Week in Review: Number 28

New Genetic Test Improves Detection of Glaucoma Risk
Often called the silent thief of sight, glaucoma is a complex eye disease that results from irreversible damage to the optic nerve. Early screening and detection well before vision loss can inform clinical decisions and thereby potentially improve quality of life for patients. This early diagnosis of glaucoma often comes from clinical assessments; however, researchers in Australia are exploring genetic variation as a promising indicator of disease risk stratification. As tested in a sample of 2,507 individuals with open-angle glaucoma from the Australian and New Zealand Registry of Advanced Glaucoma (ANZRAG), along with clinical and genetic data from 411,337 individuals in cross-sectional cohort studies from the UK Biobank (between 2006 and 2010), the researchers report that their new genetic test can identify high polygenic risk of glaucoma (top 5% of the population) comparable to heterozygous monogenic risk (specifically for the MYOC p.Gln368Ter variant, the most common single-gene variant known to cause primary open-angle glaucoma), but is more than 15 times more prevalent in the general population (and more than 6 times more common in ANZRAG). The study concludes, "Monogenic and high polygenic risk were each associated with a more than 2.5-fold increased odds of developing glaucoma and an equivalent mean age at glaucoma diagnosis, with high polygenic risk more than 15 times more common in the general population." In other words, while both monogenic risk and high polygenic risk for open-angle glaucoma are equal, polygenic risk is much more prevalent, and their new genetic test can detect that risk from the contribution of multiple genes. The senior author of the study comments, “Genetic testing is not currently a routine part of glaucoma diagnosis and care, but this test has the potential to change that. We’re now in a strong position to start testing this in clinical trials” to begin in 2022.

Elevated Complement Factor H-Related Proteins is Associated with Increased Risk of AMD
Researchers in the U.K. and Germany conducted a genome-wide association study to investigate genetic variants that determine increased risk of AMD. From 604 blood plasma samples, they identified five proteins, Complement Factor H-Related 1 to 5 (CFHR-1 to CFHR-5), as being higher in individuals with age-related macular degeneration (AMD) than those without the disease. These FHR proteins are part of the complement pathway of the innate immune system. In AMD, the complement pathway is over-activated in the back of the eye, specifically in the intercapillary septa of the retinal pigment epithelium/Bruch's membrane/choriocapillaris (RPE/BrM/CC) complex, leading to a damaging inflammatory response. The findings are novel in the sense that they expand upon earlier information pointing to only Complement Factor H and its protein FH as being implicated in AMD pathogenesis. The study also employed technological advances in mass spectrometry to measure the levels of these proteins, which are usually present at low levels in the blood and are very similar to each other. The researchers emphasize that the study demonstrates association and that research of studies over time would be needed to predict risk. However, the results are the first step toward developing tests to predict risk of AMD and potential treatments. While elevated levels of each of the five FHR proteins is associated with AMD risk, the inflammation pathway is not the only driver of AMD. Therefore, being able to measure levels of these proteins would help to identify patients who would best benefit from FHR-targeting therapies.

HtrA1 Augmentation as Potential Therapy for AMD
Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in individuals over the age of 55. Fifteen years of research identified HtrA1 protein, a serine protease enzyme encoded by the HTRA1 gene, as normally increasing with age in the retinal pigmented epithelium (RPE)-Bruch’s membrane interface, and helps to maintain normal RPE function to deliver nutrients and remove waste from the eye's photoreceptors. The present research shows that individuals with AMD-associated risk variants located on chromosome 10 have impaired expression of the HTRA1 gene, resulting in approximately 50% reduction in HtrA1 protein levels at the RPE-Bruch’s membrane interface during aging. The resulting dysfunction leads to abnormal deposits and blood vessels characteristic of AMD. The team found that reduced HTRA1 mRNA was only a risk factor in the RPE, and not in the neural retina or the choroid. According to the lead author of the study, seeing HtaA1 as protective in maintaining the RPE-Bruch's membrane interface is unexpected, given that HtrA1 protein is thought to contribute to diseases such as osteoarthritis.

