Amyloid fibril protein in familial amyloidotic polyneuropathy, Portuguese type. Definition of molecular abnormality in transthyretin (prealbumin)

Diagnostic radioimmunoassay for familial amyloidotic polyneuropathy before clinical onset

The purpose of this study is to develop an early diagnostic method for familial amyloidotic polyneuropathy (FAP) before clinical manifestations appear around the age of 30 yr. Amyloid fibrils isolated from type I FAP (FAP1) of Portuguese, Swedish, and Japanese origins consist of a variant transthyretin (TTR) that contains a methionine-for-valine substitution at position 30 or a mixture of normal TTR and this variant form. The variant TTR is present in the serum of FAP1 patients and can be measured by a radioimmunoassay (RIA) based on a nonapeptide (positions 22-30) derived from the variant TTR. Serum levels of the variant TTR in 45 Japanese FAP1 patients range from 4.71 to 17.61 mg/dl with a mean value of 9.18 mg/dl. The variant TTR is not present in the serum of 100 normal individuals, in four cases of primary and six cases of secondary amyloidosis, nor in 26 non-inheriting members of families with FAP1. The variant TTR level is measured in 24 children of 15 FAP1 patients as well. The variant TTR is already present in nine symptom-free children with the mean serum level of 11.90 mg/dl, but it is not present in 15 other children. FAP1 patients can be differentiated from non-FAP by this noninvasive diagnostic method even within families. The RIA can be applied worldwide to this intractable disorder for early diagnosis during childhood and for appropriate genetic counseling.

Polymorphism in a kappa I primary (AL) amyloid protein (BAN)

In an attempt to understand the relationship of amino acid sequence to the formation of primary or multiple myeloma-related amyloid (AL amyloid), we have determined the complete amino acid sequence of amyloid protein BAN. This protein belongs to the kappa I immunoglobulin light chain subgroup and has a polypeptide chain length of 126 amino acids. It encompasses the entire variable region, the joining segment and the first tryptic peptide of the constant region. This protein has two unique features. First, the molecule is glycosylated. At position 61 the usual arginine residue has been replaced by an asparagine with the generation of the signal sequence Asn-Phe-Thr, to which a glucosamine-containing carbohydrate unit is attached. Secondly, the protein is not monoclonal but consists of two chains which have the same variable region but different J-segments. Comparison of the BAN sequence with other amyloid and nonamyloid kappa I proteins reveals a systematic difference between the two groups. In the amyloid proteins, several hydrophilic framework residues have been replaced by hydrophobic residues. These substitutions may provide the nucleation sites for self-aggregation and fibril formation.

Beta-2 microglobulin is an amyloidogenic protein in man

Curvilinear fibrils with the tinctorial properties of amyloid were isolated from a patient with bone and joint involvement complicating chronic dialysis for renal disease. Subunit fractions of 24,000 and 12,000 mol wt were identified after gel filtration under dissociating conditions, the latter containing a significant amount of a dimer of the former. This was confirmed by Edman degradation of each fraction, which yielded the amino terminal sequence of normal human beta-2 microglobulin (B2M) to residues 20 and 30, respectively. The size of the subunit protein (12,000 mol wt) and the amino acid composition make it likely that intact B2M is a major constituent of the fibrils. B2M is thus another example of a low molecular weight serum protein, with a prominent beta-pleated sheet structure, that may adopt the fibrillar configuration of amyloid in certain pathologic states.

Biochemical marker in familial amyloidotic polyneuropathy, Portuguese type. Family studies on the transthyretin (prealbumin)-methionine-30 variant

A transthyretin variant with a methionine for valine substitution at position 30 [TTR(Met30)] 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(Met30) 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(Met30). In family studies of seven FAP kindreds, TTR(Met30) was found in 21 out of 41 asymptomatic 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(Met30), 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(Met30) 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; TTR(Met30) was present in each of these subjects. These several studies strongly suggest that the presence of TTR(Met30) in plasma constitutes a predictive biochemical marker of FAP in the preclinical phase of the disease.

Familial amyloid polyneuropathy

Amyloid fibrils were isolated from the myocardium of two patients with familial amyloid polyneuropathy. The solubilized amyloid fibril whole protein shared immunologic determinants with normal human serum prealbumin (transthyretin), but revealed subtle differences on immunoelectrophoresis and radial immunodiffusion. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, amyloid fibril whole protein was resolved into numerous bands that reacted with antitransthyretin on immunoblots. The whole protein also contained peptide fragments of fibronectin, but was devoid of amyloid P protein. An antiserum raised against the whole protein was suitable for immunocytochemistry of amyloid in paraffin sections. In contrast, commercial antitransthyretin, raised against the intact tetrameric protein failed to react with tissue amyloid. Immunochemical and immunocytochemical results support the concept that familial amyloid polyneuropathy with cardiomyopathy is due to infiltration of susceptible tissues by an anomalous transthyretin.

