BBSome-related retinitis pigmentosa

name: BBSome-related retinitis pigmentosa
creation_date: "2026-06-14T00:00:00Z"
category: Mendelian
description: >-
  BBSome-related retinitis pigmentosa is a mechanism-anchored, cross-gene lump
  for non-syndromic (isolated) retinitis pigmentosa caused by hypomorphic or
  tissue-restricted alleles in genes of the BBSome machine - the same molecular
  complex whose more severe (typically null) alleles cause Bardet-Biedl
  syndrome. It represents the photoreceptor-restricted "floor" of the
  BBSome-opathy spectrum: because the photoreceptor connecting cilium is the most
  cilium-dependent and dosage-sensitive compartment, partial loss of BBSome
  function can be expressed there alone, sparing the obesity, polydactyly, renal
  and cognitive branches that define the full syndrome. Documented loci include
  ARL6/BBS3 (retinitis pigmentosa 55), TTC8/BBS8 (retinitis pigmentosa 51, via a
  retina-specific exon), BBS1 (whose p.M390R allele spans the entire spectrum
  from non-syndromic RP to full Bardet-Biedl syndrome), BBS2 (missense alleles),
  and BBS9 (including a hypomorphic splice allele). There is no exact MONDO
  term for this mechanistic class; the entry federates the per-locus MONDO nodes
  via mappings.
disease_term:
  preferred_term: BBSome-related retinitis pigmentosa
  term:
    id: MONDO:0019200
    label: retinitis pigmentosa
classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
  mechanistic_category:
  - classification_value: ciliopathy
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0013312
      label: retinitis pigmentosa 55
    mapping_predicate: skos:relatedMatch
    mapping_source: MONDO
    mapping_justification: Per-locus non-syndromic RP entity at the ARL6/BBS3 locus federated by this lump.
  - term:
      id: MONDO:1040065
      label: ARL6-related ciliopathy
    mapping_predicate: skos:relatedMatch
    mapping_source: MONDO
    mapping_justification: Per-locus MONDO node spanning the ARL6/BBS3 allelic series (isolated RP to BBS3).
  - term:
      id: MONDO:0013274
      label: retinitis pigmentosa 51
    mapping_predicate: skos:relatedMatch
    mapping_source: MONDO
    mapping_justification: Per-locus non-syndromic RP entity at the TTC8/BBS8 locus federated by this lump.
  - term:
      id: MONDO:1040049
      label: TTC8-related ciliopathy
    mapping_predicate: skos:relatedMatch
    mapping_source: MONDO
    mapping_justification: Per-locus MONDO node spanning the TTC8/BBS8 allelic series (isolated RP to BBS8).
  - term:
      id: MONDO:1040043
      label: BBS1-related ciliopathy
    mapping_predicate: skos:relatedMatch
    mapping_source: MONDO
    mapping_justification: Per-locus MONDO node spanning the BBS1 allelic series (isolated RP to BBS1).
  - term:
      id: MONDO:1040048
      label: BBS2-related ciliopathy
    mapping_predicate: skos:relatedMatch
    mapping_source: MONDO
    mapping_justification: Per-locus MONDO node spanning the BBS2 allelic series (isolated RP to BBS2).
  - term:
      id: MONDO:0700236
      label: BBS9-related ciliopathy
    mapping_predicate: skos:relatedMatch
    mapping_source: MONDO
    mapping_justification: Per-locus MONDO node spanning the BBS9 allelic series (isolated RP to BBS9).
parents:
- Ciliopathy
synonyms:
- BBSome-machine non-syndromic retinitis pigmentosa
notes: >-
  Evidence model for this mechanism-anchored lump (the curation discipline that
  keeps it from overstating): the MECHANISM (BBSome trafficking failure ->
  rod photoreceptor degeneration) is transferred by conformance to the
  bbsome_trafficking and photoreceptor_degeneration modules, where it is richly
  evidenced; it is NOT re-asserted from the often single-family (n-of-1) locus
  reports. The LOCUS -> human-RP ASSOCIATION at each gene rests on its own cited
  reports and should be read at that (often limited) strength - do not borrow the
  Bardet-Biedl syndrome evidence to inflate it. Grading each locus association
  with ClinGen Gene-Disease Validity (CGGV) is a documented follow-up (the pinned
  ClinGen snapshot needs refreshing before those rows can be cited). Scope is the
  strict BBSome machine plus its dedicated operators (ARL6, LZTFL1, IFT27);
  IFT-B and transition-zone loci that also cause non-syndromic RP (e.g. IFT172,
  CFAP418) are out of scope here and belong to the broader ciliopathy spectrum.
