EYA1-Related Branchiootorenal Spectrum Disorder: Disease-Characteristics Report

Executive summary

EYA1-related branchiootorenal spectrum disorder (EYA1-BOSD) is an autosomal-dominant congenital developmental disorder affecting derivatives of the pharyngeal/branchial apparatus, external–middle–inner ear, and kidney/urinary tract. “Branchio-oto-renal syndrome” (BOR) denotes renal involvement; “branchio-otic syndrome” (BO/BOS) denotes an allelic presentation without recognized renal anomalies. Because renal findings can be absent, subtle, unilateral, or detected later, these are best treated as a spectrum rather than completely separate diseases. EYA1 loss of function and haploinsufficiency are the principal mechanisms. Expressivity is strikingly variable, including among relatives with the same variant. (zhang2024novellikelypathogenic pages 1-2, zhang2024novellikelypathogenic pages 4-7, ruf2004six1mutationscause pages 1-2, kochhar2007branchio‐oto‐renalsyndrome pages 1-2)

The most important recent development is improved detection of EYA1 structural variants. In a July 2024 Korean cohort of 41 people from 23 families, panel/exome sequencing diagnosed 78.3% of families, CNV analysis plus MLPA increased yield to 82.6%, and WGS—which detected a complex rearrangement and cryptic inversion—increased it to 91.3%. This unusually high yield reflects a selected rare-disease-center cohort and should not be generalized to all patients. (cho2024genomiclandscapeof pages 2-4, cho2024genomiclandscapeof pages 5-7, cho2024genomiclandscapeof media c28a0da1)

Table: This table condenses the most useful knowledge-base fields for EYA1-related branchiootorenal spectrum disorder, emphasizing recent cohort statistics, molecular mechanisms, diagnostic yield, and practical management. It also flags important areas where evidence is limited or not established.

1. Disease information

Definition and scope

BOR is defined by variable combinations of hearing loss, preauricular pits, auricular and auditory-canal malformations, second branchial-arch cysts/fistulae, and congenital kidney/urinary-tract anomalies. BO is the corresponding phenotype without identified renal disease. The historical review describes the core phenotype as “hearing loss, auricular malformations, branchial arch remnants, and renal anomalies.” (kochhar2007branchio‐oto‐renalsyndrome pages 1-2)

This report is restricted to EYA1-related disease. SIX1-related BOR/BO is phenotypically overlapping but molecularly distinct; the pathogenic role historically assigned to SIX5 remains disputed. In a 2011 series of 140 patients from 124 families, investigators found 36 EYA1 mutations in 42 unrelated patients and SIX1 findings in three, but no convincing SIX5 mutation; more recent cohort summaries likewise found no SIX5 variants. (krug2011mutationscreeningof pages 1-4, cho2024genomiclandscapeof pages 8-9)

Identifiers and synonyms

• OMIM phenotype: BOR syndrome, 113650; BO syndrome, 602588.
• Gene: EYA1, OMIM 601653, chromosome 8q13.3; HGNC-approved symbol EYA1.
• MONDO: Use the current MONDO entry for branchiootorenal syndrome and qualify it with the causal gene EYA1. The exact MONDO accession was not present in the retrieved primary texts and should be verified against the current MONDO release rather than inferred.
• Orphanet: Branchio-oto-renal syndrome is represented in Orphanet; verify the live ORPHA accession during ingestion.
• ICD-10/ICD-11: There is no sufficiently specific disease code established in the retrieved literature; coding generally uses congenital ear, branchial-cleft, hearing-loss, and renal-malformation codes.
• MeSH: No uniquely disease-specific MeSH identifier was established from the retrieved sources.
• Synonyms: branchio-oto-renal syndrome; BOR syndrome; branchiootorenal syndrome; branchio-oto-renal dysplasia; branchio-otic syndrome; BO/BOS; ear pits–deafness syndrome; preauricular pits–cervical fistulae–hearing-loss syndrome. (ruf2004six1mutationscause pages 1-2, kochhar2007branchio‐oto‐renalsyndrome pages 1-2)

