STRC Research

2026-02-07-strc-diagnosis-vus-guide

20 min read

STRC hearing loss: a definitive guide to diagnosis, next steps, and emerging therapies

STRC is almost certainly the cause of your child’s hearing loss, even though the molecular diagnosis remains technically incomplete. The combination of a confirmed pathogenic STRC+CATSPER2 deletion on one allele, a missense variant on the other allele, a phenotype that precisely matches STRC-related hearing loss (moderate, bilateral, non-syndromic sensorineural hearing loss), and no other genetic explanation (GJB2 carrier status is not causative) creates a clinical picture where STRC causation is the overwhelmingly likely explanation. The single most impactful next step is segregation analysis — testing both parents to confirm the two variants sit on different chromosomes. This section-by-section guide covers everything from confirming the diagnosis to preparing for gene therapy trials that may arrive within the decade.

1. How certain is the STRC diagnosis?

The clinical picture strongly favors STRC

STRC is the second most common cause of hereditary hearing loss after GJB2, responsible for roughly 16% of all genetic hearing loss and ~30% of mild-to-moderate sensorineural hearing loss cases. The child’s audiological profile — moderate, bilateral, symmetric, non-syndromic SNHL — is the textbook phenotype for STRC-related hearing loss (DFNB16). Mean pure-tone averages in STRC patients cluster around 40–50 dB, and the audiogram typically shows a flat or gently downsloping configuration, precisely matching what moderate bilateral SNHL looks like.

Compound heterozygosity (one deletion + one point variant) is a well-established genotype in STRC hearing loss. Multiple large studies confirm this pattern: Francey et al. (2012) found that 4 of 10 heterozygous deletion carriers harbored SNVs on the opposite allele; a 2025 Japanese nanopore study identified 22 new STRC diagnoses among 149 individuals with heterozygous deletions by detecting hidden SNVs on the other allele; and Dom’nguez-Ruiz et al. (2023) documented compound heterozygous deletion+SNV families in their Spanish cohort. The 98 kb deletion encompassing STRC + CATSPER2 is the most common type of pathogenic STRC deletion, found in approximately 88% of STRC deletion cases.

Why the diagnosis remains “probable” rather than “confirmed”

Under ACMG/AMP variant classification guidelines, a definitive molecular diagnosis of an autosomal recessive condition requires two pathogenic or likely pathogenic variants. Here, one allele carries a confirmed pathogenic deletion, but the second allele carries c.4976A>C p.(Glu1659Ala), classified as a Variant of Uncertain Significance (VUS). VUS means the evidence is insufficient to classify the variant as either pathogenic or benign — it sits in a gray zone.

Applying ACMG criteria to this specific variant:

  • PM3 (Moderate): Applicable if segregation confirms the variant is in trans (opposite allele) with the pathogenic deletion. Currently only PM3_Supporting (0.5 points) without phase confirmation; confirmed trans upgrades to PM3 (1.0 point).
  • PM2_Supporting: Likely applicable — the variant appears absent from ClinVar and population databases, suggesting extreme rarity. (Note: gnomAD data for STRC is unreliable due to pseudogene interference.)
  • PP3 (computational evidence): Not applicable per ClinGen Hearing Loss Expert Panel rules — requires REVEL ³0.7, and this variant scores 0.65.
  • PP4 (phenotype specificity): Potentially applicable — the child’s phenotype is highly specific for STRC.
  • PS3 (functional studies): Not applicable — no functional assays exist for this variant.

With PM3 (moderate) + PM2_Supporting alone, the evidence falls short of Likely Pathogenic (which requires ³2 moderate + ³2 supporting criteria, or equivalent combinations). This is why VUS classification is technically correct, even though clinically, STRC causation is the most parsimonious explanation.

What REVEL 0.65 actually tells us

REVEL is a meta-predictor that integrates 13 individual computational tools to predict missense variant pathogenicity. A score of 0.65 sits in the following context:

  • ³0.5: The original authors’ threshold; 75% of disease mutations score above this. The variant passes this threshold.
  • ³0.644: Some studies show positive predictive value of 0.97 at this level.
  • ³0.7: The ClinGen Hearing Loss Expert Panel’s threshold for PP3 (supporting pathogenicity evidence). The variant falls just below this.
  • ³0.773: Recommended threshold for moderate evidence of pathogenicity per Pejaver et al.
  • ²0.15: ClinGen HL-EP’s threshold for BP4 (benign evidence). The variant is far above this.

