No evidence for disturbed COL1A1 and A2 expression in otosclerosis

Otosclerosis is a complex bone remodeling disorder of the human otic capsule that might be associated with various mutations of A1 and A2 alleles of type-I collagen. The study herein presented, investigates the possibilty of the genetic involvement of type-I collagen in the pathogenesis of histologically confirmed otosclerosis. A total of 55 ankylotic stapes footplates were analyzed. Cortical bone fragments (n = 30), incus (n = 3) and malleus (n = 2) specimens were employed as negative controls. Specimens were divided into two groups. The first group was processed using conventional H.E. hematoxylin-eosin (H.E.) staining and type-I collagen-specific immunofluorescent assay (IFA), while the second group was examined by COL1A1 and A2-specific RT-PCR. Otosclerotic- (n = 31) and non-otosclerotic stapes footplates (n = 9) as well as cortical bones (n = 20), incus (n = 2) and malleus specimens (n = 1) showed normal and quite similar A1 and A2 allele expression confirmed by IFA. RT-PCR analysis revealed normal and consistent mRNA expression of both alleles in each specimen. Expression levels and patterns of COL1A1/A2 alleles did not show significant correlation with the histological diagnosis of otosclerosis. Type-I collagen is a highly conserved structure protein, which plays a fundamental role in the integritiy of various connective tissues. Mutations of A1 and A2 alleles result in serious systemic disorders of the skeleton, tendons and skin. Since otosclerosis is an organ-specific disease, it is difficult to explain its genetic association with type-I collagen. In conclusion, we found no evidence supporting the putative link of COL1A1 and COL1A2 alleles with otosclerosis.