BBS1

The BBS1 gene provides instructions for a protein that is part of the machinery cells use to build and maintain cilia, tiny antenna-like structures on the surface of many cells. In the eye, healthy cilia are essential for the light-sensing cells of the retina to work and survive. Because cilia are found throughout the body, BBS1 changes can affect several organ systems, and the protein has been linked to development of the eye, limbs, heart, and reproductive system. BBS1 is the most frequent cause of Bardet-Biedl syndrome, a group of related conditions that share retinal degeneration with systemic features. Conditions related to BBS1 are usually 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, so a person typically carries two disease-causing copies, one from each parent. One particular change in the gene, written as p.(Met390Arg) or M390R, is the single most common BBS1 variant reported worldwide.

Most people with BBS1-related retinal disease develop a rod-cone dystrophy, in which the rod cells that handle night and side vision are affected first, followed by the cone cells used for central and color vision. Early symptoms often include trouble seeing in dim light and a gradual narrowing of the visual field. In a single-center study of 48 people with confirmed BBS1 retinopathy, vision on average declined slowly over years of follow-up, and detailed retinal imaging documented gradual thinning of the light-sensing layers. That study also found that people carrying two copies of the common M390R change tended to have a later age of onset and reached legal blindness later than those with other genotypes. The pattern is not identical in everyone, and some people described in the literature had a cone-predominant or cone-rod pattern, or mainly central (macular) changes, rather than the typical rod-first pattern. Clinical and imaging findings do not always match electrical tests of the retina, which is one reason full testing and genetic confirmation matter. When BBS1 causes the full syndrome, retinal degeneration tends to be early and severe, and in one cohort of adults with Bardet-Biedl syndrome all participants had retinitis pigmentosa.

It is well established that BBS1 is a cause of both syndromic Bardet-Biedl syndrome and, on its own, nonsyndromic retinitis pigmentosa. BBS1 is consistently reported as the most frequently involved gene among people with Bardet-Biedl syndrome across several countries and cohorts, although how often it appears varies between populations. The M390R variant has been confirmed as reliably disease-causing and is the most common single change seen in BBS1. Researchers have documented the natural history of BBS1 retinal disease in detail, including visual acuity, visual fields, retinal imaging, and electrical recordings over many years. When compared directly, retinal degeneration in people with BBS1 tends to appear later and progress more slowly than in people with variants in BBS10, another Bardet-Biedl gene. Beyond the eye, the most frequently reported systemic features in BBS1 cohorts include obesity and extra fingers or toes (polydactyly), with kidney, genital, dental, and learning differences also described.

It is not fully predictable from a genetic result alone whether a given person with BBS1 changes will have isolated retinal disease or the full syndrome, and features can be subtle or appear later in life. In one study, people first diagnosed with nonsyndromic retinal disease who carried BBS-related variants were later found on careful re-examination to have overlooked systemic features, showing how blurry the line can be. There is wide variability in the retinal pattern, age of onset, and rate of progression even among people who share the same BBS1 variant, including within the same family. Some case reports raise questions about how inheritance works in certain individuals, such as a person with retinitis pigmentosa and polydactyly who carried only one identified BBS1 change, but such single reports are not enough to establish a general pattern. Why the same protein defect produces such different outcomes in different people is still being worked out.

As of this review, no therapy targeting BBS1 has been approved for the retinal disease. Research is active on several fronts, including laboratory work to understand how the loss of cilia function damages the retina. In laboratory models grown from patient cells representing several ciliopathy (definition: A disease caused by a problem with cilia — tiny hair-like structures on cells, including the light-sensing cells in the retina, that the cell needs to work properly.) genes including BBS1, researchers identified shared cellular changes and flagged two existing drugs as possible candidates for further study, but this is early laboratory work and not a treatment people can use. In mice carrying the BBS1 M390R change, adding a working copy of the human BBS1 gene restored male fertility but did not protect the retina, highlighting that repairing vision in this condition remains a difficult, unsolved research problem. Animal and laboratory findings like these describe research directions, not available therapies.

