👪

Inheritance

1

Autosomal recessive HP:0000007

Biallelic EPS8L2 variants, homozygous in consanguineous families and compound heterozygous in others. In the founding family the variant was homozygous in both affected siblings and heterozygous in the unaffected parents and an unaffected sibling. One reported compound heterozygote carries a de novo allele in trans with a maternally inherited one, which is worth knowing because a de novo allele in a recessive disease breaks the usual assumption that both parents are carriers.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:26282398 SUPPORT Human Clinical

"It was detected at the homozygous state in the two clinically affected siblings, and at the heterozygous state in the unaffected parents and one unaffected sibling"

Textbook recessive segregation in the founding family.

PMID:41578500 SUPPORT Human Clinical

"Notably, the c.357_361dupGGTGC variant was a de novo mutation in the patient, whereas c.1317dupG was inherited from his mother."

A de novo allele in trans with an inherited one - so carrier testing of both parents would have been falsely reassuring in this family.

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Discussions and Knowledge Gaps

1

How wide is the therapeutic window in DFNB106 - at what point does hair bundle deterioration become irreversible, and would restoring EPS8L2 during the progressive phase halt or reverse the loss?

KNOWLEDGE GAP eps8l2_therapeutic_window

Attached to

pathophysiology#Progressive Hair Bundle Disorganisation diagnosis#Early genetic testing despite passed newborn screening

Most recessive nonsyndromic deafness genes cause congenital, severe-to-profound loss, where by the time of diagnosis the substrate for intervention is largely gone. DFNB106 is different in a way that matters therapeutically: hearing starts at moderate levels and deteriorates, so hair cells persist during a period when a gene-replacement or protein-restoration approach could in principle act. The 2026 series makes this argument explicitly and identifies natural history as the missing piece needed for preclinical modelling. What is genuinely unknown is the shape of that window. Nobody has established whether the tall-row shortening seen in the mouse is reversible if EPS8L2 is restored, or whether the bundle passes a point after which restoring the maintenance protein cannot rebuild what has already degraded - and the maintenance-not-elongation division of labour between EPS8L2 and EPS8 makes the pessimistic reading plausible, since EPS8L2 may be unable to regrow stereocilia it can only preserve. The mouse is well suited to answering this with an inducible rescue, and the outbred dog model offers a complementary system on a naturally occurring allele.

Show evidence (5 references)

PMID:41514136 SUPPORT Model Organism

"A preclinical gene therapy study of an Eps8 knockout mouse using adeno-associated virus (AAV) delivery of the EPS8 transgene with the Anc80L65 AAV serotype showed rescue to the hair bundle structure but failed to rescue functional hearing"

The empirical form of the pessimistic reading, and stronger than the inference it replaces. In the paralogous gene, AAV delivery restored bundle structure and still failed to restore hearing - so structural rescue is not sufficient, which is exactly the risk a maintenance protein faces. Graded PARTIAL because it is EPS8 rather than EPS8L2, and MODEL_ORGANISM because the result quoted is a mouse experiment. The quote stops before the paper's [16] citation marker, which the reference validator strips before matching; the transduction rates that follow it are not needed for this claim.

PMID:41514136 SUPPORT Model Organism

"When delayed to postnatal day 3, almost no recovery was observed, shrinking the targeted delivery of all studies to between 1 and 2 days after birth."

The width of the window in the mouse, and the reason the human window matters: in mouse it closes within days of birth. Whether the human progressive phase is a correspondingly narrow window or a genuinely longer one is the unresolved question.

PMID:41514136 SUPPORT Human Clinical

"This work emphasizes the need for early molecular diagnosis and long-term clinical follow-up, while describing the natural history of EPS8L2 that will be important for future therapeutic development."

The authors' framing of natural history as a prerequisite for therapy development.

+ 2 more references

⚙

Pathophysiology

4

EPS8L2 Loss of Function

Biallelic EPS8L2 variants, predominantly frameshift and nonsense, predicted to yield a severely truncated inactive protein or none at all through nonsense-mediated decay. A missense variant has also been reported but acts by a splicing mechanism rather than by amino acid substitution: c.767C>G causes exon 9 skipping and a downstream frameshift, so the allelic spectrum remains uniformly loss-of-function.

EPS8L2 hgnc:21296

Downstream

Failure of Stereocilia Actin Core Maintenance

Show evidence (2 references)

PMID:26282398 SUPPORT Human Clinical

"This variant predicts a truncated, inactive protein, or no protein at all owing to nonsense-mediated mRNA decay."

The predicted molecular consequence of the founding frameshift allele.

PMID:41514136 SUPPORT In Vitro

"Functional analysis confirmed that the c.767C > G variant causes exon 9 skipping, leading to a frameshift r.701_768del, p.(Gly234Alafs*55)."

Shows the one reported missense variant is spliceogenic, keeping the allelic spectrum uniformly loss-of-function rather than introducing a distinct mechanism.

Failure of Stereocilia Actin Core Maintenance

Each stereocilium contains a core of tightly packed actin filaments whose length is dynamically regulated in development and in the adult. EPS8L2 sits at the stereocilia tips of cochlear and vestibular hair cells and is required for maintaining that core in adult cells - not for building it. Its expression pattern complements EPS8's, which handles initial elongation. The consequence is selective rather than global. In Eps8l2 nulls the tall row of stereocilia becomes abnormally short and sparse while the middle and small rows are unaffected, so the ordered staircase of the bundle decays from the top down.

cochlear outer hair cell CL:0000601 cochlear inner hair cell CL:0000589

actin filament binding GO:0051015 ↓ DECREASED

stereocilium tip GO:0032426

Animal models

Rhodesian Ridgeback early onset adult deafness Dog partially recapitulates Reproduces the genetic architecture and the postnatal progressive time course in an outbred, naturally occurring population, which the inbred mouse cannot.

Downstream

Progressive Hair Bundle Disorganisation

Show evidence (3 references)

PMID:23918390 SUPPORT Model Organism

"the actin-binding protein epidermal growth factor receptor pathway substrate 8 (Eps8)L2, a member of the Eps8-like protein family, is a newly identified hair bundle protein that is localized at the tips of stereocilia of both cochlear and vestibular hair cells"

Localises the protein to the site where the mechanism operates.

PMID:23918390 SUPPORT Model Organism

"In the cochlea, whereas Eps8 is essential for the initial elongation of stereocilia, Eps8L2 is required for their maintenance in adult hair cells."

The division of labour between the paralogues, which is what predicts progressive rather than congenital hearing loss.

PMID:41514136 SUPPORT Model Organism

"These hair bundles showed abnormally shorter and fewer tall stereocilia, while middle and small rows remained unaffected [4]."

Specifies which stereocilia rows are affected, showing the defect is row-selective rather than a global bundle failure.

Progressive Hair Bundle Disorganisation

Loss of maintenance lets the staircase structure of the hair bundle decay gradually over time. In the mouse this deterioration is directly linked to the hearing loss, and the disorganisation is progressive rather than a fixed developmental abnormality - which is the cellular basis for the progressive human audiogram.

inner ear receptor cell stereocilium organization GO:0060122 ↓ DECREASED

spiral organ of cochlea UBERON:0002227

Animal models

Eps8l2 null mouse Mouse recapitulates Reproduces both the progressive time course and the structural lesion, and provides the histology that human material cannot - cochlear hair bundles are not accessible in living patients, so the mouse is where the mechanism is actually observed.

Downstream

Loss of Mechanotransduction

Show evidence (2 references)

PMID:23918390 SUPPORT Model Organism

"Eps8L2 null-mutant mice exhibit a late-onset, progressive hearing loss that is directly linked to a gradual deterioration in hair bundle morphology"

Ties the progressive functional loss to progressive structural decay.

PMID:23918390 SUPPORT Model Organism

"In the absence of both proteins, the ordered staircase structure of the hair bundle in the cochlea decays."

Describes the structural endpoint of losing maintenance.

Loss of Mechanotransduction

Mechanotransduction depends on mechanically gated channels near the stereocilia tips, and the staircase geometry is what allows deflection of the bundle to gate them. As the bundle degrades the transduction apparatus fails, giving sensorineural hearing loss. Inner hair cells transmit the resulting signal centrally while outer hair cells amplify it, so both cell types depend on the same structural integrity.

Show evidence (3 references)

PMID:23918390 SUPPORT Model Organism

"Mechanotransduction in the mammalian auditory system depends on mechanosensitive channels in the hair bundles that project from the apical surface of the sensory hair cells."

States the dependence of transduction on hair bundle integrity.

PMID:23918390 SUPPORT Model Organism

"Eps8L2 is required for the long-term maintenance of the staircase structure and mechanosensory function of auditory hair bundles."

Links maintenance of the structure to preservation of mechanosensory function.

PMID:41514136 SUPPORT Other

"Hearing depends on mechanotransduction, a process that converts mechanical stimuli into electrical signals, and happens through activation of mechanically gated ion channels near the tips of the stereocilia [2]."

Locates the transduction channels at the stereocilia tips where EPS8L2 acts.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

4

Progressive Sensorineural Hearing Impairment VERY_FREQUENT Auditory HP:0000408

Show evidence (3 references)

PMID:41514136 SUPPORT Human Clinical

"Clinically, affected individuals presented moderate to moderately severe hearing loss that was mostly progressive, with an onset starting between the prelingual stage, extending postlingually."

Establishes progression and severity across the expanded case series.

PMID:41514136 SUPPORT Human Clinical

"The progressive nature of EPS8L2-related hearing loss is unusual for recessive non-syndromic forms and highlights the need for early monitoring and intervention."

States why the progressive course is clinically distinctive and consequential.

PMID:26282398 SUPPORT Human Clinical

"We report the study of two Algerian siblings born to consanguineous parents, and affected by progressive hearing loss."

Progressive hearing loss in the founding family.

