Identification of a new hereditary amyloidosis prealbumin variant, Tyr-77, and detection of the gene by DNA analysis

Rare Variant of Hereditary Amyloid Transthyretin Cardiomyopathy Secondary to Ser97Tyr Mutation

Hereditary transthyretin amyloidosis (hATTR) is an autosomal dominant, adult-onset disease that stems from point mutations in the TTR gene encoding the protein transthyretin. The disease is progressive and life-threatening and is associated with amyloid deposits in multiple organs including the heart, kidney, skin, eyes, nervous system, and gastrointestinal tract. Genotypic and phenotypic heterogeneity is a characteristic hallmark of hereditary transthyretin amyloidosis. Herein, we present a rare variant of hATTR cardiomyopathy secondary to Ser97Tyr mutation, having been documented only in a handful of families previously. This case serves as a valuable opportunity to elucidate the clinico-pathogenesis of this disease, highlight the aggressive nature of this genetic mutation (c.290C>A; p.Ser97Tyr), and document the response to the latest advances in treatment currently available.

Analysis of amyloidogenic transthyretin mutations using continuum solvent free energy calculations

Many proteins can undergo pathological conformational changes that result in the formation of amyloidogenic fibril structures. Various neurodegenerative diseases are associated with such pathological fibril formation of specific proteins. Transthyretin (TTR) is a tetrameric globular transport protein in the blood plasma that can dissociate, unfold, and form long and stable fibrils. Many TTR mutations are known that promote (TTR) amyloidosis and cause severe diseases. TTR amyloidosis has been studied extensively using biochemical methods and structures of various mutations in the globular form have been characterized. Recently, also the structure of a TTR fibril has been determined. In an effort to better understand why some mutations increase or decrease the tendency of amyloid formation, we have applied a combined molecular dynamics and continuum solvent approach to calculate the energetic influence of residue changes in the globular versus fibril form. For 29 out of 36 tested TTR single residue mutations, the approach correctly predicts the increased or decreased tendency for amyloidosis allowing us also to elucidate the origins of the tendency. We find that indeed the destabilization of the globular monomer or changes in dimer and tetramer stability due to mutation has a dominant influence on the amyloidogenic tendency. The continuum solvent model predicts a significantly more favorable mean energy per residue of the fibril form compared to the globular form. This effect is only slightly modulated by single-point mutations preserving the energetic preference for fibril formation upon protein unfolding. It explains why no correlation between experimental amyloidosis and calculated change in fibril stability was observed.

Renal amyloidosis: an update on diagnosis and pathogenesis

Amyloidosis is a diverse group of protein conformational disorder which is caused by accumulation and deposition of insoluble protein fibrils in vital tissues or organs, instigating organ dysfunction. Renal amyloidosis is characterized by the acellular Congo red-positive pathologic deposition of amyloid fibrils within glomeruli and/or the interstitium. It is generally composed of serum amyloid A-related protein or an immunoglobulin light chain; other rare forms lysozyme, gelsolin, fibrinogen alpha chain, transthyretin, apolipoproteins AI/AII/AIV/CII/CIII; and the recently identified form ALECT2. This disease typically manifests with heavy proteinuria, nephrotic syndrome, and finally progression to end-stage renal failure. Early diagnosis of renal amyloidosis is arduous as its symptoms appear in later stages with prominent amyloid deposition. The identification of the correct type of amyloidosis is quite troublesome as it can be confused with another related form. Therefore, the exact typing of amyloid is essential for prognosis, treatment, and correct management of renal amyloidosis. The emanation of new techniques of proteomic analysis, for instance, mass spectroscopy/laser microdissection, has provided greater accuracy in amyloid typing. This in-depth review emphasizes on the clinical features, renal pathological findings, and diagnosis of the AL and non-AL forms of renal amyloidosis.

Transthyretin amyloidosis and the kidney

The amyloidoses are protein-misfolding disorders associated with progressive organ dysfunction. Immunoglobulin light chain is the most common, amyloid A the longest recognized, and transthyretin-associated amyloidosis (ATTR) the most frequent inherited systemic form. Although ATTR, an autosomal-dominant disease, is associated with at least 100 different transthyretin (TTR) mutations, the single amino-acid substitution of methionine for valine at position 30 is the most common mutation. Each variant has a different organ involvement, although clinical differences attributed to environmental and genetic factors exist within the same mutation. Peripheral neuropathy and cardiomyopathy are broadly described, and insights into disease reveal that kidney impairment and proteinuria are also clinical features. This review combines clinical and laboratory findings of renal involvement from the main geographic regions of disease occurrence and for different mutations of TTR. Fifteen nephropathic variants have been described, but the TTR V30M mutation is the best documented. Nephropathy affects patients with late-onset neuropathy, low penetrance in the family, and cardiac dysrhythmias. Microalbuminuria can be the disorder's first presentation, even before the onset of neuropathy. Amyloid renal deposits commonly occur, even in the absence of urinary abnormalities. The experience with renal replacement therapy is based on hemodialysis, which is associated with poor survival. Because TTR is synthesized mainly in the liver, liver transplantation has been considered an acceptable treatment; simultaneous liver-kidney transplantation is recommended to avoid recurrence of nephropathy. In addition, the kidney-safety profile of new drugs in development may soon be available.

