ARHGEF18

ARHGEF18 stands for "Rho/Rac guanine nucleotide exchange factor 18." Its protein acts as a switch that turns on a family of signaling molecules called Rho GTPases. These signals control how cells shape themselves, how they organize their internal scaffolding, and how they grow and move. One of the switches it activates, RHOA, helps form tight junctions and adherens junctions, which are the seals and anchors that hold neighboring cells together. In laboratory studies, this same protein also plays a role at the base of cilia, the tiny antenna-like structures on cells. The gene is also known by aliases such as p114RhoGEF, P114-RhoGEF, SA-RhoGEF, and RP78, and it sits on chromosome 19.

In a 2017 study, researchers found altered ARHGEF18 in three unrelated people who had an adult-onset retinal degeneration. The changes seen in their retinas resembled those found in people with alterations in CRB1, another gene that helps maintain the retina's layered structure. This makes sense because both genes act in the same biological pathway that keeps retinal cells properly organized. Laboratory work in fish showed that loss of this protein disturbs the orderly arrangement of retinal cells and disrupts eye development. In mice, switching off the gene in a type of retinal support cell called Müller glia broke down a boundary in the retina called the outer limiting membrane and led to progressive retinal thinning and vision loss. Because only a handful of affected people have been described, the full range of symptoms, the typical age of onset, and how quickly vision changes over time are not yet well defined.

It is well established from basic biology that the ARHGEF18 protein activates RhoA signaling to maintain the polarity and junctions of the retinal epithelium. Animal experiments consistently show that the retina is especially sensitive to loss of this protein. The 2017 discovery reported that the disease-causing genotypes appear to keep some ARHGEF18 activity rather than eliminating it completely, and complete loss in fish was lethal early in development. The condition described in people follows a recessive pattern, meaning two altered copies of the gene are involved.

The link between ARHGEF18 and human retinal disease is recently reported and based on only three described individuals, so it should be understood as an emerging rather than long-settled association. Because the human evidence is so limited, there is not yet a clear picture of how the condition typically progresses or how much variation exists between people. Much of what is known about how the protein works comes from fish, mice, and cultured cells, and findings in these systems do not always translate directly to people. The 2025 mouse study is a preprint, meaning it had not yet completed full peer review at the time it was gathered, so its conclusions should be treated with extra caution.

As of the date of this review, no treatment targeting ARHGEF18 has been approved. Researchers have proposed this biological pathway as a possible target for future therapy, but that remains a research goal, not an available option. In the 2025 mouse study, losing the protein triggered stress signals inside retinal support cells and reduced the cells' energy production. In those mice and in cultured cells, blocking a stress-related enzyme called TBK1, or supporting cell energy with nicotinamide (a form of vitamin B3), reduced some of these harmful effects. These are early laboratory findings in animals and cells only, and they do not mean that any supplement or drug is a proven or safe treatment for people with this gene change.

• The first report linking ARHGEF18 to human retinal degeneration

  Human genetic study with supporting laboratory tests (small case series).

  What was found:

  Three unrelated individuals carried two altered copies of ARHGEF18, with retinal changes resembling those seen in people with CRB1 alterations; the variants appeared to retain some protein activity rather than eliminate it.

  Why it matters:

  This is the study that first proposed ARHGEF18 as a cause of adult-onset retinal degeneration and is the main human evidence for the gene.

  Limitation: Only three affected individuals were described, so the findings cannot yet define the full disease picture or progression.

• A mouse model of Arhgef18 loss in the retina

  Preclinical animal and cell study (preprint, not yet fully peer-reviewed).

  What was found:

  The retina developed normally at first but then broke down the outer limiting membrane, formed abnormal folds, thinned progressively, and lost vision by about two months of age; blocking the enzyme TBK1 or giving nicotinamide reduced some cellular stress.

  Why it matters:

  It shows how loss of this protein may damage the retina over time and points to pathways that researchers might explore for treatment.

  Limitation: Results are in mice and cultured cells and had not completed peer review; they do not establish a treatment for people.

• How ArhGEF18 shapes the developing retina in fish

  Laboratory animal (fish) developmental study.

  What was found:

  ArhGEF18 activates RhoA–Rock2 signaling needed to keep retinal cells properly oriented and to balance cell division; losing it disrupted retinal architecture, and the human version of the protein could rescue the defect.

  Why it matters:

  It establishes the basic biological job of the protein and shows the function is shared between fish and humans.

  Limitation: Findings come from fish embryos and describe development rather than adult human retinal disease.

• ArhGEF18 and retinal epithelial polarity

  Laboratory research summary in an animal model.

  What was found:

  The protein is needed to keep tight junctions and the cell scaffold in place; its loss increased cell proliferation and produced a severely misshapen embryonic eye with disorganized retinal cell types.

  Why it matters:

  It reinforces why the retina is particularly sensitive to changes in this protein.

  Limitation: Based on developmental animal work, not on human patients.

• ARHGEF18's role at the base of cilia

  Laboratory cell-biology study.

  What was found:

  ARHGEF18 helps recruit key components needed to build the cilium's transition zone; disrupting this pathway impaired cilia formation.

  Why it matters:

  It adds detail about a broader cellular role for the protein beyond cell junctions.

  Limitation: Conducted in cultured cells and not focused on the retina or on human disease.

The retinal condition reported with this gene is inherited in a recessive way, so a person is affected only when they carry two altered copies, one inherited from each parent. Parents of an affected person are typically unaffected carriers, and siblings may wish to discuss carrier testing with a genetic counselor. The described onset was in adulthood rather than childhood, which differs from many other inherited retinal conditions. Aside from these inheritance and onset considerations, the general caregiver guidance shown on every gene page applies here.

• How confident are you that the ARHGEF18 variants found explain my retinal findings, given how recently this gene was linked to retinal disease?
• Are both of my gene copies affected, and what does that mean for how the condition may behave?
• Does the pattern in my retina resemble the CRB1-like changes described with this gene?
• What kind of monitoring or follow-up imaging would you recommend over time?
• Would testing of family members be useful, and if so, who?
• Are there any registries or research studies collecting information on people with ARHGEF18-related retinal disease?

If a genetic test has identified ARHGEF18, confirming the result and its interpretation with a retinal specialist and a genetic counselor can help clarify what it means for you. Because this gene-disease link is recently reported, it is reasonable to ask how confident the laboratory is that these particular variants explain your findings. RP Hope's Genetic Testing resource explains what testing involves and what to ask. RP Hope's My Pathway tour can help you find resources suited to your stage.