  The lump may expand as additional BBSome-machine loci are documented with
  non-syndromic RP.
inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    BBSome-related non-syndromic retinitis pigmentosa is inherited in an
    autosomal recessive pattern, as for Bardet-Biedl syndrome.
  evidence:
  - reference: PMID:23143442
    reference_title: "BBS1 mutations in a wide spectrum of phenotypes ranging from nonsyndromic retinitis pigmentosa to Bardet-Biedl syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Variants in BBS1 are significantly associated with nonsyndromic autosomal
      recessive RP and relatively mild forms of BBS.
    explanation: >-
      Documents autosomal recessive non-syndromic RP at a BBSome-machine locus.
genetic:
- name: ARL6
  association: Pathogenic biallelic variants (specific/hypomorphic alleles)
  gene_term:
    preferred_term: ARL6
    term:
      id: hgnc:13210
      label: ARL6
  notes: >-
    ARL6/BBS3 is the BBSome membrane-recruiting GTPase. A specific missense
    allele (p.A89V) impairs a retina-specific function of the BBS3L isoform while
    sparing the general transport role, producing isolated retinitis pigmentosa
    (RP55) rather than the full syndrome. Single-family / limited evidence.
  evidence:
  - reference: PMID:21282186
    reference_title: "Functional analysis of BBS3 A89V that results in non-syndromic retinal degeneration."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      homozygosity mapping with a consanguineous family with isolated retinitis
      pigmentosa identified a missense mutation in BBS3, a known BBS gene
    explanation: >-
      Anchors the ARL6/BBS3 locus -> isolated RP association to a consanguineous
      human family; this paper's own data are zebrafish functional studies.
- name: TTC8
  association: Pathogenic biallelic variants (retina-specific splice allele)
  gene_term:
    preferred_term: TTC8
    term:
      id: hgnc:20087
      label: TTC8
  notes: >-
    TTC8/BBS8 is a core BBSome subunit. An in-frame splice mutation in a
    retina-specific BBS8 exon eliminates a 10-amino-acid sequence that is the
    major BBS8 species in photoreceptors, causing non-syndromic RP (RP51) while
    sparing the systemic syndrome.
  evidence:
  - reference: PMID:20451172
    reference_title: "A splice-site mutation in a retina-specific exon of BBS8 causes nonsyndromic retinitis pigmentosa."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      an in-frame splice mutation in BBS8, one of the genes involved in
      pleiotropic Bardet-Biedl syndrome (BBS), is sufficient to cause
      nonsyndromic retinitis pigmentosa (RP)
    explanation: >-
      Directly establishes the TTC8/BBS8 locus -> non-syndromic RP association in
      a consanguineous human pedigree.
- name: BBS1
  association: Pathogenic biallelic variants (mild end of allelic spectrum)
  gene_term:
    preferred_term: BBS1
    term:
      id: hgnc:966
      label: BBS1
  notes: >-
    BBS1 is the most common BBSome subunit gene; its recurrent p.M390R allele can
    produce the full clinical spectrum from non-syndromic RP to Bardet-Biedl
    syndrome, with cis/trans modifiers influencing expressivity. The keystone
    locus for the "organ-restricted expressivity along one allelic series" model.
  evidence:
  - reference: PMID:23143442
    reference_title: "BBS1 mutations in a wide spectrum of phenotypes ranging from nonsyndromic retinitis pigmentosa to Bardet-Biedl syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The 14 patients with 2 BBS1 variants showed the entire clinical spectrum,
      from nonsyndromic RP to full-blown BBS.
    explanation: >-
      Directly demonstrates that one BBSome-machine locus spans isolated RP to
      full BBS, the basis for lumping isolated RP with BBS by mechanism.
