From the Research
Spinocerebellar ataxia type 7 (SCA7) has visual symptoms because it specifically affects the retina and visual pathways in addition to the cerebellum, leading to macular degeneration and progressive vision loss, as evident in a case report published in 2021 1. The visual symptoms in SCA7 are caused by a CAG trinucleotide repeat expansion in the ATXN7 gene, which produces a mutant ataxin-7 protein that accumulates in both cerebellar neurons and retinal photoreceptor cells.
- This accumulation is particularly toxic to cone photoreceptors in the macula, leading to macular degeneration and progressive vision loss.
- The visual symptoms typically begin with decreased color vision and progress to complete blindness in many cases.
- The reason SCA7 affects vision while other SCAs generally don't is due to the specific expression pattern of the ATXN7 gene in retinal tissue and the particular vulnerability of photoreceptor cells to the mutant protein.
- The severity of visual symptoms often correlates with the size of the CAG repeat expansion, with larger expansions causing earlier onset and more rapid progression of visual deterioration, as reported in a study published in 2019 2.
- A review of the ophthalmic manifestations and genetics of polyglutamine autosomal dominant spinocerebellar ataxias, including SCA7, highlights the importance of recognizing and differentiating these conditions to properly diagnose and evaluate the disease 3.
- Regular ophthalmological monitoring is recommended for affected individuals, as there is currently no specific treatment to prevent or reverse the visual symptoms of SCA7.
- The widespread brain damage in SCA7 patients with progressive visual impairments has been documented in a neuropathological study published in 2008 4, which observed loss of myelinated fibers in distinct central nervous fiber tracts and widespread degeneration of the cerebellum, telencephalon, diencephalon, and lower brainstem.