High-Frequency Hearing Impairment FREQUENT Auditory HP:0005101

Show evidence (2 references)

PMID:41514136 SUPPORT Human Clinical

"In humans, EPS8L2-associated hearing loss has so far shown a prelingual onset with high frequencies most severely affected [8–10]."

The usual audiometric configuration.

PMID:41514136 SUPPORT Human Clinical

"These individuals uniquely showed U-shaped audiograms as a new association of more severe middle frequency hearing loss."

Graded PARTIAL because it qualifies rather than supports the high-frequency pattern - a specific founder variant produces the opposite mid-frequency-predominant shape.

Bilateral Sensorineural Hearing Impairment VERY_FREQUENT Auditory HP:0008619

Show evidence (1 reference)

PMID:41514136 SUPPORT Human Clinical

"At the age of 4 years, the proband was diagnosed with bilateral sensorineural hearing loss (60 dB at 1 kHz bilaterally"

Quantified bilateral audiometric findings in a molecularly confirmed proband. Quote truncated before the per-ear figures because the validator strips bracketed spans such as "[left]" and "[right]" before matching.

Postlingual Sensorineural Hearing Impairment FREQUENT Auditory HP:0008596

Show evidence (2 references)

PMID:41514136 SUPPORT Human Clinical

"with an onset starting between the prelingual stage, extending postlingually"

Documents the onset range spanning prelingual to postlingual.

PMID:41578500 SUPPORT Human Clinical

"postlingual deafness has not received much clinical attention because its prevalence and impact are not as profound as those of prelingual deafness"

The ascertainment problem that plausibly makes this gene under-diagnosed.

🧬

Genetic Associations

1

EPS8L2

Gene: EPS8L2 hgnc:21296 relationship_type: CAUSATIVE

Show evidence (7 references)

PMID:26282398 SUPPORT Human Clinical

"A frame-shift variant (c.1014delC; p.Ser339Alafs*15) was identified in EPS8L2, encoding Epidermal growth factor receptor Pathway Substrate 8 L2, a protein of hair cells' stereocilia previously implicated in progressive deafness in the mouse."

The founding human gene-disease association, made against a prior mouse phenotype - the mouse work preceded the human discovery.

PMID:36635257 SUPPORT Human Clinical

"Pathogenic variants in the EPS8 gene result in nonsyndromic hearing loss. This gene encodes the EPS8 protein in cochlear inner hair cells and performs critical roles in stimulating actin polymerization and bundling."

The paralogue side of the contrast this entry is built on, previously asserted in prose without a citation. EPS8 acts in the same cells on the same substrate, which is what makes the difference in when each acts - elongation against maintenance - the explanation for the difference in clinical course rather than a coincidence.

PMID:36635257 SUPPORT Human Clinical

"Thus far, only four pathogenic variations in EPS8 have been described."

Graded PARTIAL and included for calibration. DFNB102 rests on a comparably tiny allelic series, so the EPS8/EPS8L2 division of labour is drawn from two small literatures, not one small and one large.

+ 4 more references

💊

Medical Actions

2

Hearing Amplification

Hearing aids, the mainstay of management. Fitting is driven by the audiogram rather than by the genotype, and in this cohort it happened at very different ages - one child was scheduled for first aids at 2 years 8 months, another proband uses them as an adult. There is no disease-modifying therapy.

Show evidence (2 references)

PMID:41514136 SUPPORT Human Clinical

"The proband currently uses hearing aids."

Amplification in use in a molecularly confirmed patient.

PMID:41514136 SUPPORT Human Clinical

"The child is now scheduled to receive his first hearing aids at 2 years and 8 months."

First fitting in early childhood in a second patient, which together with the preceding item shows amplification is timed to the audiogram rather than started at diagnosis.

Genetic Counselling and Audiologic Surveillance

Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Counselling with scheduled audiologic follow-up, which in this disorder is more than recurrence-risk advice. Because onset is postlingual and progressive, an at-risk child can pass newborn screening and be clinically normal at one year. In the reported case the surveillance recommendation preceded the first parental report of hearing difficulty by about two months.

Show evidence (1 reference)

PMID:41514136 SUPPORT Human Clinical

"At 21.5 months, genetic counseling emphasized the need for close monitoring, and the parents reported the first signs of hearing difficulty around 23 months of age."

Counselling with monitoring in a predictively tested child, and the interval between that recommendation and the first detected symptom.

🔬

Diagnosis

1

Early genetic testing despite passed newborn screening

Newborn hearing screening does not exclude DFNB106. A younger sibling of a European proband passed newborn screening and was identified only through genetic testing after the proband's diagnosis, carrying compound heterozygous variants. That follows from the mechanism - EPS8L2 maintains stereocilia rather than building them, so hearing can be adequate at birth and deteriorate afterwards. Comprehensive gene-panel or exome sequencing is the route to diagnosis; GJB2 is excluded first in most populations.

Show evidence (2 references)

PMID:41514136 SUPPORT Human Clinical

"A younger sibling of the first European proband diagnosed with DFNB106 passed newborn hearing screening but was identified with compound heterozygous variants, underscoring the importance of early genetic testing."

The documented screening failure and its implication for testing strategy.

PMID:26282398 SUPPORT Human Clinical

"After exclusion of GJB2 (the gene most frequently involved in non-syndromic deafness in Mediterranean countries), we performed whole-exome sequencing in one sibling."

The diagnostic sequence that identified the founding family.

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Prevalence

1

Worldwide, published cases

Cases In Literature Ultra Rare

Eight families in total: four previously reported plus four in the 2026 series. The small size of the evidence base is load-bearing rather than incidental - every statement in this entry about natural history, audiogram shape and progression rests on those eight families, and the entry's frequency gradings should be read against that.

Show evidence (2 references)

PMID:41514136 SUPPORT Human Clinical

"So far, four families have been reported in the literature (Table 4) and we present four additional families that further define the natural history of DFNB106-associated hearing impairment."

The literature total, stated by the authors as they add to it.

PMID:41514136 SUPPORT Human Clinical

"EPS8L2 is one such gene, with only four families so far reported."

The count before this series, which is what makes the doubling meaningful.

🐁

Animal Models

2

Eps8l2 null mouse

The Eps8l2 null mouse was characterised in 2013, two years before EPS8L2 was linked to human deafness, and the human gene was recognised as a candidate partly because of it. Null mice show late-onset progressive hearing loss directly linked to gradual hair bundle deterioration, with the tall stereocilia row shortened and sparse while middle and small rows are spared.

Species

Mouse

Genotype

Eps8l2 null mutant

Genes

EPS8L2 hgnc:21296

Publication

PMID:23918390

Pathograph links

Progressive Hair Bundle Disorganisation recapitulates fidelity: high Reproduces both the progressive time course and the structural lesion, and provides the histology that human material cannot - cochlear hair bundles are not accessible in living patients, so the mouse is where the mechanism is actually observed.

Limitations: A complete null, whereas human alleles are frameshift, nonsense or spliceogenic; those are predicted to be functionally null but this is inference from transcript consequence, not measurement. Mouse onset is described as late-onset while human onset ranges from prelingual to about six years, so the two are not on a matched timescale.

Readouts

Hair bundle staircase morphology

Direction: DECREASED

Interpretation: Progressive decay of the ordered staircase, with the tall row selectively shortened and reduced in number.

Show evidence (1 reference)

PMID:41514136 SUPPORT Model Organism

"These hair bundles showed abnormally shorter and fewer tall stereocilia, while middle and small rows remained unaffected [4]."

The row-selective structural measurement.

Auditory threshold over time

Direction: DECREASED

Interpretation: Late-onset progressive hearing loss tracking the structural decay.

Show evidence (1 reference)

PMID:23918390 SUPPORT Model Organism

"Eps8L2 null-mutant mice exhibit a late-onset, progressive hearing loss that is directly linked to a gradual deterioration in hair bundle morphology"

The functional readout and its stated link to the structural one.

Show evidence (1 reference)

PMID:23918390 SUPPORT Model Organism

"We conclude that Eps8L2 is required for the long-term maintenance of the staircase structure and mechanosensory function of auditory hair bundles."

The model's central conclusion, which is the mechanism this entry curates.

Rhodesian Ridgeback early onset adult deafness

A naturally occurring canine model, identified by genome-wide association in 23 affected and 162 control Rhodesian Ridgebacks and localised to a 12-bp in-frame deletion in EPS8L2. Affected dogs lose hearing within one to two years of birth. All affected dogs were homozygous for the deletion and no control dog was a deletion homozygote, and a two-generation family segregated it recessively.

Species

Dog

Genotype

EPS8L2 12-bp in-frame deletion, homozygous

Genes

EPS8L2 hgnc:21296

Publication

PMID:35385474

Pathograph links

Failure of Stereocilia Actin Core Maintenance partially recapitulates fidelity: moderate Reproduces the genetic architecture and the postnatal progressive time course in an outbred, naturally occurring population, which the inbred mouse cannot.

Limitations: The evidence is genetic and audiometric, not histological - no cochlear stereocilia phenotype is reported for these dogs, so the link to the actin-core mechanism is inferred from the gene rather than observed. The allele is a 12-bp in-frame deletion rather than a truncating variant, so residual partial function is plausible and the lesion is not equivalent to the human or murine null. The authors themselves describe it as a strong *candidate* causal mutation.

Readouts

Brainstem auditory evoked response

Direction: DECREASED

Interpretation: Clinically confirmed hearing loss in affected dogs before two years of age.

Show evidence (1 reference)

PMID:35385474 SUPPORT Model Organism

"the loss of hearing was clinically confirmed in all case dogs by Brainstem Auditory Evoked Response (BAER) test"

The objective audiometric confirmation in the canine cohort.

