Collagen α5 and α2(IV) chain coexpression: Analysis of skin biopsies of Alport patients

Alport syndrome is a collagen type IV disease caused by mutations in the COL4A5 gene with the X-linked form being most prevalent. The resultant α5(IV) collagen chain is a component of the glomerular and skin basement membranes (SBMs). Immunofluorescent determination of the α5(IV) chain in skin biopsies is the procedure of choice to identify patients. In 30% of patients, however, the mutant protein is still found in the SBM resulting in a normal staining pattern. In order to minimize or eliminate false results, we compared the distribution of the α2(IV) chain (another SBM component) and the α5(IV) chain by standard double label immunofluorescence (IF) and by confocal laser scanning microcopy. The study was performed on 55 skin biopsies of patients suspected of Alports and five normal control specimens. In normal skin, IF showed the classical linear pattern for both collagens along the basement membrane. Additionally, decreased α5(IV) was found in the bottom of the dermal papillary basement membrane. Confocal analysis confirmed the results and show α5(IV) focal interruptions. In suspected patients, both techniques showed the same rate of abnormal α5(IV) expression: segmental in women and absent in men. Our results show a physiological variation of α5(IV) location with focal interruptions and decreased expression in the bottom of the dermal basement membrane. Comparison of α5(IV) with α2(IV) expression is simple and eliminates technical artifacts.