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In the last several years, five human plasma prealbumin (transthyretin) variants have been discovered in association with hereditary amyloidosis, a late-onset fatal disorder. We recently studied a patient of German descent with peripheral neuropathy and bowel dysfunction. Biopsied rectal tissue contained amyloid that stained with anti-human prealbumin. Amino acid sequence analysis of the patient's plasma prealbumin revealed both normal and variant prealbumin molecules, with the variant containing a tyrosine at position 77 instead of serine. We predicted a single nucleotide change in codon 77 of the variant prealbumin gene, which we then detected in the patient's DNA using the restriction enzyme SspI and a specifically tailored genomic prealbumin probe. DNA tests of other family members identified several gene carriers. This is the sixth prealbumin variant implicated in amyloidosis, and adds to the accumulating evidence that the prealbumin amyloidoses are more varied and prevalent than previously thought.

Familial amyloidotic polyneuropathy (FAP) is an autosomal dominant late-onset disorder characterized by the extracellular deposition of amyloid fibrils. In all cases studied these fibrils have been found to be composed of plasma prealbumin (transthyretin) containing a single amino acid substitution. Biochemical studies were conducted on amyloid from one patient and plasma prealbumin from his affected brother, both part of a large kindred from the Appalachian region of the United States. Sequence analysis of the amyloid subunit protein showed it to be prealbumin with about two-thirds of the molecules containing a substitution of alanine for threonine at position 60. Studies of the plasma prealbumin showed that the same substitution was present in 40-45% of the protein. Based on this substitution and the prealbumin cDNA sequence, a Pvu II restriction fragment length DNA polymorphism (RFLP) was predicted and demonstrated in DNA of both patients as well as other family members. This RFLP confirms the predicted DNA mutation responsible for the protein variant, and represents an accurate method for detection of this gene.