Fingering fibroblast growth factor receptors

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

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

Gene locus FPD1 of the dystonic Mount-Reback type of autosomal-dominant paroxysmal choreoathetosis

Genes for paroxysmal choreoathetosis have been localized to chromosomes 1p and 2q. We have reinvestigated one of the classic large autosomal-dominant pedigrees of the dystonic Mount-Reback type of paroxysmal choreoathetosis 20 years after its first assessment. These patients prefer diazepam for both prevention and treatment of attacks and did not develop addiction on an intermittent regime. Migraine occurred in a third of the patients. Genetic data localized the underlying mutation to the FPD1 locus (familial paroxysmal dyskinesia type 1) on chromosome 2q and support locus homogeneity for the Mount-Reback syndrome. The data also refine the FPD1 candidate region to 3.6 cM between the markers D2S164 and D2S2359, which may facilitate the investigation of the role of the candidate ion channel gene SLC2C.

A case of Hodgkin's lymphoma producing neuromyotonia

The syndrome of neuromyotonia produces muscle stiffness, cramps, and frequently, excessive sweating. Most cases are idiopathic, but some are associated with neoplasms, especially immune cell cancers. Voltage-gated potassium channels may be the target of an autoantibody attack in idiopathic generalized neuromyotonia (Isaacs' syndrome). The cases associated with neoplasms may also have an autoimmune etiology. We report the first case of neuromyotonia as the presenting feature of Hodgkin's lymphoma and propose a paraneoplastic mechanism that would link the purported autoimmune etiology in Isaacs' syndrome with the cancer-associated cases.

Paroxysmal dystonic choreoathetosis linked to chromosome 2q: clinical analysis and proposed pathophysiology

We describe clinical features of a large Polish-American kindred in which autosomal-dominant, paroxysmal dystonic choreoathetosis (PDC) was linked to a locus on chromosome 2q. Episodes of generalized dystonia and choreoathetosis involving the face and all extremities began in early childhood, lasted for 30 minutes to several hours, and occurred up to several times each week. There was no interruption of consciousness and EEGs were normal during the episodes. Paroxysmal dyskinesia occurred at rest both spontaneously and following caffeine or alcohol consumption. Neurologic examinations were normal between attacks. The cause of PDC is unknown. We deduced a model of PDC pathophysiology from analyzing neurophysiologic effects of alcohol and caffeine (which provoke attacks of PDC), the variably beneficial effects of levodopa-carbidopa, and the occurrence of dystonia and paroxysmal dyskinesia in biopterin synthesis disorders. We propose that nigrostriatal neurons in PDC patients have either marginally deficient dopamine synthesis or excessive alcohol- and caffeine-induced dopamine release; and that following alcohol- and caffeine-induced dopamine release, PDC patients experience a period of dopamine deficiency.

Axonal channelopathies: an evolving concept in the pathogenesis of peripheral nerve disorders

Abnormalities of peripheral nerve Na+ and K+ channels result in clinical manifestations unrelated to axonal degeneration or demyelination. Na+ channel blockade causes weakness and sensory loss associated with slowed conduction and decreased motor and sensory action potential amplitudes. K+ channel abnormalities result in high frequency repetitive action potentials (e.g., myokymia). Ion channel abnormalities may also play an important role in electrophysiologic changes seen in demyelinating disorders.