The discovery, however, was made possible by a unique repository of more than 8,000 pairs of donated human eyes to sample chromosome 10-directed AMD, narrowing down a smaller region of chromosome 10 that is likely responsible for reduced expression of HTRA1, and specifically studying HTRA1 expression in the RPE-Bruch’s membrane interface (the primary site of AMD pathogenesis) compared to the neural retina or white blood cells as was done in prior studies. The senior researcher adds, “Unfortunately, data generated by prior studies have led to the development and testing of therapies—some of which are currently in human clinical trials—designed to reduce overall levels of HtrA1, an approach that may exacerbate AMD progression.” While such contradictions might seem alarming, novel discoveries that expand and refresh the literature, and discussion about findings of different research studies, are commonplace in the scientific enterprise, including biomedical research. The research team is currently working on therapies for individuals with AMD due to mutations in chromosome 1 or chromosome 10, which, according to the researchers, together account for more than 50% of the genetic risk for developing AMD.

KCN1 Suppresses Metastatic Uveal Melanoma, in Mice
Uveal melanoma (UM) is a type of cancer of the vascular, pigmented middle layer of the eye, the uvea. Though rare among cancers, uveal melanoma is the most prevalent primary intraocular malignancy in adults and can be both vision- and life-threatening as the cancer metastasizes to other tissues of the body. Researchers have identified an inhibitory molecule, arylsulfonamide KCN1, that dampens drivers of tumorgenesis in animal models, limiting both the primary disease in the eye and metastatic tumor dissemination to the liver. The animals treated with KCN1 also survived longer, without overt side effects. Tumor progression and metastasis in uveal melanoma is associated with hypoxia-inducible transcription factor (HIF), which turns on many gene products that promote cancer growth, including proliferation, migration, invasion and adhesion of tumor cells as well as angiogenesis to feed the tumor. Two of these gene products, P4HA1 and P4HA2, promote collagen deposition in the extracellular matrix, which in turn reorganizes the extracellular matrix in a way that aids cancer progression and tumor cell invasion. Comparison of 46 patients with non-metastatic UM and 46 with metastatic UM showed that P4HA1 and P4HA2 were significantly overexpressed in patients with metastatic disease, and furthermore correlated with poor survival outcomes in UM patients, suggesting that P4HA1 and P4HA2 could serve as prognostic markers in UM. When tested in human UM cell lines, the researchers found that P4HA1 and P4HA2 were induced by hypoxia, and this induction was reduced by KCN1. In animal models injected (intraperitoneally) with KCN1, the molecule was abundantly taken up in the liver and in the eyes. KCN1 dampened tumor growth in the eye and reduced metastases in the liver, especially when administered early. Although the study suggests that “KCN1 has desirable properties as a suppressor of metastasis: It is well tolerated, has excellent distribution to the eye and the liver, and is thus ideally suited for treating metastatic UM," the researchers also caution that the drug needs further optimization before clinical use.

Gene Splicing Dysfunction in Usher Syndrome
Usher syndrome (USH) is the most common cause of combined hereditary deafness and blindness. Alternatively known as retinitis pigmentosa–dysacusis syndrome, vision loss results from progressive degeneration of the photoreceptors in the retina (RP in this case) within the first or second decade of life. More than a dozen genes and loci have been identified as contributing to the disease; however, its pathophysiology is not completely understood. Researchers in Germany investigating the pathological mechanism underlying Usher syndrome discovered that defects in a protein called SANS, synthesized from a gene named Usher syndrome type 1G (USH1G), leads to errors in pre-mRNA splicing related to cell division, ultimately leading to ciliopathy of the photoreceptors (and hair cells in the inner ear, accounting for the deafness aspect of the syndrome). Specifically, the authors explained, "We show that SANS is found in Cajal bodies and nuclear speckles, where it interacts with components of spliceosomal sub-complexes such as SF3B1 and the large splicing cofactor SON but also with PRPFs and snRNAs related to the tri-snRNP complex. SANS is required for the transfer of tri-snRNPs between Cajal bodies and nuclear speckles for spliceosome assembly and may also participate in snRNP recycling back to Cajal bodies." This new finding contrasts with earlier thinking that SANS was simply a scaffold molecule that participates in transport processes in the cytosol and cilia at the cell surface. Lack or dysfunction of SANS prevents the spliceosome in the nucleus from being correctly assembled and activated, without which genes are not correctly spliced, ultimately leading to the clinical manifestation of Usher syndrome.

In Other News
(1) Consumer Health: Are contact lenses right for you?
(2) Link between dual sensory loss and depression
(3) Wet AMD treatment breakthroughs/updates