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Background: Spinocerebellar ataxias are a group of phenotypically and genetically heterogeneous disorders characterized by progressive degeneration of the cerebellum. The expansion of a CAG repeat upstream of the PP2APR55beta gene has been recently reported as a novel cause of a dominantly inherited ataxia (SCA12) in a kindred with limb tremor as an early feature., Objective: To explore the relative frequency of SCA12 among familial and sporadic spinocerebellar ataxias in an ethnically diverse patient population., Methods: We used polymerase chain reaction to analyze CAG repeat size in a series of patients presenting to an ataxia clinic in California., Results: The SCA12 expansion was not detected in any of the cases investigated. The largest allele found had 22 repeats, a finding within the proposed nonpathogenic range. Distribution of repeat size and heterozygosity were similar to that described previously., Conclusions: These results, coupled with findings in other populations, indicate that the SCA12 mutation is a rare cause of spinocerebellar degeneration. Diagnostic testing for SCA12 should be considered in patients with cerebellum disorders and an atypical clinical phenotype, especially when tremor is initially present.

Background: The small-conductance calcium-activated potassium channel gene (hSKCa3) contains 2 CAG repeats, 1 of which is highly polymorphic. Although this repeat is not pathologically expanded in patients with schizophrenia, some studies have suggested an allelic association with schizophrenia. CAG expansions in other genes such as the alpha1 subunit of a brain-specific P/Q-type calcium channel gene cause spinocerebellar ataxia type 6, whereas the length of the CAG repeat in the RAI1 gene modifies the age of onset of spinocerebellar ataxia type 2., Objectives: To evaluate expansions in the hSKCa3 polyglutamine domain as causative for ataxia, and to study the association between the length of the polyglutamine repeat and the presence of ataxia., Methods: We analyzed this repeat in 122 patients with autosomal dominant cerebellar ataxia, or sporadic ataxia, and compared allele distribution with 750 alleles seen in 2 healthy control groups and 172 alleles in patients with Parkinson disease., Results: The distribution of alleles in ataxia patients and controls was significantly different by Wilcoxon rank test (P <.001). Twenty-two or more polyglutamine tracts were more common in ataxia patients compared with controls by chi2 analysis (P<.001)., Conclusion: Longer stretches of polyglutamines in a human potassium channel are not causative for ataxia, but they are associated with the presence of ataxia. There is no association with the presence of Parkinson disease.

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.

Genetic linkage analysis is a powerful tool to detect the chromosomal location of disease genes. It is based on the observation that genes that reside physically close on a chromosome remain linked during meiosis. For most neurologic diseases for which the underlying biochemical defect was not known, the identification of the chromosomal location of the disease gene was the first step in its eventual isolation. By now, genes that have been isolated in this way include examples from all types of neurologic diseases, from neurodegenerative diseases such as Alzheimer, Parkinson, or ataxias, to diseases of ion channels leading to periodic paralysis or hemiplegic migraine, to tumor syndromes such as neurofibromatosis types 1 and 2.

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.

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.

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.