Identification of an intronic single-point mutation in RP2 as the cause of semidominant X-linked retinitis pigmentosa.
OBJECTIVE
A large family with 11 males and 2 females with X-linked retinitis pigmentosa (XLRP) was analyzed in search of pathologic mutations.


METHODS
Of the two major XLRP genes, RPGR was analyzed by SNP cosegregation and RP2 was directly screened for mutations. The pathogenicity of a new variant was assessed in silico, in vivo, and in vitro.


RESULTS
The results of cosegregation analysis with SNPs closely located to RPGR excluded this gene as the cause of the disease in this family. Sequencing of RP2 showed a putative pathogenic variant in intron 3 at the conserved polypyrimidine tract (c.1073-9T>A). This substitution cosegregated with the disease and was not found in 220 control chromosomes. In silico analyses using online resources indicated a decreased score of intron 3 acceptor splice site for the mutated sequence. Real-time RT-PCR analysis of the RP2 splicing pattern in blood samples of patients and carrier females showed skipping of exon 4, causing a frame shift that introduced a premature stop codon. Further verification of the pathogenicity of this point mutation was obtained by expression of a minigene RP2 construct in cultured cells.


CONCLUSIONS
A transversion (T>A) at position -9 in intron 3 of RP2 causes XLRP by altering the splicing pattern and highlights the pathogenicity of intronic variants. The single point RP2 mutation leads to a wide range of phenotypic traits in carrier females, from completely normal to severe retinal degeneration, thus supporting that RP2 is also a candidate for semidominance in XLRP.
Pomares
Esther
E
Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Barcelona, Spain.
Riera
Marina
M
Castro-Navarro
Joaquín
J
Andrés-Gutiérrez
Angeles
A
Gonzàlez-Duarte
Roser
R
Marfany
Gemma
G
D000293:Adolescent; D000328:Adult; D005136:Eye Proteins / Q000235:genetics*; D005260:Female; D019204:GTP-Binding Proteins; D040181:Genetic Diseases, X-Linked / Q000235:genetics*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics*; D007438:Introns / Q000235:genetics*; D008297:Male; D008565:Membrane Proteins / Q000235:genetics*; D008875:Middle Aged; D010375:Pedigree; D017354:Point Mutation; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D012174:Retinitis Pigmentosa / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D005136:Eye Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C072178:RP2 protein, human; C099929:RPGR protein, human; D019204:GTP-Binding Proteins