The evidence summarized here is predominantly aggregated disease-level literature—cohorts, family series, and reviews—not EHR-derived individual-level data. The 2022–2024 variant reports are individual families/cases with functional follow-up. (zhang2024novellikelypathogenic pages 1-2, zhang2024novellikelypathogenic pages 4-7, cacciatori2022fromclinicalto pages 1-2)

2. Etiology, risk, protection, and gene–environment interaction

Causal factor

The primary cause is a heterozygous germline pathogenic or likely pathogenic EYA1 variant, most often producing loss of function and haploinsufficiency. Variant classes include nonsense, frameshift, splice-altering, intragenic or whole-gene deletions, and more cryptic structural rearrangements or inversions. Missense variants, especially in the conserved EYA domain, can impair protein interactions, localization, stability, or transcriptional function. More than 200 EYA1 pathogenic variants had been reported by 2024. (zhang2024novellikelypathogenic pages 1-2, zhang2024novellikelypathogenic pages 4-7, cho2024genomiclandscapeof pages 5-7)

Risk factors

• Genetic: An affected parent or heterozygous pathogenic EYA1 allele is the dominant risk factor. Each child of a heterozygous individual has a 50% transmission probability, although phenotype severity cannot be predicted reliably because of variable expressivity and reduced penetrance. De novo variants also occur. (cho2024genomiclandscapeof pages 5-7, ruf2004six1mutationscause pages 1-2, kochhar2007branchio‐oto‐renalsyndrome pages 1-2)
• Family history: Highly informative but not required because de novo disease and clinically subtle parental disease are possible.
• Modifier genes: No reproducible human modifier gene currently explains renal versus nonrenal presentation or hearing severity. Candidate modifiers within the PAX–SIX–EYA–DACH network remain biologically plausible but unvalidated clinically.
• Environment, lifestyle, infection, sex, age: No environmental toxin, infection, diet, smoking, alcohol, occupation, or sex-specific exposure is established as a cause of EYA1-BOSD. Age affects ascertainment and complications, not the congenital genetic cause.

Protective factors and gene–environment interaction

No validated protective allele or environmental protective factor is known. Likewise, no disease-specific gene–environment interaction has been demonstrated. Avoiding nephrotoxins and excessive noise may protect residual renal and auditory function but does not prevent the congenital malformations; this is prudent clinical risk reduction rather than demonstrated etiologic modification.

3. Phenotypes

Frequency and variability

In the 2024 Korean BOR/BO cohort, hearing loss occurred in 40/41 patients (98%), preauricular pits in 34/41 (83%), branchial anomalies in 27/41 (66%), and renal anomalies in 6/41 (15%). Middle-ear, inner-ear, and external auditory-canal anomalies occurred in 54%, 39%, and 20%, respectively. These are mixed EYA1/SIX1/other cases, not EYA1-only frequencies. (cho2024genomiclandscapeof pages 2-4, cho2024genomiclandscapeof media e0acb455)

A historical synthesis of genotyped EYA1 families reported deafness in 98.5%, preauricular pits in 83.6%, branchial anomalies in 68.5%, renal anomalies in 38.2%, and external-ear abnormalities in 31.5%. An older clinically defined 45-patient series reported hearing loss in 93%, pits/tags in 82%, renal anomalies in 67%, branchial fistulae in 49%, pinna deformity in 36%, and auditory-canal stenosis in 29%. Differences reflect ascertainment, genotype composition, imaging, and diagnostic criteria. (kochhar2007branchio‐oto‐renalsyndrome pages 2-3, kochhar2007branchio‐oto‐renalsyndrome pages 1-2)

Suggested phenotypic annotations include:

• Hearing loss: congenital or childhood-to-young-adult onset; conductive, sensorineural, or mixed; mild to profound; may be stable or progressive. Suggested HPO: Hearing impairment; Conductive hearing impairment; Sensorineural hearing impairment; Mixed hearing impairment; Profound hearing impairment. Hearing disability affects spoken-language acquisition, education, employment, and social participation; early detection is therefore a critical quality-of-life intervention. (neal2024usingxenopusto pages 1-3, ruf2004six1mutationscause pages 1-2, kochhar2007branchio‐oto‐renalsyndrome pages 1-2)
• Preauricular pits/sinuses and tags: congenital, usually stable; may become recurrently infected. Suggested HPO: Preauricular pit; Preauricular skin tag.
• Branchial cyst, sinus, or fistula: congenital, sometimes recognized after recurrent drainage or infection; commonly related to second branchial-arch derivatives. Suggested HPO: Branchial fistula; Branchial cyst. (neal2024usingxenopusto pages 1-3, kochhar2007branchio‐oto‐renalsyndrome pages 1-2)
• Auricular/external auditory-canal malformations: cup-shaped or malformed pinnae, canal stenosis/atresia; congenital and usually nonprogressive structurally. Suggested HPO: Abnormal pinna morphology; External auditory canal stenosis.
• Middle-ear abnormalities: malformed or fixed ossicles and other structural anomalies causing a conductive component. Suggested HPO: Abnormal middle-ear morphology; Abnormality of the ossicles.
• Inner-ear abnormalities: cochlear and vestibular malformations, including reduced cochlear turns in some patients; may contribute to sensorineural loss. Suggested HPO: Abnormal cochlear morphology; Abnormal vestibular system morphology.
• Renal/urinary anomalies: renal agenesis/aplasia, hypoplasia or dysplasia, collecting-system anomalies, hydronephrosis, and occasionally progressive proteinuria, focal glomerulosclerosis, chronic kidney disease, or kidney failure. Suggested HPO: Renal agenesis; Renal hypoplasia; Renal dysplasia; Hydronephrosis; Proteinuria; Chronic kidney disease. Severity ranges from clinically silent unilateral disease to end-stage kidney disease. (zhang2024novellikelypathogenic pages 4-7, ruf2004six1mutationscause pages 1-2, kochhar2007branchio‐oto‐renalsyndrome pages 1-2)
• Less-established associated findings: facial asymmetry, palatal abnormalities, lacrimal-duct anomalies, shoulder abnormalities, thyroid/parathyroid or pituitary findings, and developmental delay have been reported, but some may reflect larger 8q deletions, blended diagnoses, or case-level associations rather than core EYA1-BOSD. (zhang2024novellikelypathogenic pages 8-9, cho2024genomiclandscapeof pages 5-7, kochhar2007branchio‐oto‐renalsyndrome pages 1-2)

No robust BOR-specific EQ-5D, SF-36, PROMIS, or disease-specific quality-of-life dataset was identified. Quality-of-life burden is inferred primarily from hearing/language disability, recurrent branchial or pit infection, surgery, and chronic kidney disease.

4. Genetic and molecular information

Causal gene and variants

EYA1 encodes a transcriptional coactivator with a conserved C-terminal EYA domain. It lacks sequence-specific DNA-binding capacity and works with DNA-binding SIX proteins. The EYA1–SIX1 complex participates in the PAX–SIX–EYA developmental regulatory network. (zhang2024novellikelypathogenic pages 1-2, ruf2004six1mutationscause pages 1-2, kochhar2007branchio‐oto‐renalsyndrome pages 1-2)

EYA1 pathogenic variation is constitutionally germline and heterozygous, not a somatic cancer mechanism. Pathogenic alleles are expected to be absent or exceptionally rare in population databases. For example, the functionally tested c.1050+4 splice-region variant was absent from 1000 Genomes, ESP6500, gnomAD, and ExAC. Variant-level frequency should nevertheless be checked against the current gnomAD release during curation. (chen2023anovel<i>eya1<i> pages 1-1)

Representative recent variants include:

• NM_000503.6:c.639+3A>C, likely pathogenic: exon 8 skipping in a minigene assay, predicted premature termination/nonsense-mediated decay and haploinsufficiency. (zhang2024novellikelypathogenic pages 1-2, zhang2024novellikelypathogenic pages 4-7)
• c.1050+4A>C/G, pathogenic in a 2023 family: exon 11 skipping, reduced expression, cellular mislocalization, and impaired EYA1–SIX1 interaction. (chen2023anovel<i>eya1<i> pages 1-1)
• c.1425delC p.(Asp476Thrfs4), c.889C>T p.(Arg297), c.1050+1G>T, and c.1140+1G>A, reported in a 2021 Chinese cohort. (feng2021geneticandphenotypic pages 1-2)
• Recurrent 8q13.2–q13.3 deletions can remove EYA1 and neighboring genes; larger deletions may produce additional phenotypes. (cacciatori2022fromclinicalto pages 1-2)