Extended phenotype in the transthyretin Tyr77 familial amyloid polyneuropathy

The transthyretin Tyr77 variant of familial amyloid polyneuropathy (FAP) has been identified in a few North American and European patients, but the full spectrum of its clinical manifestations is still not known. We report a 3-generation family of Jewish-Yemenite origin with Tyr77 FAP presenting with atypical features. The affected individuals had sensorimotor and autonomic neuropathy and cardiomyopathy accompanied by prominent dysphagia, hearing loss and asymptomatic carpal tunnel syndrome. Brain MRI in the proband showed multifocal white matter lesions. These features extend the reported Tyr77 phenotype and support the modifying effect of additional factors on the disease expression.

Clinical variant of familial amyloid polyneuropathy

Hereditary amyloidosis with early and prominent peripheral nerve involvement is often designated familial amyloid polyneuropathy (FAP). The abnormality usually lies in the transthyretin (TTR) gene. We describe a patient with a tyr77 TTR gene mutation who presented with sensorimotor polyneuropathy but no other systemic symptoms of amyloidosis. This is one of a few documented cases of the tyr77 mutation in North America. The clinical and electrophysiologic features of this unusual cause of sensorimotor polyneuropathy are discussed.

Transthyretin mutations in hyperthyroxinemia and amyloid diseases

Over 80 different disease-causing mutations in transthyretin (TTR) have been reported. The vast majority are inherited in an autosomal dominant manner and are related to amyloid deposition, affecting predominantly peripheral nerve and/or the heart. A small portion of TTR mutations are apparently non-amyloidogenic. Among these are mutations responsible for hyperthyroxinemia, presenting high affinity for thyroxine (a TTR ligand). Compound heterozygotic individuals for TTR mutants have been described; noteworthy is the clinically protective effect exerted by a non-pathogenic over a pathogenic mutation. Current TTR mutations and their significance are briefly reviewed here.

The genetics of the amyloidoses

The amyloidoses are diseases in which abnormalities in the secondary structure of precursor proteins result in decreased solubility under physiologic conditions, with subsequent organ compromise. A total of 18 proteins have been definitively identified as amyloid precursors associated with human disease. Mutations in the genes that encode some of these proteins produce autosomal dominant disease in mid to late adult life. Until recently, the late onset has obscured the familial nature of some of the disorders. This is especially true in the apparently sporadic disease-producing deposits found even later in life. In many instances, these deposits are derived from precursors encoded by wild-type genes (perhaps influenced by alleles that are polymorphic in the normal population); in other cases, they represent autosomal dominant disease with age-dependent penetrance. The genetic aspects of amyloid diseases produced by the deposition of four different proteins have been investigated in detail and provide insights into the particular diseases and amyloidogenesis in general.

Transthyretin Tyr77 familial amyloid polyneuropathy: a clinicopathological study of a large kindred

More than 40 point mutations (producing different clinical manifestations) have been described in diverse points of the plasma protein transthyretin (TTR). The Met30 is considered the most common mutation, the Tyr77 mutation being the second most prevalent. However, data from patients with this late mutation are scarce, and usually come from isolated case reports or tables. The Tyr77 mutation is not as well characterized as the Met30 mutation, especially with respect to such aspects as prognosis or possible treatment by liver transplantation. We therefore present the clinical and pathological features of an extensive family with the Tyr77 TTR mutation, comprising 12 affected individuals over four generations. Six living individuals were followed over a 10-year period. Retrospective data were obtained with regard to the deceased family members. We found that an initial and sometimes prolonged carpal tunnel syndrome, beginning between the 6th and 7th decades, characterizes the Tyr77 mutation. In most cases this evolved to generalized peripheral nerve involvement, restrictive cardiomyopathy, and intestinal malabsortion. Although survival is usually high, there are progressive cases that should be candidates for liver transplant, before severe impairment has developed.

Peripheral nerve amyloidosis

Peripheral nerve amyloidosis is the cardinal feature of familial amyloid polyneuropathy (FAP) but can also be seen in primary light chain (AL) amyloidosis and dialysis (beta 2-microglobulin) related amyloidosis. The generalized neuropathy seen in all forms of peripheral nerve amyloidosis is similar, characterized by a severe progressive mixed neuropathy with autonomic dysfunction. Pathologically, amyloid is found in the peripheral nervous system as amorphous, eosinophilic, extracellular deposits. FAP is most commonly associated with variant plasma transthyretin (TTR), although it has also been described in association with mutant apolipoprotein A-1 and gelsolin. There are now at least 36 point mutations in the TTR gene associated with FAP and these continue to be described. Recent studies on the possible role individual point mutations in the TTR gene may play in amyloidosis have helped give us an insight into the mechanisms behind peripheral nerve amyloidosis. This article reviews the clinical and pathological features of the peripheral nerve amyloidosis and discusses theories of amyloidogenesis based on studies of FAP.

