Familial amyloidotic polyneuropathy (FAP) is a dominantly inherited form of amyloidosis usually associated with an abnormal transthyretin (TTR), previously known as prealbumin. Several disease-related variants of the protein, each with a different amino acid substitution and correlating DNA point mutation, have been identified. The TTR gene from a patient suffering from this disorder was asymmetrically amplified and directly sequenced, revealing a cytosine for thymine substitution in the second base of codon 30 and the creation of a novel Cfo I restriction endonuclease site in exon 2. This mutation results in a previously undescribed substitution of an alanine for valine in the final TTR protein. Analysis of the amino acid mutation reveals it to be a hydrophilic substitution at a hydrophobic core position. Alanine at position 30 represents the second FAP-associated mutation at position 30 in TTR.