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Recessive mutations in CLN7/MFSD8 usually cause variant late-infantile onset neuronal ceroid lipofuscinosis (vLINCL), a poorly understood neurodegenerative condition, though mutations may also cause nonsyndromic maculopathy. A series of 12 patients with nonsyndromic retinopathy due to novel CLN7/MFSD8 mutation combinations were investigated in this study.Affected patients and their family members were recruited in ophthalmic clinics at each center where they were examined by retinal imaging and detailed electrophysiology. Whole exome or genome next generation sequencing was performed on genomic DNA from at least one affected family member. Immunofluorescence confocal microscopy of murine retina cross-sections were used to localize the protein.Compound heterozygous alleles were identified in six cases, one of which was always p.Glu336Gln. Such combinations resulted in isolated macular disease. Six further cases were homozygous for the variant p.Met454Thr, identified as a founder mutation of South Asian origin. Those patients had widespread generalized retinal disease, characterized by electroretinography as a rod-cone dystrophy with severe macular involvement. In addition, the photopic single flash electroretinograms demonstrated a reduced b- to a-wave amplitude ratio, suggesting dysfunction occurring after phototransduction. Immunohistology identified MFSD8 in the outer plexiform layer of the retina, a site rich in photoreceptor synapses.This study highlights a hierarchy of MFSD8 variant severity, predicting three consequences of mutation: (1) nonsyndromic localized maculopathy, (2) nonsyndromic widespread retinopathy, or (3) syndromic neurological disease. The data also shed light on the underlying pathogenesis by implicating the photoreceptor synaptic terminals as the major site of retinal disease.

Original publication

DOI

10.1167/iovs.16-20608

Type

Journal article

Journal

Investigative ophthalmology & visual science

Publication Date

06/2017

Volume

58

Pages

2906 - 2914

Addresses

University College London Institute of Ophthalmology, London, United Kingdom 2Inherited Eye Disease Service, Moorfields Eye Hospital, London, United Kingdom 3Section of Ophthalmology and Neuroscience, Leeds Institute of Biomedical and Clinical Sciences, University of Leeds, St. James's University Hospital, Leeds, United Kingdom 4Department of Ophthalmology, St. James's University Hospital, Leeds, United Kingdom.

Keywords

for NIHR BioResource-Rare Diseases and UK Inherited Retinal Disease Consortium, Presynaptic Terminals, Humans, Membrane Transport Proteins, DNA, Microscopy, Confocal, Pedigree, DNA Mutational Analysis, Homozygote, Mutation, Adult, Middle Aged, Female, Male, Photoreceptor Cells, Vertebrate, Retinal Dystrophies, High-Throughput Nucleotide Sequencing, Exome