Haplotype analysis of French, British and other European patients with familial amyloid polyneuropathy (met 30 and tyr 77)

Familial amyloid polyneuropathy (FAP) is an autosomal dominant disorder originally and most frequently described in Portugal. The usual constituent amyloid fibril protein is transthyretin (TTR) and the most frequent mutation in the TTR gene associated with FAP (including all Portuguese cases) is that at position 30 (met 30). Three different TTR haplotypes have been described in association with the met 30 mutation in European patients. We studied the haplotypes of 27 families (24 French, 2 British and 1 Greek) with FAP met 30 by analysing three polymorphisms in introns of the TTR gene. We also studied 6 families (2 British, 3 French and 1 Spanish) with FAP tyr 77. There were two main haplotypes in French patients with FAP met 30, one most commonly seen in the French families of Portuguese descent which was the same haplotype as previously described in Portuguese patients (haplotype I) and another haplotype (III) detected in most informative French families not of Portuguese origin. The age of onset of symptoms was consistently later in French than in Portuguese patients and in patients with haplotype III as the disease-associated haplotype rather than haplotype I. British and French patients with the tyr 77 mutation had different haplotypes. The most likely explanation of these findings is multiple founders of both mutations.

Transthyretin mutations in health and disease

To date, over 40 different mutations in transthyretin (TTR) have been associated with amyloid deposition. The major unresolved problem is the correlation between the clinical heterogeneity and the genetic heterogeneity. For instance, whereas some mutations produce neuropathy and some give rise to cardiomyopathy, others produce vitreous opacities, the vast majority being neuropathic. Moreover, some mutations are not amyloidogenic but are responsible to hyperthyroxinemias (by virtue of the protein function in thyroid transport), whereas others are apparently nonpathogenic. The study of TTR variants is very important to the understanding of the amyloid formation process and to establish a relationship between the structure and function of the molecule. The results of current TTR mutation screening programs and their characterization are summarized.

Unifying features of systemic and cerebral amyloidosis

Amyloidosis is a generic term for a group of clinically and biochemically diverse diseases that are characterized by the deposition of an insoluble fibrillar protein in the extracellular space. Over 16 biochemically distinct amyloids are known. Despite this diversity, all amyloids have a particular ultrastructural and tinctorial appearance, a beta-pleated sheet structure, and are codeposited with a group of amyloid-associated proteins. The most common amyloidosis is Alzheimer's disease (AD), where A beta is the main component of the amyloid. Recently it has been found that A beta exists as a normal soluble protein (sA beta) in biological fluids. This links AD more closely to some of the systemic amyloidoses, where the amyloid precursor is found in the circulation normally. Numerous mutations have been found in the A beta precursor (beta PP) gene, associated with familial AD. Many mutations are also found in some of the hereditary systemic amyloidoses. For example, over 40 mutations in the transthyretin (TTR) gene are associated with amyloid. However, both A beta and TTR related amyloid deposition can occur with no mutation. The pathogenesis of amyloid is complex, and appears to be associated with genetic and environmental risk factors that can be similar in the systemic and cerebral amyloidoses.

Familial amyloidotic polyneuropathy with late-onset and well-preserved autonomic function: a Japanese kindred with novel mutant transthyretin (Ala97 to Gly)

We report the characteristics of one patient and two asymptomatic carriers from a Japanese family with familial amyloidotic polyneuropathy (FAP). The clinical features were somatic sensory and motor neuropathy with well-preserved autonomic function and late onset with slow insidious progression. These symptoms and signs are different from those of type 1 FAP. There were massive amyloid deposits with transthyretin (TTR) in the myocardium and the sural nerve. DNA sequencing of the TTR gene and amino acid sequence analysis of serum TTR revealed a new mutation in which Gly97 was substituted for Ala. We suggest that patients with somatic sensory and motor neuropathy of unknown origin without apparent autonomic dysfunction should be further studied for TTR mutation.

Immunoassay for transthyretin variants associated with amyloid neuropathy

An anti-transthyretin (TTR) mouse monoclonal antibody (88.6.FD6) of IgG1 subclass, obtained using as immunogen TTR from the serum of a patient with familial amyloidotic polyneuropathy, was found to bind to sera from carriers of several amyloidogenic TTR variants associated with peripheral neuropathy, but not to normal sera or sera from carriers of non-pathogenic or cardiomyopathic variants, in an ELISA performed under special conditions. Further characterization suggests that it recognizes an epitope near the N-terminal side of the TTR monomer. We propose that this epitope is exposed in amyloid and could be implicated in fibril deposition in the peripheral nervous system.

Transthyretin gene mutations in British and French patients with amyloid neuropathy

Five patients, two British and three French, with late onset amyloid neuropathy were found to have mutations of the transthyretin (TTR) gene associated with the Portuguese and German types of familial amyloid polyneuropathy. Familial amyloid polyneuropathy is rare in the United Kingdom and has not previously been defined at a molecular genetic level. None of the patients had a history of affected antecedents; the role of TTR gene analysis in diagnosing known or suspected amyloid neuropathy, regardless of family history or ethnic background, is emphasised.

