration of a subset of Purkinje cells in the cerebellum, primarily within the vermis. Ablation of the inferior olive affords protection against ibogaine-induced neurotoxicity leading to the interpretation that ibogaine itself is not directly toxic to Purkinje cells. We postulated that ibogaine produces sustained excitation of inferior olivary neurons that leads to excessive glutamate release at climbing fiber terminals, causing subsequent excitotoxic injury to Purkinje cells. The neuronal degeneration induced by ibogaine provides an animal model for studying excitotoxic injury in order to analyze the contribution of glutamate receptors to this injury and to evaluate neuroprotective strategies. Since non-N-methyl-D-aspartate (NMDA) receptors mediate Purkinje cell excitation by climbing fibers, we hypothesized that 1-4-aminophenyl-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI-52466), which antagonizes non-NMDA receptors, may have a neuroprotective effect by blocking glutamatergic excitation at climbing fiber synapses. To test this hypothesis, rats were administered systemic ibogaine plus GYKI-52466 and the degree of neuronal injury was analyzed in cerebellar sections. The results indicate that the AMPA antagonist GYKI-52466 (10 mg/kg i.p. x 3) does not protect against Purkinje cell injury at the doses used. Rather, co-administration of GYKI-52466 with ibogaine produces increased toxicity evidenced by more extensive Purkinje cell degeneration. Several hypotheses that may underlie this result are discussed. Although the reason for the increased toxicity found in this study is not fully explained, the present results show that a non-NMDA antagonist can produce increased excitotoxic injury under some conditions. Therefore, caution should be exercised before employing glutamate antagonists to reduce the risk of neuronal damage in human clinical disorders. Moreover, the contribution of different glutamate receptors to excitotoxic injury is complex and merits further analysis.

Degeneration of Purkinje cells in parasagittal zones of the cerebellar vermis after treatment with ibogaine or harmaline.

The indole alkaloids ibogaine and harmaline are beta-carboline derivatives that cause both hallucinations and tremor. Reports that ibogaine may have potent anti-addictive properties have led to initiatives that it be tested for the treatment of opiate and cocaine addiction. In this study, ibogaine-treated rats were analysed for evidence of neurotoxic effects because human clinical trials of ibogaine have been proposed. We recently found that ibogaine induces a marked glial reaction in the cerebellum with activated astrocytes and microglia aligned in parasagittal stripes within the vermis. Based on those findings, the present study was conducted to investigate whether ibogaine may cause neuronal injury or degeneration. The results demonstrate that, after treatment with ibogaine or harmaline, a subset of Purkinje cells in the vermis degenerates. We observed a loss of the neuronal proteins microtubule-associated protein 2 and calbindin co-extensive with loss of Nissl-stained Purkinje cell bodies. Argyrophilic staining of Purkinje cell bodies, dendrites and axons was obtained with the Gallyas reduced silver method for degenerating neurons. Degenerating neurons were confined to narrow parasagittal stripes within the vermis. We conclude that both ibogaine and harmaline have selective neurotoxic effects which lead to degeneration of Purkinje cells in the cerebellar vermis. The longitudinal stripes of neuronal damage may be related to the parasagittal organization of the olivocerebellar climbing fiber projection. Since these drugs produce sustained activation of inferior olivary neurons, we hypothesize that release of an excitatory amino acid from climbing fiber synaptic terminals may lead to excitotoxic degeneration of Purkinje cells.

Differential neuronal localizations and dynamics of phosphorylated and unphosphorylated type 1 inositol 1,4,5-trisphosphate receptors.

