A 6-year-old child is brought to the ENT clinic with complaints of difficulty understanding speech, especially in noisy classroom environments. Pure-tone audiometry shows a distinctive U-shaped loss centered at 1–2 kHz, with normal thresholds at 250–500 Hz and 4–8 kHz. The structure marked **A** in the audiogram represents this mid-frequency cookie-bite configuration. Tympanometry is normal (type A), and acoustic reflexes are present. The child's father has a similar hearing loss pattern. Which of the following is the most likely genetic basis for this hearing loss?

Explanation

## Why Autosomal dominant non-syndromic SENSORINEURAL hearing loss (DFNA family, commonly TECTA or COL11A2 mutations) is right The cookie-bite mid-frequency configuration marked **A** is pathognomonic for autosomal dominant non-syndromic SENSORINEURAL hearing loss, most commonly caused by mutations in TECTA (tectorial membrane protein, DFNA8/12) or COL11A2 (type XI collagen, DFNA13). The clinical presentation—bilateral symmetric SNHL with selective outer hair cell damage in the middle cochlear turns (encoding 1–2 kHz), normal type A tympanogram, present acoustic reflexes, and positive family history (father affected)—all point to this diagnosis. The U-shaped loss sparing low and high frequencies is the hallmark of hereditary DFNA-associated hearing loss. Per Cummings Otolaryngology Chapter 150, this configuration reflects selective vulnerability of mid-frequency cochlear regions to genetic defects in structural proteins. ## Why each distractor is wrong - **Autosomal recessive syndromic hearing loss with renal involvement (Alport syndrome)**: Alport syndrome presents with progressive high-frequency downsloping loss (not mid-frequency cookie-bite), and includes systemic features (progressive renal disease, ocular abnormalities, hematuria). This child has no syndromic features and a non-progressive pattern. The audiometric configuration is wrong. - **X-linked recessive hearing loss with progressive high-frequency loss**: X-linked forms typically show progressive high-frequency loss, not the static or slowly progressive mid-frequency U-shaped pattern. Male-to-male transmission (father to son) would not occur in X-linked inheritance, yet the father is affected. The pattern does not match. - **Mitochondrial inheritance with maternal transmission and progressive low-frequency loss**: Mitochondrial hearing loss shows maternal-only transmission (not father-to-child), typically progressive, and often involves low-frequency loss or flat configurations. The family history (affected father) and mid-frequency cookie-bite pattern exclude mitochondrial inheritance. **High-Yield:** Cookie-bite audiogram (U-shaped 1–2 kHz dip) + bilateral symmetric SNHL + positive family history = DFNA (autosomal dominant non-syndromic SNHL), especially TECTA or COL11A2 mutations. [cite: Cummings Otolaryngology - Head and Neck Surgery 7e, Chapter 150 (Genetic Hearing Loss); Dhingra Diseases of Ear Nose and Throat 7e]