Serum amyloid A protein (SAA) subtypes in acute and chronic inflammatory conditions

Serum amyloid A (SAA), a polymorphic high density lipoprotein associated plasma protein, is the putative circulating precursor of tissue AA protein fibrils in reactive (secondary) amyloidosis. In the present study we examined the SAA subtype pattern in various acute and chronic inflammatory states in order to find out whether disease-specific SAA isoform profiles exist. The method used to study the subtype pattern is based on electrofocusing of serum followed by immunoblotting. Our results show that the SAA subtype pattern is similar in patients with rheumatoid arthritis with or without amyloid. In addition, in amyloidotic subjects the SAA subtype response to acute tissue injury (arthroplasty) did not differ from that in patients without amyloidosis. Analysis of patients with acute and chronic infectious diseases and non-rheumatic inflammatory conditions showed similar SAA patterns in all subjects. These results suggest that the SAA subtype response to tissue injury and inflammation is similar irrespective of the initiating stimulus.

Amyloid fibrils derived from V-region together with C-region fragments from a lambda II-immunoglobulin light chain (HAR)

Amyloid fibril proteins were isolated from the spleen of a patient with IgD(lambda)-plasmocytoma by extraction and gel filtration in 5M guanidine hydrochloride. The molecular mass of the predominant polypeptide chain was approximately 5000 Da. Its complete amino-acid sequence was elucidated by stepwise automated degradation of the carboxymethylated polypeptide chain and by structural studies of tryptic and thermolysinolytic cleavage products. The length of the polypeptide chain was 58 to 59 residues and it was homologous to the amino acids in positions 8 through 65 of the variable part of an lambda-type immunoglobulin light chain, which was most closely related to the lambda II subgroup. The N-terminal sequence of this amyloid fibril protein proved to be heterogeneous, indicating cleavage after the amino acids in positions 7 and 8. Peptides from the constant part of the lambda-chain were unexpectedly found in the tryptic digest of the denatured amyloid protein HAR. One polypeptide derived from the constant region was separated from the main component by high performance liquid chromatography. Its amino-acid sequence commenced at position 111 and could be traced in 41 steps. In this case, at least two constant region fragments were shown to be constituents of the amyloid fibril protein. The association of fragments from the variable as well as the constant region is discussed with respect to amyloid formation.

Structure of the chromosomal gene for human serum prealbumin

The human prealbumin gene has been cloned and its complete nucleotide sequence determined. The gene has a size of about 6.9 kb and is composed of four exons and three introns. Two Alu family sequences having opposing polarity were found in introns. In the 5'-flanking region, we found two overlapping sequences which have extensive homology to the glucocorticoid-responsive element. Three sequences identical with the enhancer core sequence were identified in introns and the 3'-flanking region. Unusual tandem repeats of a sequence, TTTTG, were also found in the 5'-flanking region and introns.

Identification of carriers of a variant plasma prealbumin (transthyretin) associated with familial amyloidotic polyneuropathy type I

A method is described for detecting carriers of a variant plasma prealbumin that is associated with familial amyloidotic polyneuropathy (FAP) type I. It is based on the finding of an extra methionine in the variant prealbumin, at position 30 from the amino terminals. Since normal prealbumin has only one methionine (position 13), treatment with cyanogen bromide (CNBr), which cleaves only at methionines, results in two peptides. CNBr treatment of the variant prealbumin gives three peptides. The extra can then be detected in two ways: by HPLC using a reverse phase C18 column, and by sequential Edman degradation. Each method can detect as little as 1% variant prealbumin in isolated plasma prealbumin, and therefore, can identify carriers of the gene for the variant protein. Since FAP type I usually is not manifest until after the childbearing years, this method to identify carriers of the gene offers a new approach for genetic counseling of families with this disease. To date, kindreds with hereditary amyloidosis that could benefit from these studies include those with FAP type I of Swedish, Japanese, and Portuguese origins.

A variant prealbumin-related low molecular weight amyloid fibril protein in familial amyloid polyneuropathy of Japanese origin

Amyloid fibril protein with a molecular weight of 8K daltons, in addition to one of 16K daltons, has been isolated and characterized from an autopsy sample of a patient with familial amyloid polyneuropathy in a Japanese family from Ogawa Village, Nagano Prefecture. The component was shown to react with an antiserum to normal plasma prealbumin, as did the other. Following the purification by reverse phase liquid chromatography, it was digested with trypsin and the peptides, after the purification by HPLC were sequenced. The data showed that the component was a distinct fragment whose sequence was identical with that of the residues from Gly-6 to Tyr-78 of the prealbumin, except that it had a methionine for a valine at position 25. This corresponded with the position 30 where a valine residues has been reported for the sequence of the normal plasma prealbumin.

Diagnosis of familial amyloidotic polyneuropathy by recombinant DNA techniques

An amino acid substitution of Met for Val at position 30 of plasma prealbumin is known to be closely related to heredo-familial amyloidotic polyneuropathy(FAP). As a first step in development of a direct method for diagnosis of the disease, cDNA for normal human prealbumin was cloned and its nucleotide sequence was determined. Our results showed that the nucleotide substitution responsible for the Val----Met change results in formation of new restriction sites for BalI and NsiI. By Southern blot hybridization analysis, the expected restriction sites were actually detected in the prealbumin locus of patients. Thus, a method was developed for diagnosis of the disease presymptomatically and prenatally.