Type 1 inositol 1,4,5-trisphosphate receptors are phosphorylated by cyclic-AMP-dependent protein kinase A at serines 1589 and 1755, with serine 1755 phosphorylation greatly predominating in the brain. Inositol 1,4,5-trisphosphate receptor protein kinase A phosphorylation augments Ca(2+) release. To assess type 1 protein kinase A phosphorylation dynamics in the intact organism, we developed antibodies selective for either serine 1755 phosphorylated or unphosphorylated species. Immunohistochemical studies reveal marked variation in localization. For example, in the hippocampus the phosphorylated type 1 inositol 1,4,5-trisphosphate receptor is restricted to CA1, while the unphosphorylated receptor occurs ubiquitously in CA1-CA3 and dentate gyrus granule cells. Throughout the brain the phosphorylated type 1 inositol 1,4,5-trisphosphate receptor is selectively enriched in dendrites, while the unphosphorylated receptor predominates in cell bodies. Focal cerebral ischemia in rats and humans is associated with dephosphorylation of type 1 inositol 1,4,5-trisphosphate receptors, and glutamatergic excitation of cerebellar Purkinje cells mediated by ibogaine elicits dephosphorylation of type 1 inositol 1,4,5-trisphosphate receptors that precedes evidence of excitotoxic neuronal degeneration. We have demonstrated striking variations in regional and subcellular distribution of inositol 1,4,5-trisphosphate receptor phosphorylation that may influence normal physiological intracellular Ca(2+) signaling in rat and human brain. We have further shown that the subcellular distribution of inositol 1,4,5-trisphosphate receptor phosphorylation in neurons is regulated by excitatory neurotransmission, as well as excitotoxic insult and neuronal ischemia-reperfusion. Phosphorylation dynamics of type 1 inositol 1,4,5-trisphosphate receptors may modulate intracellular Ca(2+) release and influence the cellular response to neurotoxic insults.

Neurotoxicity of MDMA and related compounds: anatomic studies.

The cytotoxic effects of amphetamine derivatives were studied by immunocytochemistry to identify the cellular compartments affected by these drugs, to obtain morphologic evidence of neuronal degeneration, and to assess the potential for regeneration. The substituted amphetamines, MDA, MDMA, PCA, and fenfluramine, all release serotonin and cause acute depletion of 5-HT from most axon terminals in forebrain. (1) Unequivocal signs of axon degeneration were seen at 36-48 hour survivals: 5-HT axons exhibited increased caliber, huge, swollen varicosities, fragmentation, and dilated proximal axon stumps. (2) Fine 5-HT axon terminals were persistently lost after drug administration, while beaded axons and raphe cell bodies were spared. These two types of 5-HT axons, which arise from separate raphe nuclei and form distinct ascending projections, are differentially vulnerable to psychotropic drugs. (3) From 2-8 months after treatment, there was progressive serotonergic re-innervation of neocortex along a fronto-occipital gradient. Longitudinal 5-HT axons grew into layers I and VI from rostral to caudal, before sprouting into middle cortical layers; this bilaminar pattern of growth simulates perinatal development of 5-HT innervation. This study demonstrates differential vulnerability of 5-HT projections, evidence for axonal degeneration, and sprouting of 5-HT axons leading to re-innervation of forebrain. While the sprouting axons are anatomically similar to the type that was damaged, it is not known whether a normal pattern of innervation is re-established.

Excitotoxic insult due to ibogaine leads to delayed induction of neuronal NOS in Purkinje cells.

Ibogaine causes degeneration of Purkinje cells (PKCs), presumably via activation of neurons in the inferior olive leading to release of glutamate at climbing fiber terminals. Following ibogaine administration, some Purkinje cells express NADPH-diaphorase and neuronal NOS (nNOS), neither of which is present normally in these cells. The induction of NOS is delayed in onset, dose-related, and detected in neurons adjacent to degenerated PKCs. The results demonstrate that nNOS induction can follow excitotoxic neuronal injury or perturbation. However, NO is unlikely to participate in the initial phase of PKC damage. Both the late induction of nNOS and the spatial relationship between damaged and nNOS-expressing PKCs are consistent with a role for NO in either neuronal recovery or delayed cell death following excitotoxic injury.

Ibogaine induces glial activation in parasagittal zones of the cerebellum.

Ibogaine, an indole alkaloid, has been proposed for treatment of drug addiction, yet its mechanism, site of action, and possible neurotoxicity have not been determined. Since neuronal injury is known to activate neurologlial cells, we investigated potential neurotoxic effects of this drug in rats by examining expression of specific glial markers. After treatment with ibogaine (100 mg kg-1 i.p.; 1-3 doses), we observed increased cytochemical markers in both microglia (OX-6, OX-42, W3/25) and astrocytes (GFAP), associated with striking morphologic changes in these cells. Activated glial cells were restricted to longitudinally oriented, parasagittal stripes within the vermis of cerebellar cortex. The ibogaine-induced activation of cerebellar glial cells is highly suggestive of neuronal degeneration, most likely of Purkinje cells.

