Cases reported "Spinocerebellar Ataxias"

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1/4. Asymptomatic CTG expansion at the SCA8 locus is associated with cerebellar atrophy on MRI.

    Spinocerebellar ataxia type 8 (SCA8) is the first example of dominantly inherited ataxia reported to be caused by a dynamic mutation of the untranslated CTG trinucleotide repeat. We performed genetic and clinical analyses of a family with an isolated case with young onset cerebellar ataxia carrying an expanded 95 CTA/CTG repeats, and revealed that the asymptomatic father was also carrying a much greater expansion of 136 repeats. This paternal transmission developed a large contraction of -41 CTG repeats. The ataxia patient showed almost pure cerebellar symptoms, and a cerebral MRI of the patient demonstrated significant atrophy of the cerebellar vermis and hemispheres with preservation of brainstem and cerebrum. Although the father did not show any neurological abnormalities, his MRI demonstrated mild atrophy of the cerebellar hemispheres. The genetic phenomenon on this family has not been observed in other types of SCAs, and this reduced penetrance may cause reproduction of sporadic SCA8 frequently. Therefore, we must perform careful interviews regarding family history, and suggest the genetic and neuroradiological investigations on family members when we encounter a sporadic patient with the CTG expansion at the SCA8 locus.
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2/4. Loss-of-function EA2 mutations are associated with impaired neuromuscular transmission.

    OBJECTIVE: To examine the functional consequences of episodic ataxia type 2 (EA2)-causing nonsense and missense mutations in vitro and to characterize the basis of fluctuating weakness in patients with E2A. BACKGROUND: Mutations in CACNA1A encoding the Ca(v)2.1 calcium channel subunit cause EA2 through incompletely understood mechanisms. Although the Ca(v)2.1 subunit is important for neurotransmission at the neuromuscular junction, weakness has not been considered a feature of EA2. methods: The disease-causing mutations in three unrelated patients with EA2 and fluctuating weakness were identified by mutation screening and sequencing. Mutant constructs harboring mutations R1281X, F1406C, R1549X were transfected into COS7 cells and expressed for patch clamp studies. Single-fiber electromyography (SFEMG) was performed in patients to examine synaptic transmission at the neuromuscular junction. RESULTS: Functional studies in COS7 cells of nonsense and missense EA2 mutants demonstrated markedly decreased current densities compared with wild type. SFEMG demonstrated jitter and blocking in these patients with EA2, compared with normal subjects and three patients with SCA-6. CONCLUSION: EA2-causing missense and nonsense mutations in CACNA1A produced mutant channels with diminished whole cell calcium channel activity in vitro due to loss of function. Altered biophysical properties or reduced efficiency of plasma membrane targeting of mutant channels may contribute to abnormal neuromuscular transmission, manifesting as myasthenic syndrome.
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3/4. Meiotic CAG repeat instability in spinocerebellar ataxia type 6: maternally transmitted elongation in a presumed sporadic case.

    Spinocerebellar ataxia type 6 (SCA6) is an autosomal dominantly inherited disorder characterized by cerebellar ataxia, dysarthria and nystagmus. The molecular background for the disorder is a CAG repeat expansion in the CACNA1A gene located on chromosome 19. The size of SCA6 expanded alleles is usually stable, and variation in repeat size over successive generations is rare. We report a Danish family with one case of SCA6 resembling a sporadic case of spinocerebellar ataxia. Analysis of the CACNA1A gene showed meiotic CAG repeat instability in the transmission from a 70-year-old woman with no subjective symptoms to her symptomatic son. The CAG repeat size expanded from 22 repeats in the mother to 23 repeats in the proband. This case demonstrates maternal repeat instability and clinical anticipation in a family with SCA6.
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4/4. Predominant motor symptoms in a 74-year-old man with a small elongation in the spinocerebellar atrophy type 1 gene.

    The patient was a 74-year-old man who developed gait and bulbar disturbances, which progressed for several years. His mother and a sister complained of a similar disturbance. On admission, generalized muscle atrophy and weakness were prominent, especially in the distal portions of the legs, with bulbar involvement. The patellar tendon reflexes were retained and the achilles tendon reflexes were decreased with a positive right Babinski's sign. The ocular movements were restricted in vertical directions and, to a lesser extent, in horizontal directions. Sensory disturbance, ataxia, and extrapyramidal signs were not apparent on admission. A needle electromyogram demonstrated neurogenic changes. The laboratory examination was normal except for elevated blood glucose (320 mg/dL) and creatine kinase (1760 U/L). His general condition deteriorated so rapidly that intractable respiratory distress due to pneumonia led to a fatal outcome. The clinical diagnosis was motor neuron disease, although a familial background and a disturbance in ocular movements might have suggested other possibilities.
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