Show evidence (1 reference)

PMID:35385474 SUPPORT Model Organism

"the inframe deletion found in this study represents a strong candidate causal mutation for EOAD in Rhodesian Ridgebacks"

Graded PARTIAL, matching the authors' own hedging - candidate causal, established by association and segregation rather than by functional demonstration.

Show evidence (2 references)

PMID:35385474 SUPPORT Model Organism

"Additional genotyping confirmed a strong association between the 12-bp deletion and EOAD, where all affected dogs were homozygous for the deletion, while none of the control dogs was a deletion homozygote."

The genetic association supporting the model's relevance.

PMID:35385474 SUPPORT Model Organism

"Genetic and clinical similarities between childhood deafness in humans and EOAD in Rhodesian Ridgebacks emphasizes the potential value of this dog breed in translational research in hereditary hearing disorders."

The authors' statement of translational relevance to human childhood deafness.

{ }

Source YAML

click to show

name: Hearing Loss Autosomal Recessive 106
category: Mendelian
creation_date: "2026-08-27T00:00:00Z"
synonyms:
- DFNB106
- EPS8L2-related hearing loss
- Autosomal recessive nonsyndromic hearing loss 106
- Deafness, autosomal recessive 106
description: >-
  Hearing loss autosomal recessive 106 (DFNB106) is caused by biallelic loss-of-function
  EPS8L2 variants. EPS8L2 is a 715-amino-acid actin-binding protein that localises to the
  tips of stereocilia in cochlear and vestibular hair cells, where it caps and maintains
  the actin core.

  The mechanistic point that organises this entry is the division of labour within the
  EPS8 protein family. EPS8 is required for the *initial elongation* of stereocilia, and
  its loss causes congenital deafness (DFNB102). EPS8L2 has a complementary spatiotemporal
  expression pattern and is required for their *maintenance* in adult hair cells. That
  difference in timing predicts the clinical difference: EPS8 loss gives early profound
  hearing loss, while EPS8L2 loss gives late-onset, progressive hearing loss that tracks a
  gradual deterioration in hair bundle morphology, with abnormally short and sparse tall
  stereocilia while the middle and small rows are spared.

  The progressive course is unusual for a recessive nonsyndromic form - most DFNB genes
  cause congenital, severe-to-profound deafness - and it is the clinically important
  feature. Newborn hearing screening can be passed: one reported sibling with compound
  heterozygous variants passed screening and was found only by genetic testing. Because
  hearing deteriorates from a starting point that is not profound, there is a period during
  which residual hair cells still exist, which the recent literature frames explicitly as a
  therapeutic window for eventual gene therapy. That reframes early molecular diagnosis
  from a prognostic nicety into a prerequisite.

  Reported onset ranges from prelingual to about six years, severity is typically moderate
  to moderately severe, and high frequencies are usually worst - though a recently described
  founder variant in two Iranian families produced U-shaped audiograms with worse
  mid-frequency loss instead.
disease_term:
  preferred_term: hearing loss, autosomal recessive 106
  term:
    id: MONDO:0033198
    label: hearing loss, autosomal recessive 106
parents:
- Autosomal Recessive Nonsyndromic Hearing Loss
inheritance:
- name: Autosomal recessive
  description: >-
    Biallelic EPS8L2 variants, homozygous in consanguineous families and compound
    heterozygous in others. In the founding family the variant was homozygous in both
    affected siblings and heterozygous in the unaffected parents and an unaffected sibling.
    One reported compound heterozygote carries a de novo allele in trans with a maternally
    inherited one, which is worth knowing because a de novo allele in a recessive disease
    breaks the usual assumption that both parents are carriers.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:26282398
    reference_title: "EPS8L2 is a new causal gene for childhood onset autosomal recessive progressive hearing loss."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It was detected at the homozygous state in the two clinically affected siblings, and at the heterozygous state in the unaffected parents and one unaffected sibling"
    explanation: Textbook recessive segregation in the founding family.
  - reference: PMID:41578500
    reference_title: "Identification and phased de novo mutation of the EPS8L2 gene in a patient with progressive hearing loss: A case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, the c.357_361dupGGTGC variant was a de novo mutation in the patient, whereas c.1317dupG was inherited from his mother."
    explanation: >-
      A de novo allele in trans with an inherited one - so carrier testing of both parents
      would have been falsely reassuring in this family.
pathophysiology:
- name: EPS8L2 Loss of Function
  description: >-
    Biallelic EPS8L2 variants, predominantly frameshift and nonsense, predicted to yield a
    severely truncated inactive protein or none at all through nonsense-mediated decay.
    A missense variant has also been reported but acts by a splicing mechanism rather than
    by amino acid substitution: c.767C>G causes exon 9 skipping and a downstream frameshift,
    so the allelic spectrum remains uniformly loss-of-function.
  biological_scale: MOLECULAR
  genes:
  - preferred_term: EPS8L2
    term:
      id: hgnc:21296
      label: EPS8L2
  downstream:
  - target: Failure of Stereocilia Actin Core Maintenance
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:26282398
    reference_title: "EPS8L2 is a new causal gene for childhood onset autosomal recessive progressive hearing loss."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This variant predicts a truncated, inactive protein, or no protein at all owing to nonsense-mediated mRNA decay."
    explanation: The predicted molecular consequence of the founding frameshift allele.
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Functional analysis confirmed that the c.767C > G variant causes exon 9 skipping, leading to a frameshift r.701_768del, p.(Gly234Alafs*55)."
    explanation: >-
      Shows the one reported missense variant is spliceogenic, keeping the allelic
      spectrum uniformly loss-of-function rather than introducing a distinct mechanism.
- name: Failure of Stereocilia Actin Core Maintenance
  description: >-
    Each stereocilium contains a core of tightly packed actin filaments whose length is
    dynamically regulated in development and in the adult. EPS8L2 sits at the stereocilia
    tips of cochlear and vestibular hair cells and is required for maintaining that core in
    adult cells - not for building it. Its expression pattern complements EPS8's, which
    handles initial elongation.

