Clinical, histopathological, and in silico pathogenicity analyses in a pedigree with familial amyloidosis of the Finnish type (Meretoja syndrome) caused by a novel gelsolin mutation

PURPOSE: Familial amyloidosis of the Finnish type (FAF) is an inherited amyloidosis arising from mutations in the gelsolin protein (GSN). The disease includes facial paralysis, loose skin, and lattice corneal dystrophy. To date, FAF has been invariably associated with substitution of Asp214 in GSN. We describe the clinical, histopathological, and genetic features of a family with FAF due to a novel GSN mutation. METHODS: Five affected adult individuals in a three-generation FAF pedigree were included in the study. Histopathological analysis was performed on an eyelid skin biopsy from one patient. Genetic analysis included next-generation sequencing (NGS) and Sanger sequencing for confirmation of the GSN variant. Several tools for in silico analysis of pathogenicity for the novel variant and to predict the effect of the amino acid replacement on protein stability were used. RESULTS: Three older adult affected patients exhibited corneal lattice dystrophy, cutis laxa, and facultative peripheral neuropathy. Two younger adult individuals presented only with corneal amyloid deposits. NGS identified a heterozygous GSN c.1631T>G transversion, predicting a novel p.Met544Arg mutation. All in silico tools indicated that p.Met544Arg is deleterious for GSN functionality or stability. CONCLUSIONS: The results expand the molecular spectrum of GSN-linked systemic amyloidosis. The novel p.Met544Arg pathogenic variant is predicted to affect gelsolin function, presumably by impairing a potential calcium-sensitive, actin-binding region.