In the 2024 Korean cohort, 12/23 families (52%) had EYA1 variants: coding SNVs, canonical splice variants, and structural variants. Across reviewed cohort studies, structural variants constituted 8.7% of reported mutations; approximately 89% of those SVs were EYA1 deletions, with smaller numbers of inversions and complex rearrangements. (cho2024genomiclandscapeof pages 5-7)

Classification and consequences

Classification should follow ACMG/AMP criteria with segregation, phenotype specificity, population frequency, predicted loss of function, RNA studies, and structural-variant evidence. Deep intronic or noncanonical splice variants should not be upgraded solely from prediction; RNA/minigene evidence can be decisive, as illustrated by c.639+3A>C. (zhang2024novellikelypathogenic pages 4-7, chen2023anovel<i>eya1<i> pages 1-1)

Haploinsufficiency is the dominant model. Some missense alleles may exert severe loss-of-function or interaction defects, but a general dominant-negative mechanism has not been established for all EYA1 missense variants. No clinically validated EYA1 epigenetic signature, disease-specific methylation assay, or recurrent acquired chromatin alteration was identified.

5. Environmental information

EYA1-BOSD is not an infectious, toxic, radiation-induced, occupational, nutritional, or lifestyle-mediated disorder. No causative pathogen or actionable environmental exposure was identified. General measures—avoiding nephrotoxic medication when alternatives exist, controlling blood pressure in kidney disease, preventing recurrent skin-pit/branchial infections, and protecting residual hearing—are complication-reduction measures, not etiologic therapy.

6. Mechanism and pathophysiology

Causal chain

1. Upstream trigger: a heterozygous EYA1 loss-of-function, splice, deletion, or function-disrupting missense/SV allele.
2. Molecular defect: reduced EYA1 dosage or abnormal localization/stability and impaired interaction with SIX1.
3. Regulatory failure: deficient EYA1–SIX1 transcriptional complexes and altered developmental target-gene expression in preplacodal/otic ectoderm, pharyngeal apparatus, cranial mesenchyme, and metanephric progenitor/ureteric-bud signaling compartments.
4. Cellular-developmental consequences: abnormal survival, proliferation, differentiation, induction, and branching morphogenesis of ear and kidney primordia.
5. Anatomical outcome: malformed auditory structures, persistent branchial remnants, and congenital renal/urinary anomalies.
6. Clinical outcome: conductive/sensorineural/mixed hearing loss, pits/fistulae/cysts, and a variable risk of chronic kidney disease. (zhang2024novellikelypathogenic pages 1-2, zhang2024novellikelypathogenic pages 4-7, ruf2004six1mutationscause pages 1-2)

The landmark biochemical study states that SIX1 mutations cause disease “by disruption of EYA1–SIX1–DNA complexes”; all three tested mutations affected EYA1–SIX1 interaction, while homeodomain mutations impaired specific DNA binding. Although that experiment tested SIX1 alleles, it establishes the functional complex in which EYA1 operates. (ruf2004six1mutationscause pages 1-2)

Mouse evidence indicates that Eya1 deficiency produces absent ears and kidneys with abnormal apoptosis of organ primordia. Zebrafish eya1 models impair cell survival and differentiation in the inner ear and lateral line. Xenopus experiments show that BOR-associated perturbation of the network changes neural-border, neural-crest, preplacodal, and otic gene-expression domains and reduces otic-capsule, otolith, lumen, and sensory-patch structures. These are model-organism findings, not direct measurements from patient fetal tissues. (zhang2024novellikelypathogenic pages 8-9, neal2024usingxenopusto pages 1-3, ruf2004six1mutationscause pages 1-2)

Suggested ontology annotations:

• GO biological processes: ear morphogenesis; inner ear development; sensory-organ development; kidney development; metanephros development; branching morphogenesis; regulation of transcription by RNA polymerase II; apoptotic process; cell differentiation.
• GO molecular functions: transcription coactivator activity; protein binding; phosphatase activity.
• GO cellular component: nucleus; transcription-regulator complex.
• Cell Ontology labels: otic epithelial cell/otic placode cell; inner-ear sensory hair cell; cranial neural-crest cell; metanephric mesenchymal cell; ureteric-bud epithelial cell. Exact current CL accessions should be ontology-validated during ingestion.