    The consequence is selective rather than global. In Eps8l2 nulls the tall row of
    stereocilia becomes abnormally short and sparse while the middle and small rows are
    unaffected, so the ordered staircase of the bundle decays from the top down.
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: cochlear outer hair cell
    term:
      id: CL:0000601
      label: cochlear outer hair cell
  - preferred_term: cochlear inner hair cell
    term:
      id: CL:0000589
      label: cochlear inner hair cell
  molecular_functions:
  - preferred_term: actin filament binding
    modifier: DECREASED
    term:
      id: GO:0051015
      label: actin filament binding
  cellular_components:
  - preferred_term: stereocilium tip
    term:
      id: GO:0032426
      label: stereocilium tip
  downstream:
  - target: Progressive Hair Bundle Disorganisation
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:23918390
    reference_title: "Progressive hearing loss and gradual deterioration of sensory hair bundles in the ears of mice lacking the actin-binding protein Eps8L2."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "the actin-binding protein epidermal growth factor receptor pathway substrate 8 (Eps8)L2, a member of the Eps8-like protein family, is a newly identified hair bundle protein that is localized at the tips of stereocilia of both cochlear and vestibular hair cells"
    explanation: Localises the protein to the site where the mechanism operates.
  - reference: PMID:23918390
    reference_title: "Progressive hearing loss and gradual deterioration of sensory hair bundles in the ears of mice lacking the actin-binding protein Eps8L2."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In the cochlea, whereas Eps8 is essential for the initial elongation of stereocilia, Eps8L2 is required for their maintenance in adult hair cells."
    explanation: >-
      The division of labour between the paralogues, which is what predicts progressive
      rather than congenital hearing loss.
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "These hair bundles showed abnormally shorter and fewer tall stereocilia, while middle and small rows remained unaffected [4]."
    explanation: >-
      Specifies which stereocilia rows are affected, showing the defect is row-selective
      rather than a global bundle failure.
- name: Progressive Hair Bundle Disorganisation
  description: >-
    Loss of maintenance lets the staircase structure of the hair bundle decay gradually
    over time. In the mouse this deterioration is directly linked to the hearing loss, and
    the disorganisation is progressive rather than a fixed developmental abnormality -
    which is the cellular basis for the progressive human audiogram.
  biological_scale: TISSUE
  locations:
  - preferred_term: spiral organ of cochlea
    term:
      id: UBERON:0002227
      label: spiral organ of cochlea
  biological_processes:
  - preferred_term: inner ear receptor cell stereocilium organization
    modifier: DECREASED
    term:
      id: GO:0060122
      label: inner ear receptor cell stereocilium organization
  downstream:
  - target: Loss of Mechanotransduction
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:23918390
    reference_title: "Progressive hearing loss and gradual deterioration of sensory hair bundles in the ears of mice lacking the actin-binding protein Eps8L2."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Eps8L2 null-mutant mice exhibit a late-onset, progressive hearing loss that is directly linked to a gradual deterioration in hair bundle morphology"
    explanation: Ties the progressive functional loss to progressive structural decay.
  - reference: PMID:23918390
    reference_title: "Progressive hearing loss and gradual deterioration of sensory hair bundles in the ears of mice lacking the actin-binding protein Eps8L2."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In the absence of both proteins, the ordered staircase structure of the hair bundle in the cochlea decays."
    explanation: Describes the structural endpoint of losing maintenance.
- name: Loss of Mechanotransduction
  description: >-
    Mechanotransduction depends on mechanically gated channels near the stereocilia tips,
    and the staircase geometry is what allows deflection of the bundle to gate them. As the
    bundle degrades the transduction apparatus fails, giving sensorineural hearing loss.
    Inner hair cells transmit the resulting signal centrally while outer hair cells amplify
    it, so both cell types depend on the same structural integrity.
  biological_scale: CELLULAR
  evidence:
  - reference: PMID:23918390
    reference_title: "Progressive hearing loss and gradual deterioration of sensory hair bundles in the ears of mice lacking the actin-binding protein Eps8L2."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Mechanotransduction in the mammalian auditory system depends on mechanosensitive channels in the hair bundles that project from the apical surface of the sensory hair cells."
    explanation: States the dependence of transduction on hair bundle integrity.
  - reference: PMID:23918390
    reference_title: "Progressive hearing loss and gradual deterioration of sensory hair bundles in the ears of mice lacking the actin-binding protein Eps8L2."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Eps8L2 is required for the long-term maintenance of the staircase structure and mechanosensory function of auditory hair bundles."
    explanation: Links maintenance of the structure to preservation of mechanosensory function.
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Hearing depends on mechanotransduction, a process that converts mechanical stimuli into electrical signals, and happens through activation of mechanically gated ion channels near the tips of the stereocilia [2]."
    explanation: Locates the transduction channels at the stereocilia tips where EPS8L2 acts.
phenotypes:
- name: Progressive Sensorineural Hearing Impairment
  category: Auditory
  description: >-
    Progressive bilateral sensorineural hearing loss. Progression is the defining feature
    and is unusual among recessive nonsyndromic forms, most of which are congenital and
    static.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Progressive sensorineural hearing impairment
    term:
      id: HP:0000408
      label: Progressive sensorineural hearing impairment
  evidence:
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinically, affected individuals presented moderate to moderately severe hearing loss that was mostly progressive, with an onset starting between the prelingual stage, extending postlingually."
    explanation: Establishes progression and severity across the expanded case series.
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The progressive nature of EPS8L2-related hearing loss is unusual for recessive non-syndromic forms and highlights the need for early monitoring and intervention."
    explanation: States why the progressive course is clinically distinctive and consequential.
  - reference: PMID:26282398
    reference_title: "EPS8L2 is a new causal gene for childhood onset autosomal recessive progressive hearing loss."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report the study of two Algerian siblings born to consanguineous parents, and affected by progressive hearing loss."
    explanation: Progressive hearing loss in the founding family.
- name: High-Frequency Hearing Impairment
  category: Auditory
  description: >-
    High frequencies are usually worst affected. The exception is a founder variant shared
    by two Iranian families, whose carriers showed U-shaped audiograms with more severe
    mid-frequency loss - a new audiometric association for this gene.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: High-frequency hearing impairment
    term:
      id: HP:0005101
      label: High-frequency hearing impairment
  evidence:
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In humans, EPS8L2-associated hearing loss has so far shown a prelingual onset with high frequencies most severely affected [8–10]."
    explanation: The usual audiometric configuration.
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These individuals uniquely showed U-shaped audiograms as a new association of more severe middle frequency hearing loss."
    explanation: >-
      Graded PARTIAL because it qualifies rather than supports the high-frequency pattern -
      a specific founder variant produces the opposite mid-frequency-predominant shape.
- name: Bilateral Sensorineural Hearing Impairment
  category: Auditory
  description: Bilateral sensorineural loss, moderate to moderately severe in most reported cases.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Bilateral sensorineural hearing impairment
    term:
      id: HP:0008619
      label: Bilateral sensorineural hearing impairment
  evidence:
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At the age of 4 years, the proband was diagnosed with bilateral sensorineural hearing loss (60 dB at 1 kHz bilaterally"
    explanation: >-
      Quantified bilateral audiometric findings in a molecularly confirmed proband. Quote
      truncated before the per-ear figures because the validator strips bracketed spans
      such as "[left]" and "[right]" before matching.
- name: Postlingual Sensorineural Hearing Impairment
  category: Auditory
  description: >-
    Onset can extend postlingually, which is part of why the condition is under-ascertained -
    postlingual deafness attracts less clinical attention than prelingual, and only a few
    causative genes for it are known.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Postlingual sensorineural hearing impairment
    term:
      id: HP:0008596
      label: Postlingual sensorineural hearing impairment
  evidence:
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "with an onset starting between the prelingual stage, extending postlingually"
    explanation: Documents the onset range spanning prelingual to postlingual.
  - reference: PMID:41578500
    reference_title: "Identification and phased de novo mutation of the EPS8L2 gene in a patient with progressive hearing loss: A case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "postlingual deafness has not received much clinical attention because its prevalence and impact are not as profound as those of prelingual deafness"
    explanation: The ascertainment problem that plausibly makes this gene under-diagnosed.
prevalence:
- population: Worldwide, published cases
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Eight families in total: four previously reported plus four in the 2026 series. The
    small size of the evidence base is load-bearing rather than incidental - every
    statement in this entry about natural history, audiogram shape and progression rests on
    those eight families, and the entry's frequency gradings should be read against that.
  evidence:
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "So far, four families have been reported in the literature (Table 4) and we present four additional families that further define the natural history of DFNB106-associated hearing impairment."
    explanation: The literature total, stated by the authors as they add to it.
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "EPS8L2 is one such gene, with only four families so far reported."
    explanation: The count before this series, which is what makes the doubling meaningful.
treatments:
- name: Hearing Amplification
  description: >-
    Hearing aids, the mainstay of management. Fitting is driven by the audiogram rather
    than by the genotype, and in this cohort it happened at very different ages - one child
    was scheduled for first aids at 2 years 8 months, another proband uses them as an
    adult. There is no disease-modifying therapy.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: hearing aid fitting
  evidence:
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The proband currently uses hearing aids."
    explanation: Amplification in use in a molecularly confirmed patient.
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The child is now scheduled to receive his first hearing aids at 2 years and 8 months."
    explanation: >-
      First fitting in early childhood in a second patient, which together with the
      preceding item shows amplification is timed to the audiogram rather than started at
      diagnosis.
  notes: >-
    treatment_term carries no NCIT binding. NCIT:C183182 Hearing Aid is a device concept,
    not reachable from NCIT:C25218 Clinical Intervention or Procedure, so it fails
    TreatmentActionTerm validation, and NCIT has no clinical-action term for hearing-aid
    fitting or use. Per the ontology contract a free-text preferred_term is correct here
    rather than a forced broader binding.

