KIZ

KIZ provides the instructions for kizuna, a protein that localizes to the centrosome and helps strengthen and stabilize that region of the cell. The centrosome helps organize cilia, and kizuna is considered a ciliary protein. In the retina, the light-sensing 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.) cells depend on a specialized structure called the connecting cilium to function, and laboratory work has traced kizuna's mouse counterpart to the base of this cilium. When both copies of KIZ are affected, this ciliary function is disrupted and photoreceptors gradually die. The condition follows 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, which means a person typically needs a disease-causing change in both copies of the gene to be affected. KIZ is also known by other names, including RP69 and PLK1S1.

KIZ-associated disease is described as a rod-cone dystrophy, another name for retinitis pigmentosa, in which the rod cells that handle night and side vision are affected first. Many people described in the reports had night-blindness for years or decades before central vision and the visual field began to narrow. The central macula is often relatively spared, but some people instead have a phenotype (definition: The observable traits or symptoms a condition actually produces in a person — as opposed to the genotype, the underlying genetic cause.) dominated by macular changes. A common feature is cystoid macular changes, small fluid-filled spaces in the central retina that can blur central vision. One long-term imaging study characterized KIZ-associated disease as an early-onset, severe rod-cone dystrophy with measurable yearly progression of retinal atrophy. In contrast, one 62-year-old patient with a start-codon variant had a relatively mild course with cone responses still retained into the seventh decade of life, showing that severity is not uniform. A rare complication called Coats-like vasculopathy, involving abnormal retinal blood vessels, has been reported in inherited retinal disease including a KIZ case, and can cause significant vision loss.

KIZ was identified as a cause of 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.) rod-cone dystrophy in 2014 through whole-exome sequencing of affected families. Follow-up laboratory work confirmed that the protein sits at the base of cilia and supported its role in this retinal disease. A specific change, c.226C>T (p.Arg76*), is a founder mutation among people of Jewish descent, meaning it traces back to a shared ancestor and is more common in that population. In a large cohort of 31 people with KIZ changes, the disease tended to be less severe than that seen with two other RP genes, DHDDS and FAM161A. KIZ has also turned up in clinical exome-sequencing programs for inherited retinal disease in more than one affected person, supporting its inclusion on diagnostic gene panels. One imaging study measured the pace of change, reporting that the atrophic area of the retinal pigment epithelium grew by about 4.9% per year in affected people.

Because kizuna is a ciliary protein, the original researchers noted the importance of checking for systemic (whole-body) features, yet the published cohorts describe disease that is largely limited to the eye. It remains unclear exactly why some people have severe early disease while others have a milder, later course, even with disruptive-looking variants. Laboratory studies also found that skin-cell (fibroblast) models did not reproduce the expected effects of the mutations, so researchers have called for better cell models to understand how KIZ changes damage the retina.

No therapy targeting the KIZ gene has been approved. Some doctors have used topical dorzolamide, a carbonic anhydrase inhibitor eye drop, to reduce cystoid macular changes in individual KIZ patients, with reported improvement, but this treats a complication rather than the underlying gene defect. On the research side, scientists have tested a laboratory pipeline that uses RNA editing to try to correct nonsense (premature stop) mutations, including one in KIZ, but this work is preclinical (definition: Research done in cells or animals, before a treatment is considered ready to be studied in people.) and not an available treatment. Researchers have also cautioned that the common KIZ founder mutation disrupts a splicing signal and causes skipping of a portion of the gene, which may make RNA-based approaches less effective for that particular change.

• Discovery of KIZ as a retinal disease gene

  Human genetic study with supporting laboratory and mouse work.

  What was found:

  They identified disease-causing KIZ variants in several unrelated people and showed the protein localizes to the base of cilia, linking this ciliary gene to autosomal recessive rod-cone dystrophy.

  Why it matters:

  This established KIZ as a genuine cause of retinitis pigmentosa and explained its likely mechanism through faulty cilia.

  Limitation: Only a small number of affected people carried KIZ variants, and much of the mechanistic work was done in mice and cells rather than the human retina.

• A large KIZ cohort and a founder mutation

  Human cohort study with laboratory RNA analysis.

  What was found:

  The c.226C>T change was a founder mutation among people of Jewish descent, disease tended to be milder than with two other RP genes, and the mutation disrupts a splicing signal that causes part of the gene to be skipped.

  Why it matters:

  It clarifies who is most likely to carry KIZ changes and warns that RNA-based therapies may be less effective for this particular mutation.

  Limitation: The cohort was concentrated in one population, and the therapy implications are inferred from cell-level findings, not tested in people.

• Preclinical RNA editing for nonsense mutations

  Laboratory and cellular research.

  What was found:

  The approach identified guide sequences capable of editing several disease-causing mutations at the RNA level in laboratory models.

  Why it matters:

  It represents an early step toward a possible future therapy strategy for certain KIZ mutations.

  Limitation: This is preclinical work in cells, not a tested or available treatment in people.

• Long-term progression on retinal imaging

  Small observational human case series with quantitative imaging.

  What was found:

  Retinal pigment epithelium atrophy grew by about 4.9% per year and photoreceptors were progressively lost, with the disease characterized as an early-onset, severe rod-cone dystrophy.

  Why it matters:

  Quantifying the rate of change helps set expectations and could help design future studies of treatment.

  Limitation: Only four patients were studied, so the measured rates may not represent everyone with KIZ disease.

• A milder case with retained cone vision

  Single human case report.

  What was found:

  Despite a disruptive variant, the patient had a relatively mild rod-cone dystrophy with cone responses retained into the seventh decade of life.

  Why it matters:

  It shows that even severe-looking variants can be compatible with useful vision into older age, underscoring how variable this condition can be.

  Limitation: Findings from one patient cannot predict outcomes for others.

KIZ-associated retinitis pigmentosa 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, so an affected person's siblings each have a chance of being affected or of being unaffected carriers, and testing of relatives is a personal decision best made with a genetic counselor. Because the common c.226C>T change is a founder mutation among people of Ashkenazi Jewish descent, family origin can be relevant information to share with the care team. Beyond these points, the general guidance shown on every gene page applies.

• Does my specific KIZ variant give any indication of how severe or fast-progressing the disease is likely to be?
• Do I have any signs of cystoid macular changes, and if so, would a carbonic anhydrase inhibitor eye drop be appropriate?
• Given that KIZ is a ciliary gene, are there any systemic features you would recommend monitoring?
• How often should my retina be imaged to track any progression?
• What does autosomal recessive inheritance mean for my children, siblings, and other relatives?
• Are there registries or natural history studies for KIZ-associated retinitis pigmentosa that I could learn more about?

Confirming a KIZ result and understanding what it means for you and your relatives is something a genetic counselor can help with. Because cystoid macular changes are common in KIZ-associated disease and can respond to treatment, regular monitoring by a retinal specialist may be useful to discuss. To see whether any current studies might be relevant, you can use RP Hope's Clinical Trials Finder with KIZ preselected rather than trying to judge eligibility on your own.