Genotype and clinical phenotype analysis of 42 patients with delayed nonsyndromic hearing loss

Objective:The aim of this study is to analyze the mutation characteristics of GJB2 and SLC26A4 gene in patients with delayed non-syndromic hearing loss, which is beneficial to the early detection and intervention of delayed deafness. Methods:Sanger sequencing technology was used to detect two common genes in 139 patients with non-syndromic deafness, six hot spot mutations in GJB2 gene and SLC26A4 gene, and single heterozygous mutations found in GJB2 gene and SLC26A4 gene were detected by whole exome sequencing. Results:Among the 25 patients with deafness caused by GJB2 gene mutation, 12 of them passed universal newborn hearing screening and then developed delayed extremely severe hearing loss. The onset time of hearing loss was 6-48 months. All the genotypes were homozygous or compound heterozygous mutation of c. 235delC, especially genotype of GJB2 c. 235delC homozygous and c. 235delC/c. 299-300 delAT compound heterozygous mutations, and the CT manifestations were normal. Among the 42 patients with deafness caused by SLC26A4 gene mutation, 30 of them passed universal newborn hearing screening and developed delayed deafness. The onset time of hearing loss was three months to ten years old. Among them, the genotypes of 21 patients were compound heterozygous mutation, and 9 patients were homozygous mutation of c. 919-2A>G, especially genotypes were SLC26A4 c. 919-2A>G/c. 665G>T and c. 919-2A>G /c. 2027T>A compound heterozygous mutation. The CT findings of 19 cases showed single enlarged vestibular aqueduct, and 11 cases showed enlarged vestibular aqueduct with Mondini malformation. Conclusion:For the children who have passed universal newborn hearing screening, the genotypes detected are GJB2 c. 235delC homozygous, SLC26A4 c. 919-2A>G homozygous or compound heterozygous mutations, especially genotypes GJB2 c. 235delC homozygous, c. 235delC/c. 299-300delAT compound heterozygous mutations and SLC26A4 c. 919-2A>G/c. 665G>T and c. 919-2A>G/c. 2027T>A compound heterozygous mutation. Attention should be paid to the hearing problems of children all the time, and the possibility of delayed deafness in the future should be considered.