Amyloid polyneuropathy with transthyretin Arg50 in a Japanese case from Osaka

A Japanese patient with systemic amyloidosis associated with a transthyretin (TTR) variant Arg50 is presented. This 41-year-old man became impotent and developed decreased pain sensation in his hands, and then sensory loss and muscle wasting in his lower legs, and cardiomyopathy appeared. The symptoms progressed and he died of congestive heart failure at age 46. There were amyloid deposits in all organs studied and massive amyloid deposition was seen in the peripheral nerves and cardiac muscles. Amyloid fibrils extracted from heart tissue contained TTR. A genetic mutation, causing a Ser50-->Arg substitution of the TTR molecule, was identified in another family member. Plasma TTR was shown to be a mixture of normal TTR Ser50 and mutant TTR Arg50 in the 2 subjects.

Novel variant transthyretin gene (Ser50 to Ile) in familial cardiac amyloidosis

We detected a point mutation in the transthyretin (TTR) gene in a patient with familial cardiac amyloidosis by using PCR-DCP (DNA conformation polymorphism) analysis that is based on the diversity in electrophoretic mobility of single-stranded DNAs and/or heteroduplex DNAs in PCR products. The PCR products of the transthyretin gene were denatured in the presence of formamide and electrophoresed in a non-denaturing polyacrylamide gel to detect an electrophoretic change due to a sequence variation. An unusual DNA fragment was visualized by silver staining in the PCR products of the exon 3 from the patient. Subsequent sequencing analysis revealed a T to A transversion and led to a replacement of Ser by Ile at codon 50 of the TTR gene.

A New Transthyretin Mutation Associated with Amyloidotic Vitreous Opacities

An inherited type of amyloidosis was suspected in an individual of Italian descent who presented with vitreous opacities. Although no family history of amyloidosis was apparent, the patient's transthyretin gene was examined and found not to possess any of the known transthyretin mutations. Complete DNA sequencing revealed a substitution of adenine for thymine in the second base of codon 84 causing an amino acid change of asparagine for isoleucine. The mutation was confirmed by demonstrating the loss of an Sfa N1 restriction endonuclease site. Allele-specific DNA amplification by polymerase chain reaction also was used to confirm the mutation. Either of these tests can be used for diagnosis. Asparagine 84 represents the second mutation associated with amyloidosis to occur at codon 84.

A second transthyretin mutation at position 33 (Leu/Phe) associated with familial amyloidotic polyneuropathy

Genomic DNA was isolated from peripheral blood lymphocytes of a patient with familial amyloidotic polyneuropathy (FAP) and the transthyretin (TTR) gene examined for sequence mutations. Polymerase chain reaction was used to asymmetrically amplify the TTR exons. Direct DNA sequencing of the PCR product revealed a C for T mutation at the first base of codon 33 located in exon 2 of one transthyretin gene. This resulted in a substitution of leucine for phenylalanine at position 33. Exons 3 and 4 were examined and found to be normal. The mutation creates a novel DdeI restriction site at the point of the mutation.

Polymorphism of apolipoprotein A-II (apoA-II) among inbred strains of mice. Relationship between the molecular type of apoA-II and mouse senile amyloidosis

Three types of apolipoprotein A-II (apoA-II) proteins (A, B and C) were predicted from the nucleotide sequence of apoA-II cDNA. Substitution of amino acid residues was noted at four positions (type A: Pro-5, Asp-20, Met-26, Ala-38; B: Pro-5, Glu-20, Val-26, Val-38; C: Gln-5, Glu-20, Val-26, Ala-38). Each type was identifiable by digestion of amplified apoA-II DNA by PCR, using restriction-fragment-length polymorphism of the apoA-II gene for restriction enzymes Cfr13I and MspI. The molecular type of apoA-II was determined among 23 strains of mice including nine of the senescence accelerated mouse series developed in our laboratory. Examination of types of apoA-II and amyloid deposition in the F2 and F3 hybrid mice showed that apoA-II amyloid deposition was present only in the mice homozygous for type C apoA-II and which were 12-17 months of age. The molecular type of apoA-II may be a factor involved in the development of senile amyloidosis in mice.

Finnish type of familial amyloidosis: cosegregation of Asp187----Asn mutation of gelsolin with the disease in three large families

Familial amyloidosis of Finnish type (FAF) is one of the familial amyloidotic polyneuropathy (FAP) syndromes, a group of inherited disorders characterized by extracellular accumulation of amyloid and by clinical symptoms and signs of polyneuropathy. FAF, an autosomal dominant trait, belongs to those rare monogenic disorders which occur with increased frequency in the Finnish population: only single FAF cases have been reported from other populations. In most types of FAP syndromes the accumulating protein is a transthyretin variant. However, recent evidence has suggested that the amyloid peptides in FAF are related to gelsolin, an actin modulating protein. The gelsolin fragments isolated from at least one patient with amyloidosis have been reported to have an amino acid substitution, with asparagine replacing aspartic acid at position 187 of the plasma gelsolin. In this study allele-specific oligonucleotides were used to analyze three large FAF families with multiple affected individuals as well as healthy family members. We found the corresponding G-A mutation in nucleotide 654 of the plasma gelsolin gene to cosegregate with the disease. The result was confirmed by sequencing and strongly suggests that the mutation has caused all the FAF cases of these families. Since the disease is clustered in restricted areas on the southern coast of Finland, this mutation most probably causes the majority, if not all, of FAF cases in Finland.

