Transthyretin-related familial amyloidotic polyneuropathy

Transthyretin-related familial amyloidotic polyneuropathy (FAP) is a fatal hereditary amyloidosis. Until 20 years ago, FAP was thought to be restricted to endemic occurrence in certain areas. However, owing to progress in biochemical and molecular genetic analyses, FAP is now believed to occur worldwide. As of today, reports of about 100 different points of single or double mutations, or a deletion in the transthyretin gene, have been published, and several different phenotypes of FAP have been documented, even for the same mutation in the transthyretin gene. We present herein the current clinicopathological, biochemical, molecular genetic, and epidemiological aspects of transthyretin-related FAP, and we introduce a new diagnostic procedure for the disease.     

Autonomic neuropathy in familial amyloidotic polyneuropathy

Familial amyloidotic polyneuropathy (FAP) is characterized by both sensimotor and autonomic dysfunction. Autonomic disturbance involving the gastrointestinal tract, the urinary bladder, the cardiac conduction system, and the peripheral circulation has been described. In this study simple, non-invasive tests of autonomic function based on heart rate variability were applied to 12 patients with FAP and 12 healthy volunteers. The heart rate variation during normal breathing, deep breathing and during tilt from recumbent to standing position was measured. All tests showed significantly less heart rate variation in patients than in controls and the heart rate variation decreased with increasing severity of neurological disability, but the small number of patients in our study does not allow any further comparison between subgroups. Our study thus indicates impaired cardiovascular autonomic function in patients with FAP and we believe that these findings might also be of importance in other forms of systemic amyloidosis.     

Endothelium-dependent vasodilatation in patients with familial amyloidotic polyneuropathy

We examined endothelium-dependent vasodilatation in 15 familial amyloidotic polyneuropathy (FAP) amyloidogenic transthyretin (ATTR) Valine30Methionine (Val30Met) patients and 12 healthy volunteers. Using ultrasonography, we measured the radial artery diameters under both baseline and hyperemic conditions. Endothelium-dependent vasodilatation was expressed as a percent increase in the diameters of the radial artery after induced hyperemia. Endothelium-dependent vasodilatation tended to decrease in the patients, compared with healthy volunteers. Responses were not elicited at all in patients with disease of more than 9 years' duration. Linear negative correlation was observed between endothelium-dependent vasodilatation and disease duration (P < 0.01). Correlation between endothelium-dependent vasodilatation and degree of autonomic dysfunction was significant (P = 0.0524) and for age was close to significance (P = 0.051). These results suggest that the peripheral vasomotor dysfunction in FAP patients may predominantly depend on the amount of amyloid deposition around the vessels through the course of illness.     

Alpha 2-adrenergic receptor in familial amyloidotic polyneuropathy

alpha 2-Adrenergic receptor binding has been studied in platelet membranes from 16 patients with type 1 familial amyloidotic polyneuropathy (FAP) at various clinical stages and 15 normal subjects. Binding of the radioligand [3H]yohimbine to platelet membranes was used to examine alpha 2-adrenergic receptors. The number of alpha 2-adrenergic receptors were significantly lower in patients of the early stage than in normal subjects. Then, the numbers tended to be higher than those of normal subjects in the intermediate stage, and they were higher in the single advanced-stage patient studied. The reduction in alpha 2-adrenergic receptor numbers in platelet membranes from patients of the early stage might be explained by the down-regulation of the receptors in vascular smooth muscle, but it remains uncertain whether a high number of alpha 2-adrenergic receptors observed in the single advanced-stage patient might be explained by the up-regulation of the receptors.     

Variant transthyretin in cerebrospinal fluid in familial amyloidotic polyneuropathy

Structurally abnormal transthyretin is a precursor protein of amyloid fibrils in type I familial amyloidotic polyneuropathy (FAP). This variant transthyretin has an amino acid substitution of methionine for valine at position 30. The purpose of this study was to clarify whether this variant transthyretin also circulates in the cerebrospinal fluid (CSF) of patients with type I FAP. CSF transthyretin of the patients was purified and its primary structure determined. Sequence determination indicated that transthyretin consisted of a mixture of normal and variant transthyretin. Variant transthyretin was present in the CSF of all 5 Japanese FAP patients studied. The CSF concentration of variant transthyretin was high (0.72 +/- 0.15 mg/dl, mean +/- S.D.), suggesting that variant transthyretin is synthesized in the choroid plexus. Variant transthyretin was not present in any of 20 controls. The CSF concentration of total transthyretin in FAP patients was 1.74 +/- 0.42 mg/dl, which was not significantly different from controls.     