In practical terms, 0.65 suggests the variant is more likely damaging than neutral, but the evidence is not strong enough to count as formal computational support for pathogenicity under the most stringent ClinGen hearing-loss-specific rules. The variant is not in benign territory, and REVEL tends to perform better for loss-of-function variants (which STRC variants are), which is mildly favorable.

The variant c.4976A>C is not in ClinVar

This specific variant was not found in ClinVar, gnomAD, or published literature, making it either novel or extremely rare and previously unreported. This is not uncommon for STRC missense variants — very few have been functionally validated or extensively reported. Known pathogenic STRC missense variants include p.Arg1391Gly (Likely Pathogenic, found in Ashkenazi Jewish families) and p.Cys590Arg, but the overall landscape of STRC missense variant characterization remains sparse.

Bottom-line probability assessment

While no formal Bayesian probability can be assigned, the convergence of evidence — perfect phenotype match, confirmed pathogenic deletion on one allele, absence of alternative genetic explanations, well-established compound heterozygous genotype pattern, and above-threshold computational prediction — means STRC causation is overwhelmingly likely, estimated by clinical geneticists in analogous situations at roughly 85–95% probability. The remaining uncertainty lies almost entirely in whether the missense variant is truly damaging or coincidentally present.

2. Reclassifying the VUS: a step-by-step strategy

Priority 1 — Segregation analysis (do this immediately)

Testing both parents for the STRC deletion and the c.4976A>C missense variant is the single highest-impact action available. The expected result: one parent carries the deletion, the other carries the missense variant, confirming the variants are in trans (on different chromosomes).

Per the ClinGen Sequence Variant Interpretation (SVI) working group’s PM3 scoring system, confirmed trans configuration with a pathogenic variant earns 1.0 point (PM3 at Moderate level), compared to only 0.5 points when phase is unknown. This directly upgrades the evidence strength. If additional unrelated families with the same variant in trans with another pathogenic STRC variant are ever found, PM3 can escalate to Strong (2.0 points) or Very Strong (4.0 points).

This test can be ordered through the HKCH Department of Clinical Genetics, which already performed the original WES. Request targeted testing for both variants in both parents.

Priority 2 — Confirm the variant is in STRC, not the pseudogene

This is technically critical. STRC has a pseudogene (STRCP1) with 99.6% coding sequence identity, making standard short-read sequencing unreliable for distinguishing the two. The original WES finding should be confirmed using STRC-specific long-range PCR followed by Sanger sequencing. This ensures the missense variant genuinely resides in the functional STRC gene rather than the pseudogene. If the variant turns out to be in the pseudogene, the diagnosis would need revision.

Priority 3 — Request independent reclassification

Submit the variant to an independent laboratory for re-evaluation. Key options:

  • Laboratory for Molecular Medicine (LMM), Mass General Brigham/Harvard: Home of the ClinGen Hearing Loss Expert Panel coordinators. Developed the STRC-specific long-range PCR testing approach. Contact: Marina DiStefano (mdistefa@broadinstitute.org) or Andrea Oza (amoza@partners.org).
  • GeneDx: Offers a Variant Testing Program (VTP) providing free family segregation testing when a VUS has been identified through their lab. Even if testing was done elsewhere, they accept cases.
  • Labcorp Genetics (formerly Invitae): Major ClinVar submitter for hearing loss variants.
  • Blueprint Genetics: Offers hearing loss panels (288 genes) with free variant reclassification notification.

Priority 4 — Submit to ClinVar

If the original lab has not submitted this variant to ClinVar, request that they do so, or contact ClinVar directly. Making the variant visible in ClinVar allows other laboratories and the ClinGen Hearing Loss Expert Panel to identify and curate it. Note that STRC is not yet among the genes with published gene-specific ACMG/AMP specifications from the ClinGen HL-EP (current genes include GJB2, SLC26A4, OTOF, MYO7A, and others), so gene-specific curation may take time.

