Molecular Analysis of the Human Microphthalmia Associated Homeobox Gene CHX10 and Hyperopia Gene MFRP in Angle Closure Glaucoma Patients With Small Ocular Dimensions

Abstract

Purpose:: Primary angle closure glaucoma (PACG), the genetic basis of which has yet to be elucidated, is a major form of glaucoma in Asia. Ocular characteristics related to PACG such as anterior position of the lens, increased lens thickness and shallow anterior chamber suggests the involvement of genes that regulate ocular dimensions in the pathogenesis of PACG. Both CHX10, a retinal homeobox gene associated with microphthalmia, and MFRP, associated with nanopthalmos and hyperopia, are characterized by small eyes and thus represent good candidate genes for PACG. In order to investigate the possible involvement of CHX10 and MFRP genes in PACG we screened these 2 genes in a subset of PACG patients with the smallest ocular dimensions.

Methods:: Both chronic and acute PACG patients with axial lengths measuring less than 23 mm were selected for analysis. The 5 exons of CHX10 and the 13 exons of MFRP were PCR amplified on patient DNA, using intronic primers and subjected to bi-directional sequencing using BigDye Terminator v3.1 chemistries and analyzed on an ABI PRISM 3100 Genetic Analyzer.

Results:: Altogether 46 chronic and acute PACG patients of Chinese ethnicity were studied. In CHX10 2 heterozygous missense (G243D (1/46) and D291N (4/46) and 2 synonymous (S157S and P250P) mutations were identified. The G243D variant in CHX10 was not identified in over 160 control chromosomes. In MFRP 3 heterozygous missense mutations (Val136Met, Arg257His and Cys197Tyr) were identified, as well as several synonymous (Tyr164Tyr and His180His) mutations. Of the three missense mutations, Cys197Tyr variant found in a single PACG case is noteworthy as the substituted cysteine residue is fully conserved in cubilin domains of very different proteins. The PACG patient with the MFRP Cys197Tyr mutation also carried the CHX10 D291N variation. The PACG patient with the CHX10 G243D mutation also carried the rare MFRP Arg257His variation suggesting a digenic mode of inheritance of PACG.

Conclusions:: PACG is likely to be a complex disease with multiple gene interactions responsible for the disease. Observations made in this study suggest a possible role for both CHX10 and MFRP in PACG, mediated via a digenic interaction. Similar digenic gene interactions have been suggested for MYOC and CYP1B1 genes in open angle glaucoma.

Keywords: gene/expression • genetics • development