Abnormal transthyretin in asymptomatic relatives in familial amyloidotic polyneuropathy

Familial amyloidotic polyneuropathy (FAP) has been biochemically and genetically proven to be an inherited molecular disorder of transthyretin. (The term transthyretin has been suggested by the Nomenclature Committee of the international Union of Biochemistry and the International Union of Pure and Applied Chemistry for the protein that has heretofore been called prealbumin.) We have experienced three cases that included typical clinical, electrophysiologic, and neuropathologic manifestations of FAP, and yet no known family history of the disorder. The patients and members of their families were studied by radioimmunoassay for a variant transthyretin with a methionine-for-valine substitution at position 30. All three patients had the variant transthyretin in the serum, at concentrations of 54.5, 87.9, and 105.9 mg/L (5.45, 8.79, and 10.59 mg/dL). Although parents and siblings had neither neurologic nor electromyographic evidence of FAP, some of these family members had serum concentrations of variant transthyretin as high as those of the propositi. It was from these asymptomatic parents that the "nonfamilial" patients inherited the gene for FAP. Further study is needed to define the mechanisms retarding or preventing, as well as those promoting, the clinical development of FAP when the variant transthyretin is present in the serum at a high level.     

Bleeding manifestations in 24 patients with familial amyloidotic polyneuropathy

Focal or generalized hemorrhage is a commonly encountered complication in patients with many kinds of amyloidosis. We studied 24 patients (18 males, 6 females) with familial amyloidotic polyneuropathy and found that five had experienced one or more bleeding episodes. In four of these five patients, bleeding occurred in the terminal stage. The incidence of hemorrhage in familial amyloidotic polyneuropathy is lower than that of other types of amyloidosis or that which has been reported in this disease. In our experience clotting abnormalities were rare; clotting factor deficiency appeared not to exist in familial amyloidotic polyneuropathy.     

Studies of protease and protease inhibitors in familial amyloidotic polyneuropathy

Serum levels of 6 protease inhibitors, alpha 1-antitrypsin, Cl inactivator, alpha 2-macroglobulin, antithrombin-3, alpha 1-antichymotrypsin and inter-alpha-trypsin inhibitor were measured in patients with familial amyloidotic polyneuropathy (FAP) and a control group without neurologic disease. No significant differences were observed between the 2 groups. The proteolytic effect of brinase, an enzyme from Aspergillus oryzae, on amyloid tissue sections from patients with FAP was also evaluated. Amyloid fibrils were degraded by brinase, while the tissue structure remained fairly intact.     

Evidence of oxidative stress in familial amyloidotic polyneuropathy type 1

OBJECTIVE: To evaluate the oxidative state in patients with familial amyloidotic polyneuropathy type 1 (FAP1). DESIGN: From 3 unrelated families, patients with FAP1 carrying a transthyretin Met-30 mutation were studied. The diagnosis was confirmed by genetic analysis. Eleven of 21 patients carried the mutation; all were symptomatic and were clinically assessed using a clinical score. All of the patients were evaluated for copper-zinc superoxide dismutase type 1 activity in red blood cells using spectrophotometry. Plasma total reactive antioxidant potential was studied using a chemiluminescent method. The results were compared with those obtained from an age-matched control group. SETTING: A public and academic multidisciplinary research clinic. RESULTS: Six of the 11 FAP1-positive patients disclosed superoxide dismutase type 1 activity values greater than 55 U/mg of protein (upper control limit), whereas 9 of 10 patients in whom total reactive antioxidant potential was measured had values below the lower limit of the control group. No relationship was found between the levels of superoxide dismutase type 1 activity and the severity of the clinical involvement. CONCLUSIONS: Oxidative stress may be part of the mechanisms leading to tissue damage in patients with FAP1. The lack of correlation between the laboratory findings and the severity of clinical involvement may signal that oxidative processes are at work throughout the natural history of the disease.     

The aortic alpha1-adrenergic receptor in familial amyloidotic polyneuropathy

Summary To assess the pathophysiology of the sympathetic nervous system in familial amyloidotic polyneuropathy (FAP), we used³H-bunazosin to identify and characterize the alpha₁-adrenergic receptor in human aortic membranes. The binding of³H-bunazosin was rapid, readily reversible, stereospecific, and saturable. The Scatchard analysis described a single class of binding sites with a dissociation constant (K_D) of 0.370±0.035nM and a maximal binding capacity (Bmax) of 11.8±1.30 fmol/mg protein in control patients. Competition analysis demonstrated the alpha₁-adrenergic specificity of the³H-bunazosin binding sites in human aortic membranes. The K_D and Bmax of³H-bunazosin binding in four FAP patients was 0.274±0.052 nM and 7.79±0.15 fmol/mg protein, respectively; these values did not differ significantly from those in 14 control patients. An increase in Bmax or affinity of alpha₁-adrenergic receptors may not be the cause for denervation supersensitivity in FAP.     

Type I familial amyloidotic polyneuropathy (Japanese type)

Our recent studies on familial amyloidotic polyneuropathy (FAP) were reviewed. Since the clinical picture of our FAP is slightly different from those of the Portuguese type, the Swedish type, and the Jewish type, structural identification of the amyloid fibril proteins should be clarified on a molecular basis. Further investigation on the effectiveness of dimethyl sulfoxide (DMSO) or a search for other useful new drugs is greatly required.