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Si-Liang Peng, Huanan Ren, Norma Fajardo, Irma Lopez, Robert K Koenekoop; A possible new gene for cone-rod dystrophy. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1780. doi: https://doi.org/.
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Cone-rod dystrophies (CRD) are rare inheritable retinal disorders that result in dysfunction and death of cone and rod photoreceptors, and can present as syndromic or non-syndromic forms. To date, 22 CRD genes are known, but more than 70% of the genes responsible for cone-rod dystrophy remain unsolved. In this case review, we hypothesize that a spastic paraplegia gene can cause hereditary spastic paraplegia, but also results in isolated cone-rod dystrophy in the heterozygous state.
A 43 years-old French-Canadian female presented to our clinic with decreased colour vision, photophobia, hearing loss and bilateral central scotoma, but no other systemic disease. The diagnosis of CRD was made based on clinical findings, electroretinogram (ERG) and fundus autofluorescence (FAF). Her 34 years-old brother was diagnosed with hereditary spastic paraplegia at a young age, and has high myopia without significant visual complaints. Their other sister, aged 36, does not have any visual or systemic symptoms.<br /> <br /> All three siblings underwent genetic testing for spastic paraplegia (SPG), followed by ERG, FAF and optical coherence tomography (OCT) of the retina. Their DNA was sent for sequencing and the Asper Ophthalmics Next-Generation Sequencing (NGS) CRD panel to rule out 22 other CRD genes.
The genetic panel screening was negative for all currently known CRD genes (Asper Ophthalmics NGS) in all three siblings. The brother was found to have a homozygous frameshift mutation in SPG and the proband with CRD was heterozygous for the same mutation. However, only the brother demonstrated systemic manifestations of hereditary spastic paraplegia and only the proband had significant visual dysfunction.
Our results are consistent with our hypothesis that SPG is a new gene for CRD, and may demonstrate different phenotypes depending on the pattern of expression. Further study with larger sample sizes are underway to confirm our findings.
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