The transthyretin cDNA sequence is normal in transthyretin-derived senile systemic amyloidosis

A variety of mutations leading to amino acid substitutions have been described in the transthyretin gene in association with different familial amyloidoses and have been implicated to be involved in the pathogenesis of amyloid deposits. However, there has been disagreement whether or not a transthyretin mutation is present in the most common form of transthyretin-derived amyloid, namely senile systemic amyloidosis. Therefore, the cDNA sequence of liver transthyretin was determined in a 91-year-old patient with typical senile systemic amyloidosis. This sequence was completely normal and lacked any variation. We conclude that in senile systemic amyloidosis factors other than the presence of a sequentially variant transthyretin must determine the amyloid fibril formation.

Production of recombinant human transthyretin with biological activities toward the understanding of the molecular basis of familial amyloidotic polyneuropathy (FAP)

Transthyretin (TTR) is a plasma protein interacting with thyroxine T4 and retinol binding protein (RBP). Several variants of TTR with single amino acid substitutions have been identified as the major components of the amyloid fibrils of familial amyloidotic polyneuropathy (FAP), a fetal, autosomal dominant genetic disease. The elucidation of the molecular nature of the variants distinct from that of the wild-type TTR is crucial for understanding the amyloidogenesis in FAP, but our understanding is very poor mainly because of the unavailability of pure variant TTRs. In the present study, we used an Escherichia coli OmpA secretion vector (Ghrayeb et al., 1984) and achieved an effective production of the variant TTRs related to FAP including Met-30, Ile-33, Ala-60, Tyr-77, Met-111, and Ile-122 types. The variant TTRs produced in this system were efficiently secreted to the culture media. The chemical analysis showed that the secreted TTR (Met-30 type) has the same N-terminus as the native one. IEF analyses also indicated that the secreted product is properly processed as assessed by its pI. Furthermore, the secreted TTR was shown to have biological activities, namely, the thyroxin binding activity and the ability to associate with retinol binding protein, indicating that the secreted TTR polypeptide is properly folded. The present work also demonstrated that the processing/secretion of the recombinant TTR molecules in E. coli was strongly affected by single amino acid substitutions.

A new transthyretin variant from a patient with familial amyloidotic polyneuropathy has asparagine substituted for histidine at position 90

A new transthyretin variant which lost an Sph I cleavage site within exon 3 has been characterized. A 260 bp sequence containing exon 3 was amplified using the polymerase chain reaction, and the variant was found to possess a Bsm I cleavage site not present in normal transthyretin. This led to the conclusion that the histidine at position 90 was replaced by asparagine, and amino acid analysis supported the conclusion. The discovery of this mutation suggests that intermolecular binding between hydrophobic polypeptide loops on the surface of transthyretin can lead to familial amyloidotic polyneuropathy.

Recent advances in the molecular pathology of familial amyloid polyneuropathy

The familial amyloid polyneuropathies (FAP) represent a heterogeneous spectrum of clinical syndromes differing regarding age of onset, rate of progression, and distribution of organ involvement and affecting people from different ethnic groups. Several mutant forms of transthyretin (TTR, formerly referred to as prealbumin) have been identified both in circulating plasma and in amyloid deposits from FAP patients. It is possible that a common factor in the amyloidogenesis process exists among the different forms which might be related to a change produced by the mutation in the three-dimensional structure of TTR. Other genetic or acquired factors affecting tissue composition might also play a role in pathogenesis. The intervening factors in amyloidogenesis in FAP, other than the presence of mutant TTR, are largely unknown and deserve future study.

Diagnosis of familial amyloidotic polyneuropathy in France

Two cases of familial amyloidotic polyneuropathy (FAP) in a French family are reported. Clinical onset was in the fifth and sixth decades with decreased sensation in the lower limbs followed by involvement of the upper extremities. Motor changes appeared later and evolved to restrict ambulation. Cardiac involvement with congestive heart failure and arrhythmias was the cause of death. DNA analysis was performed on ten members of this family. Restriction enzyme analysis of amplification products of exons 2, 3 and 4 of the prealbumin gene were negative for the methionine-30, alanine-60 and serine-84 mutations but positive for the tyrosine-77 mutation. The tyrosine-77 prealbumin mutation was first described in a family from Illinois with origin in Germany. The discovery of the tyrosine-77 gene in the family from Picardy may help to determine the origin of this disease and tell us if one mutation has been spread around the world, as we suspect, with many kindreds having the methionine-30 gene, or whether there have been separate spontaneous mutational events, perhaps a peculiarity of this site in the prealbumin gene.