• A hidden BBS1 variant causing retinitis pigmentosa without the syndrome

  Human case series with laboratory functional analysis

  What was found:

  A branchpoint variant that disrupts normal gene processing, paired with the milder M390R change, caused isolated retinal disease with macular involvement and no other syndrome features.

  Why it matters:

  It confirms BBS1 can cause nonsyndromic RP and shows why looking beyond standard coding regions can be important for a molecular diagnosis.

  Limitation: Only four individuals were studied, so broader frequency and range of outcomes are not established.

• Gene therapy in a BBS1 mouse rescued fertility but not the retina

  Animal (mouse) laboratory research

  What was found:

  The added gene restored male fertility but did not prevent retinal degeneration, in part because it was barely expressed in the light-sensing layer.

  Why it matters:

  It illustrates both the promise and the real difficulty of designing gene therapy that reaches and protects the retina in this condition.

  Limitation: Findings in mice do not necessarily translate to people, and this is not an available treatment.

• Long-term study of vision in people with BBS1 retinal disease

  Observational human cohort study

  What was found:

  Vision declined gradually on average, about one in five had isolated (nonsyndromic) retinal disease, obesity and polydactyly were the most common systemic features, and people with two copies of the common M390R change had later onset and reached legal blindness later.

  Why it matters:

  This is one of the largest and longest natural-history descriptions of BBS1 retinal disease and helps set expectations for monitoring.

  Limitation: It was retrospective and from a single center, so results may not represent every population or care setting.

• Comparing how vision changes in BBS1 versus BBS10

  Multicenter observational human study

  What was found:

  Most people in both groups had a rod-cone pattern, but retinal degeneration appeared earlier and progressed faster in BBS10 than in BBS1.

  Why it matters:

  It shows that the specific gene involved influences the course of vision loss, which is useful context for people with a BBS1 result.

  Limitation: Data were gathered retrospectively from different centers, and numbers for each subtype were modest.

• Rethinking the line between nonsyndromic RP and Bardet-Biedl syndrome

  Observational human study with reverse phenotyping

  What was found:

  Careful reassessment uncovered previously unrecognized systemic features in many, and using a genotype-first framework reclassified several people as having Bardet-Biedl syndrome.

  Why it matters:

  It shows that a genetic result can prompt evaluations that change the diagnosis and guide surveillance, counseling, and management.

  Limitation: It was a small, single-region cohort, and diagnostic thresholds differed depending on the framework used.

Unlike many isolated retinal conditions, BBS1 can be part of a body-wide condition, so families may need to watch for and manage features such as obesity, extra fingers or toes, kidney and genital differences, dental changes, and learning or developmental differences. Because retinal symptoms in the syndrome often begin in childhood, early school and developmental support alongside eye care can be important. Diagnosis is sometimes delayed for years because the syndrome's features vary and can be subtle, so keeping a coordinated, multidisciplinary care team helps. The recessive inheritance pattern means siblings may also be affected or be carriers, which is worth discussing with a genetic counselor.

• Do my genetic results point toward isolated retinal disease or toward Bardet-Biedl syndrome with systemic involvement?
• Which systemic evaluations (kidney, metabolic, hormonal, developmental) would you recommend given my specific BBS1 variants?
• What retinal pattern do my imaging and electrical tests suggest, and how might that guide monitoring?
• Given the variability seen with BBS1, how often should my vision be reassessed?
• Should other family members consider genetic testing or counseling based on the recessive inheritance pattern?
• Are there registries or gene-focused studies that might be relevant for me to learn about?

Because BBS1 can involve more than the eyes, a full evaluation that looks for systemic features and confirms the specific variants can be valuable, and early diagnosis supports appropriate monitoring and counseling. Confirming the exact genetic change also clarifies whether a result points toward isolated retinal disease or the broader syndrome, since some deep intronic or splice-region changes are missed by standard panels and may need genome sequencing to detect. Sharing a confirmed genetic diagnosis with a retinal specialist and a genetic counselor can help plan follow-up and family testing. For personalized help finding studies, RP Hope's Clinical Trials Finder can screen options with BBS1 preselected.