CFAP418

CFAP418 (formerly called C8orf37) provides the instructions for a protein that is present in many tissues but is especially active in the retina, brain, and heart. In the retina, the protein is located at the base of the primary cilium of retinal pigment epithelium cells and near the connecting cilium of photoreceptors, the light-sensing cells. CFAP418-related retinal disease is inherited in an autosomal recessive (definition: An inheritance pattern where a person needs an altered copy of a gene from both parents to be affected. Parents with only one copy are usually unaffected carriers.) pattern, meaning a person typically has disease-causing changes in both copies of the gene, one inherited from each parent. Because the same gene has been reported in several different diagnoses, a genetic result naming CFAP418 does not by itself predict exactly which condition, symptoms, or course a given person will experience.

Researchers have described a range of retinal conditions in people with CFAP418 variants, most often cone-rod dystrophy or retinitis pigmentosa, frequently with early involvement of the macula (the central part of the retina). In some people described in the studies, the disease began in infancy, while in others symptoms started during adolescence. In people with a more retinitis pigmentosa–like pattern, researchers reported night blindness followed by gradual loss of the visual field, sometimes progressing to severe central vision loss. In people with a cone-rod dystrophy pattern, reported early symptoms included light sensitivity (photophobia) or loss of visual sharpness, along with atrophy of the central retina. Additional eye findings reported across several families include macular atrophy, cataracts, and high myopia (severe near-sightedness). Some individuals with CFAP418 variants have also had features beyond the eye, such as extra fingers or toes (polydactyly), and in some cases the full picture of Bardet-Biedl syndrome, which can include obesity, kidney abnormalities, and learning differences. Researchers have emphasized wide variability in features and severity, even among relatives who carry the same variant.

It is well established that changes in both copies of CFAP418 can cause inherited retinal degeneration, and the gene has been reported in cone-rod dystrophy, retinitis pigmentosa, and Bardet-Biedl syndrome. The gene was first linked to autosomal recessive (definition: An inheritance pattern where a person needs an altered copy of a gene from both parents to be affected. Parents with only one copy are usually unaffected carriers.) retinal dystrophies with early macular involvement in 2012, using families with disease-causing variants. Early macular atrophy is a recurring feature reported across multiple families and populations. Laboratory and animal studies have helped clarify what the protein does: mouse studies show that loss of the gene disrupts the formation of photoreceptor (definition: A light-sensing cell in the retina. Rods (used for night and peripheral vision) and cones (used for color and detail) are the two types.) outer segment discs, the structures that capture light, leading to degeneration of both rod and cone cells. Other laboratory work suggests the protein binds certain lipids (fats) and helps maintain healthy cell membranes, and that it interacts with FAM161A, another protein important for photoreceptor survival. A particular variant, p.Trp185Ter, has been reported repeatedly in patients of Asian descent, which some researchers suggest may represent a recurrent change in those populations.

The precise biological function of the CFAP418 protein is still being worked out, and the gene record describes it as a protein of unknown function. Laboratory studies have reached differing conclusions about whether the protein acts primarily as a ciliary protein or works elsewhere in the photoreceptor (definition: A light-sensing cell in the retina. Rods (used for night and peripheral vision) and cones (used for color and detail) are the two types.) cell body, so its exact role remains under investigation. Why some people with CFAP418 variants develop only eye disease while others develop the multisystem features of Bardet-Biedl syndrome is not fully understood. Because much of the human evidence comes from small families and case series, precise ages of onset and rates of progression cannot be predicted for any individual. How often CFAP418 accounts for inherited retinal disease is not precisely known and appears to vary across populations, and many reports come from consanguineous families.

RP Hope's reviewed records do not currently identify a gene-specific approved treatment for CFAP418-related retinal disease. Much of the current research is laboratory- and animal-based and is aimed at understanding how loss of the protein damages photoreceptors, which is an important step toward any future therapy. A mouse model lacking the gene has been developed and described by researchers as a valid model for future therapeutic studies, but this is early-stage laboratory research and not a treatment. Large-scale mouse studies have also confirmed that loss of this gene affects retinal function, supporting its role in disease. These findings are promising for understanding the disease but do not represent therapies available to patients today.

• First identification of the gene in inherited retinal dystrophy

  Human genetic study with laboratory (immunohistochemistry) work, small number of families.

