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Published on: December 5, 2020
RETINAL MANIFESTATIONS OF SPINOCEREBELLAR ATAXIA TYPE 7 IN TWO CONSECUTIVE GENERATIONS
Gary Yip1, Martha Henao, Lynn L Huang
1Loma Linda University Eye Institute, Loma Linda, California.
Insights
Spinocerebellar ataxia Type 7 (SCA-7) involves expanded CAG repeats, leading to progressive neurodegeneration and vision loss. This case highlights genetic anticipation, where the disease worsens with each generation, sometimes diagnosed in children before parents.
Area of Science:
- Genetics
- Neuroscience
- Ophthalmology
Background:
- Spinocerebellar ataxia Type 7 (SCA-7) is an inherited neurodegenerative disorder.
- It is characterized by progressive cerebellar ataxia and vision loss due to cone photoreceptor degeneration.
- SCA-7 is caused by an expansion of CAG trinucleotide repeats in the ATXN7 gene.
Observation:
- A 5-year-old female presented with failure to thrive and suspected ataxia.
- Ocular examination revealed retinal pigment epithelium changes and significantly reduced visual acuity.
- Genetic testing confirmed SCA-7 with 96 CAG repeats; her father also diagnosed with SCA-7 (47 CAG repeats) despite prior misdiagnosis.
Findings:
- The patient exhibited symptoms consistent with SCA-7, including ataxia and vision impairment.
- Genetic analysis revealed a significant CAG repeat expansion in the patient, indicative of SCA-7.
- The father's milder presentation and lower CAG repeat count (47) demonstrated genetic anticipation, where repeat length and disease severity increase with transmission.
Implications:
- This case underscores the phenomenon of genetic anticipation in SCA-7, where offspring present with more severe symptoms at an earlier age.
- Earlier diagnosis of SCA-7 is crucial for effective patient and family counseling, potentially avoiding unnecessary investigations.
- Increased awareness of SCA-7 and its genetic anticipation patterns can improve diagnostic accuracy and management strategies for affected families.
Purpose:
To report a diagnosis of spinocerebellar ataxia Type 7 (SCA-7) first diagnosed in the daughter followed by the father, with proven genetic testing and display of progressive anticipation of disease penetrance.
Methods:
A 5-year-old African American female admitted for failure to thrive underwent full ocular examination and fundus photography, with genetic confirmation of SCA-7. The father carried a previous diagnosis of possible solar retinopathy; however, with further genetic testing, he was also found to have SCA-7.
Results:
The patient was admitted for failure to thrive with suspicion of ataxia neurodegenerative disorder. Visual acuity was hand motion. Fundus examination showed retinal pigment epithelium pigmentary changes in the macula and peripheral retina. Further genetic workup revealed 96 CAG repeat expansion compared with a normal of <20 repeats. Ocular examination of patient's father displayed a milder form of retinopathy with genetic testing showing 47 CAG repeat expansion. Diagnosis of SCA-7 was made displaying genetic anticipation.
Conclusion:
Spinocerebellar ataxia Type 7 is a disease of expanded CAG repeats showing genetic anticipation. Patients display progressive cerebellar ataxia, dysarthria dysphagia, slow saccadic eye movements, and cone photoreceptor loss leading to progressive vision loss. CAG repeat length tends to expand with transmission resulting in dramatic symptoms in offspring sometimes resulting in diagnosis before parents' diagnosis. Awareness of this condition may help in earlier diagnosis and unnecessary testing resulting in more effective counseling for the patient and their family.
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