Inner ear histopathological findings in Alport syndrome

Abstract

Cochlear histopathological findings of a patient affected by Alport syndrome (AS) are presented and the main histopathological, genetic and clinical aspects of this condition are reviewed. AS is an inherited disorder of the basement membranes, arising from mutations in type IV collagen (COL4 genes that code for the α3, α4, and α5 chains of type IV collagen), the major collagenous constituent of these structures. Our histopathological findings partly coincide with those of recent studies and reveal a separation of the sensory organ and basilar membrane and some loss of fibrocytes in the spiral ligament in the apical turn accompanied by signs of endolymphatic hydrops. A ‘narrow’ tunnel of Corti, with cells filling this space as described recently, and hypothesized to represent a premature stage of development, could not be verified. We suggest that this filling of open spaces within the sensory organ may represent preparation artefacts. Thicker and more tangential sectioning often mimics cells to be present within Nuel's space and the tunnel of Corti. This study further shows that in human development of the organ of Corti no cells locate within the tunnel when it begins to open between gestational weeks 16 and 19. Alteration of micromechanics, as well as distortions in the spiral ligament followed by changes in the endocochlear potential, may account for the hearing loss in this genetically heterogeneous syndrome.

• human
• hearing loss
• genetic mutation
• basilar membrane
• type IV collagen