No validated patient metabolomic, lipidomic, proteomic, single-cell, spatial-transcriptomic, or integrated multi-omic disease signature exists. Recent Xenopus work combined transcriptomic, yeast-two-hybrid, and proteomic approaches to nominate Six1 targets and cofactors, but these remain developmental candidates rather than clinical biomarkers. (neal2024usingxenopusto pages 1-3)

7. Anatomical structures affected

Primary structures are the second pharyngeal/branchial apparatus, pinna and preauricular region, external auditory canal, middle-ear ossicles/cavity, cochlea and vestibular labyrinth, and kidney/urinary collecting system. Secondary consequences include auditory neural-development effects and chronic renal parenchymal damage. (neal2024usingxenopusto pages 1-3, kochhar2007branchio‐oto‐renalsyndrome pages 2-3, kochhar2007branchio‐oto‐renalsyndrome pages 1-2)

Suggested UBERON labels include pharyngeal arch, external ear, pinna, external acoustic meatus, middle ear, auditory ossicle, inner ear, cochlea, vestibular apparatus, kidney, metanephros, ureteric bud, and urinary collecting system. At the subcellular level, the principal compartment is the nucleus, where the EYA1–SIX1 transcriptional complex acts.

Findings may be unilateral, bilateral, or asymmetric. Hearing loss and pits are frequently bilateral but need not be; renal disease may range from unilateral hypoplasia/agenesis to bilateral dysplasia, and severity on one side does not reliably predict the other.

8. Temporal development and natural history

The anatomical disorder originates prenatally during organogenesis. Pits, branchial remnants, ear malformations, and renal anomalies are congenital, although ascertainment can occur later. Hearing loss may be evident on newborn screening or emerge from early childhood through young adulthood; severity ranges from mild to profound. (ruf2004six1mutationscause pages 1-2, kochhar2007branchio‐oto‐renalsyndrome pages 1-2)

There is no formal staging system. The course is lifelong and component-specific:

• Structural malformations are generally stable.
• Hearing may remain stable or progress; otitis media can add a fluctuating conductive component.
• Branchial cysts/fistulae and preauricular sinuses can have episodic drainage or infection.
• Renal function may remain normal with unilateral disease or progress through proteinuria/CKD to kidney failure in severe cases. A 2024 family included small kidneys through end-stage disease, emphasizing intrafamilial variability. (zhang2024novellikelypathogenic pages 4-7)

There is no spontaneous molecular remission. Critical intervention windows include newborn/early-childhood hearing detection and language habilitation, early baseline renal imaging/function assessment, and timely treatment of recurrent branchial or pit infection.

9. Inheritance and population

Inheritance is autosomal dominant. Penetrance is high but incomplete, and expressivity is markedly variable within and between families. Anticipation and parent-of-origin effects were proposed historically but subsequently discounted; no repeat-expansion mechanism is known. Germline mosaicism is biologically possible but its frequency is unquantified. Consanguinity is not a characteristic risk factor for this dominant condition. (ruf2004six1mutationscause pages 1-2, kochhar2007branchio‐oto‐renalsyndrome pages 1-2)

The often-cited incidence/prevalence is approximately 1:40,000, with BOR/BO historically estimated to account for about 2% of profound childhood deafness. These estimates are old and not population-registry-quality contemporary statistics. (feng2021geneticandphenotypic pages 1-2, ruf2004six1mutationscause pages 1-2, kochhar2007branchio‐oto‐renalsyndrome pages 1-2)

No consistent sex bias is established. Disease occurs across ancestries. Reported renal-anomaly frequencies differed among East Asian literature sets—14% in Chinese, 39% in Japanese, and 41% in Korean cases—but ascertainment and cohort composition make a true ancestry effect uncertain. (feng2021geneticandphenotypic pages 7-8)

No robust carrier frequency, founder effect, or geographic hotspot for EYA1-BOSD was identified. Because pathogenic variants are generally private and rare, population carrier frequency cannot be inferred safely from the 1:40,000 clinical estimate.

