LCA5

The LCA5 gene provides the code for a protein named lebercilin, which is thought to be involved in the function of cilia — tiny hair-like structures that cells use to move material from one place to another. In the retina, lebercilin sits at the connecting cilium of photoreceptors, the narrow bridge through which a light-sensing cell ships proteins to its outer segment where light is actually detected. When lebercilin is missing or does not work, this transport is disrupted and the photoreceptors gradually break down. Changes in both copies of LCA5 cause Leber congenital amaurosis type 5, one of the most severe forms of inherited retinal degeneration. Leber congenital amaurosis is a group of early-onset retinal diseases; LCA5 is one of many genes that can cause it, and the reviewed evidence describes it as affecting the eye rather than as part of a broader syndrome.

Leber congenital amaurosis typically causes blindness or severe visual impairment before the age of one year. Common early signs include nystagmus (involuntary eye movements), night blindness, and difficulty seeing that is present from very early in life. In a Spanish study, people with LCA5 changes showed progressive loss of visual acuity and visual field, leading to blindness toward the third decade of life. Examination often shows a pigmentary retinopathy with atrophic changes in the macula, the central part of the retina used for detailed vision. The electroretinogram (definition: A test (often abbreviated ERG) that measures the retina's electrical response to light, used to check how well photoreceptors are working.), a test of how the retina responds to light, is usually severely reduced or undetectable in LCA. Even so, the severity is not identical for everyone, and some people described in the studies had milder, more slowly progressing disease sometimes described as early-onset retinitis pigmentosa. Detailed retinal imaging has also found that some individuals retain islands of photoreceptors, near the center of the retina and occasionally in the periphery, despite very poor vision.

LCA5 is well established as a rare cause of Leber congenital amaurosis, first confirmed in humans nearly two decades ago and repeatedly found in retinal-disease cohorts worldwide. How often it appears differs by population; it accounted for a small fraction of cases in French and international cohorts but a notably higher share in a Spanish cohort. The 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.) way, and many reported families come from communities where marriage between relatives is more common, which increases the chance of inheriting two altered copies. Most disease-causing LCA5 changes are so-called truncating or null mutations that are expected to eliminate a working protein. Laboratory work in mice, zebrafish, and human stem-cell-derived retinal tissue consistently shows that loss of lebercilin disrupts the connecting cilium and the outer segment of photoreceptors, matching what is seen in patients.

The exact steps by which loss of lebercilin leads photoreceptors to die are still not fully understood. Why some people with LCA5 changes have profound blindness from birth while others have milder, later-progressing disease is not fully explained by the specific mutation alone. A rarer form of LCA involving a coloboma (a gap in eye tissue) has been shown NOT to be caused by LCA5 in at least one family, underscoring that not every early-onset retinal condition traces back to this gene. Whether the early benefits seen in the ongoing gene therapy (definition: A treatment that delivers a working copy of a gene into cells to take over for a copy that isn't functioning properly.) trial will last over many years, and how they would apply to people with different severities, is not yet known.

As of the date of this review, no approved treatment specifically targets LCA5. A gene therapy (definition: A treatment that delivers a working copy of a gene into cells to take over for a copy that isn't functioning properly.) called OPGx-001, which delivers a healthy copy of the human LCA5 gene into the retina using a harmless carrier virus, is being tested in an early-stage clinical trial. In the first three treated adults, there were no serious side effects related to the therapy or procedure, and measures of cone-based vision improved and lasted for at least twelve months. This is an early safety-and-feasibility study in a very small number of severely affected people, not evidence of a proven or widely available cure. Supporting laboratory research adds context: replacing the LCA5 gene partially restored retinal structure and function in mice, and small molecules improved protein trafficking in human stem-cell-derived retinal tissue. These laboratory and animal findings are research tools that help guide future therapies; they are not treatments available to patients.

• First-year results of an LCA5 gene therapy trial

  Early-phase human clinical trial (safety and preliminary efficacy)

  What was found:

  There were no serious treatment-related side effects, and cone-based vision improved by roughly one order of magnitude on light-sensitivity testing, lasting at least twelve months and improving performance on a mobility test.

  Why it matters:

  This is the first human evidence that replacing the LCA5 gene may improve vision in this severe condition.

  Limitation: Only three severely affected adults were treated in one eye each, follow-up was short, and long-term durability and effects in milder disease are unknown.

• Gene replacement in a mouse model of LCA5

  Preclinical animal and cell research

  What was found:

  Treated mice regained some retinal electrical responses and light-driven behaviors, and patient cells restored lebercilin protein and normal cilia.

  Why it matters:

  These results provided the scientific groundwork for testing LCA5 gene therapy in people.

  Limitation: Results in mice and cultured cells do not guarantee the same benefit, extent, or durability in humans.

• Small-molecule treatment in LCA5-deficient human retinal organoids

  Laboratory research in human stem-cell-derived tissue

  What was found:

  Loss of LCA5 shortened outer segments and misplaced key proteins, and two small molecules reduced these defects and improved protein trafficking.

  Why it matters:

  It suggests drug-based approaches, in addition to gene therapy, might one day be explored for LCA5-related retinal ciliopathy.

  Limitation: This is early cellular research only, not tested in people, and does not represent an available treatment.

• LCA5 in a Spanish LCA and retinitis pigmentosa cohort

  Observational human genetic and clinical study

  What was found:

  LCA5 mutations were found in six families with LCA, at a higher frequency than reported elsewhere, and all affected people had nystagmus, night blindness, and progressive loss toward blindness by the third decade.

  Why it matters:

  It gives a clear picture of how LCA5 disease typically progresses and shows that gene frequency varies between populations.

  Limitation: Findings come from one population with many related families and describe a small number of LCA5 cases.

• Largest LCA5 patient series and phenotype range

  Large observational human genetic study

  What was found:

  LCA5 accounted for about 2% of cases; most changes were protein-truncating and caused severe LCA, but two families had a milder early-onset RP-like course, and some patients retained central photoreceptor structure.

  Why it matters:

  It establishes that LCA5 is a rare cause of childhood retinal disease and that severity can vary, which matters for counseling and future treatment.

  Limitation: It is a laboratory-and-records study; milder cases were few, so conclusions about the mild end of the spectrum rest on small numbers.

Because LCA5 disease usually begins in infancy or early childhood, families may need to plan early for a child's visual development, learning, and access to education. 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 means both parents typically carry one altered copy, and full siblings have a chance of being affected or of being carriers, which is something a genetic counselor can explain for your family. The reviewed evidence describes LCA5 as affecting the eye rather than as part of a wider syndrome, but confirming this with your care team is reasonable, since a few LCA genes can involve other organs.

• Has my specific LCA5 result been confirmed as the cause of my (or my child's) retinal condition, and are both gene copies affected?
• Given my current vision and retinal imaging, how severe and how progressive is my form of LCA5 disease likely to be?
• Does my retinal imaging show any preserved photoreceptors that could matter for future treatment approaches?
• Is the LCA5-specific gene therapy trial something I could be evaluated for, and what would eligibility involve?
• Are there systemic or other tests you would recommend to be sure this is limited to the eye?
• How often should my vision and retina be monitored going forward?

A confirmed genetic diagnosis is the foundation for understanding an LCA5 result and for considering whether current or future research might be relevant. Discussing the result with a retinal specialist and a genetic counselor can help clarify what it means for you and your family. Because research is moving quickly for LCA5, keeping in touch with your care team about study opportunities may be worthwhile, and RP Hope's Clinical Trials Finder can help with personalized screening.