  What was found:

  They identified disease-causing changes in C8orf37 (now CFAP418) and found the protein at the base of cilia in retinal cells; affected people had cone-rod dystrophy or retinitis pigmentosa with early macular involvement, and some had extra fingers or toes.

  Why it matters:

  This established CFAP418 as a cause of inherited retinal disease and pointed to a role for cilia in the retina.

  Limitation: Based on a small number of consanguineous families, so it may not capture the full range of presentations.

• Link to Bardet-Biedl syndrome (BBS21)

  Single human case plus animal (zebrafish) functional validation.

  What was found:

  A loss-of-function change in the gene was found in a patient with multiple BBS features, and zebrafish experiments reproduced BBS-related and vision problems, establishing this as BBS21.

  Why it matters:

  It confirmed that CFAP418 variants can cause the multisystem Bardet-Biedl syndrome, not just isolated eye disease.

  Limitation: Human evidence rests on one patient; the functional work is in an animal model.

• How loss of the protein disrupts membranes and photoreceptors

  Preclinical laboratory and animal (mouse) mechanism study.

  What was found:

  The protein binds certain lipids and helps keep cell membranes balanced; without it, membrane and mitochondrial processes went wrong in photoreceptors.

  Why it matters:

  It proposes a disease mechanism (membrane lipid imbalance) that may be shared with other retinal disease genes and could inform future therapy research.

  Limitation: Findings are from cells and mice, not humans, and do not indicate any available treatment.

• Clinical features of rod and cone photoreceptor disease

  Observational human case series.

  What was found:

  Symptoms began in infancy or adolescence; retinitis pigmentosa patients had night blindness and visual field loss, while cone-rod dystrophy patients had light sensitivity and central vision loss, and one family also showed polydactyly.

  Why it matters:

  It describes the range of vision changes and ages of onset reported with this gene and hinted at a possible syndromic overlap.

  Limitation: Only eight patients, so findings may not generalize to everyone with CFAP418 variants.

• Broader body-wide features and clinical variability

  Observational human cohort study with reverse phenotyping.

  What was found:

  A splice variant in CFAP418 was the most common in the group, and re-evaluation revealed previously unrecognized features such as obesity, polydactyly, and kidney abnormalities, reclassifying several patients as having Bardet-Biedl syndrome; features varied widely even within families.

  Why it matters:

  It shows that some people labeled with eye-only disease may have unrecognized systemic features, supporting broader evaluation and counseling.

  Limitation: Single-country cohort with many related families, which may limit how broadly it applies.

A helpful starting point is to ask the person what kind of assistance, if any, they would prefer, rather than assuming help is needed with every activity. Low-vision rehabilitation and accessible technology can support independence and are worth discussing with the care team. Because CFAP418 is inherited in an autosomal recessive (definition: An inheritance pattern where a person needs an altered copy of a gene from both parents to be affected. Parents with only one copy are usually unaffected carriers.) pattern, family members may have questions about their own status, and genetic counseling can address these. Emotional and community support matters, and first-person accounts from others navigating an RP diagnosis can be found through RP Hope's stories. For people who also have systemic features such as those seen in Bardet-Biedl syndrome, coordinated care across specialists may be relevant to discuss. RP Hope's My Pathway tour can help families find resources suited to their stage.

• Based on my genetic result and eye examination, which specific retinal condition best describes my situation?
• Given the CFAP418 link to Bardet-Biedl syndrome in some people, should I be evaluated for any features outside the eye?
• What does my result suggest about how my vision might change over time, and how often should I be monitored?
• What does autosomal recessive inheritance mean for my children, siblings, or other relatives?
• Would a low-vision rehabilitation referral be helpful for me now or in the future?
• Are there registries or research studies you would suggest I learn more about?

A genetic result naming CFAP418 is something to review carefully with a retinal specialist and a genetic counselor, who can put it in the context of a personal eye examination and family history. Because CFAP418 has been linked to features outside the eye in some people, it may be useful to discuss whether an evaluation for systemic features such as kidney function, weight, or other findings is appropriate. Genetic counseling can help explain the autosomal recessive (definition: An inheritance pattern where a person needs an altered copy of a gene from both parents to be affected. Parents with only one copy are usually unaffected carriers.) inheritance pattern and what it may mean for family members. RP Hope's resources for people who are newly diagnosed explain what genetic testing involves and offer questions to bring to a genetic counselor. RP Hope's My Pathway tool can guide patients and families to relevant resources at any stage.