Purpose: Glaucoma is a heterogeneous disease influenced by genetic risk factors. However, not all genetic risk factors have been identified. The aim of this project is to localize genetic factors influencing known glaucoma endophenotypes: intraocular pressure (IOP), central corneal thickness (CCT), and vertical cup-to-disc ratio (VCDR).
Methods: This family-based study design utilizes phenotypic and genomic data from a single well-characterized pedigree residing in the Jiri region of Nepal. Measures of IOP, CCT and VCDR were obtained by Goldmann applanation tonometry, OCT, and slit lamp biomicroscopy, respectively. Using a genome-wide genotype data set (~550,000 SNPs), we performed a genome-wide linkage scan for IOP, CCT, and VCDR adopting a quantitative approach in SOLAR. For localized quantitative trait locus (QTL) signals, we screened all SNPs within the 1-LOD (95% confidence) interval using the classical measured genotype approach to association analysis and allowing for non-independence amongst the pedigree members.
Results: For this study, phenotypic and genotype data from 1,163 (55% female) members of the Jirel population were available. The mean age of the sample is 43.8 (SD=15.7) years. IOP (h2=19%, p=6.1×10-5), CCT (h2=57%, p=1.6×10-26), and VCDR (h2=48%, p=9.7×10-22) were significantly heritable. We localized a significant QTL for VCDR on chromosome 4 (LOD=3.05 at 86.83 Mb). The top association signal within this QTL was for an intronic SNP (rs4148155; p=2.01×10-6, b=0.24) in the ABCG2 (ATP binding cassette subfamily G member 2) gene, which satisfied our QTL-specific Bonferroni-corrected significance criterion (p<6.59×10-5). ABCG2 is a known stem cell marker, which is positively expressed in clonal human trabecular meshwork stem cells. Another positional candidate gene of note is SCD5 (Stearoyl-CoA desaturase 5), which is shown to suppress neurite outgrowth, a marker of neuronal differentiation. SCD5 is of significant interest given that expression of myocilin (MYOC) also inhibits neurite outgrowth.
Conclusions: To our knowledge, the VCDR QTL on chromosome 4 is a novel locus and does not overlap with other glaucoma endophenotypes or glaucoma disease status. These results highlight the importance of continued evaluation of genetic factors influencing glaucoma endophenotypes in under-studied populations, such as the Jirels, as new information may be elucidated.
Miller, Sarah E.; Blackburn, Nicholas B.; Thapa, Suman S.; Laston, Sandra; Kumar, Satish; Peralta, Juan M.; Subedi, Janarden; Blangero, John; Williams-Blangero, Sarah; and Johnson, Matthew P., "Genetic analysis localizes a novel locus on chromosome 4q for the glaucoma endophenotype, cup-to-disc ratio: The Jiri Eye Study" (2019). School of Medicine Publications and Presentations. 10.
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Association for Research in Vision and Ophthalmology (ARVO) 2019
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