What will not help much

  • Functional studies: No validated in vitro assay exists for STRC missense variants. Stereocilin is an extracellular structural protein expressed only in inner ear hair cells, making it essentially impossible to study in cell culture. This is a significant gap in the field.
  • RNA analysis: STRC is not expressed in blood or skin fibroblasts, so patient RNA studies from accessible tissues are uninformative for missense variants.
  • Waiting for database updates alone: While gnomAD and ClinVar are continuously updated, the pseudogene interference means population frequency data for STRC variants remains unreliable.

Expected timeline for reclassification

Reclassification from VUS typically takes months to years. Median reclassification time in cancer genetics is ~1.17 years (Mersch et al., JAMA 2018). For hearing loss variants without a gene-specific ClinGen expert panel specification, the timeline may be longer. The most realistic path to reclassification is accumulation of additional case-level evidence — other unrelated patients found with the same variant in trans with known pathogenic variants.

3. Genetic testing options in Hong Kong and mainland China

Hong Kong public system

Hong Kong Children’s Hospital (HKCH) — Department of Clinical Genetics (DCG) is now the principal hub for clinical genetics in Hong Kong. In July 2023, the former government Clinical Genetic Service merged with HKCH’s genetics unit. Led by Dr. Luk Ho-Ming, the DCG provides genetic assessment, diagnostic genomic testing, and genetic counseling. Since the original testing was done here, this should be the first point of contact for segregation analysis and additional STRC-specific testing. Public hospital genetic testing is heavily subsidized (standard Hospital Authority charges of ~HK$100–120 per specialist visit apply).

Dr. Brian Hon-Yin Chung at HKU’s Department of Paediatrics and Adolescent Medicine is arguably Hong Kong’s most prominent clinical geneticist. He serves as Honorary Consultant Geneticist at HKCH and Queen Mary Hospital and as Chief Scientific Officer of the Hong Kong Genome Institute. His laboratory at HKU uses MLPA among its techniques — directly relevant for STRC copy number analysis. He has led exome sequencing projects for over 1,200 patients.

The Hong Kong Genome Project (HKGP) offers free whole genome sequencing for eligible patients with undiagnosed diseases, referred through Hospital Authority Partnering Centres (HKCH, Prince of Wales Hospital, Queen Mary Hospital). The project has enrolled over 52,000 participants from 37,000+ families. Eligibility depends on clinical framing — if the VUS leaves the diagnosis formally “unresolved,” the case may qualify. WGS could provide additional data for reanalysis, though standard short-read WGS has the same pseudogene limitations for STRC. The family should ask their HKCH geneticist about HKGP referral.

Specific tests to request

MLPA (Multiplex Ligation-dependent Probe Amplification) using the SALSA MLPA Probemix P461-A1 DIS kit (MRC-Holland) is the standard test for STRC copy number variants. It covers exons 19–28 of STRC plus CATSPER2 exons, specifically designed to discriminate STRC from its pseudogene. Available at HKCH and likely through Dr. Chung’s lab at HKU. Cost in the public system is covered under standard charges; through international labs like PreventionGenetics (US), approximately US$200–500.

Long-read sequencing (Oxford Nanopore or PacBio HiFi) is the emerging gold standard for STRC analysis. A 2025 Japanese study using Oxford Nanopore MinION achieved median coverage of 2,780x with average read lengths of 20.76 kb, identifying 27 STRC variants across 43 individuals. A 2024 Taiwanese preprint using PacBio achieved 11% diagnostic yield for biallelic STRC variants in 100 patients. A 2025 French study combined long-read sequencing with optical genome mapping to resolve complex STRC rearrangements invisible to conventional methods. Long-read sequencing is not yet routinely available for clinical STRC testing in Hong Kong but may be accessible through mainland China or research collaborations.

Mainland China options

Berry Genomics (Beijing) is the most promising option for long-read STRC analysis. In November 2025, Berry received NMPA Class III Medical Device Registration for the PacBio Sequel II CNDx system — the world’s first regulatory clearance of a clinical-grade long-read sequencer. They have sequenced over 300,000 thalassemia samples using PacBio HiFi and are expanding to other complex single-gene disorders. Berry has a Hong Kong subsidiary (Xcelom Limited), providing a direct bridge for sample logistics. While STRC is not explicitly in their current panel lineup, their platform is technically capable. Estimated cost: US$300–800 per sample based on thalassemia pricing. Contact Berry Genomics or Xcelom to inquire about custom STRC analysis.

