Identification Of The Causative Gene Of A Nonsyndromic Retinitis Pigmentosa Pedigree

Retinitis Pigmentosa (RP) is a most commom genetic eye disorder which is caused by the progressive degeneration of retinal photoreceptor cells (including rods and cones) or retinal pigment epithelial cells leading to progressive loss of vision. The incidence of this disease in Han population reaches up to1/1000. The pathogenesis of RP is reasonably complicated involved with diverse biological pathways. According to the clinical features RP can be classified into2forms:nonsyndromic and syndromic, the nonsyndromic RP encompassing65%of all cases. RP possesses the extremely complicated inheritance patterns, including the classical Mendelian inheritance mode and other rare atypical inheritance patterns. Almost42%of nonsyndromic RP cases are sporadic, without any family history of RP. Furthermore, RP have the tremendous genetic and phenotypic heterogeneity, and there are at least65genes related to this disease. However, these RP-related genes altogether account for only about60%of RP cases, about40%RP cases are still left with unknown mechanisms.Purpose:This study was aimed to detect the underlysing pathogenic mutation and explore its pathogenesis in a NSRP pedigree always maintaining unknown genetic status since they came to our lab, and provide the genetic counseling and procreation guidance for the patients and other family members to avoid the birth defect of RP.Methods:1. Based on the previous genetic analysis, we perform the PCR and Sanger sequencing on one patient of the NSRP pedigree to further screen the mutations of SNRNP200and KLHL7.2. We perform Multiplex Ligation-dependent Probe Amplification (MLPA) on one patient of the NSRP pedigree to detect the deletions and duplications mutations of RP-related genes including RHO、RP1、 IMPDH1、PRPF31、RP2and RPGR.3. We perform Exome Sequencing on two patients of the NSRP pedigree to identify the underlying pathogenic mutations by combination with bioinformatics analysis.Results:1. The SNRNP200and KLHL7genes pathogenic mutations were not found in this pedigree by sanger sequencing;2. The RP-related genes deletions and duplications mutations were not found in this pedigree by MLPA;3. Combining exome sequencing and bioinformatics analysis, it revealed the presence of2heterozygous mutations c.784G>A (p.Glu262Lys) and c.787G>A (p.Glu263Lys) in APOE gene. These two mutations located on the same one chromosome, forming a rare mutant of ApoE7-Suita. The mutant is co-segregation with the disease and not found in200unrelated controls. Additionally, C.2030C>A heterozygous mutation of PDE6B gene has been found in all patients of this pedigree, which is not co-segregation with phenotype.Conclusion:1. Based on the early genetic analysis, we excluded micromutations in coding sequences of SNRNP200and KLHL7by Sanger Sequencing. Meanwhile, large duplications and deletions in exons of RHO, RP1, IMPDH1, PRPF31, RPGR and RP2have also been excluded by MLPA. 2. This is the first report founding that a rare mutant of APOE gene is co-segregation in RP family by the application of exome sequencing combining with bioinformatics analysis, accroding to which we speculate that APOE gene mutations are probablely related with RP.3. Since the heterozygous mutation of C.2030C>A in recessive gene PDE6B exists in all patients of this pedigree, the possibility of the combined action of PDE6B and APOE in pathogenesy of RP could not be denied absolutely...