POLR3A-related spastic ataxia: new mutations and a look into the phenotype.

Adolescent-onset spastic ataxia is a proposed novel phenotype in compound heterozygous carriers of an intronic mutation (c.1909 + 22G > A) in the POLR3A gene. Here, we present ten new cases of POLR3A-related spastic ataxia and discuss the genetic, clinical and imaging findings. Patients belonged to six pedigrees with hereditary spastic paraplegia or cerebellar ataxia of unknown origin. All affected subjects presented with compound heterozygous variants, comprising c.1909 + 22G > A in combination in each pedigree with one of the following novel mutations (Thr596Met, Tyr665LeufsTer11, Glu198Ter, c.646-687_1185 + 844del). The new mutations segregated with the phenotype in all families. The phenotype combined variable cerebellar ataxia, gait and lower limb spasticity, involvement of central sensory tracts and in some cases also intention tremor. The reportedly characteristic hyperintensity along the superior cerebellar peduncle on MRI was observed in ~ 80% of the cases. Our study extends the clinical and molecular phenotype further supporting the pathogenic role of the c.1909 + 22G4A intronic mutation and identifying four novel causative mutations in POLR3A-related spastic ataxia. Certain characteristic MRI features may be useful to guide genetic diagnosis.

Cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS) with chronic cough and preserved muscle stretch reflexes: evidence for selective sparing of afferent Ia fibres.

The aim of this study was to describe five patients with cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) with chronic cough and preserved limb muscle stretch reflexes. All five patients were in the seventh decade of age, their gait imbalance having been initiated in the fifth decade. In four patients cough antedated gait imbalance between 15 and 29 years; cough was spasmodic and triggered by variable factors. Established clinical picture included severe hypopallesthesia predominating in the lower limbs with postural imbalance, and variable degree of cerebellar axial and appendicular ataxia, dysarthria and horizontal gaze-evoked nystagmus. Upper- and lower-limb tendon jerks were preserved, whereas jaw jerk was absent. Vestibular function testing showed bilateral impairment of the vestibulo-ocular reflex. Nerve conduction studies demonstrated normal motor conduction parameters and absence or severe attenuation of sensory nerve action potentials. Somatosensory evoked potentials were absent or severely attenuated. Biceps and femoral T-reflex recordings were normal, while masseter reflex was absent or attenuated. Sympathetic skin responses were normal. Cranial MRI showed vermian and hemispheric cerebellar atrophy predominating in lobules VI, VII and VIIa. We conclude that spasmodic cough may be an integral part of the clinical picture in CANVAS, antedating the appearance of imbalance in several decades and that sparing of muscle spindle afferents (Ia fibres) is probably the pathophysiological basis of normoreflexia.