Investigation of Visual System Involvement in Spinocerebellar Ataxia Type 14

Novel heterozygous PRPH2 variant identified in a patient with spinocerebellar ataxia type 14 and macular dystrophy

PURPOSE

To report on a patient with spinocerebellar ataxia type 14 (SCA14) and macular dystrophy with identification of a novel PRPH2 variant.

METHODS

Case report.

RESULTS

A 63-year-old female with molecularly confirmed SCA14 presented with symmetric pigmentary disturbances in a perifoveal distribution resembling a pattern macular dystrophy. She had no history of using medications with recognized toxic macular effects. Subsequent genetic testing confirmed a novel heterozygous missense variant of unknown significance in PRPH2 (PRPH2: c.694 G>A, p.(Ala232Thr)).

CONCLUSIONS

To our knowledge, this is the first case of macular dystrophy identified in a patient with SCA14. While it is possible that the macular dystrophy observed in this patient might be an under-reported phenotype associated with SCA14, the pattern of macular changes is consistent with PRPH2-related disorders. The identified missense variant is predicted to be damaging by most in silico models, and the residue is highly conserved, adding support to a dual genetic diagnosis in this case.

Patient-Related Outcome Measures for Oculomotor Symptoms in the Cerebellar Ataxias: Insights from Non-Cerebellar Disorders

In patients with cerebellar ataxia (CA), symptoms related to oculomotor dysfunction significantly affect quality of life (QoL). This study aimed to analyze the literature on patient-related outcome measures (PROMs) assessing QoL impacts of vestibular and cerebellar oculomotor abnormalities in patients with CA to identify the strengths and limitations of existing scales and highlight any areas of unmet need. A systematic review was conducted (Medline, Embase) of English-language original articles reporting on QoL measures in patients with vertigo, dizziness or CA. Pre-specified parameters were retrieved, including diseases studied, scales applied and conclusions drawn. Our search yielded 3671 articles of which 467 studies (n = 111,606 participants) were deemed relevant. The most frequently studied disease entities were (a) non-specific dizziness/gait imbalance (114 studies; 54,581 participants), (b) vestibular schwannomas (66; 15,360), and (c) vestibular disorders not further specified (66; 10,259). The Dizziness Handicap Inventory (DHI) was the most frequently used PROM to assess QoL (n = 91,851), followed by the Penn Acoustic Neuroma Quality-of-Life Scale (n = 12,027) and the Activities-Specific Balance Confidence Scale (n = 2'471). QoL-scores capturing symptoms related to oculomotor abnormalities in CA were rare, focused on visual impairments (e.g., National-Eye-Institute Visual Function Questionnaire, Oscillopsia Functional Impact, oscillopsia severity score) and were unvalidated. The DHI remains the most widely used and versatile scale for evaluating dizziness. A lack of well-established PROMs for assessing the impact of oculomotor-related symptoms on QoL in CA was noted, emphasizing the need for developing and validating a new QoL-score dedicated to the oculomotor domain for individuals with CA.

Spinocerebellar ataxia type 14: refining clinicogenetic diagnosis in a rare adult-onset disorder

Objectives

Genetic variant classification is a challenge in rare adult‐onset disorders as in SCA‐PRKCG (prior spinocerebellar ataxia type 14) with mostly private conventional mutations and nonspecific phenotype. We here propose a refined approach for clinicogenetic diagnosis by including protein modeling and provide for confirmed SCA‐PRKCG a comprehensive phenotype description from a German multi‐center cohort, including standardized 3D MR imaging.

Methods

This cross‐sectional study prospectively obtained neurological, neuropsychological, and brain imaging data in 33 PRKCG variant carriers. Protein modeling was added as a classification criterion in variants of uncertain significance (VUS).

Results

Our sample included 25 cases confirmed as SCA‐PRKCG (14 variants, thereof seven novel variants) and eight carriers of variants assigned as VUS (four variants) or benign/likely benign (two variants). Phenotype in SCA‐PRKCG included slowly progressive ataxia (onset at 4–50 years), preceded in some by early‐onset nonprogressive symptoms. Ataxia was often combined with action myoclonus, dystonia, or mild cognitive‐affective disturbance. Inspection of brain MRI revealed nonprogressive cerebellar atrophy. As a novel finding, a previously not described T2 hyperintense dentate nucleus was seen in all SCA‐PRKCG cases but in none of the controls.

Interpretation

In this largest cohort to date, SCA‐PRKCG was characterized as a slowly progressive cerebellar syndrome with some clinical and imaging features suggestive of a developmental disorder. The observed non‐ataxia movement disorders and cognitive‐affective disturbance may well be attributed to cerebellar pathology. Protein modeling emerged as a valuable diagnostic tool for variant classification and the newly described T2 hyperintense dentate sign could serve as a supportive diagnostic marker of SCA‐PRKCG.