Isolation and characterization of cardiac amyloid in familial amyloid polyneuropathy type IV (Finnish): relation of the amyloid protein to variant gelsolin

Amyloid subunit protein was isolated from familial amyloid polyneuropathy type IV (Finnish type) cardiac tissue and purified to homogeneity. N-terminal amino acid sequence analysis shows that the amyloid protein is a fragment of the inner region of human gelsolin. When compared with the predicted sequence of human plasma gelsolin, the amyloid protein contains an asparagine-for-aspartic acid substitution at position 15 corresponding to residue 187 of the secreted protein. Antibodies raised against the amyloidogenic region of gelsolin specifically stained the amyloid deposited in tissues in familial amyloidosis type IV. The results show that the subunit amyloid protein in familial amyloid polyneuropathy type IV represents a unique type of amyloid derived from a variant (Asn-187) gelsolin molecule by limited proteolysis.

A mutation in apolipoprotein A-I in the Iowa type of familial amyloidotic polyneuropathy

Immunoblotting of isoelectric focusing gels of plasma and direct genomic DNA sequencing have been used to characterize a mutation in apolipoprotein A-I associated with the familial amyloidotic polyneuropathy originally described by Van Allen in an Iowa kindred. An arginine for glycine substitution in apolipoprotein A-I identified in the proband's amyloid fibrils was determined to be the result of a mutation of guanine to cytosine in the apolipoprotein A-I gene at the position corresponding to the first base of codon 26. Direct sequencing of genomic DNA of three affected individuals who died in the 1960s confirmed the inheritance of the disorder. Immunoblot analysis detected the variant apolipoprotein A-I in the proband's plasma and in several at-risk members of the kindred. In addition, allele-specific amplification by the polymerase chain reaction was used to detect carriers of the variant gene.

A homozygous transthyretin variant associated with senile systemic amyloidosis: evidence for a late-onset disease of genetic etiology

Senile systemic amyloidosis (SSA) is a late-onset disease characterized by deposition of amyloid fibrils containing transthyretin (TTR). Amino acid sequencing of protein isolated from the amyloid fibrils of a patient with SSA identified TTR containing a position - 122 isoleucine-for-valine substitution. This change led to the prediction of a genomic G-to-A transition, destroying an MaeIII restriction site. We confirmed the presence of the variant DNA fragment both by Southern blotting and by visualization of MaeIII digests of DNA amplified around codon 122, by using the polymerase chain reaction. The patient's DNA was entirely resistant to MaeIII cleavage; therefore, only the mutant sequence was present. DNA from none of either 24 controls or six other SSA patients contained the variant. Quantitative Southern blotting demonstrated that the patient's DNA contained two copies of the TTR gene per genome; the mutation was therefore homozygous rather than hemizygous. In the present case, the homozygous mutation TTR (122 Val----Ile) is associated with SSA, a finding which is consistent with autosomal recessive inheritance of this condition.

Diagnosis of Maryland/German familial amyloidotic polyneuropathy using allele-specific, enzymatically amplified, genomic DNA

Diagnoses of familial amyloidotic polyneuropathies have been traditionally based on attempts to distinguish clinical features and ancestry or geographic origin of cases. Most are associated with extracellular deposition of a variant prealbumin (also known as transthyretin). Recent molecular studies demonstrated eight distinct amyloid-associated point mutations in the prealbumin gene on the long arm of chromosome 18 that are associated with hereditary amyloidosis. These findings provide for means of diagnosis using recombinant DNA methods. In a family with the Maryland/German type of familial amyloidotic polyneuropathy, the proband and 2 of 5 at-risk offspring were diagnosed using the polymerase chain reaction. Allele-specific enzymatic amplification of genomic DNA demonstrated the histidine-58 variant prealbumin gene. This study confirms the point mutation of the prealbumin gene as a cause for this type of familial amyloidotic polyneuropathy. Preclinical diagnosis illustrates the potential for development of treatment strategies prior to disease onset.

Fibril in senile systemic amyloidosis is derived from normal transthyretin

The amyloid fibril in senile systemic amyloidosis (SSA), like that of familial amyloidotic polyneuropathy, is derived from transthyretin (TTR). SSA, however, is a common disease, affecting to some degree 25% of the population greater than 80 years old. In familial amyloidotic polyneuropathy, the amyloidogenesis has been considered to depend on point mutations leading to TTR variants. We show that the TTR molecule in SSA, on the other hand, has a normal primary structure. Factors other than the primary structure of TTR must therefore be important in the pathogenesis of TTR-derived amyloid.

Finnish hereditary amyloidosis. Amino acid sequence homology between the amyloid fibril protein and human plasma gelsoline

Amyloid fibrils were isolated from the kidney of a patient with Finnish hereditary amyloidosis. After solubilization of the fibrils in guanidine-HCl, fractionation by gel filtration, and purification by reverse-phase high-performance liquid chromatography, a homogeneous amyloid protein with an apparent Mr of 9000 was obtained. The protein was subjected to enzymatic digestion by trypsin and endoproteinase Lys-C. The amino acid sequences were determined for 6 of the released peptides and they were all found to be identical to the reported, deduced primary structure of human plasma gelsoline in the region of amino acids 235-269. The results show that the amyloid fibril protein in Finnish hereditary amyloidosis represents a new type of amyloid protein that shows amino acid sequence homology with gelsoline, an actin-modulating protein.