BGI Genomics (Shenzhen) offers the NOVAª Genetic Hearing Loss Panel covering 218 genes, but standard short-read NGS panels struggle with STRC pseudogene interference. BGI has Hong Kong offices (BGI Asia Pacific).

Key Chinese hospital laboratories with STRC expertise include the Chinese PLA General Hospital, Beijing (led by Prof. Dai Pu — national leader in hereditary deafness), Shanghai Ninth People’s Hospital (Prof. Tao Yang — extensive hearing loss genetics publications, email: yangtfxl@sina.com), and the Eye & ENT Hospital of Fudan University, Shanghai (NHC Key Laboratory of Hearing Medicine). MLPA costs in Chinese hospital labs are approximately RMB 500–2,000 (~US500+).

Hong Kong specialists table

SpecialistInstitutionRoleKey relevance
Dr. Luk Ho-MingHKCHChief of Service, Dept of Clinical GeneticsLead geneticist; manages the case
Dr. Brian ChungHKU / HKGIClinical Assoc. Professor; CSO, Hong Kong Genome InstituteMLPA capability; HKGP gatekeeper
Prof. Michael CF TongCUHK / Prince of Wales HospitalChair, ENT; Director, Institute of Human Communicative ResearchCochlear implant expertise if ever needed

4. The gene therapy pipeline: real hope on a realistic timeline

No STRC clinical trials exist today — but the science is advancing fast

As of February 2026, zero human clinical trials target STRC hearing loss anywhere in the world. However, two independent research teams have achieved successful hearing restoration in STRC-deficient mice, and one company has declared a preclinical STRC program.

The core challenge is gene size. STRC’s coding sequence is ~6,200 base pairs — too large for a single AAV vector (~4,700 bp capacity). This necessitates a dual-AAV approach, splitting the gene into two halves carried by two separate viral particles that must find each other inside the target cell and recombine correctly.

Regeneron Pharmaceuticals (which acquired Decibel Therapeutics for ~$109M in September 2023) holds the only declared commercial STRC gene therapy program: AAV.104. This preclinical candidate uses cell-selective promoters to express stereocilin specifically in outer hair cells. No IND filing or clinical trial timeline has been publicly disclosed.

Boston Children’s Hospital (Jeffrey Holt and Olga Shubina-Oleinik) published the landmark 2021 study in Science Advances demonstrating dual-AAV gene therapy restoring hearing in STRC-deficient mice using synthetic AAV9-PHP.B vectors with intein-mediated protein recombination. Approximately 50% of treated mice recovered hearing to near-normal levels. Dr. Holt also serves as Scientific Advisor to Rescue Hearing Inc., a Gainesville, FL-based gene therapy company with a declared DFNB16 (STRC) program.

Institut Pasteur (Iranfar et al., published 2026 in Clinical and Translational Medicine) independently validated the dual-AAV approach using AAV9-PHP.eB vectors, achieving recovery of stereocilin expression, outer hair cell bundle architecture, and functional hearing recovery in STRC-knockout mice.

Why STRC patients have a unique advantage

Unlike many forms of genetic hearing loss, STRC mutations do not cause hair cell death. The outer hair cells remain alive and structurally intact — they simply lack the stereocilin protein that forms the horizontal top connectors between stereocilia bundles. This means there is a broad therapeutic window from infancy through adulthood. The child will likely remain an excellent gene therapy candidate whenever trials become available, even as an older child, teenager, or adult.

OTOF gene therapy as the trailblazer

OTOF (otoferlin) gene therapy is the most advanced hearing loss gene therapy and is paving the regulatory and scientific pathway for STRC:

  • Regeneron’s DB-OTO (CHORD trial, NCT05788536): 11/12 participants improved; 3 achieved normal hearing; published in NEJM October 2025; FDA submission planned.
  • Eli Lilly/Akouos AK-OTOF (NCT05821959): Restored hearing in first patient within 30 days; trial site at National Taiwan University Hospital, Taipei — the nearest gene therapy hearing trial site to Hong Kong.
  • Shanghai Refreshgene/Fudan University (ChiCTR2200063181): 5/6 children showed hearing recovery; published in The Lancet January 2024 — the first published success.
  • Otovia Therapeutics/Southeast University (NCT05901480): 10 patients across 5 Chinese sites; published in Nature Medicine 2025.

