Abstract. Amyloid fibril protein in patients with familial amyloidotic polyneuropathy is known to be chemically related to transthyretin (TTR), the plasma protein that is usually referred to as prealbumin. A genetically abnormal TTR may be involved in this disease. (Saraiva,

The immunocytochemical localization of cellular retinol-binding protein (CRBP), of plasma retinol-binding protein (RBP), and of plasma transthyretin (TTR) was studied in rat liver and kidney. The studies employed normal rats, retinol-deficient rats, and rats fed excess retinol . Antisera were prepared in rabbits against purified rat CRBP, RBP, and TTR . The primary antibodies and goat anti-rabbit IgG were purified by immunosorbent affinity chromatography, using the respective pure antigen coupled to Sepharose as the immunosorbent . This procedure effectively removed cross-reactive and heterophile antibodies, which permitted the specific staining and localization of each antigen by the unlabeled peroxidase-antiperoxidase method . CRBP was found to be localized in two cell types in the liver, the parenchymal cells and the fat-storing cells . Diffuse cytoplasmic staining for CRBP was seen in all the parenchymal cells . Much more intense staining for CRBP was seen in the fat-storing cells . The prominence of the CRBP-positive fat-storing cells changed markedly with vitamin A status . Thus, these cells were most prominent, and appeared most numerous, in liver from rats fed excess retinol . Both RBP and TTR were localized within liver parenchymal cells . The intensity of RBP staining increased markedly in retinol-deficient rat liver, consistent with previous biochemical observations . With the methods employed, specific staining for RBP or TTR was not seen in cells other than the parenchymal cells . In the kidney, all three proteins (CRBP, RBP, and TTR) were localized in the proximal convoluted tubules of the renal cortex . Staining for RBP was much more intense in normal kidney than in kidney from retinol-deficient rats. These findings reflect the fact that RBP in the tubules represents filtered and reabsorbed RBP . The pattern of specific staining for CRBP among the various tubules was very similar to that seen for RBP on adjacent, serial sections of kidney . The function of CRBP in the kidney is not known .It is now well established that specific binding proteins for retinol exist in plasma and in the intracellular compartment in a number of tissues. These proteins play important roles in the metabolism of vitamin A. Thus, retinol-binding protein (RBP)`, the specific plasma transport protein for vitamin A, transports retinol from its storage site in the liver to peripheral target tissues in the body. A different protein, cellular retinolbinding protein (CRBP) is found within cells in many tissues.Since the initial isolation of human RBP in 1968 (1), 'Abbreviations used in this paper are : CRBP, cellular retinol-binding protein ; RBP, retinol-binding protein ; TTR, transthyretin . 1696extensive studies in many laboratories have provided considerable information about the structure, metabolism, and biological roles of RBP (see references 2-4 for recent reviews) . RBP, with a molecular weight close to 21,000 and one binding site for retinol, is synthesized in (5) and secreted by the liver . RBP in plasma stro...

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A transthyretin variant with a methionine for valine substitution at position 30 ITTR(Met3')l is found in Portuguese patients with familial amyloidotic polyneuropathy (FAP). Effective, rapid, small-and semimicro-scale (immunoblotting) procedures were developed to determine whether or not TTR(Met3) is present in the plasma of an individual subject. The immunoblotting procedure employs only 0.10 ml of serum and can serve as a reliable procedure for the screening of large numbers of persons for the presence of TTR(Met3). In family studies of seven FAP kindreds, TTR(Met3') was found in 21 out of 41 asymptonatic FAP offspring, and its presence was not related to either age or sex. Thus, the mutant TTR segregated in accordance with the known autosomal dominant mode of inheritance of FAP. Total plasma TTR levels were not reduced in asymptomatic FAP offspring who were carriers of TTR(Met34), and no difference was observed between carriers and noncarriers of the mutant TTR. The ratios of the variant to normal TTR in plasma were estimated in asymptomatic FAP offspring and were similar to those found in FAP patients. In contrast, TTR(Met3') was relatively enriched in cerebrospinal fluid samples from two FAP patients. The significance of this finding is not known, but might relate to the preferential deposition of amyloid in the nervous system in FAP.A limited study was conducted involving simultaneous analysis of both stored (collected in 1975) and fresh serum from 20 FAP offspring, all of whom had been asymptomatic in 1975. In every subject, the results obtained with the stored and the fresh serum samples were in agreement. Six of these subjects developed clinical FAP since 1975; TIR(Met3o) was present in each of these subjects. These several studies strongly suggest that the presence of TTR(MetP) in plasma constitutes a predictive biochemical marker of FAP in the preclinical phase of the disease.

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