Progressive ataxia and palatal tremor associated with dense pontine calcification: A unique case

Biallelic MYORG mutation carriers exhibit primary brain calcification with a distinct phenotype

Primary familial brain calcification (PFBC) is a rare neurogenetic disorder with diverse neuropsychiatric expression. Mutations in four genes cause autosomal dominant PFBC: SLC20A2, XPR1, PDGFB and PDGFRB. Recently, biallelic mutations in the MYORG gene have been reported to cause PFBC with an autosomal recessive pattern of inheritance. We screened MYORG in 29 unrelated probands negatively screened for the autosomal dominant PFBC genes and identified 11 families with a biallelic rare or novel predicted damaging variant. We studied the clinical and radiological features of 16 patients of these 11 families and compared them to that of 102 autosomal dominant PFBC patients carrying a mutation in one of the four known autosomal dominant PFBC genes. We found that MYORG patients exhibited a high clinical penetrance with a median age of onset of 52 years (range: 21-62) with motor impairment at the forefront. In particular, dysarthria was the presenting sign in 11/16 patients. In contrast to patients with autosomal dominant PFBC, 12/15 (80%) symptomatic patients eventually presented at least four of the following five symptoms: dysarthria, cerebellar syndrome, gait disorder of any origin, akinetic-hypertonic syndrome and pyramidal signs. In addition to the most severe clinical pattern, MYORG patients exhibited the most severe pattern of calcifications as compared to the patients from the four autosomal dominant PFBC gene categories. Strikingly, 12/15 presented with brainstem calcifications in addition to extensive calcifications in other brain areas (lenticular nuclei, thalamus, cerebellar hemispheres, vermis, ±cortex). Among them, eight patients exhibited pontine calcifications, which were observed in none of the autosomal dominant PFBC patients and hence appeared to be highly specific. Finally, all patients exhibited cerebellar atrophy with diverse degrees of severity on CT scans. We confirmed the existence of cerebellar atrophy by performing MRI voxel-based morphometry analyses of MYORG patients with autosomal dominant PFBC mutation carriers as a comparison group. Of note, in three families, the father carried small pallido-dentate calcifications while carrying the mutation at the heterozygous state, suggesting a putative phenotypic expression in some heterozygous carriers. In conclusion, we confirm that MYORG is a novel major PFBC causative gene and that the phenotype associated with such mutations may be recognized based on pedigree, clinical and radiological features.

An elderly man with progressive ataxia and palatal tremor presenting with dizziness and oculopalatal tremor

A 74-year-old man was referred to our department for dizziness and progressive unsteady gait over 6 years. His family history was unremarkable. Neurological examination showed dysarthria, saccadic eye movement, palatal tremor (1.7 Hz)-synchronous with rotational ocular movement, and truncal ataxia. T2-weighted magnetic resonance imaging (MRI) of the brain revealed hyperintense and hypertrophic bilateral inferior olivary nuclei at the medulla and mild cerebellar atrophy. On the basis of neurological findings of oculopalatal tremor and cerebellar ataxia with brain MRI findings, the diagnosis of progressive ataxia and palatal tremor (PAPT) was made. PAPT should be included in differential diagnosis of dizziness observed in elderly individuals.

Clinico-Pathological Correlation in Progressive Ataxia and Palatal Tremor: A Novel Tauopathy

Palatal tremor (PT) is an uncommon movement disorder that has been subdivided into essential and symptomatic forms. A distinct subgroup of the symptomatic form presents with progressive ataxia and PT. The histopathology of progressive ataxia and PT has not been previously determined. This study consisted of a clinical review, histopathology, and electron microscopy of the brain of a man with progressive ataxia and PT. The inferior olivary hypertrophy was symmetrical and homogenous, and no focal pathologic lesions could be identified in the brainstem. Insoluble tau deposits were found in neurons, exclusively infratentorially. We present the clinical and pathological evaluation of a case of progressive ataxia and PT that provide evidence for a unique form of 4R tauopathy.