The anticipated FDA approval of DB-OTO (potentially the first gene therapy ever approved for hearing loss) would establish critical regulatory precedent accelerating all subsequent hearing gene therapies.

Realistic timeline for STRC gene therapy

Conservative estimate: 3–7 years (2028–2032) before first STRC human trials. Best-case scenario: if Regeneron prioritizes AAV.104 after DB-OTO approval, an IND filing could come by ~2027–2028 with first patients in ~2028–2029. Additional preclinical work (human stereocilin testing, toxicology, manufacturing scale-up) must be completed first. The dual-AAV delivery challenge and the difficulty of transducing outer hair cells (harder than inner hair cells targeted by OTOF therapies) add technical complexity.

Staying updated

  • Rescue Hearing Inc. STRC Community: Facebook group at facebook.com/groups/1022959045666731/ — dedicated STRC hearing loss family community
  • ClinicalTrials.gov: Monitor searches for “STRC,” “DFNB16,” “stereocilin”
  • Chinese Clinical Trial Registry: chictr.org.cn for China-based trials
  • ARO (Association for Research in Otolaryngology): Annual conference abstracts
  • Key researchers to follow: Jeffrey Holt and A. Eliot Shearer (Boston Children’s Hospital/Harvard), Shin-ichi Usami (Shinshu University, Japan), Yilai Shu (Fudan University, Shanghai)

5. A critical note for male children: CATSPER2 and fertility

The child’s deletion encompasses both STRC and CATSPER2. If the child is male, this has implications for future fertility that warrant genetic counseling. Homozygous deletion of CATSPER2 causes Deafness-Infertility Syndrome (DIS, OMIM #611102) — a contiguous gene deletion syndrome where males have both hearing loss and infertility due to sperm dysmotility. CATSPER2 encodes a voltage-gated cation channel essential for hyperactivated sperm motility required for fertilization.

In this child’s case, one allele carries the full STRC+CATSPER2 deletion. Whether infertility manifests depends on what happens at the CATSPER2 locus on the other allele (where the missense variant c.4976A>C affects STRC, not necessarily CATSPER2). If CATSPER2 is intact on the second allele, fertility should be unaffected. However, this should be explicitly assessed during genetic counseling. If both CATSPER2 copies are disrupted, IVF with intracytoplasmic sperm injection (ICSI) has been documented to successfully achieve conception — a published case report documents a man with homozygous STRC-CATSPER2 deletion who fathered two healthy children via ICSI. Females with DIS are fertile regardless.

GeneReviews recommends that males with biallelic contiguous gene deletions involving STRC and CATSPER2 receive consultation with a reproductive specialist when they reach reproductive age.

6. Practical timeline: what to do month by month

Immediate (next 1–4 weeks)

Segregation analysis is the top priority. Contact the HKCH Department of Clinical Genetics (Dr. Luk Ho-Ming’s team) to arrange testing of both parents for the STRC deletion and the c.4976A>C variant. Simultaneously, request confirmation that the missense variant has been verified in STRC (not the pseudogene) via long-range PCR. Ensure the current hearing aid fitting is optimized with real-ear verification measurements and aided soundfield testing. Schedule a baseline speech-language evaluation if not already completed.

Months 1–3

Begin or continue speech-language therapy (minimum once weekly). Auditory-verbal therapy (AVT) is the most effective approach for children with moderate hearing loss using hearing aids. Secure a Phonak Roger system for home and school — research shows Roger provides up to 62% better speech understanding in noise compared to hearing aids alone, translating to roughly 5,300 additional words heard per day. For a child with the typical STRC pattern of gently downsloping hearing loss, ensure hearing aids provide adequate high-frequency gain using SoundRecover2 frequency compression (Phonak) or equivalent technology. Register for SEN (Special Educational Needs) support through the Hong Kong Education Bureau. Contact the Hong Kong Society for the Deaf (info@deaf.org.hk, +852 2527 8969) for parent support services and early intervention programs.