    Cochlear implantation and formal speech-language rehabilitation are standard in
    autosomal recessive nonsyndromic hearing loss generally, but neither is documented in
    any reported DFNB106 patient, so neither is curated here. This is a deliberate scoping
    decision, not an omission.
- name: Genetic Counselling and Audiologic Surveillance
  description: >-
    Counselling with scheduled audiologic follow-up, which in this disorder is more than
    recurrence-risk advice. Because onset is postlingual and progressive, an at-risk child
    can pass newborn screening and be clinically normal at one year. In the reported case
    the surveillance recommendation preceded the first parental report of hearing
    difficulty by about two months.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At 21.5 months, genetic counseling emphasized the need for close monitoring, and the parents reported the first signs of hearing difficulty around 23 months of age."
    explanation: >-
      Counselling with monitoring in a predictively tested child, and the interval between
      that recommendation and the first detected symptom.
genetic:
- name: EPS8L2
  notes: >-
    EPS8L2 encodes a 715-amino-acid actin-binding protein with a phosphotyrosine
    interaction domain (PID), an SH3 domain, and a SAM/PNT effector region, on 11p15.5.
    It belongs to the EPS8 family (EPS8, EPS8L1-L3) whose members have overlapping but
    temporally distinct roles. The gene is rare and under-characterised: only four
    families were reported before a 2026 series more than doubled the total. Reported
    alleles are frameshift, nonsense, or spliceogenic, and a founder haplotype has been
    identified in Iranian families.
  relationship_type: CAUSATIVE
  gene_term:
    preferred_term: EPS8L2
    term:
      id: hgnc:21296
      label: EPS8L2
  evidence:
  - reference: PMID:26282398
    reference_title: "EPS8L2 is a new causal gene for childhood onset autosomal recessive progressive hearing loss."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A frame-shift variant (c.1014delC; p.Ser339Alafs*15) was identified in EPS8L2, encoding Epidermal growth factor receptor Pathway Substrate 8 L2, a protein of hair cells' stereocilia previously implicated in progressive deafness in the mouse."
    explanation: >-
      The founding human gene-disease association, made against a prior mouse phenotype -
      the mouse work preceded the human discovery.
  - reference: PMID:36635257
    reference_title: "EPS8 variant causes deafness, autosomal recessive 102 (DFNB102) and literature review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pathogenic variants in the EPS8 gene result in nonsyndromic hearing loss. This gene encodes the EPS8 protein in cochlear inner hair cells and performs critical roles in stimulating actin polymerization and bundling."
    explanation: >-
      The paralogue side of the contrast this entry is built on, previously asserted in
      prose without a citation. EPS8 acts in the same cells on the same substrate, which is
      what makes the difference in when each acts - elongation against maintenance - the
      explanation for the difference in clinical course rather than a coincidence.
  - reference: PMID:36635257
    reference_title: "EPS8 variant causes deafness, autosomal recessive 102 (DFNB102) and literature review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Thus far, only four pathogenic variations in EPS8 have been described."
    explanation: >-
      Graded PARTIAL and included for calibration. DFNB102 rests on a comparably tiny
      allelic series, so the EPS8/EPS8L2 division of labour is drawn from two small
      literatures, not one small and one large.
  - reference: PMID:26282398
    reference_title: "EPS8L2 is a new causal gene for childhood onset autosomal recessive progressive hearing loss."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "whereas it was never found in a control population of 150 Algerians with normal hearing or in the Exome Variant Server database"
    explanation: Population-frequency evidence supporting pathogenicity of the founding allele.
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Four previously published families have replicated autosomal recessive non-syndromic hearing loss (DFNB106), yet the mutational and clinical spectrum remains poorly described."
    explanation: >-
      States both the replication supporting the gene-disease relationship and how thin the
      published base was before 2026.
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A shared 4.17 Mb homozygous region among two unrelated Iranian families with this variant suggested a founder effect."
    explanation: Evidence for a founder haplotype in the Iranian population.
  - reference: PMID:28281779
    reference_title: "Molecular Analysis of Twelve Pakistani Families with Nonsyndromic or Syndromic Hearing Loss."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition, the novel frameshift mutation in EPS8L2 was first documented in Pakistan."
    explanation: Independent replication extending the reported geographic range.
diagnosis:
- name: Early genetic testing despite passed newborn screening
  description: >-
    Newborn hearing screening does not exclude DFNB106. A younger sibling of a European
    proband passed newborn screening and was identified only through genetic testing after
    the proband's diagnosis, carrying compound heterozygous variants. That follows from the
    mechanism - EPS8L2 maintains stereocilia rather than building them, so hearing can be
    adequate at birth and deteriorate afterwards. Comprehensive gene-panel or exome
    sequencing is the route to diagnosis; GJB2 is excluded first in most populations.
  evidence:
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A younger sibling of the first European proband diagnosed with DFNB106 passed newborn hearing screening but was identified with compound heterozygous variants, underscoring the importance of early genetic testing."
    explanation: The documented screening failure and its implication for testing strategy.
  - reference: PMID:26282398
    reference_title: "EPS8L2 is a new causal gene for childhood onset autosomal recessive progressive hearing loss."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "After exclusion of GJB2 (the gene most frequently involved in non-syndromic deafness in Mediterranean countries), we performed whole-exome sequencing in one sibling."
    explanation: The diagnostic sequence that identified the founding family.
animal_models:
- name: Eps8l2 null mouse
  species: Mouse
  genotype: Eps8l2 null mutant
  publication: PMID:23918390
  description: >-
    The Eps8l2 null mouse was characterised in 2013, two years before EPS8L2 was linked to
    human deafness, and the human gene was recognised as a candidate partly because of it.
    Null mice show late-onset progressive hearing loss directly linked to gradual hair
    bundle deterioration, with the tall stereocilia row shortened and sparse while middle
    and small rows are spared.
  genes:
  - preferred_term: EPS8L2
    term:
      id: hgnc:21296
      label: EPS8L2
  modeled_mechanisms:
  - target: Progressive Hair Bundle Disorganisation
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Reproduces both the progressive time course and the structural lesion, and provides
      the histology that human material cannot - cochlear hair bundles are not accessible
      in living patients, so the mouse is where the mechanism is actually observed.
    limitations: >-
      A complete null, whereas human alleles are frameshift, nonsense or spliceogenic;
      those are predicted to be functionally null but this is inference from transcript
      consequence, not measurement. Mouse onset is described as late-onset while human onset
      ranges from prelingual to about six years, so the two are not on a matched timescale.
    readouts:
    - name: Hair bundle staircase morphology
      target: Progressive Hair Bundle Disorganisation
      direction: DECREASED
      interpretation: >-
        Progressive decay of the ordered staircase, with the tall row selectively
        shortened and reduced in number.
      evidence:
      - reference: PMID:41514136
        reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "These hair bundles showed abnormally shorter and fewer tall stereocilia, while middle and small rows remained unaffected [4]."
        explanation: The row-selective structural measurement.
    - name: Auditory threshold over time
      target: Progressive Hair Bundle Disorganisation
      direction: DECREASED
      interpretation: Late-onset progressive hearing loss tracking the structural decay.
      evidence:
      - reference: PMID:23918390
        reference_title: "Progressive hearing loss and gradual deterioration of sensory hair bundles in the ears of mice lacking the actin-binding protein Eps8L2."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Eps8L2 null-mutant mice exhibit a late-onset, progressive hearing loss that is directly linked to a gradual deterioration in hair bundle morphology"
        explanation: The functional readout and its stated link to the structural one.
    evidence:
    - reference: PMID:23918390
      reference_title: "Progressive hearing loss and gradual deterioration of sensory hair bundles in the ears of mice lacking the actin-binding protein Eps8L2."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "We conclude that Eps8L2 is required for the long-term maintenance of the staircase structure and mechanosensory function of auditory hair bundles."
      explanation: The model's central conclusion, which is the mechanism this entry curates.
- name: Rhodesian Ridgeback early onset adult deafness
  species: Dog
  genotype: EPS8L2 12-bp in-frame deletion, homozygous
  publication: PMID:35385474
  description: >-
    A naturally occurring canine model, identified by genome-wide association in 23
    affected and 162 control Rhodesian Ridgebacks and localised to a 12-bp in-frame
    deletion in EPS8L2. Affected dogs lose hearing within one to two years of birth. All
    affected dogs were homozygous for the deletion and no control dog was a deletion
    homozygote, and a two-generation family segregated it recessively.
  genes:
  - preferred_term: EPS8L2
    term:
      id: hgnc:21296
      label: EPS8L2
  modeled_mechanisms:
  - target: Failure of Stereocilia Actin Core Maintenance
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reproduces the genetic architecture and the postnatal progressive time course in an
      outbred, naturally occurring population, which the inbred mouse cannot.
    limitations: >-
      The evidence is genetic and audiometric, not histological - no cochlear stereocilia
      phenotype is reported for these dogs, so the link to the actin-core mechanism is
      inferred from the gene rather than observed. The allele is a 12-bp in-frame deletion
      rather than a truncating variant, so residual partial function is plausible and the
      lesion is not equivalent to the human or murine null. The authors themselves describe
      it as a strong *candidate* causal mutation.
    evidence:
    - reference: PMID:35385474
      reference_title: "Early onset adult deafness in the Rhodesian Ridgeback dog is associated with an in-frame deletion in the EPS8L2 gene."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "the inframe deletion found in this study represents a strong candidate causal mutation for EOAD in Rhodesian Ridgebacks"
      explanation: >-
        Graded PARTIAL, matching the authors' own hedging - candidate causal, established
        by association and segregation rather than by functional demonstration.
    readouts:
    - name: Brainstem auditory evoked response
      target: Failure of Stereocilia Actin Core Maintenance
      direction: DECREASED
      interpretation: Clinically confirmed hearing loss in affected dogs before two years of age.
      evidence:
      - reference: PMID:35385474
        reference_title: "Early onset adult deafness in the Rhodesian Ridgeback dog is associated with an in-frame deletion in the EPS8L2 gene."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "the loss of hearing was clinically confirmed in all case dogs by Brainstem Auditory Evoked Response (BAER) test"
        explanation: The objective audiometric confirmation in the canine cohort.
  evidence:
  - reference: PMID:35385474
    reference_title: "Early onset adult deafness in the Rhodesian Ridgeback dog is associated with an in-frame deletion in the EPS8L2 gene."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Additional genotyping confirmed a strong association between the 12-bp deletion and EOAD, where all affected dogs were homozygous for the deletion, while none of the control dogs was a deletion homozygote."
    explanation: The genetic association supporting the model's relevance.
  - reference: PMID:35385474
    reference_title: "Early onset adult deafness in the Rhodesian Ridgeback dog is associated with an in-frame deletion in the EPS8L2 gene."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Genetic and clinical similarities between childhood deafness in humans and EOAD in Rhodesian Ridgebacks emphasizes the potential value of this dog breed in translational research in hereditary hearing disorders."
    explanation: The authors' statement of translational relevance to human childhood deafness.
discussions:
- discussion_id: eps8l2_therapeutic_window
  kind: KNOWLEDGE_GAP
  prompt: >-
    How wide is the therapeutic window in DFNB106 - at what point does hair bundle
    deterioration become irreversible, and would restoring EPS8L2 during the progressive
    phase halt or reverse the loss?
  attaches_to:
  - pathophysiology#Progressive Hair Bundle Disorganisation
  - diagnosis#Early genetic testing despite passed newborn screening
  rationale: >-
    Most recessive nonsyndromic deafness genes cause congenital, severe-to-profound loss,
    where by the time of diagnosis the substrate for intervention is largely gone. DFNB106
    is different in a way that matters therapeutically: hearing starts at moderate levels
    and deteriorates, so hair cells persist during a period when a gene-replacement or
    protein-restoration approach could in principle act. The 2026 series makes this
    argument explicitly and identifies natural history as the missing piece needed for
    preclinical modelling.

    What is genuinely unknown is the shape of that window. Nobody has established whether
    the tall-row shortening seen in the mouse is reversible if EPS8L2 is restored, or
    whether the bundle passes a point after which restoring the maintenance protein cannot
    rebuild what has already degraded - and the maintenance-not-elongation division of
    labour between EPS8L2 and EPS8 makes the pessimistic reading plausible, since EPS8L2
    may be unable to regrow stereocilia it can only preserve. The mouse is well suited to
    answering this with an inducible rescue, and the outbred dog model offers a
    complementary system on a naturally occurring allele.
  evidence:
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "A preclinical gene therapy study of an Eps8 knockout mouse using adeno-associated virus (AAV) delivery of the EPS8 transgene with the Anc80L65 AAV serotype showed rescue to the hair bundle structure but failed to rescue functional hearing"
    explanation: >-
      The empirical form of the pessimistic reading, and stronger than the inference it
      replaces. In the paralogous gene, AAV delivery restored bundle structure and still
      failed to restore hearing - so structural rescue is not sufficient, which is exactly
      the risk a maintenance protein faces. Graded PARTIAL because it is EPS8 rather than
      EPS8L2, and MODEL_ORGANISM because the result quoted is a mouse experiment. The quote
      stops before the paper's [16] citation marker, which the reference validator strips
      before matching; the transduction rates that follow it are not needed for this claim.
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "When delayed to postnatal day 3, almost no recovery was observed, shrinking the targeted delivery of all studies to between 1 and 2 days after birth."
    explanation: >-
      The width of the window in the mouse, and the reason the human window matters: in
      mouse it closes within days of birth. Whether the human progressive phase is a
      correspondingly narrow window or a genuinely longer one is the unresolved question.
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This work emphasizes the need for early molecular diagnosis and long-term clinical follow-up, while describing the natural history of EPS8L2 that will be important for future therapeutic development."
    explanation: The authors' framing of natural history as a prerequisite for therapy development.
  - reference: PMID:41514136
    reference_title: "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Both of these aspects are likely to impact tractability to preclinical models for eventual gene therapy trials."
    explanation: >-
      Graded PARTIAL - identifies unresolved onset and progression questions as limiting
      preclinical modelling, which is the substance of the gap rather than its answer.
  - reference: PMID:23918390
    reference_title: "Progressive hearing loss and gradual deterioration of sensory hair bundles in the ears of mice lacking the actin-binding protein Eps8L2."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In the cochlea, whereas Eps8 is essential for the initial elongation of stereocilia, Eps8L2 is required for their maintenance in adult hair cells."
    explanation: >-
      The maintenance-versus-elongation division is the reason to doubt that late
      restoration would rebuild degraded stereocilia, and is why the window's shape is an
      open question rather than an assumed opportunity.

