Electrophysiological Evaluation of Macular Dystrophies

Macular dystrophies are a heterogeneous group of genetic disorders that often severely threatens the bilateral central vision of the affected patient. While advances in molecular genetics have been instrumental in the understanding and diagnosis of these disorders, there remains significant phenotypical variation among patients within any particular subset of macular dystrophies. Electrophysiological testing remains a vital tool not only to characterize vision loss for differential diagnosis but also to understand the pathophysiology of these disorders and to monitor the treatment effect, potentially leading to therapeutic advances. This review summarizes the application of electrophysiological testing in macular dystrophies, including Stargardt disease, bestrophinopathies, X-linked retinoschisis, Sorsby fundus dystrophy, Doyne honeycomb retina dystrophy, autosomal dominant drusen, occult macular dystrophy, North Carolina macular dystrophy, pattern dystrophy, and central areolar choroidal dystrophy.

New Noncoding Base Pair Mutation at the Identical Locus as the Original NCMD/MCDR1 in a Mexican Family, Suggesting a Mutational Hotspot

Purpose

To clinically and molecularly study a newly found family with North Carolina macular dystrophy (NCMD/MCDR1) from Mexico.

Methods

This retrospective study comprised 6 members of a 3-generation Mexican family with NCMD. Clinical ophthalmic examinations, including fundus imaging, spectral-domain optical coherence tomography, electroretinography, and electrooculography, were performed. Genotyping with polymorphic markers in the MCDR1 region was performed to determine haplotypes. Whole-genome sequencing (WGS) was performed followed by variant filtering and copy number variant analysis.

Results

Four subjects from 3 generations were found to have macular abnormalities. The proband presented with lifelong bilateral vision impairment with bilaterally symmetric vitelliform Best disease-like appearing macular lesions. Her 2 children had bilateral large macular coloboma-like malformations, consistent with autosomal dominant NCMD. The 80-year-old mother of the proband had drusen-like lesions consistent with grade 1 NCMD. WGS and subsequent Sanger sequencing found a point mutation at chr6:99593030G>C (hg38) in the noncoding region of the DNase I site thought to be a regulatory element of the retinal transcription factor gene PRDM13. This mutation is the identical site/nucleotide as in the original NCMD family (#765) but is a guanine to cytosine change rather than a guanine to thymine mutation, as found in the original NCMD family.

Conclusions

We report a new noncoding mutation at the same locus (chr6:99593030G>C) involving the same DNase I site regulating the retinal transcription factor gene PRDM13. This suggests that this site, chr6:99593030, is a mutational hotspot.

The possible pathogenesis of macular caldera in patients with North Carolina macular dystrophy

BACKGROUND

This study provides a detailed description of a Chinese family with North Carolina macular dystrophy (NCMD) and explores its possible pathogenesis.

METHODS

Five individuals from a three-generation family underwent general ophthalmic examination, multi-imaging examinations and visual electrophysiology examinations when possible. Genetic characterization was carried out by target region sequencing and high-throughput sequencing in affected patients.

RESULTS

Despite severe fundus changes, patients had relatively good visual acuity. Genetic analysis showed that affected patients had PRDM13 gene duplication and heterozygous mutations of the ABCA4 gene. Optical coherence tomography (OCT) showed an abnormal retinal pigment epithelium (RPE) layer in patients with grade 2 lesions, while the neurosensory retina was relatively normal. In grade 3 patients, RPE and choroid atrophy were greater than that of the neurosensory retina, showing concentric atrophy.

CONCLUSIONS

RPE and choroidal atrophy were found to play an important role in the development of macular caldera.

A novel tandem duplication of PRDM13 in a Chinese family with North Carolina macular dystrophy

PURPOSES

North Carolina macular dystrophy (NCMD) is a rare autosomal dominant inherited disorder characterized by macular impairment with a variety of phenotypic manifestations. The aims of this study were to assess the clinical features of a Chinese family with NCMD and to identify the underlying genetic cause of the disease.

METHODS

Three patients from a Chinese family were included in this study. Detailed ophthalmological examinations were performed, including best corrected visual acuity (BCVA), slit lamp, dilated indirect ophthalmoscopy, fundus photography, optical coherence tomography (OCT), fundus autofluorescence, full-field electroretinography (ERG), and electrooculography (EOG). Genomic DNA was extracted from peripheral blood samples. Whole-genome sequencing and long-read genome sequencing were applied to detect the pathogenic variants. Sanger sequencing was performed to confirm the breakpoints.

RESULTS

All three patients had macular involvement ranging from patchy yellowish-white lesions to big-area thinning, which are typical for NCMD. The BCVA ranged from 20/50 to 20/20. OCT revealed varying degrees of macular structure disorganization. The ERG responses were normal, and the Arden ration of the EOG was reduced. A novel 134.6 kb (g.99932464-100067110dup) tandem duplication on chromosome 6 (NC_000006.11) encompassing the entire CCNC and PRDM13 genes and a DNase 1 hypersensitivity site in the MCDR1 locus was identified.

CONCLUSION

A novel large tandem duplication in MCDR1 locus was confirmed in a Chinese family with NCMD with a variety of macular phenotypes.