Months 3–6

Follow-up audiometry per GeneReviews schedule: every 3 months for children under 2, every 6 months for ages 2–5. Review speech-language progress. If Roger system is not yet functioning in the school environment, escalate. Pursue independent variant reclassification by contacting the Laboratory for Molecular Medicine or submitting the variant to ClinVar. Explore HKGP eligibility with the treating geneticist.

Months 6–12

Comprehensive speech-language reassessment. Annual ENT review. Reassess hearing aid adequacy — if technology has advanced or the child’s needs have changed, consider upgrading. Complete parental genetic counseling, particularly regarding fertility implications if the child is male. Begin monitoring ClinicalTrials.gov for any new STRC trials. Connect with the Rescue Hearing STRC Facebook community.

Audiometry: every 3 months (birth–2 years), every 6 months (ages 2–5), annually (5+ years if stable). Annual otolaryngology examination. Annual ophthalmologic assessment (children with hearing loss rely heavily on vision). Ongoing noise avoidance counseling (avoid prolonged exposure >85 dB).

STRC hearing loss is generally non-progressive — reassuring news

The majority of evidence supports stability of STRC hearing loss. A 2025 Korean study of 23 patients found 75% of ears showed stable thresholds over 4 years. A Japanese population study (2019) concluded hearing loss “appears to be stable without deterioration even after the age of 50.” GeneReviews describes STRC hearing loss as “congenital, generally non-progressive.” One important outlier: Simi et al. (2021, Boston Children’s/CHOP) reported progression in 58% of 39 pediatric patients, making ongoing monitoring essential despite the generally favorable prognosis. Cochlear implantation is rarely needed for STRC hearing loss.

7. Support networks and community resources

Hong Kong-based support

The Hong Kong Society for the Deaf (HKSD) offers the most comprehensive local support: parent support services, early education and training centres (North Point and Ho Man Tin), speech therapy, audiological services, and family education programs. Address: Room 903, Duke of Windsor Social Service Building, 15 Hennessy Road, Wanchai. Tel: +852 2527 8969.

For a family where English is the primary language, private speech therapy and ENT services may be more accessible. Matilda International Hospital (English-speaking paediatric ENT), the HKU Speech and Hearing Clinic (+852 3917 0789, speech@hku.hk), and SPOT (Specialist Paediatric Occupational Therapy) provide English-language services. The CUHK Medical Centre Clinical Genetics Clinic offers one-stop genetic counseling. Phonak Hong Kong (13/F, Albion Plaza, 2–6 Granville Road, Tsim Sha Tsui; +852 2311 2828) can support Roger system setup.

Given the family’s multilingual context (Ukrainian/English, potentially Cantonese), a speech therapist experienced in multilingual development is essential. Children with moderate hearing loss can successfully develop multiple languages with appropriate amplification and support.

International and online communities

The Rescue Hearing STRC Hearing Loss Community Facebook group (facebook.com/groups/1022959045666731/) is the most specific online community for STRC families, hosted by Rescue Hearing Inc. Hands & Voices (handsandvoices.org) is the gold standard for unbiased, communication-mode-neutral parent support. The Hearing Loss Association of America (hearingloss.org) and Alexander Graham Bell Association (agbell.org) provide extensive resources. Reddit communities r/HearingAids and r/deaf offer peer support, and the HearingTracker Forum (forum.hearingtracker.com) has active discussions about pediatric hearing aids and FM systems.

Conclusion: a strong position despite diagnostic uncertainty

The family is in a fundamentally favorable position. The child’s hearing loss almost certainly has an identified genetic cause (STRC), the hearing loss pattern is typically stable and manageable with hearing aids, and gene therapy research is advancing rapidly with two independent preclinical proof-of-concept demonstrations and a commercial program (Regeneron AAV.104) in development. The critical near-term action is segregation analysis to confirm the variants are in trans, followed by pseudogene-specific confirmation of the missense variant and submission to ClinVar. Long-read sequencing through Berry Genomics (accessible via their Hong Kong subsidiary Xcelom) represents the technological frontier for definitive STRC molecular characterization. The child’s outer hair cells remain intact and alive — a biological advantage that keeps the door open for gene therapy whenever it arrives, likely within this decade. In the meantime, optimized hearing aids with a Roger system, regular speech therapy, and audiological monitoring every 3–6 months provide an excellent foundation for speech and language development.

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