GENETIC LINKAGE STUDY OF PRIMARY CONGENITAL GLAUCOMA

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Primary Congenital Glaucoma (PCG) is an inherited eye disorder that is responsible for 0.01-0.04% of the blind people. In majority of cases PCG is inherited as an autosomal recessive trait and genetic redisposition regarded as a major factor in the development of this condition. Accordingly, we are proposing to identify and characterize the genetic factors underlying this condition by genetic linkage analysis and positional mapping. Through the study of multiply affected families with PCG, and by virtue of positional mapping our specific aim is to map the PCG gene. In order to achieve this, we have identified and ascertained over 80 families segregating for PCG. This panel is consist of a total of 105 affecteds (67 M & 38 F) and 173 sibs of probands (84 M & 89 F) providing a total of 261 potential informative meioses. Of these, a total of 25 families have already been sampled. We have selected a group of 19 families as our initial screening panel consisting of 2-4 affected sibs and up to 11 normal sibs. Most of the affected were born to two consanguineous marriages, thus ensuring the recessive mode of inheritance. This panel consists of 44 affected and 55 normal sibs, providing a total of 99 potential informative meioses. By using this panel, we are planning to search for genetic linkage of PCG with a series of DNA markers from region of certain chromosomes (i.e., 2q33-qter, 3q26-q27, distal portion of 6p, 9p24-pter, 11p 15, 11q12 and 16p) that are suggested to be associated with this phenotype. We use PCR and Silver staining to genotype our families for linkage evaluation (LOD score method). We have so far performed 1,317 genotypes on 17 DNA markers and excluded the PCG locus from certain regions of chromosomes 1, 6 and 9. We will continue our genotyping from other regions using highly polymorphic DNA markers (i.e., Simple Tandem Repeat Polymorphisms). This process will continue until the linkage of PCG is established and possibility of genetic heterogeneity amongst PCG families is explored. Saturation mapping and construction of multipoint linkage map flanking the PCG locus will then be initiated. If a functional gene is identified as the cause of PCG screening for mutations will be constituted by PCR-SSCP. The long term objective of this proposal is the identification of a biological marker that can be used for prenatal testing and early diagnosis of at risk individuals. This will be the first critical step for cloning of the PCG gene and identification of individual mutations which could explain the precise pathological mechanisms leading to this condition. This will also provide an initial step in understanding the complexity of the human eye, its embryology and function, that eventually leads to the development of specific rational medical or surgical treatment.