Evaluation of the Genetic Association and mRNA Expression of the <i>COL1A1</i> , <i>BMP2</i> , and <i>BMP4</i> Genes in the Development of Otosclerosis

Abstract

<b><i>Background:</i></b> Otosclerosis (OTSC) is a genetically heterogeneous disorder, characterized by abnormal bone growth in the middle ear, affecting the stapes bone. Previous studies have shown that single nucleotide polymorphisms (SNPs) of the <i>COL1A1, BMP2,</i> and <i>BMP4</i> genes are linked to susceptibility of OTSC, musculoskeletal degenerative diseases, and bone remodeling. <b><i>Aims</i></b>: To evaluate the genetic association and expression levels of <i>COL1A1</i>, <i>BMP2</i>, and <i>BMP4</i> genes with OTSC in the Indian population. <b><i>Methods</i></b>: A total of 320 otosclerotic and 320 control samples were screened for four SNPs (rs1107946, rs11327935, rs2269336, and rs1800012) of the <i>COL1A1</i> gene; rs3178250 of the <i>BMP2</i> gene; and rs17563 of the <i>BMP4</i> gene using single-strand conformation polymorphism analysis, and restriction fragment length polymorphism analyses. Genotypic, haplotypic, and linkage disequilibrium analyses were performed to assess the potential associations of these SNPs with OTSC. <i>COL1A1</i>, <i>BMP2</i>, and <i>BMP4</i> mRNA expression levels were analyzed by semiquantitative RT-PCR and real-time PCR. <b><i>Results</i></b>: Genotypes of two SNPs, rs1800012 and rs17563, were found to be associated with OTSC (the rs1800012 GT genotype, <i>p</i> = 0.0022, OR = 0.481; and the rs17563 TC genotype, <i>p</i> = 0.0225, OR = 1.471). Haplotypic analyses revealed that the <i>COL1A1</i> haplotype G-T-C-T (<i>p</i> = 0.021) was significantly increased among controls. Functional studies revealed an unexpected decrease in mRNA expression of <i>COL1A1</i> but an increased expression of the <i>BMP2</i> and <i>BMP4</i> genes in otosclerotic stapes tissues. <b><i>Conclusions</i></b>: Our findings suggest that OTSC is a heterogeneous disorder, but that the GT genotype of the rs1800012 locus is protective and that the TC genotype at the rs17563 locus is a risk factor. In addition, our studies indicate that changes in the expression of the <i>COL1A1</i>, <i>BMP2</i>, and <i>BMP4</i> genes may contribute to the genetic susceptibility of OTSC by regulating their mRNA levels.