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BBS7
Bardet-Biedl syndrome 7
BBS7 is located on the long (q) arm of chromosome 4, at band 4q27. Arm ratio per GRCh38 - banding schematic.
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Overview
BBS7 (Bardet-Biedl syndrome 7) is located on chromosome 4 at band 4q27 and encodes a 715-amino-acid protein essential for ciliary biology. Cilia are microscopic antenna-like structures that project from the surface of most human cells, serving as signalling hubs and sensory organelles. The BBS7 protein forms part of the BBSome, a multi-subunit complex responsible for trafficking proteins to and from cilia, thereby maintaining their structure and function. When both copies of BBS7 carry pathogenic variants, the resulting ciliary dysfunction affects multiple organ systems including the retina, kidneys, and central nervous system, producing the characteristic features of Bardet-Biedl syndrome.
What the gene does
The BBS7 protein functions as a core component of the BBSome, an octameric protein complex that orchestrates intracellular trafficking within cilia. Cilia depend on precisely regulated transport systems to maintain their unique protein composition, as the ciliary membrane is continuous with but functionally distinct from the plasma membrane. The BBSome acts as an adaptor, coupling cargo proteins to motor complexes that move along the ciliary microtubule skeleton. This enables the selective import of signalling receptors into cilia and the removal of proteins that would otherwise accumulate and disrupt ciliary architecture. BBS7 interacts directly with other BBSome subunits to stabilise the complex and facilitate cargo recognition. Through these trafficking functions, the BBSome supports multiple ciliary signalling pathways, including those involved in developmental patterning, sensory perception, and metabolic regulation. Loss of functional BBS7 protein impairs BBSome assembly, leading to defective ciliary protein transport and a cascade of cellular signalling abnormalities.
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Chromosome location
BBS7 is located on the long arm of chromosome 4 at cytogenetic band 4q27. This chromosomal region spans several megabases and contains multiple genes, with BBS7 occupying a discrete genomic segment within this interval. The gene comprises multiple exons that together encode the 715-amino-acid protein product.
Protein structure
Domain architecture has not been experimentally characterised in detail for this protein. The 715-amino-acid BBS7 polypeptide adopts a three-dimensional fold that enables its incorporation into the larger BBSome complex, where it contributes structural stability and mediates protein-protein interactions with other BBSome subunits.
Key variants
Pathogenic variants in BBS7 follow an autosomal recessive inheritance pattern, meaning that individuals require changes in both gene copies to develop Bardet-Biedl syndrome. The variant spectrum includes missense changes that disrupt protein folding or subunit interactions, as well as nonsense and frameshift variants that introduce premature termination signals. Some variants cluster in regions critical for BBSome assembly, whilst others affect surfaces involved in cargo recognition or complex stabilisation.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.133dup | p.Met45fs | Pathogenic/Likely pathogenic | ★★☆☆ | Bardet-Biedl syndrome 7 |
c.1579dup | p.Cys527fs | Pathogenic | ★★☆☆ | Bardet-Biedl syndrome 7 |
c.1845C>G | p.Tyr615Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Bardet-Biedl syndrome 7 |
c.1846C>T | p.Gln616Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Bardet-Biedl syndrome 7 |
c.1968del | p.Gln657fs | Pathogenic | ★★☆☆ | Bardet-Biedl syndrome 7 |
c.529-2A>G | - | Pathogenic/Likely pathogenic | ★★☆☆ | Bardet-Biedl syndrome 7 |
c.580_582del | p.Ala194del | Pathogenic/Likely pathogenic | ★★☆☆ | Retinal dystrophy |
c.613_614del | p.Glu205fs | Pathogenic/Likely pathogenic | ★★☆☆ | Bardet-Biedl syndrome 7 |
c.688T>C | p.Trp230Arg | Pathogenic/Likely pathogenic | ★★☆☆ | Bardet-Biedl syndrome |
c.690G>A | p.Trp230Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Bardet-Biedl syndrome 7 |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Biallelic pathogenic variants in BBS7 cause Bardet-Biedl syndrome, a genetically heterogeneous ciliopathy characterised by retinal degeneration, polydactyly, obesity, renal abnormalities, and developmental delay. The condition exhibits substantial clinical variability, with some individuals experiencing severe multiorgan involvement from early childhood whilst others manifest a more limited phenotype. Features typically emerge progressively, with vision loss often beginning in childhood due to rod-cone dystrophy, and obesity developing during early school years. Renal structural abnormalities may be present from birth or develop later, and cognitive impairment ranges from mild learning difficulties to more significant intellectual disability.
No disease links recorded for this gene in our reference set.
Inheritance pattern
Conditions caused by pathogenic BBS7 variants typically follow autosomal recessive inheritance.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
UK clinical status
BBS7 appears on multiple NHS Genomic Medicine Service gene panels with green (high evidence) classification, reflecting its well-established role in human disease. Relevant panels include Bardet Biedl syndrome, Fetal anomalies, Intellectual disability, Ophthalmological ciliopathies, Rare multisystem ciliopathy disorders, Renal ciliopathies, Retinal disorders, Severe early-onset obesity, and Skeletal dysplasia. The gene is also listed in the Developmental Disorders Genotype-to-Phenotype database (DDG2P) and the Limb disorders panel, underscoring its involvement in diverse developmental and metabolic pathways mediated by ciliary signalling.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
How is BBS7-related Bardet-Biedl syndrome inherited?
BBS7-related Bardet-Biedl syndrome follows autosomal recessive inheritance, meaning an individual must inherit a pathogenic variant from both parents to develop the condition. Parents who each carry one variant are typically unaffected.
What is the BBSome and why does it matter?
The BBSome is a multi-protein complex that transports molecules within cilia, the cellular antennae that sense environmental signals. When BBS7 or other BBSome components are disrupted, ciliary signalling fails across multiple organs, producing the diverse features of Bardet-Biedl syndrome.
Why does BBS7 appear on so many NHS gene panels?
Because cilia function in numerous organ systems, BBS7 variants affect multiple developmental and physiological processes. The gene appears on panels for retinal, renal, skeletal, metabolic, and neurodevelopmental disorders, reflecting the wide-ranging impact of ciliary dysfunction.