10. Diagnostics

Clinical criteria

Typical BOR/BO is diagnosed clinically by any of the following:

1. three major criteria;
2. two major plus two minor criteria; or
3. one major criterion plus an affected first-degree relative meeting criteria.

Major criteria are branchial anomalies, hearing loss, preauricular pits, renal anomalies, and—in some contemporary formulations—auricular deformity. Minor criteria include external-, middle-, or inner-ear anomalies, preauricular tags, facial asymmetry, and palatal abnormalities. A molecularly confirmed person who does not meet these combinations may be labeled atypical BOR/BO. (cacciatori2022fromclinicalto pages 1-2, cho2024genomiclandscapeof pages 2-4, kochhar2007branchio‐oto‐renalsyndrome pages 2-3, cho2024genomiclandscapeof media e0acb455)

Clinical evaluation

Recommended baseline characterization includes:

• otoscopic and dysmorphology examination;
• age-appropriate pure-tone/behavioral audiometry, tympanometry, otoacoustic emissions, and/or auditory brainstem response;
• temporal-bone CT when anatomy will influence surgery or implant planning; MRI when cochlear nerve/soft-tissue assessment is needed;
• renal and urinary-tract ultrasound;
• urinalysis/protein quantification, serum creatinine/eGFR, electrolytes, and blood pressure;
• nephrology review for structural disease, reduced function, hypertension, or proteinuria.

There is no diagnostic enzyme assay, circulating protein/metabolite biomarker, characteristic biopsy requirement, or validated liquid biopsy.

Genetic-testing strategy

1. Use a hearing-loss/BOR/CAKUT panel or sequencing of EYA1 and SIX1, with EYA1 deletion/duplication analysis built in. For an explicitly EYA1-focused phenotype, single-gene sequencing plus dosage analysis is reasonable.
2. If sequencing is negative, perform exon-level and whole-gene CNV testing by MLPA or equivalent validated methods and consider chromosomal microarray for a larger 8q13 deletion, particularly if developmental or additional congenital features are present.
3. If suspicion remains high, use WGS with structural-variant calling; WGS can detect inversions and complex or balanced rearrangements missed by exome/CNV methods.
4. RNA or minigene analysis is useful for noncanonical splice-region VUSs.
5. Karyotyping/FISH is not routine but may clarify a cytogenetically visible rearrangement. Mitochondrial and repeat-expansion testing are not disease-specific. (cacciatori2022fromclinicalto pages 1-2, zhang2024novellikelypathogenic pages 4-7, cho2024genomiclandscapeof pages 2-4, cho2024genomiclandscapeof pages 5-7)

The 2024 stepwise data—78.3%, 82.6%, and 91.3% cumulative yield after sequencing, MLPA/CNV, and WGS—visually demonstrate why negative exome sequencing does not exclude EYA1-BOSD. (cho2024genomiclandscapeof media c28a0da1)

Differential diagnosis

Important alternatives include SIX1-related BOR/BO, isolated preauricular pits or branchial-cleft anomalies, nonsyndromic hearing loss, PAX2-related renal-coloboma syndrome, SALL1-related Townes–Brocks syndrome, 22q11.2 deletion syndrome, CHARGE syndrome, Alport syndrome, branchio-oculo-facial syndrome, otofaciocervical spectrum, and broader CAKUT syndromes. Distinguishing clues are the combination of branchial remnants, pits, ear architecture, hearing phenotype, renal imaging, ocular/anal/limb/palatal findings, and molecular testing.

Cascade testing is appropriate for relatives after a familial variant is found. Population newborn screening tests hearing, not EYA1 specifically. Prenatal diagnosis and preimplantation genetic testing are technically possible for a known familial variant, but phenotype severity remains unpredictable.

11. Outcome and prognosis

No reliable five- or ten-year survival statistic or disease-specific mortality rate exists. Life expectancy is likely near normal for many individuals with preserved renal function, but severe bilateral renal dysplasia or progressive CKD can cause substantial morbidity and mortality. Prognosis is therefore driven chiefly by renal reserve and hearing severity rather than by the presence of pits or branchial remnants.