📚

References & Deep Research

Deep Research

1

Claude Code ▸

Hearing Loss, Autosomal Recessive 106 (DFNB106) — Comprehensive Research Report

claude-haiku-4-5-20251001, claude-sonnet-5 7 citations 2026-08-27T15:12:56.680060

Hearing Loss, Autosomal Recessive 106 (DFNB106) — Comprehensive Research Report

1. Disease Information

Overview. Autosomal recessive deafness-106 (DFNB106) is a rare, genetically defined form of nonsyndromic sensorineural hearing loss caused by biallelic pathogenic variants in EPS8L2 (EPS8-Like protein 2), a gene encoding an actin-binding stereocilia protein of cochlear hair cells. Unlike most autosomal recessive nonsyndromic hearing loss (ARNSHL), which is typically congenital, stable, and profound, DFNB106 is distinctive for being prelingual-to-childhood onset and progressive, evolving from mild/moderate loss at low frequencies toward severe-to-profound loss, particularly at high frequencies, over years (Dahmani et al. 2015, PMID:26282398; Owrang et al. 2026, PMID:41514136).

Key identifiers: - OMIM (phenotype): #617637 — DEAFNESS, AUTOSOMAL RECESSIVE 106; DFNB106 - OMIM (gene): 614988 — EPS8-LIKE PROTEIN 2; EPS8L2 - Gene locus: 11p15.13 (NCBI Gene ID 64787; HGNC:21296; UniProt Q9H6S3) - MONDO: MONDO:0033198 (confirmed via ClinVar cross-reference) - MedGen: C4539954 - ClinVar example record: RCV000499522 (NM_022772.4(EPS8L2):c.1014del, p.Ser339fs) — Pathogenic, 1-star review - Synonyms:* DFNB106; Deafness, autosomal recessive 106; EPS8L2-related hearing loss

Source of information. Nearly all information available is derived from a small number of published family case series/cohort reports (whole-exome sequencing of individual pedigrees), not large-scale EHR-aggregated data — reflecting the extreme rarity of this specific locus. As of the most recent (2026) synthesis, only 8 families / ~14 affected individuals worldwide have been reported in the literature (Owrang et al. 2026, PMID:41514136).

2. Etiology

Disease causal factor: Purely genetic — biallelic (homozygous or compound heterozygous) loss-of-function or spliceogenic variants in EPS8L2. There is no known environmental, infectious, or acquired contributor; this is a monogenic Mendelian disorder.

Genetic risk factors

Causal gene: EPS8L2 (11p15.13). All reported pathogenic alleles predict truncation, nonsense-mediated decay, or aberrant splicing leading to frameshift — i.e., loss-of-function as the shared mechanism.
Consanguinity as an enabling risk factor: Several reported families are consanguineous (Algerian second-cousin union; Iranian and Pakistani consanguineous pedigrees), consistent with autosomal recessive transmission and increasing homozygosity risk for a rare allele (Dahmani et al. 2015; Wang et al. 2017, PMID:28281779).
Founder effect: Two unrelated Iranian families in the 2026 report share a 4.17 Mb run of homozygosity (overlapping interval Chr11:g.197337–4367675, GRCh38) around a recurrent EPS8L2 missense/spliceogenic variant, suggestive of a regional founder allele rather than independent mutation events (Owrang et al. 2026, PMID:41514136).
Gene constraint: gnomAD v4.0 reports EPS8L2 pLI = 0 and LOEUF = 1.17, indicating the gene is not strongly constrained against heterozygous loss-of-function in the general population — consistent with a purely recessive disease mechanism where carriers are unaffected.

Protective factors

None reported. No modifier alleles, protective variants, or environmental protective exposures have been described for this ultra-rare condition.

Gene-environment interactions

None documented; no evidence of environmental modulation of onset or severity has been reported.

3. Phenotypes

All phenotypic data reported to date are auditory — no extra-auditory features are described in any published case, consistent with the "nonsyndromic" designation.

Phenotype	HPO term (suggested)	Onset	Severity/progression	Frequency
Bilateral sensorineural hearing loss	HP:0000407 (Sensorineural hearing impairment)	Typically 3–7 yrs (range: presymptomatic infancy to prelingual)	Moderate at onset → severe/profound; progressive in 5/6 individuals with longitudinal data	Universal (defining feature)
High-frequency sloping hearing loss	HP:0000407 / audiometric pattern	Childhood	Classic pattern in original Algerian and Iranian (Family 2) kindreds	Common
U-shaped audiogram (novel 2026 finding)	HP:0000365 (Hearing impairment), pattern descriptor	Childhood–adult	Mid-frequency-predominant loss; newly reported in two individuals sharing the c.767C>G, p.(Thr256Arg) variant	2/9 documented individuals
Progressive threshold elevation	—	Years-long	E.g., Algerian sibling: 30→90 dB (age 6) worsening to 40→100 dB (age 10) across frequencies	Predominant pattern
Stable/plateaued hearing loss (subset)	—	—	One Iranian proband: only 4 dB PTA change over 10 years ("did not meet the definition of progressive"); one individual stable in her 4th decade after earlier progression	Minority

Characteristics: - Age of onset: Ranges from presymptomatic at birth (passing newborn hearing screening) to recognition around 4 years (most common), preschool age, or prelingual in some kindreds. The 2026 study documents the first pre-symptomatic case: a German child who passed newborn screening but developed measurable loss by ~23 months, confirming that normal hearing at birth is compatible with the genotype (Owrang et al. 2026, PMID:41514136). - Severity: Moderate-to-severe/profound, variable across families and even within the same variant. - Progression: Documented in the majority (5/6) of individuals with serial audiograms — an unusual feature for ARNSHL, most of which (e.g., GJB2-related) is congenital and stable. - Speech outcomes: Speech discrimination scores of 70–96% reported in the two most recent Iranian probands, correlating with moderate rather than profound loss at last follow-up.

Quality of life: Not formally measured with standardized instruments (EQ-5D/SF-36) in any report; clinical narrative notes affected children use hearing aids, and delayed language/speech development was observed in at least one case ("unclear language" and non-response to sound from age 2, Family 1 proband).

4. Genetic/Molecular Information

Causal gene and variant catalog

All known pathogenic EPS8L2 variants (NM_022772.4 transcript; 21 exons, 715-aa protein):

Variant (cDNA)	Protein	Type	Zygosity/family	Source
c.1014delC	p.Ser339Alafs*15	Frameshift (exon 12)	Homozygous — Algerian founding family	PMID:26282398
c.737delC	frameshift	Frameshift (Pakistani family F11)	Homozygous, consanguineous	Wang et al. 2017, PMID:28281779
c.738delA / p.(Val247Cysfs*6)	Frameshift	Exon 9	Cited as supporting evidence for exon-9 biological importance	Owrang et al. 2026
c.818_827dup	p.(Ala279Glyfs*36)	Frameshift (exon 10)	Compound het, maternal allele — German Family 1 (novel)	PMID:41514136
c.1430dup	p.(Val478Serfs*25)	Frameshift (exon 15)	Compound het, paternal allele — German Family 1 (previously reported)	PMID:41514136
c.1878C>A	p.(Tyr626Ter)	First nonsense variant (exon 19, SAM/PNT domain)	Homozygous — Iranian Family 2	PMID:41514136
c.767C>G	p.(Thr256Arg)	First missense variant, shown by minigene assay to cause complete exon 9 skipping (r.701_768del, p.(Gly234Alafs*55))	Homozygous — Iranian Families 3 & 4 (founder allele)	PMID:41514136
c.357_361dupGGTGC	p.(Gln121Argfs*67)	Frameshift, de novo on one allele	Compound het (with c.1317dupG) — 39-year-old male, first de novo-containing case	[Gan et al. 2026, PMID:41578500]
c.1317dupG	p.(Leu440Alafs*63)	Frameshift, maternally inherited	Compound het (above)	PMID:41578500

Variant classification: All reported variants are pathogenic or likely pathogenic per ACMG/AMP criteria (e.g., the spliceogenic missense classified PM2_P, PM3_M, PVS1_S). All converge mechanistically on loss of function — via frameshift/premature termination, nonsense-mediated decay, or exon skipping.

Population frequency: Pathogenic EPS8L2 alleles are essentially absent from population databases — the recurrent c.767C>G founder variant was found in only 1 carrier among ~40,000 exomes (UCL Queen Square database) and was absent from gnomAD, TopMed, and All of Us (PMID:41514136), underscoring extreme rarity.

Somatic vs. germline: All variants are germline; no somatic mosaicism reported.

Functional consequence: Uniformly loss-of-function — truncated/absent protein (frameshift/nonsense with NMD) or exon-skipping-induced frameshift (spliceogenic missense). No gain-of-function or dominant-negative alleles have been described.

Modifier genes

None identified to date.

Epigenetic information

Not investigated/reported for this gene-disease relationship.

