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PRPF31-associated retinitis pigmentosa presents a fascinating enigma: some mutation carriers are blind, while others are asymptomatic. We identify the major molecular cause of this incomplete penetrance through three cardinal features: (1) there is population variation in the number (3 or 4) of a minisatellite repeat element (MSR1) adjacent to the PRPF31 core promoter; (2) in vitro, 3-copies of the MSR1 element can repress gene transcription by 50 to 115-fold; (3) the higher-expressing 4-copy allele is not observed among symptomatic PRPF31 mutation carriers and correlates with the rate of asymptomatic carriers in different populations. Thus, a linked transcriptional modifier decreases PRPF31 gene expression that leads to haploinsufficiency. This result, taken with other identified risk alleles, allows precise genetic counseling for the first time. We also demonstrate that across the human genome, the presence of MSR1 repeats in the promoters or first introns of genes is associated with greater population variability in gene expression indicating that copy number variation of MSR1s is a generic controller of gene expression and promises to provide new insights into our understanding of gene expression regulation.

Original publication




Journal article


Scientific reports

Publication Date





UCL Institute of Ophthalmology, University College London, London, EC1V 9EL, UK.


Humans, Retinitis Pigmentosa, Eye Proteins, Genetics, Population, Gene Expression, Transcription, Genetic, Gene Expression Regulation, Binding Sites, Repetitive Sequences, Nucleic Acid, Conserved Sequence, Gene Frequency, Genotype, Phenotype, Penetrance, Alleles, Genes, Reporter, Scavenger Receptors, Class A, Promoter Regions, Genetic, Position-Specific Scoring Matrices, DNA Copy Number Variations, Nucleotide Motifs