Case-Control Genotyping of the c.788C>T Variant of Transforming Growth Factor-Beta 1 Gene in Otosclerosis in the South Indian Population.

BACKGROUND

Otosclerosis is a common conductive hearing loss resulting from abnormal bone metabolism. The c.788C>T variant in the transforming growth factor-beta 1 gene is associated with otosclerosis in all studied populations, except the Indian population. In this study, we predicted the functional effects of reported variants in transforming growth factor-beta 1 and analyzed the c.788C>T variant in a case-control cohort from India and in the genomes present in public databases.

METHODS

Clinically confirmed otosclerosis cases (n=120) and controls (n=120) were recruited and genotyped by polymerase chain reactionrestriction fragment length polymorphism and DNA sequencing. In addition, Ensembl 1000 Genome, Ensembl NHLBI Exome, GnomAD, and Genome Asia 100K human genome databases were analyzed for allele frequency.

RESULTS

Among the 3 variants studied, a significant functional effect was observed only for the c.788C>T variant. This variant was found in 1 case but absent in all others and controls. Odds ratio, 95% CI, and P-value under the dominant model were 1.00, 0.0197-50.8116, and 1.00, respectively. Analysis of genomic databases showed a frequency of 0-11.21% and 0-1.25% for the c.788C>T variant and the individuals homozygous for this variant, respectively.

CONCLUSION

We did not find any genetic association between the c.788C>T variant and otosclerosis in the South Indian population; however, it was not monomorphic as had previously been reported from the Odisha population of Eastern India. Moreover, contrary to an earlier report that the c.788C>T variant was never found in a homozygous condition, homozygous individuals were found in the European, Asian, Latin American, and Ashkenazi Jews populations.