The Traboulsi Laboratory

Director: Elias I. Traboulsi, M.D.
Department of Ophthalmic Research
Cole Eye Institute
9500 Euclid Avenue, i32
Office telephone: 216/ 444-5822
Fax: 216/ 445-3670
Email: traboue@ccf.org

Front Row: Elias I. Traboulsi, M.D.
Back Row: Kholoud Al-khayer, M.D., Daniel Chung, D.O., and Ahmad Yazdani, M.D.

Goals and Projects of The Center for Genetic Eye Diseases and the Traboulsi and Hagstrom Laboratories:

The Center for Genetic Eye Diseases houses the DNA collection from patients with a wide range of inherited eye diseases and malformations of the eye and ocular adnexae. The patients are recruited from the Cole Eye Institute and from collaborating physicians and scientists from around the United States and the world. The collection is comprised of several thousand DNA samples and is expanding. Dr. Traboulsi’s laboratory team works very closely with that of Stephanie Hagstrom, Ph.D., and several of the projects are combined between the two laboratories.

Gene Mapping Projects:

Identification of a New Gene for Autosomal Dominant Congenital Posterior Polar Cataracts on Chromosome 10q.  (In collaboration with Drs. Qing Wang and Andre Megarbane)

Congenital cataracts are an important cause of visual impairment in infants, children and adults. Between 25% and 50% of cases are inherited, most often in an autosomal dominant fashion. To date, 19 loci and 11 genes have been identified for inherited cataracts. The purpose of this study is to refine the chromosomal locus, screen candidate genes and identify a novel gene for autosomal dominant congenital posterior polar cataracts on chromosome 10q. We have recruited a four-generation Lebanese family with congenital posterior polar cataracts for this study. Forty members were examined clinically and blood samples were collected for DNA extraction after informed consent was obtained. A genome-wide screen for the responsible locus was conducted using fluorescein-labelled microsatellite markers spaced at 10cM intervals. Genotyping was done and linkage analysis was performed.

Two-point LOD scores were calculated using MLINK in LINKAGE version 5.2. A significant positive LOD score of 3.56 at a recombination fraction of 0.00 (q = 0.00) was found with marker D10S2470 in the chromosomal 10q24-q26 region. D10S2470 is located in a 16 cM interval between markers D10S2327 and D10S677, both of which yielded negative LOD scores. Screening of the PITX3 gene which is associated with congenital cataracts and maps in the same general chromosomal region failed to show any mutations.

We propose to refine and narrow this chromosomal locus, and to screen candidate genes in the region for mutations. The refinement of the locus involves constructing fluorescein-labeled microsatellite markers at 2 cM intervals from marker D10S2470, genotyping family members for these markers, and performing linkage analysis to further narrow the locus. Screening candidate genes in the refined chromosomal region will be conducted using single strand conformation polymorphism (SSCP) and direct genomic sequencing. Direct sequencing of genomic sequences from patients and unaffected individuals will allow the identification of the responsible mutation.

The identification of additional genes for congenital cataracts will allow a better understanding of the pathogenesis and this important group of disorders and will shed light on possible modes of future prevention and therapy.

The Genetics of Keratoconus

Keratoconus is a progressive non-inflammatory condition in which the cornea protrudes as it becomes thinner and assumes a conical shape. Patients with this disease experience a decrease in visual acuity from high astigmatism, and later from corneal edema and opacification. Reduced vision from keratoconus remains the most common indication for penetrating keratoplasty.

To date, no definite genetic loci for familial keratoconus have been identified using linkage analysis in informative pedigrees. Mutations in a few sporadic cases of keratoconus and posterior polymorphous corneal dystrophy have been recently reported in VSX1, a developmental gene presumed to be important in retinal growth. In the present study, we plan to identify the gene(s) responsible for keratoconus.

We propose:

1. To locate the chromosomal locus/(loci) for keratoconus in selected families that exhibit an autosomal dominant pattern of inheritance. Genome-wide screen will be done utilizing fluorescein-labeled microsatellite DNA markers.

2. To identify mutations in the VSX1 gene that presumably cause a minority of cases of keratoconus. This will be done through conventional mutation analysis techniques.

3. To identify the causative gene for keratoconus. This will be achieved through candidate gene analysis in the chromosomal region that will be identified as containing the locus for keratoconus and/or through the cloning of genes from that region.

