NEW YORK (GenomeWeb) – A Taiwanese team has found that many newborns testing positive for deafness-related variants in the GJB2 gene but passing a conventional newborn hearing test developed progressive hearing loss in childhood, suggesting that genetic screening might be able to detect them earlier.
As they reported last week in Genetics in Medicine, the researchers followed 82 infants — each identified as having one of three hearing loss-related GJB2 allele combinations during a newborn screen — over up to six years. Although more than half of the children passed hearing tests as infants, the researchers found that many of the genetically predisposed infants experienced hearing loss by their fifth birthday.
"We demonstrated that newborn genetic screening might compensate for inherent limitations of conventional [universal newborn hearing screening] by detecting subjects with mild [sensorineural hearing impairment] and those at risk for late-onset [sensorineural hearing impairment]," the study's authors wrote.
The children followed for the study came from a group of 5,173 infants were received standard newborn hearing screens and who were also genetically screened for four deafness-related mutations in the GJB2 and SLC26A4 genes. The changes were selected due to their prevalence in Taiwan, the team noted, and together the alterations account for more than 80 percent of known deafness mutations in that population in terms of allele frequency.
Of the 82 infants who tested positive for a hearing loss-related mutation, 62 had p.V37I/p.V37I alleles in GJB2 and 16 had a p.V37I/c.235delC version of the gene. Four had an adenine to guanine change at m.1555 in the mitochondrial 12S ribosomal RNA gene. Hundreds more infants had risky variants affecting just one copy of their GJB2 or SLC26A4 genes.
Though infant performance on universal hearing tests differed depending on the type of test used and the risk variants they carried, the researchers noted that just over 56 percent of those with deafness-linked genotypes passed hearing tests administered at birth.
Over the first few follow ups, the researchers found that more than half of children with GJB2 p.V37I/p.V37I or p.V37I/c.235delC had lost the ability to hear sounds below 25 decibels by their third birthday. That notched up to nearly 60 percent for children with the former genotype and more than 54 percent with the latter genotype at the five year mark. Almost 15 percent to 20 percent of children with those genotypes had problems hearing sounds at 40 decibels.
Children with the m.1555 variant in the 12S rRNA gene underwent only four audiological assessments, the team noted, and longitudinal outcomes were not reported for that group in the study. The results overall suggest that newborn genetic tests can highlight children at risk of progressive hearing loss might be missed by conventional screening for hearing problems.
The researchers cautioned, though, that "implementing population-wide genetic screening for deafness involves multiple issues and demands careful appraisal with regard to the potential psychosocial impacts on families and economic burden on the healthcare system."
Consequently, they called for continued research and additional longitudinal studies into the consequences of deafness-related genetic screens and clinical outcomes for those who are tested at birth.