Hereditary amyloidosis: detection of variant prealbumin genes by restriction enzyme analysis of amplified genomic DNA sequences

The autosomal dominant prealbumin amyloidoses are late-onset disorders characterized by varying degrees of peripheral neuropathy, nephropathy and cardiomyopathy. To date, seven different single amino acid mutations in the plasma protein prealbumin (transthyretin) have been found to be associated with amyloidosis and each is the result of a single nucleotide change in the prealbumin gene. By virtue of the restriction endonuclease sites created by the point mutations which give rise to the protein variants, direct DNA tests using Southern analysis have already been developed for detection of the Met-30, Ile-33, Ala-60, Tyr-77 and Ser-84 prealbumin genes. As an alternative to Southern analysis, we have amplified discrete regions of the prealbumin gene using polymerase chain reaction (PCR) and used restriction enzyme analysis of the PCR products to detect the Met-30, Ala-60, Tyr-77 and Ser-84 prealbumin genes after agarose gel electrophoresis and staining with ethidium bromide. In comparison to Southern analysis these alternative tests yield results much more quickly and avoid the use and handling of radioactively labeled probes.

Amyloidosis of the nervous system

Various types of amyloid fibril deposits occur in the nervous system with unique clinical characteristics and pathogeneses. Genetic mutations cause the familial amyloidotic polyneuropathies and acquired polyneuropathies occurring particularly in patients suffering from hypernephromas and myelomas also result from the production of abnormal proteins. Amyloid fibril deposits in cerebral plaques and vessels consisting of beta-protein are seen in acquired and familial Alzheimer's disease and in Down's syndrome individuals over 40 years of age. This amyloid fibril deposition could result from a mutational, transcriptional or post-translational alteration in these pathologic processes with most evidence supporting the latter. Other diseases including hereditary cerebral hemorrhage of the Dutch type and Batten's disease involve beta-amyloid deposition. The features of the familial and transmissible forms of the spongiform encephalopathies are associated with the prion protein which comprises the amyloid fibril deposits in these conditions. This wide variety of nervous system disorders having amyloid deposits as their primary or subsidiary characteristic make studies of these conditions intriguing models for research workers in clinical, pathologic and molecular biologic fields.

Prenatal detection of a gene for hereditary amyloidosis

Autosomal dominant amyloidosis of the Indiana/Swiss type (familial amyloidotic polyneuropathy type II) is a late-onset disorder characterized by carpal tunnel syndrome, peripheral neuropathy, vitreous opacities, and cardiomyopathy. The genetic basis of the disease is a variant of plasma prealbumin (transthyretin) which has a serine for isoleucine substitution at amino acid 84 of the 127 residue prealbumin molecule. Using the polymerase chain reaction (PCR), we amplified exon 3 of the prealbumin gene in DNA extracted from amniocytes of a fetus at-risk of carrying the serine-84 prealbumin gene. By allele-specific oligonucleotide analysis as well as restriction enzyme analysis of the amplification products it was determined that the fetus was a carrier of the serine-84 variant gene. This finding was confirmed at birth by Southern blot analysis using DNA obtained from cord blood. This is the first report of the prenatal detection of a gene for hereditary amyloidosis.

A new mutation causing familial amyloidotic polyneuropathy

The DNA from an individual with familial amyloidotic polyneuropathy was examined. It did not possess any of the mutations which have previously been associated with familial amyloidotic polyneuropathy. However, a novel 7.0 kb Sph I restriction fragment was discovered, and the mutation creating it was localized to exon 3 of the transthyretin gene. This mutation was inherited from a parent, and may result in an amino acid substitution for glu89, his90 or ala91. The patient's transthyretin has a lower pI than normal transthyretin.

Direct sequencing of the gene for Maryland/German familial amyloidotic polyneuropathy type II and genotyping by allele-specific enzymatic amplification

Direct genomic DNA sequencing has been used to characterize the mutation associated with familial amyloidotic polyneuropathy in the Maryland/German kindred. A mutation of thymine to adenine in the prealbumin (transthyretin) gene at the position corresponding to the second base of codon 58 in the prealbumin mRNA gives a histidine for leucine substitution in the plasma protein. Since the mutation does not result in a change in the restriction pattern of the prealbumin gene, a new method for the direct detection of single base changes in genomic DNA was developed using the polymerase chain reaction and an allele-specific oligonucleotide primer.

Pleiotropy revisited: molecular explanations of a classic concept

As commonly used, pleiotropy refers to multiple effects on phenotype of a single mutant gene. The importance of this concept to medical genetics has waxed and waned since its formulation soon after the rediscovery of Mendel's laws. Initially, the view that all aspects of a phenotype, and hence all manifestations of a mendelian syndrome, derive from a single function (or dysfunction) of a mutant allele gained ascendancy. Support for the importance of pleiotropy gradually diminished, and reached a low point in the 1940s with the one gene-one enzyme hypothesis. Studies of mammals and humans with heritable disorders of connective tissue sustained the notion that "genuine" pleiotropy probably did not exist. However, the demise of the relevance of pleiotropy was premature. Detailed understanding of gene organization, expression, and mutation indicates several mechanisms, such as multifunctional proteins, alternative splicing of messenger RNA, and overlapping coding sequences, through which genuine pleiotropy likely occurs in normal development and function, in mendelian syndromes, and in conditions due to somatic mutation. Furthermore, a broad definition of pleiotropy is warranted to subsume syndromes caused by abnormal function of contiguous genes, such as through large deletions, mutation of regulatory elements that coordinate expression, or less clearly understood "position effects." Thus, the use of pleiotropy in the context of aneuploidy syndromes is not inappropriate.

