Familial amyloidotic polyneuropathy with muscle, vitreous, leptomeningeal, and cardiac involvement: phenotypic, pathological, and MRI description

Transthyretin mutagenesis: impact on amyloidogenesis and disease

Transthyretin (TTR), a homotetrameric protein found in plasma, cerebrospinal fluid, and the eye, plays a pivotal role in the onset of several amyloid diseases with high morbidity and mortality. Protein aggregation and fibril formation by wild-type TTR and its natural more amyloidogenic variants are hallmarks of ATTRwt and ATTRv amyloidosis, respectively. The formation of soluble amyloid aggregates and the accumulation of insoluble amyloid fibrils and deposits in multiple tissues can lead to organ dysfunction and cell death. The most frequent manifestations of ATTR are polyneuropathies and cardiomyopathies. However, clinical manifestations such as carpal tunnel syndrome, leptomeningeal, and ocular amyloidosis, among several others may also occur. This review provides an up-to-date listing of all single amino-acid mutations in TTR known to date. Of approximately 220 single-point mutations, 93% are considered pathogenic. Aspartic acid is the residue mutated with the highest frequency, whereas tryptophan is highly conserved. "Hot spot" mutation regions are mainly assigned to β-strands B, C, and D. This manuscript also reviews the protein aggregation models that have been proposed for TTR amyloid fibril formation and the transient conformational states that convert native TTR into aggregation-prone molecular species. Finally, it compiles the various in vitro TTR aggregation protocols currently in use for research and drug development purposes. In short, this article reviews and discusses TTR mutagenesis and amyloidogenesis, and their implications in disease onset.

Clinicopathological Features of Amyloid Neuropathy: A Four Decade Experience

BACKGROUND

Peripheral neuropathy is one of the manifestations of primary or familial amyloidosis. Published studies from India are limited.

MATERIALS AND METHODS

We reviewed the clinical and pathological features of amyloid neuropathy diagnosed at our Institute over the last 39 years.

RESULTS

Fifty-five cases of amyloid neuropathies were diagnosed between 1981 and 2019, constituting 0.28% of peripheral nerve biopsies (55/19,081). Age at presentation ranged from 24 to 81 years (mean-48 years) with male preponderance [M:F = 3.58:1]. Duration of symptoms at presentation varied from 3 months to 10 years (mean-2.31 years). Majority presented with small fiber neuropathy (85%). Pure sensory symptoms predominated in 23%, while 72% had sensorimotor neuropathy and 35.8% had autonomic involvement, with isolated autonomic failure in one patient. Amyloid neuropathy was clinically suspected in 22.6% of nonfamilial cases. Familial amyloid neuropathy was suspected in eight patients. Genetic testing detected ATTR and gelsolin mutation in one each of tested patients. Nerve biopsies revealed characteristic birefringent amyloid deposits stained mahogany brown by Congo red predominantly surrounding endoneurial microvessels (34.5%), also in perineurium and epineurium in 25.45% cases. Preferential loss of small diameter myelinated fibers was noted. Axonal degeneration or regeneration was conspicuously absent.

CONCLUSION

Amyloid neuropathy is uncommon (0.28% of nerve biopsies in our series). Nerve biopsy is essential for the diagnosis. We report our experience of amyloid neuropathy and underscore the importance of making an assiduous search for amyloid deposits in the appropriate setting. Awareness of this entity is important for early diagnosis in the light of emerging therapeutic advances.

Familial amyloidotic polyneuropathy and transthyretin

There has been much progress in our understanding of transthyretin (TTR)-related amyloidosis including familial amyloidotic polyneuropathy (FAP), senile systemic amyloidosis and its related disorders from many clinical and experimental aspects. FAP is an inherited severe systemic amyloidosis caused by mutated TTR, and characterized by amyloid deposition mainly in the peripheral nervous system and the heart. Liver transplantation is the only available treatment for the disease. FAP is now recognized not to be a rare disease, and to have many variations based on genetical and biochemical variations of TTR. This chapter covers the recent advances in the clinical and pathological aspects of, and therapeutic approaches to FAP, and the trend as to the molecular pathogenesis of TTR.