Maternal grandmother
Maternal grandmother was estranged from the family, but after the findings in the family she was contacted. She endorses having a retinal problem since age 40 that has lead her to be legally blind. As per her primary ophthalmologist she presented in her 40s with a retinitis pigmentosa like picture with chronic cystoid macular edema.
Genetic testing
Initial DNA sequencing and deletion/duplication testing detectable mutation in the RS 1 gene was performed in both male siblings, with negative results. A retinal dystrophy panel with sequencing of 244 genes, including RS1 was done in case III:2 and was reported as normal. A research-based retinal dystrophy with deletion/duplication testing of over 100 genes was obtained
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Although a negative ERG is seen in 50% of patients with XLRS, it is neither necessary nor pathognomonic for the diagnosis of XLRS.2,3,10 Therefore, even in the absence of this electrophysiological finding in one of the brothers, the findings were still considered highly suggestive of XLRS. However, the mother and sister had both abnormal fundus findings associated with abnormal FAF and ERG which have never been reported in female carriers of XLRS.2,10,15 In fact, phenotypic expression of XLRS in carrier state has only been reported in monosomy X, consaguinuity, uniparental dysomy, or skewed X-inactivation.10,15–17
Indeed on further testing, our family had a deletion in exon 4 of the CRX gene. This proved the maculopathy to be cystoid and associated with an autosomal dominant retinal dystrophy. The overlap in FAF findings between CME and non-CME macular cystoid spaces suggests that perhaps FAF is helpful in early detection of macular changes rather than in diagnosing a specific retinal disorder. The possible involvement of various retinal layers in XLRS makes the differentiation from cystoid macular edema (CME) or cystoid maculopathy associated with other retinal dystrophies difficult by OCT