Background—Familial amyloidosis of the Finnish type (FAF, Finnish hereditary amyloidosis) is caused by a 654G-A mutation in the gelsolin gene on chromosome 9 resulting in the expression of mutant Asn-187 gelsolin which is abnormally proteolytically processed generating amyloidogenic fragments that polymerise into amyloid fibrils. We have recently shown that in a Danish and a Czech family with a clinical syndrome similar to FAF, including corneal lattice dystrophy, cranial neuropathy and skin changes, the disease is caused by another mutation at the same position, namely 654G-T predicting a Tyr-for-Asp substitution at 187 in secreted gelsolin.
Aim—To undertake a closer examination of the Danish subtype of FAF and report immunohistochemical and biochemical findings.
Results—Immunostaining of plasma gelsolin isolated from heterozygous FAF of the Danish subtype revealed a pattern similar to that found in FAF-Asn 187. The > 60 kDa gelsolin species contain an epitope characteristic of the amyloid forming region as revealed by an amyloid specific antibody, whereas the ~50 kDa fragments are devoid of it. Compared with the wild-type gelsolin peptide (Asp-187), the corresponding mutant peptide (Tyr-187) showed dramatically increased fibrillogenicity as revealed by quantitative thioflavine-T based fluorimetry; ultrastructurally, amyloid-like fibrils were formed by the mutant peptide. Immunohistochemistry showed that antibodies directed against residues 231–242 of secreted gelsolin, representing the carboxy terminus of the sequence forming the amyloid protein (residues 173–243) laid down in the tissues in a fibrillar form in FAF, specifically labelled the amyloid deposited in rectum and skin in the Danish (654G-T) subtype.
Conclusions—The 654G-T mutation in the gelsolin gene gives rise to an amyloid disease clinically and pathogenetically similar to that caused by the 654G-A mutation.
Key Words: amyloidosis • Finnish familial amyloidosis • gelsolin mutation 654G-T • fibrillogenesis