This study was based on a concurrent newborn genetic and hearing screening program in Nantong city. From January 2016 to December 2020, newborn infants were recruited and received combined screening for free, funded in part by the municipal government and research project foundations. The population-based longitudinal databank for all children with hearing loss in Nantong city commenced in January 2016 and maintained indefinite recruitment and ongoing follow-up.

The severity of hearing loss was graded as mild (26-40 dB), moderate (41-60 dB), severe (61-80 dB), and profound (≥81 dB). Genomic DNA was extracted by a blood filter paper nucleic acid extraction kit (CapitalBio, Beijing, China) and tested using a deafness gene variant detection array kit (CapitalBio, Beijing, China) with LuxScan 10K-B Microarray Scanner (CapitalBio, Beijing, China). The genetic screening entailed genotyping 15 variants in 4 genes: c.35delG, c.176\_191del16, c.235delC, c.299\_300delAT (GJB2 gene); c.1174A\>T, c.1226G\>A, c.1229C\>T, c.1975G\>C, c.2027T\>A, c.2168A\>G, c.IVS7-2A\>G, c.IVS15 + 5G\>A (SLC26A4 gene); m.1494C\>T, m.1555A\>G (MT-RNR1 gene); c.538C\>T (GJB3 gene). The results were categorized as (1) negative, (2) carrier (GJB2 or SLC26A4, heterozygous mutations; MT-RNR1 mutations; GJB3 mutations; or heterozygous mutations in multiple genes), and (3) refer (GJB2 or SLC26A4, homozygous or compound heterozygous mutations). This study was approved by the ethics committees of Nantong municipal Health Commission and all hospitals involved. Written informed consent was obtained from the infant's parents. This study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline for cohort studies.