Haplotype analysis of familial amyloidotic polyneuropathy. Evidence for multiple origins of the Val----Met mutation most common to the disease

Familial amyloidotic polyneuropathy (FAP) is an autosomal dominant genetic disease characterized by systemic accumulation of amyloid fibrils. A major component of FAP amyloid has been identified as variant transthyretin (TTR, also called prealbumin). In particular, a variant with the substitution 30Val----Met has been commonly found in FAP of various ethnic groups. To understand the origin and spread of the Val----Met mutation, we analyzed DNA polymorphisms associated with the TTR gene in six Japanese FAP families and several Portuguese FAP patients. Three distinct haplotypes associated with the Val----Met mutation were identified in Japanese FAP families, one of which was also found in Portuguese patients. On the other hand, it was found that the Val----Met mutation can be explained by a C-T transition at the CpG dinucleotide sequence of a mutation hot spot. Thus, our findings indicate that the Val----Met mutation has probably recurred in the human population, to generate FAP families of independent origin.

Molecular genetics of amyloid neuropathy in Europe

The Portuguese type of familial amyloid polyneuropathy (FAP type I), a disabling autosomal dominant disorder with onset in early adult life, is caused by a point mutation in the transthyretin (TTR; previously known as prealbumin) gene. DNA analysis in thirteen European families (one British, two French, one Italian, one Greek, and eight Cypriot) showed that members of all those from Cyprus and Greece, and one from France, carried the FAP type I mutation. Patients from seven of these ten kindreds were not known to have a genetic disease before this study, which demonstrated the mutation in 16 of 43 clinically unaffected relatives. 2 of these were aged over 50 years. TTR gene analysis has useful applications in genetic counselling, including prenatal diagnosis, in identifying the cause of seemingly sporadic cases of amyloid neuropathy, and in epidemiological studies of FAP.

Familial amyloidotic polyneuropathy: transthyretin (prealbumin) variants in kindreds of Italian origin

As part of an epidemiological study that aims to characterize chemically the mutation(s) in transthyretin (TTR) related to familial amyloidotic polyneuropathy (FAP) of different ethnic origins, studies were carried out on TTR from two FAP kindreds of Italian origin. Two different criteria were employed in the characterization of TTR from these kindreds: (1) immunoblotting of cyanogen bromide fragments for screening of TTR(Met30) and (2) isoelectric focusing. TTR(Met30) was not detected but other substitutions were demonstrated using isoelectric focusing techniques. One of the variants found is a basic TTR variant. The substitutions occurring in the variant TTRs of these two kindreds are not known and are presently under study.

Variant apolipoprotein AI as a major constituent of a human hereditary amyloid

Amyloid fibrils were isolated from spleen and liver of a patient who died with Familial Amyloidotic Polyneuropathy Type III (Iowa). The major protein constituent of the fibrils was found to be the amino terminal portion (residues 1-83) of apolipoprotein AI with an arginine for glycine substitution at position 26. This is the first report of an apolipoprotein as a major amyloid constituent in a form of autosomal dominant hereditary amyloidosis in humans.

A DNA test for Indiana/Swiss hereditary amyloidosis (FAP II)

Autosomal dominant amyloidosis of the Indiana/Swiss type is a late-onset disorder characterized by carpal tunnel syndrome, progressive peripheral neuropathy, vitreous deposits, and cardiomyopathy. This disorder was originally described in a large Indiana family of Swiss descent and is also known as familial amyloidotic polyneuropathy (FAP) type II. In the Indiana family, the genetic basis of the disease is a variant of plasma prealbumin (transthyretin), which has a serine-for-isoleucine substitution at amino acid 84 of the 127-residue prealbumin molecule. We predicted that the corresponding mutation in the prealbumin gene consisted of a T-to-G change in codon 84 (which created an AluI recognition site) and then demonstrated the extra AluI site in the DNA of patients by Southern blot analysis with a genomic prealbumin probe. This verifies the protein findings at the DNA level and provides a direct, reliable DNA test for the Ser-84 prealbumin gene associated with Indiana/Swiss hereditary amyloidosis.

Evidence that the amyloid fibril protein in senile systemic amyloidosis is derived from normal prealbumin

Familial amyloidosis in different kindreds is associated with a variety of point mutations in the prealbumin gene, resulting in prealbumin variants which are believed to be amyloidogenic, i.e. prone to form amyloid fibrils. In the most common amyloid-associated variant, there is a methionine for valine substitution in position 30. We have studied the prealbumin-derived amyloid protein ASc1 in the common age-related senile systemic amyloidosis. Evidence is presented that there is no abnormality in the primary structure of prealbumin in this disease and that, in addition to complete prealbumin, fibrils contain prealbumin fragments lacking a significant part of the N-terminus.