Polychromasia capsulare is an uncommon autosomal dominant lens disorder characterized by a circular peripheral polychromatic band of the anterior lens capsule. A green hue to the capsule is most prominent, but a variety of colors are also observed on slit-lamp examination. Vision is not affected, even in individuals in their 50s. The trait has been detected in very early childhood, and may be possibly present from birth.

We identified a large Ohio pedigree with this condition that spans four generations. Nine of twenty-five members exhibit the trait. Blood samples have been collected and DNA has been extracted. We propose to map the gene for this disorder using conventional genotyping and linkage analysis methods. This will lay the groundwork for further genetic investigation of candidate genes in the region of the gene locus. The identification of the gene involved in this condition will provide insight into the physiology and metabolism of the lens epithelium and its capsule. The lens capsule is abnormal in such common disorders as pseudoexfolation and less common genetic diseases such as Alport syndrome and Wilson’s disease.

It is probable that the discoloration of the capsule in polychromasia capsulare is a result of either an abnormality of basement membrane formation or the deposition of abnormal material by the lens epithelium in that portion of the capsule. The understanding of the pathophysiology of polychromasia capsulare will also potentially improve our understanding of the mechanism of copper deposition and cataract formation in Wilson’s disease, benign monoclonal gammopathy and hypercupremia, and thus provide clues to their therapy.

Mutation Analysis Projects:

These are projects aimed at identifying mutations of candidate genes in selected patients. The results of the mutation screens are then combined with the phenotypic information to gain a better understanding of the molecular etiology of inherited diseases and the effects of individual mutations on the clinical phenotype.

The RPE65 gene (retinal pigment epithelium) is located on chromosome 1. Mutations are associated with Leber Congenital Amaurosis (LCA),  a severe congenital retinal dystrophy involving rods and cones. We screened 30 patients from families with at least one affected member. We found two mutations in the RPE65 gene that consists of 14 exons. One of the mutations was in exon 2, a two base pair deletion, the other in exon 9, a base substitution that caused a stop mutation (nonsense) and creates a restriction site in the same exon . It is important to detect RPE65 mutations in humans because of the successful gene therapy of the retinal degeneration in a dog with a mutation of this gene.

 The CRX gene (cone–rod homeobox) is located on chromosome 19. Mutations are also associated with LCA. We screened the same patients using the same methodology in the previous project . No mutations have been found to date.

Mutation analysis of the other genes that cause LCA are under way.

 The FOXC2 gene (Homo sapiens forkhead box C2) is located on chromosome 6 and consists of one exon. Mutations cause an additional row of eyelashes associated with lymphedema in the lower limbs. We found a disease-causing mutation in one Cleveland family with the distichiasis-lymphedema syndrome.

The ARIX gene has been found to be mutated in patients with recessive congenital fibrosis of the extraocular muscles (CFEOM2). An ongoing collaborative study with Dr. Ahmad Yazdani from Mashad, Iran, has resulted in the discovery in our laboratory of the first nonsense mutation in this gene, establishing it as the gene causing this rare form of strabismus. We continue to collaborate with Dr. Elizabeth Engle from Boston Children’s Hospital on the study of this group of disorders of extraocular motor nuclei development. Dr. Yazdani has spent a year of sabbatical research work in our laboratory working on the identification of mutations in CFEOM.

Mutations in EFEMP1 cause an autosomal dominant form of drusen and macular degeneration called malattia leventinese or Doyne’s macular dystrophy. We identified a mutation in EFEMP1 in an Ohio/Baltimore family and currently collaborate with Cole Eye Institute colleague Alan Marmorstein, Ph.D., and his team on finding more about the role of EFEMP1 in the genesis of macular degeneration.

Daniel Chung, D.O., is a fellow in pediatric ophthalmology and ophthalmic genetics. He is in his second year of training and works on the genetic mapping of congenital cataracts and keratoconus. After graduating from medical school, Dr. Chung served as a research fellow at the National Eye Institute. He completed his residency training in ophthalmology in Akron, Ohio.

Ahmad Yazdani, M.D., is a visiting research physician from Mashad, Iran, and works on the genetics of congenital fibrosis of the extraocular muscles.

Al-Khayyer, M.D., is a research assistant and works on the genetics of Leber Congenital Amaurosis and other mutation analysis projects in the laboratory.

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