Organization of raphe-cortical projections in rat: a quantitative retrograde study.

Retrograde transport of a fluorescent dye was employed to study the projections from raphe nuclei to neocortex in the rat. The spatial distributions of labeled raphe cells were analyzed quantitatively to determine whether the nuclei are topographically organized with respect to different cortical targets. The dorsal raphe nucleus (DRN), exclusive of the lateral wing regions, has a predominantly (3:1) ipsilateral projection with decreasing numbers of cells projecting to frontal, parietal, and occipital cortex. Overlapping cell groups within the DRN project differentially to these three cortical areas: DRN cells innervating frontal cortex extend more rostrally and laterally than those to either parietal or occipital cortex. The medium raphe and B9 projections are bilaterally symmetric, with equal cell numbers projecting to frontal, parietal, and occipital cortex. The rostro-caudal distributions of cells that project to disparate cortical areas differ in B9 but not in MR. The percentage of cortically projecting cells that are serotonergic is 80% for the DRN, 60% in the MR and 33% in the B9 cell group. The dorsal raphe nucleus and the B9 cell group are organized heterogeneously, and overlapping sets of neurons project differentially upon particular areas of neocortex. In contrast, the median raphe nucleus projects uniformly upon the neocortex and does not exhibit topographic organization. The three rostral raphe nuclei (DR, MR and B9) are each organized according to different rules with regard to their efferent projections to cortex. The differential organization of the raphe nuclei suggests that groups of cells within these three raphe nuclei are likely to innervate different combinations of cortical targets and thus to have different functional effects.

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.

The olivocerebellar projection mediates ibogaine-induced degeneration of Purkinje cells: a model of indirect, trans-synaptic excitotoxicity.

Ibogaine, an indole alkaloid that causes hallucinations, tremor, and ataxia, produces cerebellar neurotoxicity in rats, manifested by degeneration of Purkinje cells aligned in narrow parasagittal bands that are coextensive with activated glial cells. Harmaline, a closely related alkaloid that excites inferior olivary neurons, causes the same pattern of Purkinje cell degeneration, providing a clue to the mechanism of toxicity. We have proposed that ibogaine, like harmaline, excites neurons in the inferior olive, leading to sustained release of glutamate at climbing fiber synapses on Purkinje cells. The objective of this study was to test the hypothesis that increased climbing fiber activity induced by ibogaine mediates excitotoxic Purkinje cell degeneration. The inferior olive was pharmacologically ablated in rats by a neurotoxic drug regimen using 3-acetylpyridine, and cerebellar damage attributed to subsequent administration of ibogaine was analyzed using immunocytochemical markers for neurons and glial cells. The results show that ibogaine administered after inferior olive ablation produced little or no Purkinje cell degeneration or glial activation. That a lesion of the inferior olive almost completely prevents the neurotoxicity demonstrates that ibogaine is not directly toxic to Purkinje cells, but that the toxicity is indirect and dependent on integrity of the olivocerebellar projection. We postulate that ibogaine-induced activation of inferior olivary neurons leads to release of glutamate simultaneously at hundreds of climbing fiber terminals distributed widely over the surface of each Purkinje cell. The unique circuitry of the olivocerebellar projection provides this system with maximum synaptic security, a feature that confers on Purkinje cells a high degree of vulnerability to excitotoxic injury.

Methylenedioxyamphetamine (MDA) and methylenedioxymethamphetamine (MDMA) cause selective ablation of serotonergic axon terminals in forebrain: immunocytochemical evidence for neurotoxicity.

