Analysis of the TCP–1 Gene (T–Complex Polypeptide–1) in Patients With Neovascular Age–Related Macular Degeneration

Abstract

Purpose: : To examine the candidate gene TCP–1, chosen for its expression pattern and its functional role in apoptosis, as a possible contributor to the pathophysiology of neovascular age–related macular degeneration (AMD).

Methods: : We ascertained 66 extremely discordant sibpairs where at least one member (the index patient; mean age = 72.6) had neovascular AMD and another member (the unaffected sibling; mean age = 77.0) had normal maculae and was past the age at which the affected sibling was diagnosed with neovascular AMD. Disease status was confirmed by fundus photographs or a home visit (n=4) by at least two of the investigators. Six highly polymorphic microsatellite markers (D6S1035, D6S1577, D6S1633, D6S415, D6S437, D6S442), located within 5 cM on either side of the TCP–1 gene (6q25.3–26) and having an average heterozygosity of 82.5%, were used to amplify patient DNA samples. PCR products were genotyped on an ABI 3730 DNA Analyzer. Gene Mapper Version 3.5 was used to determine allele sizes for each marker in each individual. The resulting data was reviewed separately by two readers. Additionally, two of the markers with the highest heterozygosity, D6S1035 (86%) and D6S1633 (83%), were re–amplified and re–genotyped for at least half of the sibpairs to confirm initial genotyping results. Identity–by–state (IBS) scores were calculated from the number of alleles (ie., 0, 1 or 2 alleles) shared between a sibpair for each of the 6 markers. Using heterozygosities for each marker, observed and expected (null hypothesis of no linkage) IBS values were compared across all sibpairs using the chi–squared test.

Results: : Markers D6S1577 (n = 39), D6S422 (n = 55), D6S1633 (n = 66), D6S415 (n = 64), D6S437 (n = 54), and D6S1035 (n = 49) were statistically significant, demonstrating no association of TCP1 with neovascular AMD, p> 0.97.

Conclusions: : Overall, our analysis supports a lack of association between the TCP–1 gene and neovascular AMD in our extremely discordant sibpair population; however, these results may demonstrate that the TCP–1 gene is associated with a factor or condition other than neovascular AMD that is concordant among these sibpairs.

Keywords: age-related macular degeneration • linkage analysis • genetics