Tamara R. Vrabec

Clinical variability of Stickler syndrome: role of exon 2 of the collagen COL2A1 gene.

Stickler syndrome (progressive arthro-ophthalmopathy) is a genetically heterogeneous disorder resulting from mutations in at least three collagen genes. The most common disease-causing gene is COL2A1, a 54-exon-containing gene coding for type II collagen. At least 17 different mutations causing Stickler syndrome have been reported in this gene. Phenotypically, it is also a variably expressed disorder in which most patients present with a wide range of eye and extraocular manifestations including auditory, skeletal, and orofacial manifestations. Some patients, however, present without clinically apparent systemic findings. This observation has led to difficulty distinguishing this Stickler phenotype from other hereditary vitreoretinal degenerations, such as Wagner syndrome and Snowflake vitreoretinal degeneration. In this regard, review of the literature indicates type II collagen exists in two forms resulting from alternative splicing of exon 2 of the COL2A1 gene. One form, designated as type IIB (short form), is preferentially expressed in adult cartilage tissue. The other form, designated as type IIA (long form), is preferentially expressed in the vitreous body of the eye. Because of this selective tissue expression, mutations in exon 2 of the COL2A1 gene have been hypothesized to produce this Stickler syndrome phenotype with minimal or absent extraocular findings. We review the evidence for families with exon 2 mutations of the collagen COL2A1 gene presenting in a distinct manner from families with mutations in the remaining 53 exons, as well as other hereditary vitreoretinal degenerations without significant systemic manifestations.

S-Antigen: preparation and characterization of site-specific monoclonal antibodies

Previous attempts to prepare monoclonal antibodies (MAbs) against S-antigen, a photoreceptor cell protein involved in the visual process and a potent autoantigen for the induction of experimental autoimmune uveitis (EAU), have yielded MAbs which define only carboxyl terminal epitopes. In this study we devised alternate strategies to prepare five MAbs directed to other regions of the molecule. MAbC10C10 and MAbH11-A2 were prepared against synthetic peptides known to be uveitopathogenic and they were selected for more detailed studies. MAbC10C10 was generated against synthetic peptide BSA281-302 which contains a predictive consensus sequence for defined T cell epitopes (GIALD) as well as a consensus sequence for GTP-binding proteins. One human adenosine deaminase synthetic peptide containing an extensive amino acid sequence homology to BSA281-302 was a potent inhibitor of MAbC10C10 binding in a competitive inhibition radioimmunoassay. MAbH11-A2 was generated against peptide BSA303-332 which also contains a uveitopathogenic site. The binding site of MAbH11-A2 was determined to be within amino acid positions 305 to 314 (NLASSTIIKE) in S-antigen. This binding site corresponded closely to the binding site of an affinity-purified rat polyclonal antibody raised to human S-antigen. MAb5C6.47 was isolated from a mouse hyperimmunized with bovine S-antigen and was specific for a highly conserved sequence near the amino terminus, amino acid residues 42 to 48 (DGVVLVD). Both MAbC10C10 and MAb5C.47 were useful in screening gt11 cDNA libraries expressing S-antigen polypeptides as fusion proteins. Our results demonstrate the feasibility of producing site-specific MAbs potentially useful in the study of T cell-mediated immune mechanisms in EAU as well as in the phototransduction of vision.

Identification of a stop codon mutation in exon 2 of the collagen 2A1 gene in a large stickler syndrome family

PURPOSEnTo describe the clinical features and identify the mutation responsible for an autosomal dominant vitreoretinal degeneration occurring in a previously unreported large family.nnnDESIGNnCohort study.nnnMETHODSnFamily members were evaluated clinically over a 30-year period. Genealogical investigation, genetic linkage to known vitreoretinal degenerations, and mutation screening of the COL2A1 gene were performed.nnnRESULTSnWe identified a single large family (2,384 total family members) with vitreoretinal degeneration spanning 12 generations. We reviewed the clinical records of 165 family members (95 affected and 70 unaffected). The common clinical findings in affected individuals included early-onset posterior perivascular retinal degeneration, vitreous degeneration, and retinal detachment. The incidence of retinal detachment was 57% (95/165) and the mean age of onset was 15.2 years. Orofacial, skeletal, and auditory abnormalities were seen in 0%, 5%, and 7.5%, respectively, in a subset of 28 affected subjects. Linkage to the collagen COL2A1 locus was demonstrated and a cytosine to adenosine transition identified within exon 2, leading to the creation of a stop codon at position 86 (Cys86Stop).nnnCONCLUSIONSnIdentification of the mutation in this family enables diagnosis of individuals at risk for potentially blinding complications in this condition at an early age. Given the variability of the Stickler phenotype, mutation detection allows for more comprehensive genetic counseling and directs clinical monitoring to family members inheriting the disease gene.

Autosomal dominant Stargardt-like macular dystrophy.

Autosomal dominant Stargardt-like macular dystrophy is one of the early onset macular dystrophies. It is characterized clinically in its early stages by visual loss and by the presence of atrophic macular changes with or without the presence of yellowish flecks. It is an important retinal dystrophy to study, not only because it has implications in the care and treatment of patients with the condition, but because it also provides important information regarding retinal function. Review of the literature suggests that many of the reported families are linked to chromosome 6q. Genetic and genealogical evidence suggests that these families have descended from a common ancestor or founder. The recent identification of a disease-causing gene that is involved in fatty acid metabolism may have implications in the study of the more common age-related macular degeneration. We review the recent clinical, genetic, and genealogical aspects of autosomal dominant Stargardt-like macular dystrophy.

