Disease-causing Gene Identification Of Human Juvenile Macular Dystrophy

Eye is one of most important organs of human being, the function of eye is to collect information of outside of the world and then transfer this information to brain to form an image-the vision of human being. The principle of how an eye works is similar to the principle of which a camera works. A camera collects an image of an object through its lens and generates an image in a film; similarly human eyes collect the lights of objects through cornea, lens and generate images in the retinal, then the retinal transfer the images to brain and produce a vision. In this process, the retinal, a soft thin tissue, plays a most important role. A retinal can be divided into a central retinal region where is macular located and a peripheral retinal region. Retinal dystrophy may result in a vision loss or even cause legally blindness. When a macular is involved in a dystrophy, we call this phenotype macular dystrophy. Macular dystrophy can be happened in juvenile which is juvenile macular dystrophy or in old people which is age-related macular degeneration. The main cause of juvenile macular dystrophy is the mutant genes which regulate the development of retinal macular or play a critical role in maintain the normal function of retinal macular. Unfortunately, so far we do not have affective methods yet for early diagnosis, treatment and prevention of juvenile macular dystrophy. The disease-causing gene identification of juvenile macular dystrophy will eventually help us to understand the pathogenesis of this disease, and will provide the possibilities of early diagnosis, therapy and prevention of this disease. In this study, we collected large pedigrees of juvenile macular dystrophy to study the genetic mutation of affected patients using genetic linkage analysis, sequencing analysis and the successful results of human genome project. The main achievements of this study are listed below:1. Collection of large families of juvenile macular dystrophyJuvenile macular dystrophy is a group of monogenic diseases. Positional cloning is a very powerful method for the disease-causing gene identification of monogenic diseases in which the disease linked loci are mapped by linkage analysis using large disease related families. So, the pedigree collection, especially large families, is a critical part for monogenic disease gene study. The phenotype determination of a disease is very important for genetic study because misdiagnosis will result in a wrong linked locus or no true locus mapped. In this study, we collected 2 well-characterized macular dystrophy families for further studies.2. The disease locus/gene identification by linkage analysis and mappingThe genetic study of juvenile macular dystrophy is actually to identify the known loci/genes and mutation or to map and identify novel loci/genes.(1) Identification of a disease locus/gene and a mutation for a pedigree by linkage analysis and sequencing analysis of known genes.Bardet-Biedl syndrome is an autosomal recessive disorder characterized by pleiotropic defects, retinal dystrophy is one of the main clinical features. We collected a large Chinese consanguineous family with Bardet-Biedl syndrome. After the clinical phenotype was carefully determined and DNA was extracted from blood of the patients, we performed linkage analysis for this family using short tandem repeat (STR) marker for all 13 known BBS loci or 14 know BBS genes. We found that the disease of this family is linked to BBS7/BBS12 locus, and we identified a disease-causing mutation S556R in BBS7 in this family after the sequence analysis. This is the first time to identify a disease-causing mutation in a Chinese BBS family, and this mutation is a novel mutation in BBS7.(2) A novel juvenile macular dystrophy locus mapped by a whole genome wide scanAlthough several disease loci/genes responsible for macular dystrophy have been identified, no of them has been identified through Chinese population study. In current study, we collected a large pedigree with autosomal dominant retinal dystrophy. The disease phenotype of this family is unique characterized by macular dystrophy in the central retinal and retinal retinitis pigmentosa (RP) in the peripheral retinal. After known loci for retinal dystrophy were excluded by linkage analysis using short tandem repeat (STR) markers, we performed a whole genome wide scan using a cutting-edge technique-The HumanLinkage-12 BeadChip of Illumina Company of United States. In this method, 6090 Single nucleotide polymorphism (SNP) in human chromosomes have been used for linkage analysis. Then we calculated the Lod Scores which indicate a distance between the position of SNP and the disease-causing gene of the family. After the whole genome wide scan and linkage analysis, we identified the strong positive signals, in which one of the loci was a true linked locus for this family.3. Identification of a novel disease locus of retinal dystrophy and determination of the minimum genetic interval (MGI) for this locusThe true disease locus had to be further confirmed by halotype analysis for all strong positive loci based on the previous whole genome wide scan and analysis. Then the minimum genetic interval (MGI) for this locus was narrowed down by haplotype analysis. Through these steps, we linked the disease locus of this family to 7p21-a novel disease locus for retinal dystrophy.