Purpose: To isolate the protein that collects in increased amounts beneath the corneal epithelium in familial subepithelial corneal amyloidosis (FSCA), also known as gelatinous droplike corneal dystrophy, and to identify it by N-terminal amino acid sequencing.
Methods: Peptides resulting from pepsin digestion of a unique protein isolated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis from frozen tissue from two corneas with FSCA were purified by high-pressure liquid chromatography followed by protein sequence analysis. The protein was identified by amino acid sequencing, Western blotting, and immunohistochemistry.
Results: A protein was identified in two corneas with FSCA that was not present in normal corneas or in corneas with other disorders. The amino acid sequences of two peptides derived from this protein were identical to portions of lactoferrin. The unique protein reacted with rabbit antihuman lactoferrin after Western blotting. The presence of lactoferrin in the amyloid within affected corneas was confirmed using the immunoperoxidase method on formalin-fixed, paraffin-embedded tissue sections and lactoferrin antiserum.
Conclusions: Corneal tissue with FSCA contains lactoferrin, and this is the first form of amyloidosis found to be associated with this protein. Because lactoferrin is a product of lacrimal glands, the corneal lactoferrin may be derived from the tears. Because the gene for lactoferrin is on chromosome 3 (3q21-q23), this locus is a potential site for the FSCA gene.