Inhibition of Experimental Autoimmune Uveoretinitis by Oral Administration of S-Antigen and Synthetic Peptides

S-Antigen, a photoreceptor cell protein, is highly efficient in inducing experimental autoimmune uveoretinitis (EAU), a severe inflammation of the uveal tract and retina of the eye. S-Antigen and six synthetic peptides, all of which correspond to known T-cell or B-cell recognition sites, were tested for their ability to induce oral tolerance to EAU in LEW rats. Feeding three 1-mg doses of native S-Antigen or three doses of one synthetic peptide, designated BSA(343-362) (200 micrograms per dose), reduced the incidence and severity of EAU induced by immunization with 50 micrograms of S-Antigen. Another peptide, BSA(270-289), was able to inhibit EAU only when a low dose (10 micrograms) of the uveitogenic S-Antigen was used to induce EAU. Animals which received 200 micrograms doses of four other immunologically active peptides, BSA(31-51), BSA(143-162), BSA(303-327) and BSA(333-352), were not significantly protected. Furthermore, animals fed BSA(343-362) were significantly less susceptible to EAU induced by adoptive transfer (tEAU) of the uveitogenic R9 T-cell lines. Con A-activated lymphocytes purified from spleens of rats fed peptide BSA(343-362) transferred partial resistance to tEAU induced by adoptive transfer of R9 line cells. The resistance of orally tolerized rats to induction of EAU by adoptive transfer of an activated, pathogenic T-cell line, and the ability of lymphocytes from orally-tolerized animals to transfer resistance to tEAU shows that effector mechanisms can be inhibited by oral feeding as well as the afferent mechanisms reported here and elsewhere. Circulating levels of IgG specific for S-Antigen were not affected by feeding any of the peptides.

Taches de Bougie

BACKGROUNDnPosterior segment lesions, including taches de bougie, may be the presenting sign of sarcoidosis. In patients with unrecognized sarcoidosis, taches de bougie may be misinterpreted as the lesions of birdshot chorioretinopathy (BCR) or multifocal choroiditis (MFC).nnnMETHODSnIn a retrospective study, the authors identified 22 patients with taches de bougie and sarcoidosis. A tissue biopsy showed noncaseating granulomas in 17 patients. All available ophthalmic and medical records of these patients were reviewed.nnnRESULTSnTwo patterns of taches de bougie were observed. Sixteen patients (73%) had small, discrete white spots in the inferior or nasal periphery, indistinguishable from the lesions of MFC. In six patients (27%), larger, posterior, pale yellow-orange streaks developed that were identical to the lesions of BCR. Visual prognosis was better with posterior streaks. The chest x-ray was normal in 5 of 16 patients with peripheral spots and in 3 of 6 patients with posterior streaks. Serum angiotensin-converting enzyme was negative in 5 of 14 patients. Gallium scan showed increased hilar uptake in five patients, three of whom had a normal chest x-ray. Human lymphocyte antigen A29 was positive in one of nine patients.nnnCONCLUSIONSnSarcoidosis should be considered in patients with fundus findings that resemble BCR or MFC. Initial evaluation should include chest x-ray and testing the angiotensin-converting enzyme level. These test results may be negative in patients outside the 20- to 40-year age group for typical sarcoid. Further evaluation with nondirected conjunctival biopsy and whole-body gallium scan may be indicated in certain patients, including (1) those with BCR or MFC with normal chest x-ray and elevated angiotensin-converting enzyme level; (2) patients older than 50 years with MFC; or (3) human lymphocyte antigen A29-negative BCR.

X-linked retinoschisis: report of a family with a rare deletion in the xLRS1 gene ☆

PURPOSEnTo describe the clinical features and identify the disease causing mutation in a family with X-linked retinoschisis.nnnDESIGNnCohort study.nnnMETHODSnGenealogical investigation and mutation screening of the XLRS1 gene were performed in a four generation family of Icelandic ancestry. Three affected family members were evaluated clinically over a 29-year period.nnnRESULTSnA rarely reported, four base pair deletion (375- 378 del AGAT) in exon 5 of the XLRS1 gene was found in all affected males. A high degree of intrafamilial variability was observed in the progression of the disorder over 29 years.nnnCONCLUSIONSnIdentification of the disease causing mutation in this family allows for the diagnosis of individuals at risk for this inherited macular degeneration. Furthermore, the long-term follow-up of subjects with identical mutations helps to better characterize the highly variable clinical course of this disorder.

Autosomal dominant Stargardt-like macular dystrophy: identification of a new family with a mutation in the ELOVL4 gene.

PURPOSEnTo describe the clinical features and identify the mutation responsible for an autosomal dominant macular degeneration occurring in a four-generation family.nnnMETHODSnFamily members underwent clinical examination and genealogical characterization. Mutation screening of the ELOVL4 gene was performed.nnnRESULTSnPatients reported visual loss occurring at a mean age of 20 years. Fundus examination revealed varying degrees of central macular atrophy with or without flecks in all affected individuals. DNA sequence analysis showed a 5-bp deletion in exon 6 of the ELOVL4 gene, confirming the diagnosis of autosomal dominant Stargardt-like macular dystrophy. Genealogical analysis showed that this family represents a new affected branch of a previously described 12-generation family (31 branches) with this disorder.nnnCONCLUSIONSnWe characterized a new branch of a family with autosomal dominant Stargardt-like macular dystrophy. Identification of the disease-causing gene allows for improved genetic counseling of affected individuals.