The psychotropic amphetamine derivatives 3,4-methylenedioxyamphetamine (MDA) and 3,4-methylenedioxymethamphetamine (MDMA) have been used for recreational and therapeutic purposes in man. In rats, these drugs cause large reductions in brain levels of serotonin (5-HT). This study employs immunocytochemistry to characterize the neurotoxic effects of these compounds upon monoaminergic neurons in the rat brain. Two weeks after systemic administration of MDA or MDMA (20 mg/kg, s.c., twice daily for 4 d), there is profound loss of serotonergic (5-HT) axons throughout the forebrain; catecholamine axons are completely spared. Regional differences in drug toxicity are exemplified by partial sparing of 5-HT axons in hippocampus, lateral hypothalamus, basal forebrain, and in some areas of neocortex. The terminals of 5-HT axons are selectively ablated, while axons of passage and raphe cell bodies are spared. Thickened preterminal fibers exhibit increased staining due to damming-up of neurotransmitter and other axonal constituents. Fine 5-HT axon terminals are extremely vulnerable to these drugs, whereas terminal-like axons with large varicosities survive, raising the possibility that some 5-HT axons may be resistant to the neurotoxic effects. At short survivals, visualization of greatly swollen, fragmented 5-HT axons provides anatomic evidence for degeneration of 5-HT projections. The results establish that MDA and MDMA produce structural damage to 5-HT axon terminals followed by lasting denervation of the forebrain. Both drugs have similar effects, but MDA produces a greater reduction of 5-HT axons than does MDMA at the same dosage. The selective degeneration of 5-HT axons indicates that these drugs may serve as experimental tools to analyze the organization and function of 5-HT projections. Caution should be exercised until further studies determine whether these compounds may be hazardous in man.

Kinetic analysis of respiratory tract proteins recovered during a sequential lavage protocol.

Although bronchoalveolar lavage (BAL) has been used as a research tool for over a decade, the technique of lavage has varied markedly between laboratories. For example, lavage instillate volumes from 50 to 300 ml have been used, and yet the influence of the variable of total lavage volume on subsequent protein recovery is uncertain. We performed sequential BAL (50 ml/aliquot; total volume, 300 ml) of the right middle lobe of 14 normal volunteers and separately processed and analyzed recovered aliquots for the absolute and relative concentrations of several protein substances. These proteins include free secretory component and secretory IgA, which emanate from airway secretions, and IgG, which is thought to transude from more distal alveolar sites. Analysis of these data showed a marked decrease in the absolute concentration of all proteins measured in serial aliquots. Analysis of protein ratios in sequential aliquots, however, revealed no significant change from the first to the fifth recovered aliquot. Finally, we analyzed the influence of the size of the first recovered aliquot on absolute and relative concentrations of proteins. Here there seemed to be a trend indicating preferential recovery of airway proteins in smaller aliquots. This was significant for the ratio of free secretory component to albumin (p less than 0.05). We conclude that lung proteins are efficiently and homogeneously sampled with 100 ml of lavage instillate. Larger volumes will add more protein but not alter protein ratios. Lavage with smaller volumes may preferentially sample airway proteins.

3,4-Methylenedioxymethamphetamine and 3,4-methylenedioxyamphetamine destroy serotonin terminals in rat brain: quantification of neurodegeneration by measurement of [3H]paroxetine-labeled serotonin uptake sites.

This study examines the effects of repeated systemic administration (20 mg/kg s.c., twice daily for 4 days) of 3,4-methylenedioxymethamphetamine (MDMA) and 3,4-methylenedioxyamphetamine (MDA) on levels of brain monoamines, their metabolites and on the density of monoamine uptake sites in various regions of rat brain. Marked reductions (30-60%) in the concentration of 5-hydroxyindoleacetic acid were observed in cerebral cortex, hippocampus, striatum, hypothalamus and midbrain at 2 weeks after a 4-day treatment regimen of MDMA or MDA; less consistent reductions in serotonin (5-HT) content were observed in these brain regions. In addition, both MDMA and MDA caused comparable and substantial reductions (50-75%) in the density of [3H]paroxetine-labeled 5-HT uptake sites in all brain regions examined. In contrast, neither MDMA nor MDA caused any widespread or long-term changes in the content of the catecholaminergic markers (i.e., norepinephrine, dopamine, 3,4 dihydroxyphenylacetic acid and homovanillic acid) or in the number of [3H]mazindol-labeled norepinephrine or dopamine uptake sites in the brain regions examined. These data demonstrate that MDMA and MDA cause long-lasting neurotoxic effects with respect to both the functional and structural integrity of serotonergic neurons in brain. Furthermore, our measurement of reductions in the density of 5-HT uptake sites provides a means for quantification of the neurodegenerative effects of MDMA and MDA on presynaptic 5-HT terminals.

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 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.