Localization of a Gene for Keratoconus to a 5.6-Mb Interval on 13q32

Abstract

Purpose Keratoconus (KTCN) is a noninflammatory thinning and anterior protrusion of the cornea that results in steepening and distortion of the cornea, altered refractive powers, and reduced visual acuity. Several loci responsible for a familial form of KTCN have been mapped, however; no mutations in any genes have been identified for any of these loci. There is also evidence that VSX1 and SOD1 may be involved in the etiology of KTCN. The purpose of this study was to verify the available data and to identify a new keratoconus susceptibility locus. Methods KTCN without other ocular or systemic features was diagnosed in 18 families. VSX1 and SOD1 sequencing was performed on affected individuals and control subjects. Genomewide linkage analysis was then performed in all families using polymorphic microsatellite markers with an average spacing of 5 cM. Next, single-nucleotide polymorphism (SNP) arrays, fluorescence in situ hybridization (FISH) analysis, and a comparative genomic hybridization array were used in one family to assess a candidate region on 13q32. Results All previously reported KTCN loci were excluded. VSX1 and SOD1 were sequenced, and no potentially functional variants were found. One KTCN family yielded a maximum multipoint parametric LOD score of 4.1 and multipoint non-parametric linkage (NPL) LOD score of 3.2. Multipoint linkage and haplotype analysis narrowed the locus to a 5.6-Mb region between the SNPs rs9516572 and rs3825523 on 13q32. Conclusions The results exclude VSX1 and SOD1 as potential disease-causing genes in these families and localize a novel gene for keratoconus to a 5.6-Mb interval on 13q32.

Variants in SKP1, PROB1, and IL17B genes at keratoconus 5q31.1–q35.3 susceptibility locus identified by whole-exome sequencing

“…The pedigrees of Ecuadorian KTCN families have been previously described. 14,16 Briefly, the diagnosis of KTCN was based on visual acuity testing, intraocular pressure assessment, biomicroscopic evaluation, and fundus examination with dilation. In addition, a topographic study (Humphrey Atlas Topograph; Carl Zeiss Meditec, Jena, Germany) with a computer-assisted videokeratoscope was performed in all affected individuals as well as in individuals with a suspected corneal abnormality.…”

“…14 The quality of the DNA samples were ascertained by electrophoresis and determined to be of high quality (size 423 kb) with no visible degradation. The quantity of samples was assessed spectrophotometrically using a NanoDrop instrument (Thermo Scientific, San Jose, CA, USA).…”

“…[12][13][14][15] Whole-exome sequencing (WES), which allows determination of the rare and unique coding sequence variants in an individual personal genome, can be also utilized in familial studies. However, due to a number of candidate genes generated by linkage analysis or WES, the evaluation of each individual variant is challenging.…”

Keratoconus: an inflammatory disorder?

“…51,52 Some of the genes with reported mutations are SOD1 (locus 21q22.11), VSX1 (locus 20p11.2), and DOCK9 (locus 13q32), which regulate the expression of superoxide dismutase (SOD), photoreceptor cells, and G protein, respectively. [53][54][55] Recently, mutations in MIR184 have been identified as an uncommon cause of keratoconus. 55,56 LOX (locus 5q23.2), the gene encoding lysyl oxidase (LOX) enzyme, which is involved in collagen and elastin cross-linking, have also been related to keratoconus.…”

Linkage Analysis as an Approach for Disease-related Loci Identification

“…Genetic studies have led to the identification of several loci on many chromosomes, linked to KTCN, including 1p36.23-36.21, 2p24, 2q13, 3p14-q13, 5q14.3-q21.1, 5q21.2, 5q32-q33, 9q34, 13q32, 14q11.2, 14q24.3, 15q15.1, 15q22. 33-24.2, 16q22.3-q23.1, 17p13, 20q12 [13][14][15][16][17][18][19][20][21][22][23][24][25]. To date, most of the identified loci have not been replicated in other populations.…”