MULTIMODAL IMAGING OF A FAMILY WITH SPINOCEREBELLAR ATAXIA TYPE 7 DEMONSTRATING PHENOTYPIC VARIATION AND PROGRESSION OF RETINAL DEGENERATION

Multimodal Ophthalmic Imaging in Spinocerebellar Ataxia Type 7

The aim of this case series and narrative literature review is to highlight the importance of multimodal imaging in the ophthalmological examination of patients with spinocerebellar ataxia type 7 and provide a summary of the most relevant imaging techniques. Three patients with SCA7 were included in this case series. A literature review revealed twenty-one publications regarding ocular manifestations of SCA7, and the most relevant aspects are summarized. The role of different imaging techniques in the follow-up of SCA7 patients is analyzed, including color vision testing, corneal endothelial topography, color fundus photography (CFP) and autofluorescence, near infrared reflectance imaging, spectral domain optical coherence tomography (SDOCT), visual field examination, and electrophysiological tests. SDOCT provides a rapid and non-invasive imaging evaluation of disease progression over time. Additional examination including NIR imaging can provide further information on photoreceptor alteration and subtle disruption of the RPE, which are not evident with CFP at an early stage. Electrophysiological tests provide essential results on the state of cone and rod dystrophy, which could be paramount in guiding future genetic therapies. Multimodal imaging is a valuable addition to comprehensive ophthalmological examination in the diagnosis and management of patients with SCA7.

A Proposal for Classification of Retinal Degeneration in Spinocerebellar Ataxia Type 7

The aim of this study is to propose a classification system for the spinocerebellar ataxia type 7 retinal degeneration (SCA7-RD). Twenty patients with molecularly confirmed SCA7 underwent slit lamp examination, fundus photography, and optical coherence tomography (Spectralis®). Scale for the Assessment and Rating of Ataxia (SARA) and International Cooperative Ataxia Rating Scale (ICARS) were applied, and age, sex, age at symptom onset, and number of CAG expansions were recorded. After analyzing the ophthalmological findings in each participant, a panel of retinal disease experts created a qualitative classification system for SCA7-RD comprising four stages. We assessed the correlations of retinal degeneration severity with SARA and ICARS scores, number of CAG repeats in ATXN7 allele, and age at symptom onset. We graded retinal degeneration as stage 1 in nine participants, as stage 2 in five, and as stage 3 in six. No differences in age and visual symptoms duration were found between groups. SARA and ICARS scores correlated with the severity of SCA7-RD on the classification system (p = 0.024 and p = 0.014, respectively). After adjusting for disease duration, retinal disease stage association with SARA and ICARS scores remained significant (ANCOVA, p < 0.05). The classification system for SCA7-RD was able to characterize different disease stages representing the landmarks in the cone-rod dystrophy natural history. Neurodegeneration appears to occur in parallel in the cerebellum and in the visual pathway. We conclude that retinal degeneration in SCA7 is a potential biomarker of the neurological phenotype severity.

Ophthalmic Manifestations and Genetics of the Polyglutamine Autosomal Dominant Spinocerebellar Ataxias: A Review

Spinocerebellar ataxia (SCA) is a part of the cerebellar neurodegenerative disease group that is diverse in genetics and phenotypes. It usually shows autosomal dominant inheritance. SCAs, always together with the cerebellar degeneration, may exhibit clinical deficits in brainstem or eye, especially retina or optic nerve. Interestingly, autosomal dominant SCAs share a common genetic mechanism; the length of the glutamine chain is abnormally expanded due to the increase in the cytosine–adenine–guanine (CAG) repeats of the disease causing gene. Studies have suggested that the mutant ataxin induces alteration of protein conformation and abnormal aggregation resulting in nuclear inclusions, and causes cellular loss of photoreceptors through a toxic effect. As a result, these pathologic changes induce a downregulation of genes involved in the phototransduction, development, and differentiation of photoreceptors such as CRX, one of the photoreceptor transcription factors. However, the exact mechanism of neuronal degeneration by mutant ataxin restricted to only certain type of neuronal cell including cerebellar Purkinje neurons and photoreceptor is still unclear. The most common SCAs are types 1, 2, 3, 6, 7, and 17 which contain about 80% of autosomal dominant SCA cases. Various aspects of eye movement abnormalities are evident depending on the degree of cerebellar and brainstem degeneration in SCAs. In addition, certain types of SCAs such as SCA7 are characterized by both cerebellar ataxia and visual loss mainly due to retinal degeneration. The severity of the retinopathy can vary from occult macular photoreceptor disruption to extensive retinal atrophy and is correlated with the number of CAG repeats. The value of using optical coherence tomography in conjunction with electrodiagnostic and genetic testing is emphasized as the combination of these tests can provide critical information regarding the etiology, morphological evaluation, and functional significances. Therefore, ophthalmologists need to recognize and differentiate SCAs in order to properly diagnose and evaluate the disease. In this review, we have described and discussed SCAs showing ophthalmic abnormalities with particular attention to their ophthalmic features, neurodegenerative mechanisms, genetics, and future perspectives.

Progress of macular atrophy during 30 months' follow-up in a patient with spinocerebellar ataxia type1 (SCA1)

PURPOSE

To report the 30-months' course of macular dystrophy in a patient with genetically confirmed spinocerebellar ataxia type1 (SCA1).

METHODS

Detailed ophthalmological examinations including best-corrected visual acuity (BCVA), perimetry, multimodal fundus imaging, and electrophysiological recordings were performed on a 52-year-old woman with SCA1. The number of CAG sequence repeats of the candidate gene was verified.

RESULTS

The baseline decimal BCVA was 0.2 OD and 0.3 OS. Goldman perimetry showed relative central scotomas and slight enlargements of Mariotte blind spot bilaterally. Ophthalmoscopy revealed no abnormalities in the macula and optic disk. Fundus autofluorescence (FAF) showed a circular hyperautofluorescence and round-shaped hypoautofluorescence in the macula. Optical coherence tomography (OCT) showed a loss of the interdigitation zone and ellipsoid zone (EZ) in the macula. Full-field scotopic and photopic Full-field electroretinograms (ERGs) were normal, and multifocal ERGs were decreased in the central area. After 30 months, the BCVA had not changed, but the FAF showed a spark-like hypoautofluorescence in the macula. The abnormal area of the EZ had expanded toward the periphery, and the rate of EZ loss was 199.7%/year OD and 206.8%/year OS. Genetic examinations revealed an increase in the number of heterozygous CAG repeats in the ATXN1 gene, and the CAG repeat number of the mutant allele ranged from 43 to 48.

CONCLUSIONS

The full-field scotopic and photopic ERGs were normal. The mfERGs were significantly smaller in the central region. OCT demonstrated bilateral photoreceptor atrophy in the macula, and the rate of EZ loss was more rapid than in other macular dystrophies. Spark-like hypoautofluorescence appeared during the course of the disease process which might be a specific feature of SCA1-related retinopathy.