Long-term morbidity includes communication and educational disability, recurrent infections, repeated otologic or branchial surgery, chronic kidney disease, hypertension, proteinuria, and kidney failure. Hearing rehabilitation can substantially improve function, but response depends on conductive versus sensorineural components and detailed anatomy. No validated molecular prognostic biomarker or reliable EYA1 genotype–phenotype model predicts renal outcome. Marked intrafamilial variability is itself an important counseling point. (feng2021geneticandphenotypic pages 7-8, zhang2024novellikelypathogenic pages 4-7, zhang2024novellikelypathogenic pages 1-2)

12. Treatment

There is no disease-modifying pharmacotherapy for EYA1 haploinsufficiency and no approved gene, cell, RNA, or targeted therapy.

• Hearing: conventional air-conduction or bone-conduction hearing aids as anatomically appropriate; speech/language therapy and educational support; cochlear implantation for suitable severe–profound sensorineural loss; selected canal/ossicular surgery after careful imaging and counseling. Outcomes from middle-ear surgery are inconsistent: a 2021 cohort reported unsuccessful procedures but hearing gains with cochlear implantation, whereas a 2023 family report documented postoperative improvement. This supports individualized rather than routine reconstructive surgery. (feng2021geneticandphenotypic pages 1-2, chen2023anovel<i>eya1<i> pages 1-1)
• Renal: standard CAKUT/CKD care—blood-pressure and proteinuria control, avoidance of nephrotoxins, treatment of urinary infection or obstruction, nephrology surveillance, dialysis, and transplantation when indicated.
• Branchial and preauricular lesions: antibiotics for acute bacterial infection and complete surgical excision for recurrently infected or persistently draining cysts, sinuses, or fistulae.
• Rehabilitation/support: audiology, otolaryngology, nephrology, clinical genetics, speech-language therapy, school accommodations, and psychosocial support.

Suggested NCIT intervention labels include Genetic Counseling; Genetic Testing; Audiometry; Hearing Aid; Cochlear Implantation; Speech Therapy; Surgical Resection/Excision; Renal Ultrasound; Hemodialysis; Peritoneal Dialysis; and Kidney Transplantation. Exact NCIT accessions should be validated in the current release.

No relevant disease-specific interventional trial or NCT identifier was retrieved. Pharmacogenomic guidance is not EYA1-specific.

13. Prevention

Primary prevention by vaccination, diet, lifestyle, or exposure avoidance is not available. Before pregnancy, genetic counseling can explain the 50% transmission risk, variable expression, prenatal diagnosis, and preimplantation genetic testing. Secondary prevention consists of cascade testing, newborn hearing screening, early molecular diagnosis, renal ultrasound/function assessment, and testing of apparently mildly affected relatives. Tertiary prevention includes early auditory habilitation, renal surveillance, blood-pressure/proteinuria management, avoidance of nephrotoxins, and treatment of recurrent branchial/pit infection.

Because phenotype severity cannot be predicted from the familial allele, reproductive counseling must avoid implying that prenatal genotype predicts whether a child will have BO, mild BOR, or severe renal disease.

14. Other species and natural disease

No well-established naturally occurring veterinary EYA1 branchiootorenal syndrome was identified. There is no infectious transmission or zoonotic potential. Comparative value instead comes from experimentally studied orthologs in:

• Mus musculus—NCBI Taxonomy 10090, Eya1;
• Danio rerio—Taxonomy 7955, eya1;
• Xenopus laevis—Taxonomy 8355, eya1 orthologs;
• Drosophila melanogaster—Taxonomy 7227, eyes absent (eya).

The conserved EYA–SIX developmental network explains why these species are informative despite differences in ear and kidney anatomy. NCBI Gene IDs and VBO breed terms should be resolved directly from current organism databases; breed-specific natural disease is not established.