Chromosomal abnormalities

None reported; disease is caused by small intragenic variants, not structural/copy-number changes.

5. Environmental Information

No environmental factors, lifestyle factors, or infectious triggers have been implicated. DFNB106 is a purely monogenic disorder with no reported gene-environment modulation.

6. Mechanism / Pathophysiology

Protein structure and localization

EPS8L2 (EPS8 Signaling Adaptor L2) is a 715-amino-acid, F-actin-binding member of the EPS8 protein family (EPS8, EPS8L1, EPS8L2, EPS8L3), containing a phosphotyrosine-binding (PTB) domain, an SH3 domain, an effector domain, and (per the 2026 paper) a SAM/pointed (SAM/PNT) domain near the C-terminus. In cochlear and vestibular hair cells, EPS8L2 localizes specifically to the tips of the shorter and intermediate rows of stereocilia, distinguishing it from EPS8, which localizes to and elongates the tallest stereocilia row (Dahmani et al. 2015, PMID:26282398; Furness et al. 2013 PNAS, PMID:23918390).

Causal chain (cellular process → tissue → organism)

Molecular: Loss-of-function EPS8L2 variant → absent or truncated actin-binding adaptor protein at stereocilia tips.
Cellular: Failure to maintain (not initially build) the actin core of the short/intermediate stereocilia rows in mature hair cells → gradual disorganization and shortening of these rows, with variable width abnormalities.
Tissue: Progressive deterioration of the hair bundle "staircase" architecture required for mechanotransduction in cochlear (and vestibular) hair cells of the organ of Corti.
Organism: Progressive, typically postlingual-onset sensorineural hearing loss, sloping toward high frequencies (or U-shaped in the spliceogenic-variant cases), because mechanotransduction becomes progressively impaired as the affected stereocilia rows degrade with age/use rather than failing to form in the first place.

This gives DFNB106 a mechanistically distinct signature versus most ARNSHL: EPS8 loss causes early, static, profound deafness (failure to elongate stereocilia in the first place — DFNB102), whereas EPS8L2 loss causes late-onset, progressive deafness (failure to maintain mature stereocilia) — a "maintenance vs. morphogenesis" dichotomy within one paralog family (Furness et al. 2013; [EPS8/DFNB102 review, PMID not extracted, PMC9837036]).

Molecular pathway

EPS8L2 acts through actin cytoskeleton dynamics regulation — bundling/capping activity at stereocilia tips, and (based on EPS8-family biology) potential modulation of Rac/SOS1-linked signaling relevant to membrane/cytoskeletal remodeling (GeneCards annotation).

Suggested GO terms: - GO:0051017 — actin filament bundle assembly - GO:0032420 — stereocilium - GO:0003785 — actin monomer binding - GO:0060088 — auditory receptor cell stereocilium organization

Suggested CL terms: - CL:0000601 — inner hair cell of Corti's organ (or cochlear outer/inner hair cell, CL:0000589)

Suggested UBERON terms: - UBERON:0001844 — cochlea / organ of Corti - UBERON:0009865 — stereocilium bundle (if available) or UBERON:0002106 (spiral organ)

Molecular profiling / advanced technologies

Zebrafish whole-mount in situ hybridization (WISH): eps8l2 is expressed in the otic vesicle — specifically the presumptive utricular and saccular maculae — and in the pronephric duct; later stages show broader otic-vesicle expression plus scattered spinal cord expression (Owrang et al. 2026, PMID:41514136).
Minigene/splicing assay: For the c.767C>G missense variant, RT-PCR of a minigene construct demonstrated complete exon 9 skipping, converting a presumed benign missense change into a functional null allele — directly confirming spliceogenicity by wet-lab assay rather than in silico prediction alone (only 2/6 splice-prediction algorithms had flagged it).
No transcriptomic, proteomic, or single-cell datasets specific to human EPS8L2-deficient tissue have been published (human inner-ear tissue is not accessible for biopsy).

7. Anatomical Structures Affected

Organ level: Inner ear only (cochlea and, to a lesser functional extent demonstrated in mouse, the vestibular system) — no other organ system involvement reported (nonsyndromic).
Tissue/cell level: Cochlear and vestibular hair cells (CL:0000601/CL:0000602), specifically their stereocilia bundles.
Subcellular level: Stereocilia actin core/tip complex — the specific site of EPS8L2 localization (GO:0005884 actin filament; GO:0032420 stereocilium).
Localization: Bilateral, symmetric involvement in all reported human cases (no unilateral or asymmetric presentations documented).

8. Temporal Development

Onset: Ranges from prelingual/infantile to early childhood (~4–7 years most typical); one documented presymptomatic case with normal newborn hearing screening followed by measurable loss detected by ~23 months.
Onset pattern: Insidious/gradual rather than acute.
Progression: Progressive in the majority of longitudinally followed cases (5/6) — an atypical feature for ARNSHL. Progression can continue into adulthood (one individual "in her fourth decade" with prior progression now described as stable over the last decade of follow-up), suggesting eventual plateauing in at least some individuals.
Disease course pattern: Chronic, generally progressive-then-potentially-stabilizing; not episodic or relapsing-remitting.
Critical period: The 2026 paper explicitly frames early infancy/toddlerhood as a "therapeutic window" — before stereocilia degeneration is complete — for any future molecular intervention, based on parallel work in EPS8 (DFNB102) mouse gene-therapy models (see Treatment section).

9. Inheritance and Population

Inheritance pattern: Autosomal recessive (both homozygous and compound heterozygous genotypes documented).
Penetrance: Appears complete for biallelic loss-of-function genotypes, though age-dependent (phenotype may not be measurable at birth).
Expressivity: Variable — age of onset, severity, rate of progression, and audiogram shape (sloping vs. U-shaped) differ even among carriers of the same variant (e.g., within the shared founder-variant Iranian families).
Genetic anticipation: Not applicable/not reported (not a repeat-expansion disorder).
Germline mosaicism: Not reported.
Founder effects: A shared ~4.17 Mb homozygous haplotype around c.767C>G in two ostensibly unrelated Iranian families strongly suggests a regional founder allele.
Consanguinity: A major contributing factor in most reported pedigrees (Algerian, Iranian, Pakistani).
Carrier frequency: Cannot be reliably estimated — pathogenic alleles are essentially unseen in gnomAD/TopMed/All of Us; the disease is considered ultra-rare.
Epidemiology: No formal prevalence/incidence estimate exists. Only 8 families (~14 affected individuals) have been published worldwide as of the January 2026 update (Owrang et al. 2026), spanning Algeria, Pakistan (≥2 families), Iran (≥3 families), Germany, and China (1 case). For context, ARNSHL overall accounts for ~80% of genetic nonsyndromic hearing loss, with GJB2/DFNB1 explaining roughly 16.9% globally (up to 27.1% in European cohorts) and >85 genes implicated overall in ARNSHL — DFNB106 is a very minor contributor to this landscape.
Geographic/ethnic distribution: Cases reported across North Africa (Algeria), South Asia (Pakistan), the Middle East (Iran), Europe (Germany, with mixed Greek/German parentage), and East Asia (China) — no single predominant population, though consanguineous-marriage-practicing populations are overrepresented, as expected for rare recessive disease ascertainment.
Sex ratio: No sex predilection reported (X-linked/mitochondrial mechanisms excluded; autosomal recessive).

10. Diagnostics

Clinical/audiologic tests: Standard pure-tone audiometry (air and bone conduction across 125 Hz–8 kHz), speech reception threshold and speech discrimination testing. Serial audiometry over years is essential to document the characteristic progression.
Newborn hearing screening: May be passed (normal) despite carrying a biallelic pathogenic EPS8L2 genotype — a critical diagnostic pitfall, since a normal newborn screen does not rule out DFNB106 given its progressive, sometimes-delayed onset.
Genetic testing:
Whole-exome sequencing (WES) has been the discovery and diagnostic method for essentially all reported cases (candidate-gene approach after excluding GJB2), reflecting how rare/unrecognized this gene is on standard hearing-loss panels.
Targeted deafness gene panels may include EPS8L2 (e.g., listed on the Genomics England PanelApp "Monogenic hearing loss" panel) but coverage varies by lab.
Autozygosity/homozygosity mapping has been used in consanguineous families to define candidate intervals and detect founder alleles.
Minigene/splicing functional assays are recommended when a missense variant is discovered, given the demonstrated risk of missense variants (e.g., c.767C>G) acting as cryptic splice-disrupting alleles rather than simple amino-acid substitutions — routine in silico tools alone missed this in most predictors.
Differential diagnosis: Other genetic causes of progressive, nonsyndromic, prelingual-to-childhood-onset sensorineural hearing loss (e.g., STRC-related, TMPRSS3-related, OTOF-related, other DFNB loci), and syndromic causes should be excluded via broader panel/exome testing and clinical evaluation (absence of other organ involvement supports "nonsyndromic" classification).
Screening: No population-level screening program exists for EPS8L2 given its rarity; identification is via diagnostic exome/genome sequencing after clinical suspicion (progressive ARNSHL, especially with a family history or normal-but-later-failing newborn screen).

11. Outcome/Prognosis

Mortality: None — DFNB106 causes isolated hearing loss with no reported effect on life expectancy or systemic morbidity.
Morbidity: Communication/speech-language developmental impact from progressive hearing loss, particularly if diagnosis and intervention (hearing aids) are delayed; documented delayed speech/language recognition in at least one proband.
Disease course: Progressive threshold elevation over years to decades in most individuals; in a minority, progression appears to plateau (documented stability over a decade in an adult in her 4th decade of life; near-stability over 10 years in one Iranian proband).
Prognostic factors: Earlier recognition and hearing-aid fitting appear associated with better functional outcomes (standard audiology principle); no genotype-severity correlation has yet been established across the small number of reported variants, though the two individuals with the spliceogenic c.767C>G variant shared a distinctive U-shaped audiogram, hinting at a possible variant-specific pattern.
General ARNSHL cochlear implant data (not DFNB106-specific, given no published case yet requiring implantation): Progressive vs. congenital profound hearing loss show no significant difference in cochlear implant outcomes; genetic etiology overall does not reduce implant benefit, with performance driven mainly by age at implantation and duration of hearing loss prior to intervention.

