National Ear Care Day: Hereditary Hearing Loss Gene Screening Chip Effectively Detects Four Common Deafness-Causing Genes

Today marks the 18th National Ear Care Day. The second national sample survey on persons with disabilities, conducted in 2006, revealed that the number of people with hearing disabilities in China had reached 27.8 million. Hearing impairment has become the second most common birth defect in China. Sixty percent of deafness cases are genetically related, making genetic screening for deafness crucial for prediction, prevention, and diagnosis.

According to VCBeat, 6 out of every 100 individuals with normal hearing carry genetic defects associated with deafness. If two carriers of the same type of deafness-related genetic defect marry, their risk of having a child with deafness is 25%. Regarding etiology, genetics is the leading cause of deafness. A molecular epidemiological survey on deafness conducted by the Deafness Molecular Diagnosis Center of the Chinese PLA General Hospital (301 Hospital) across 28 provinces and municipalities in China revealed that hereditary deafness accounts for 60% of all deafness cases. The most common deafness-causing genes in the Chinese population are GJB2, SLC26A4, mitochondrial 12S rRNA, and GJB3.

These four genes are associated with distinct clinical manifestations: GJB2 is primarily responsible for congenital severe-to-profound sensorineural hearing loss; SLC26A4 (PDS) is mainly linked to enlarged vestibular aqueduct syndrome (EVAS), causing either congenital or acquired severe-to-profound sensorineural hearing loss; mitochondrial 12S rRNA mutations predominantly lead to drug-induced hearing loss (e.g., from aminoglycosides); and GJB3 primarily results in acquired high-frequency sensorineural hearing loss.

Some patients are not born deaf; however, due to carrying the mitochondrial 12S rRNA gene, they may develop hearing loss after receiving common medications such as gentamicin for colds and fevers during childhood. Nevertheless, if this genetic carrier status is identified in advance, hearing loss can be prevented by avoiding the use of aminoglycoside antibiotics in daily life. Most children with hearing loss have a family history of the condition.

Most deaf individuals are unable to speak, not due to pathology of the vocal organs, but because hearing loss prevents them from perceiving speech, thereby depriving them of opportunities to imitate and learn language. In China, there are over 800,000 children aged 0–6 years, and approximately 30,000 children with hearing impairment are born each year. The critical period for rapid language development in children is primarily between 0 and 3 years of age. Infants with normal hearing typically begin babbling between 4 and 9 months, and no later than 11 months; this serves as an important milestone in language development.

If an infant does not enter the babbling stage within 11 months after birth, they will be unable to engage in normal language learning between the ages of two and three. Failure to promptly identify and address hearing impairments before the age of two—through interventions such as hearing aids, cochlear implants, and speech-language therapy—will result in missing the optimal window for rehabilitation. Once a child surpasses three years of age, language acquisition becomes significantly more challenging.

Currently, the primary measure for addressing congenital hearing defects in newborns is hearing screening; however, some children with delayed-onset deafness cannot be detected through traditional hearing screening. Implementing genetic screening for deafness in newborns enables early detection, early intervention, and early treatment, thereby preventing the development of mutism secondary to deafness.

With the implementation of the national “two-child policy,” China has witnessed a baby boom, making the prevention of birth defects particularly important.Targeting common deafness-causing genes, the National Engineering Research Center for Beijing Biochip Technology has developed the world’s first deafness gene screening chip, providing Chinese people with a tool for precise diagnosis of hereditary deafness. To date, it remains the only chip product approved by the China Food and Drug Administration (CFDA) for deafness gene testing (Approval No.: Guo Shi Yao Jian Xie (Zhun) Zi 2009 No. 3400725).

To date, the genetic hearing loss gene detection microarray has screened over 2 million individuals across China, making it the largest-scale product globally for the diagnostic screening of genetic diseases using biochip technology.

Currently, more than 20 provinces and municipalities across China have adopted this technology for newborn screening. Deafness gene screening helps identify the underlying cause and predict treatment outcomes. For instance, in children with congenital hearing impairment caused by GJB2 gene mutations, the auditory nerve, auditory conduction pathways, and speech centers are intact; these patients can achieve favorable rehabilitation outcomes through cochlear implantation. Additionally, screening enables avoidance of triggering factors and delays the progression of hearing loss. Mutations in the SLC26A4 gene can cause enlarged vestibular aqueduct syndrome (EVAS), a congenital malformation of the inner ear. Affected infants may have normal hearing at birth, but exposure to triggers such as head trauma, noise, or infections can lead to a rapid decline in hearing, potentially resulting in profound deafness.

Children with this condition should avoid the aforementioned triggers as much as possible to delay the progression of hearing loss. Medication guidance is essential to prevent drug-induced deafness: Individuals with mitochondrial gene mutations are highly sensitive to aminoglycoside antibiotics (such as gentamicin and streptomycin). Even short-term use at low doses can result in profound deafness, a phenomenon commonly referred to as "deafness after a single injection."

Therefore, pediatric patients carrying this mutation and their maternal relatives should avoid the use of aminoglycoside antibiotics to prevent drug-induced hearing loss. Guidance on marriage, childbearing, and prenatal diagnosis: For families that have already given birth to a deaf child, prenatal genetic diagnosis can be performed during subsequent pregnancies to avoid having another deaf child. For parents whose first child is a carrier of a deafness gene, prenatal genetic diagnosis can be conducted for the second pregnancy to prevent the birth of a deaf child. Carriers of deafness genes should receive premarital counseling; they should avoid procreating with partners who carry the same mutant genotype, or undergo prenatal genetic counseling and diagnosis. These are highly effective measures.