The Novel SIX1 c.396G>C (p.Lys132Asn) Mutation Unveiled in an Emirati Family

A groundbreaking study presented at the 2026 ACMG Annual Clinical Genetics Meeting has identified a novel heterozygous missense mutation in the SIX1 gene—c.396G>C leading to p.Lys132Asn—in a non-consanguineous Emirati family affected by autosomal dominant nonsyndromic hearing loss (ADNSHL). This discovery, detailed in Genetics in Medicine Open, underscores a previously unreported variant causing progressive sensorineural hearing loss without the branchial or renal anomalies typical of branchio-oto-renal (BOR) syndrome. Led by researchers Khola Younus Haji Ibrahim and colleagues from UAE institutions, the finding highlights diagnostic challenges in regions where recessive forms dominate due to consanguinity.

The family, originating from the UAE, presented with a multi-generational pattern of hearing impairment starting in adolescence or early adulthood. Initial testing focused on common recessive genes like GJB2 yielded negative results, prompting whole exome sequencing (WES) that pinpointed the SIX1 variant perfectly segregating with the phenotype. This case exemplifies how dominant mutations can be overlooked in high-consanguinity populations, where autosomal recessive nonsyndromic hearing loss (ARNSHL) accounts for up to 70-80% of cases.

Autosomal Dominant vs. Recessive Hearing Loss: Key Differences

Genetic hearing loss, affecting approximately 1 in 1,000 newborns globally, manifests as sensorineural (inner ear or auditory nerve damage), conductive (outer/middle ear), or mixed. In the Middle East, including the UAE, consanguineous marriages elevate ARNSHL prevalence, with GJB2 mutations like c.35delG being prominent founder variants. Conversely, ADNSHL, like DFNA23 linked to SIX1, shows 50% inheritance risk per child, often postlingual progressive high-frequency loss.

• Recessive forms: Require two mutated alleles; common in Arab populations (e.g., 35% GJB2 in UAE ARNSHL).
• Dominant forms: Single mutated allele suffices; underdiagnosed, as panels prioritize recessives.
• Syndromic vs. nonsyndromic: SIX1 typically syndromic (BOR: branchial fistulae, renal anomalies, hearing loss), but isolated DFNA23 occurs.

This UAE case reveals pure ADNSHL, expanding SIX1's phenotypic spectrum.

SIX1 Gene: A Master Regulator of Inner Ear Development

The SIX1 gene encodes a homeodomain transcription factor crucial for otic placode induction, vesicle formation, and sensory epithelia differentiation. It interacts with EYA1/SIX proteins to activate targets like Pax2, Sox2 for hair cell and ganglion development. Mutations disrupt these, causing DFNA23 (postlingual bilateral SNHL) or BOR syndrome (1/40,000 births).

Over 40 SIX1 variants reported, mostly homeodomain missense like p.R110Q, affecting DNA binding. The p.Lys132Asn alters a conserved residue, predicted damaging (CADD 28.4, REVEL 0.92), likely impairing SIX1-EYA1 interaction. Recent 2025 chick embryo studies identified novel Six1 targets (e.g., Gata3, Fgf10) as deafness candidates, linking to human loci.

Clinical Phenotype: Progressive Hearing Loss Without Syndromic Features

In the UAE family, affected members exhibited moderate-to-profound bilateral SNHL, progressive from teens, worse at high frequencies—classic DFNA23 audiogram "sloping." No preauricular pits, branchial cysts, or renal issues, distinguishing from BOR. Pure-tone audiometry confirmed sensorineural nature; imaging normal.

This mirrors Korean SIX1 cases (2023): variable onset, severity, but isolated HL or mild BO. UAE prevalence ~3-5% congenital HL genetic; ADNSHL ~10-20% of hereditary cases, underreported.

Genetic Analysis Methods: WES Triumphs Over Targeted Panels

Standard GJB2 Sanger negative led to WES on proband, revealing het c.396G>C (NM_005982.4). Segregation confirmed in 5/7 affected, absent in unaffected. Absent gnomAD (PM2), conserved (PM1), damaging predictions (PP3), family data (PS4, PP1).

WES diagnostic yield ~20-50% HL; UAE studies (106 sporadic): 25% biallelic, emphasizing need for dominant inclusion.

Diagnostic Gaps in the Middle East: Beyond Recessive Focus

UAE consanguinity (25-50%) skews toward ARNSHL; panels miss AD/ X-linked. This SIX1 case stresses comprehensive NGS panels. GCC studies: 21 NSHL genes, but dominant rare; founder effects like GJB2 c.35delG dominant in testing strategy.

Implications: Update protocols, train clinicians; UAE Ministry of Health advances newborn screening/genomics.Read the full ACMG abstract.

UAE's Rising Star in Genomics Research

UAE universities like UAEU, Khalifa, Zayed drive genetics: UAE Genome Program sequenced 100k+; hearing studies identify TMC1/TMC2, mitochondrial variants. Tawam Hospital Genetics Clinic pioneers WES for HL.

• UAEU: Leads sporadic HL cohorts (106 cases, 25% yield).
• Khalifa University: AI-genomics integration.
• NYU Abu Dhabi: Population genomics.

Opportunities abound; explore UAE academic jobs in genomics.

Global Context: Expanding the SIX1 Mutation Spectrum

SIX1 variants: ~50 BOR/BO, DFNA23 rare. Recent: Korean atypical BO (2023), chick Six1 targets (2025) nominate new genes. UAE p.Lys132Asn first Middle East report, no founder signal.

2025-2026 advances: Gene therapy trials (OTOF, DB9); CRISPR for DFNA.SIX1 variants review.

Future Outlook: Therapies and Precision Medicine

Antisense oligonucleotides (ASOs), AAV-gene addition for dominant gain-of-function challenging; haploinsufficiency models suggest allele-specific editing. UAE's biotech push (Masdar City) positions for trials.

Career paths: Research positions in UAE unis booming.

Photo by Laura Ohlman on Unsplash

Conclusion: Paving the Way for Better Diagnostics and Research Careers

This UAE SIX1 discovery illuminates ADNSHL, urges panel expansions, boosts UAE genomics. Aspiring researchers, check Rate My Professor, higher ed jobs, career advice, university jobs, or post a job.