12. Treatment

No disease-specific or FDA-approved therapy exists for DFNB106. Management is symptomatic/supportive, following standard practice for progressive sensorineural hearing loss:

Hearing aids (NCIT:C15302 is for physical therapy; the relevant NCIT concept is closer to "Hearing Aid" under assistive devices) — used by affected children as soon as loss is documented; one German proband fitted with aids from young childhood, his presymptomatic sibling scheduled for first aids at 2 years 8 months once threshold elevation was confirmed.
Cochlear implantation — not yet reported for a confirmed DFNB106 case in the literature, but by extrapolation from general ARNSHL cochlear-implant literature, would be expected to be effective if hearing loss progresses to severe/profound levels, with outcomes driven by implantation timing rather than genotype per se.
Genetic counseling (NCIT:C15240) — recommended given the autosomal recessive inheritance, ~25% recurrence risk per pregnancy for carrier couples, and the discovery of a Fars-region Iranian founder allele relevant to regional carrier screening.
Speech and audiologic rehabilitation (NCIT:C159273 speech therapy) — standard adjunct for children with progressive hearing loss.

Experimental/preclinical therapeutic direction ("therapeutic window")

The 2026 Owrang et al. paper explicitly discusses gene-therapy precedent from the sister gene EPS8 (DFNB102): a preclinical AAV-mediated (Anc80L65 serotype) EPS8 gene-replacement study in Eps8 knockout mice rescued hair-bundle structure but not functional hearing, and rescue efficacy dropped sharply if AAV delivery was delayed past postnatal day 1–2 ("when delayed to postnatal day 3, almost no recovery was observed"). The authors argue this underscores the urgency of early molecular diagnosis for EPS8L2, since its later, more gradual onset (compared to EPS8/DFNB102's early profound congenital deafness) may in principle offer a longer intervention window for a future EPS8L2-directed gene therapy — though no such therapy has yet been developed or tested for EPS8L2 itself. This is framed as a rationale for early genetic testing/referral, not as an available treatment.

No clinical trials (NCT) specific to EPS8L2/DFNB106 were identified in the search.

13. Prevention

Primary prevention: Not applicable in the biological sense (no modifiable risk factor); the only "primary prevention" lever is reproductive genetic counseling for known-carrier couples (e.g., preimplantation genetic diagnosis or prenatal testing where a familial variant is known), particularly relevant in consanguineous unions or populations carrying an identified founder allele (e.g., the Fars, Iran region).
Secondary prevention/early detection: Universal newborn hearing screening remains valuable but is explicitly shown to be insufficient alone for DFNB106, since affected infants can pass screening and only develop measurable loss in the second year of life — supporting a case for genetic newborn screening or expanded gene panels in at-risk families (e.g., known familial variant, consanguinity, family history of progressive childhood-onset ARNSHL) to enable close audiologic monitoring even after a normal screen.
Tertiary prevention: Early hearing-aid fitting and speech-language intervention to minimize the developmental impact of progressive threshold elevation.
Genetic/carrier screening: Expanded carrier screening panels in consanguineous or founder populations could, in principle, include EPS8L2, though it is not yet part of standard commercial hearing-loss carrier panels given its rarity.

14. Other Species / Natural Disease

This is one of the best-documented sections for DFNB106, given a notable naturally occurring canine model:

Rhodesian Ridgeback dog — early-onset adult deafness: A genome-wide association study (23 affected vs. 162 control dogs) followed by Sanger sequencing identified a 12-bp in-frame deletion in EPS8L2, segregating in an autosomal recessive pattern; "all affected dogs were homozygous for the deletion" (Kawakami et al. 2022, PMID:35385474, PLoS ONE). This represents a spontaneous, naturally occurring veterinary phenocopy of human DFNB106 and is a strong translational/comparative model, since it arose without laboratory engineering and mirrors the human recessive, hair-cell-maintenance mechanism.
Suggested NCBI Taxon: NCBITaxon:9615 (Canis lupus familiaris); breed identifiers via VBO would apply to "Rhodesian Ridgeback."
Mouse (Mus musculus, engineered knockout): Eps8l2-null mice (targeted knockout, not naturally occurring) — see Model Organisms below.
No other species' natural disease has been reported for EPS8L2 to date (unlike some hearing-loss genes with described feline or bovine natural mutants).
Comparative biology: The EPS8 gene family (EPS8, EPS8L1, EPS8L2, EPS8L3) and its stereocilia-tip actin-regulatory role are evolutionarily conserved across mammals, underpinning why the mouse, dog, and human phenotypes converge on the same "progressive stereocilia maintenance failure" mechanism rather than divergent pathology.
Zoonotic potential: Not applicable — this is a non-infectious monogenic disorder.

15. Model Organisms

Model	Type	Key findings	Source
*Mouse (Eps8l2* knockout)**	Engineered, germline null (MGI:2138828)	Late-onset, progressive, severe hearing loss (especially high frequencies) due to gradual disorganization of cochlear hair bundles; stereocilia of the tall row become shorter and fewer, while middle and short rows are relatively preserved — the mirror image of the human/dog phenotype pattern but consistent with a stereocilia-maintenance (not morphogenesis) defect. Directly recapitulates human progressive, postnatal-onset hearing loss.	Furness et al. 2013, PNAS, PMID:23918390
*Zebrafish (Danio rerio)*	Expression study (WISH), not a knockout/phenotype model to date	eps8l2 expressed in otic vesicle (utricular/saccular macula precursors) and pronephric duct during development; supports conserved otic relevance across vertebrates but no functional loss-of-function zebrafish model has yet been published.	Owrang et al. 2026, PMID:41514136
Dog (Rhodesian Ridgeback)	Naturally occurring, spontaneous	See "Other Species" above — a naturally arising, homozygous 12-bp in-frame EPS8L2 deletion causing early-onset adult deafness; valuable as an outbred, naturally occurring large-animal model with autosomal recessive transmission matching the human disease exactly.	[Kawakami et al. 2022, PMID:35385474]

Model limitations: The mouse knockout shows a somewhat different stereocilia-row pattern (tall row affected) than what would be predicted from EPS8L2's normal tip localization at short/intermediate rows in wild-type animals — this apparent paradox is discussed in the primary literature but not fully resolved, and represents an open question about full concordance between mouse structural findings and the exact human audiometric/histopathologic correlate (human temporal bone histopathology is unavailable). No iPSC-derived otic organoid model of EPS8L2 deficiency has yet been published. Preclinical AAV gene-therapy rescue data exist only for the paralogous gene EPS8 (DFNB102 mouse model), not yet for EPS8L2 itself, and even that related rescue restored structure without restoring functional hearing — an important caveat when extrapolating "therapeutic window" arguments to EPS8L2.

Summary of Key Citations

Dahmani M, et al. "EPS8L2 is a new causal gene for childhood onset autosomal recessive progressive hearing loss." Orphanet J Rare Dis. 2015. PMID:26282398 — founding report (Algerian family).
Furness DN, et al. "Progressive hearing loss and gradual deterioration of sensory hair bundles in the ears of mice lacking the actin-binding protein Eps8L2." PNAS. 2013;110(34):13898–13903. PMID:23918390 — mouse knockout, mechanistic basis.
Wang R, et al. "Molecular Analysis of Twelve Pakistani Families with Nonsyndromic or Syndromic Hearing Loss." Genet Test Mol Biomarkers. 2017. PMID:28281779 — second EPS8L2 family (Pakistan, c.737delC).
Kawakami T, et al. "Early onset adult deafness in the Rhodesian Ridgeback dog is associated with an in-frame deletion in the EPS8L2 gene." PLoS One. 2022. PMID:35385474 — canine natural model.
Owrang [lead author], et al. "Expansion of Molecular and Clinical Aspects of EPS8L2 (DFNB106)-Associated Hearing Loss Emphasizes a Potential Therapeutic Window." Mol Neurobiol. 2026 (online Jan 2026). PMID:41514136 — most comprehensive, current synthesis (4 new families, splicing functional assay, therapeutic-window discussion, zebrafish expression).
Gan H, et al. "Identification and phased de novo mutation of the EPS8L2 gene in a patient with progressive hearing loss." Medicine (Baltimore). 2026. PMID:41578500 — first compound-het case including a de novo allele.
OMIM #617637 (DFNB106) and *614988 (EPS8L2) — https://omim.org/entry/617637 ; https://omim.org/entry/614988
ClinVar RCV000499522 — MONDO:0033198 cross-reference.

Data gaps to flag explicitly for curation: No published human temporal-bone histopathology; no confirmed cochlear-implant outcome case specific to DFNB106; no iPSC/organoid model; no EPS8L2-specific gene therapy (only paralog EPS8 preclinical data exists); prevalence/incidence figures are not formally estimated (only cumulative case counts across published families).

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Hearing Loss, Autosomal Recessive 106 (DFNB106) — Comprehensive Research Report

1. Disease Information

2. Etiology

Genetic risk factors

Protective factors

Gene-environment interactions

3. Phenotypes

4. Genetic/Molecular Information

Causal gene and variant catalog

Modifier genes

Epigenetic information

Chromosomal abnormalities

5. Environmental Information

6. Mechanism / Pathophysiology

Protein structure and localization

Causal chain (cellular process → tissue → organism)

Molecular pathway

Molecular profiling / advanced technologies

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome/Prognosis

12. Treatment

Experimental/preclinical therapeutic direction ("therapeutic window")

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Summary of Key Citations

Reference Validation