15. Model organisms

• Mouse Eya1 loss-of-function: absent or severely abnormal ears and kidneys, abnormal apoptosis of organ primordia, and broader craniofacial/endocrine-organ defects. It strongly models severe developmental consequences but is often more extreme than heterozygous human disease. (zhang2024novellikelypathogenic pages 8-9, ruf2004six1mutationscause pages 1-2)
• Zebrafish dog-eared/eya1: defective survival and differentiation in the inner ear and lateral-line sensory system. It is valuable for live developmental imaging and sensory-cell biology but does not reproduce mammalian middle-ear or metanephric anatomy directly.
• Xenopus: microinjection, mutant-expression, transcriptomic, protein-interaction, and proteomic approaches permit rapid study of preplacodal, cranial, and otic development. BOR-associated network variants alter craniofacial/otic expression domains and reduce otic structures. Limitations include overexpression artifacts and amphibian anatomical differences. (neal2024usingxenopusto pages 1-3)
• Cellular/minigene systems: patient-variant splice assays, immunoprecipitation, localization, and expression studies directly test RNA and protein consequences. They are strong for ACMG functional evidence but do not reproduce multicellular kidney/ear morphogenesis. (zhang2024novellikelypathogenic pages 1-2, zhang2024novellikelypathogenic pages 4-7, chen2023anovel<i>eya1<i> pages 1-1)

Recent developments and expert interpretation

Three 2023–2024 developments are most actionable. First, functional RNA assays can convert plausible noncanonical splice VUSs into clinically interpretable findings; the 2024 c.639+3A>C study demonstrated exon skipping and a loss-of-function mechanism. Its abstract concludes that the report “enriches the mutational spectrum of pathogenic variants in the EYA1 gene.” (zhang2024novellikelypathogenic pages 1-2, zhang2024novellikelypathogenic pages 4-7)

Second, WGS is increasingly important after negative sequencing and dosage testing. The 2024 Korean study reported that integrating WGS detected “cryptic inversion and complex genomic rearrangement,” ultimately reaching a 91% diagnostic yield. This supports explicit structural-variant analysis rather than merely broader SNV panels. (cho2024genomiclandscapeof pages 2-4, cho2024genomiclandscapeof pages 5-7)

Third, developmental multi-omics is expanding candidate networks: the 2024 Xenopus review reports transcriptomic, yeast-two-hybrid, and proteomic approaches that “revealed a large number of new candidates.” These results improve biological understanding but have not yet produced validated human modifiers, biomarkers, or therapies. (neal2024usingxenopusto pages 1-3)

Evidence limitations

BOR literature combines clinically diagnosed BOR/BO, EYA1-positive disease, SIX1-positive disease, and genetically unresolved cases. Consequently, mixed-cohort frequencies must not be represented as EYA1-specific penetrance. Prevalence estimates are historical; modern population-based incidence, sex ratio, survival, quality-of-life, and renal natural-history data are sparse. Case reports establish possibility—not frequency—of kidney failure, developmental delay, pituitary findings, or unusual glomerular lesions. Finally, database accessions and ontology IDs not printed in the retrieved literature should be validated against live MONDO, Orphanet, HPO, GO, CL, UBERON, NCIT, ClinVar, and gnomAD releases before production ingestion.

References

1. (zhang2024novellikelypathogenic pages 1-2): Hui Zhang, Jian Gao, Hanjun Wang, Mengli Liu, Shuangshuang Lu, Hongen Xu, Wenxue Tang, and Guoxi Zheng. Novel likely pathogenic variant in the eya1 gene causing branchio oto renal syndrome and the exploration of pathogenic mechanisms. BMC Medical Genomics, Apr 2024. URL: https://doi.org/10.1186/s12920-024-01858-y, doi:10.1186/s12920-024-01858-y. This article has 6 citations and is from a peer-reviewed journal.

2. (zhang2024novellikelypathogenic pages 4-7): Hui Zhang, Jian Gao, Hanjun Wang, Mengli Liu, Shuangshuang Lu, Hongen Xu, Wenxue Tang, and Guoxi Zheng. Novel likely pathogenic variant in the eya1 gene causing branchio oto renal syndrome and the exploration of pathogenic mechanisms. BMC Medical Genomics, Apr 2024. URL: https://doi.org/10.1186/s12920-024-01858-y, doi:10.1186/s12920-024-01858-y. This article has 6 citations and is from a peer-reviewed journal.

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