- name: BBS2
  association: Pathogenic biallelic variants (missense alleles)
  gene_term:
    preferred_term: BBS2
    term:
      id: hgnc:967
      label: BBS2
  notes: >-
    BBS2 is a core BBSome subunit. Specific missense alleles cause non-syndromic
    retinitis pigmentosa, established in Moroccan Jewish and Ashkenazi Jewish
    families.
  evidence:
  - reference: PMID:25541840
    reference_title: "Association between missense mutations in the BBS2 gene and nonsyndromic retinitis pigmentosa."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our study shows that BBS2 mutations can cause nonsyndromic retinitis
      pigmentosa and highlights yet another candidate for this genetically
      heterogeneous condition.
    explanation: >-
      Establishes the BBS2 locus -> non-syndromic RP association in multiple
      human families with cosegregating missense mutations.
- name: BBS9
  association: Pathogenic biallelic variants (including hypomorphic splice allele)
  gene_term:
    preferred_term: BBS9
    term:
      id: hgnc:30000
      label: BBS9
  notes: >-
    BBS9 (PTHB1) is a core BBSome subunit. A novel BBS9 mutation has been
    reported with non-syndromic retinitis pigmentosa, and a separate hypomorphic
    splice-affecting allele produces a mild, essentially non-syndromic rod-cone
    dystrophy - illustrating the hypomorphic-allele -> photoreceptor-restricted
    mechanism.
  evidence:
  - reference: PMID:22353939
    reference_title: "In search of triallelism in Bardet-Biedl syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      including the occurrence of nonsyndromic retinitis pigmentosa in a family
      with a novel BBS9 mutation
    explanation: >-
      Documents the BBS9 locus -> non-syndromic RP association in a human family.
  - reference: PMID:38534779
    reference_title: "Autosomal Recessive Rod-Cone Dystrophy with Mild Extra-Ocular Manifestations Due to a Splice-Affecting Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      individuals with non-syndromic IRD or IRD with very mild extra-ocular
      manifestations
    explanation: >-
      A hypomorphic BBS9 splice allele produces a mild, essentially non-syndromic
      retinal phenotype, supporting inclusion in the BBSome-RP lump.
pathophysiology:
- name: Partial BBSome trafficking deficiency from hypomorphic alleles
  conforms_to: "bbsome_trafficking#BBSome-Dependent Ciliary Cargo Trafficking Failure"
  description: >-
    Hypomorphic or tissue-restricted alleles of BBSome-machine genes (e.g. a
    retina-specific BBS8 exon, the BBS3L isoform, or the mild BBS1 p.M390R
    allele) cause partial loss of BBSome-dependent ciliary cargo trafficking. The
    deficit is expressed in or restricted to the photoreceptor, the most
    cilium-dependent cell type, rather than across all organ branches.
  cellular_components:
  - preferred_term: primary cilium
    term:
      id: GO:0005929
      label: cilium
  biological_processes:
  - preferred_term: protein localization to cilium
    term:
      id: GO:0061512
      label: protein localization to cilium
    modifier: ABNORMAL
  evidence:
  - reference: PMID:20451172
    reference_title: "A splice-site mutation in a retina-specific exon of BBS8 causes nonsyndromic retinitis pigmentosa."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Subsequent studies showed the exon to be expressed exclusively in the
      retina and enriched significantly in the photoreceptor layer.
    explanation: >-
      Shows a retina-restricted BBSome-subunit element, explaining how a partial
      / tissue-specific lesion restricts disease to the photoreceptor.
  - reference: PMID:21282186
    reference_title: "Functional analysis of BBS3 A89V that results in non-syndromic retinal degeneration."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      These data aid in our understanding of why patients with the BBS3 A89V
      missense mutation only present with isolated retinitis pigmentosa.
    explanation: >-
      Functional evidence that a gene-specific allele restricts the BBSome defect
      to a retina-specific role, producing isolated RP.
  - reference: PMID:38534779
    reference_title: "Autosomal Recessive Rod-Cone Dystrophy with Mild Extra-Ocular Manifestations Due to a Splice-Affecting Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we suggest that this variant is likely hypomorphic. This is in agreement
      with the relatively mild phenotype observed in the patient.
    explanation: >-
      Directly ties a hypomorphic (partial-loss) BBSome-subunit allele to a mild,
      photoreceptor-restricted phenotype - the core mechanism of this lump.
  downstream:
  - target: Rod photoreceptor degeneration
    description: Photoreceptor-restricted BBSome trafficking failure drives rod photoreceptor death.
- name: Rod photoreceptor degeneration
  conforms_to: "photoreceptor_degeneration#Rod Photoreceptor Apoptosis"
  description: >-
    Photoreceptor-restricted BBSome trafficking failure produces rod-predominant
    photoreceptor degeneration, the shared final common pathway of retinitis
    pigmentosa.
  cell_types:
  - preferred_term: rod photoreceptor cell
    term:
      id: CL:0000604
      label: retinal rod cell
  - preferred_term: photoreceptor cell
    term:
      id: CL:0000210
      label: photoreceptor cell
  locations:
  - preferred_term: retina
    term:
      id: UBERON:0000966
      label: retina
  evidence:
  - reference: PMID:23143442
    reference_title: "BBS1 mutations in a wide spectrum of phenotypes ranging from nonsyndromic retinitis pigmentosa to Bardet-Biedl syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In patients with electroretinographic responses, a rod-cone pattern of
      photoreceptor degeneration was observed.
    explanation: >-
      Documents the rod-cone photoreceptor degeneration pattern in
      BBSome-machine non-syndromic RP.
  downstream:
  - target: Progressive visual loss
    description: Ongoing photoreceptor loss causes progressive visual impairment.
phenotypes:
- name: Rod-cone dystrophy
  category: Ocular
  diagnostic: true
  description: >-
    Non-syndromic rod-cone dystrophy / retinitis pigmentosa is the defining and
    sole organ manifestation in this mechanism class.
  phenotype_term:
    preferred_term: rod-cone dystrophy
    term:
      id: HP:0000510
      label: Rod-cone dystrophy
  evidence:
  - reference: PMID:20451172
    reference_title: "A splice-site mutation in a retina-specific exon of BBS8 causes nonsyndromic retinitis pigmentosa."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      an in-frame splice mutation in BBS8, one of the genes involved in
      pleiotropic Bardet-Biedl syndrome (BBS), is sufficient to cause
      nonsyndromic retinitis pigmentosa (RP)
    explanation: >-
      Establishes isolated retinitis pigmentosa as the phenotype at a
      BBSome-machine locus.
  - reference: PMID:23143442
    reference_title: "BBS1 mutations in a wide spectrum of phenotypes ranging from nonsyndromic retinitis pigmentosa to Bardet-Biedl syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In patients with electroretinographic responses, a rod-cone pattern of
      photoreceptor degeneration was observed.
    explanation: >-
      Confirms the rod-cone dystrophy pattern in BBSome-machine non-syndromic RP.
- name: Visual impairment
  category: Ocular
  description: >-
    Reduced visual acuity from progressive photoreceptor degeneration.
  phenotype_term:
    preferred_term: Visual impairment
    term:
      id: HP:0000505
      label: Visual impairment
  evidence:
  - reference: PMID:23143442
    reference_title: "BBS1 mutations in a wide spectrum of phenotypes ranging from nonsyndromic retinitis pigmentosa to Bardet-Biedl syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In 8 of 14 patients, visual acuity was significantly reduced.
    explanation: >-
      Documents clinically significant visual impairment in BBSome-machine
      non-syndromic RP.
references:
- reference: PMID:23143442
  title: >-
    BBS1 mutations in a wide spectrum of phenotypes ranging from nonsyndromic
    retinitis pigmentosa to Bardet-Biedl syndrome.
  findings: []
- reference: PMID:20451172
  title: >-
    A splice-site mutation in a retina-specific exon of BBS8 causes nonsyndromic
    retinitis pigmentosa.
  findings: []