Amyloidosis is a condition marked by the accumulation of insoluble beta-sheet fibrillar protein aggregates in tissues that can be acquired or hereditary. Hereditary amyloidogenic transthyretin (hATTR) amyloidosis is an autosomal-dominant disease caused by pathogenic variants in the TTR gene. The TTR protein is essential for transporting thyroxine and retinol-binding protein and is primarily synthesized in the liver, becoming unstable as a result of the pathogenic mutations. Inherited pathogenic variants lead to the protein’s misfolding, aggregation, and deposition as amyloid fibrils in different organs, resulting in progressive multisystem dysfunction. hATTR amyloidosis is a heterogenous disease, characterized by a wide range of clinical manifestations affecting the peripheral (both somatic and autonomic) nervous system, heart, kidneys, and central nervous system (CNS); however, the heart and peripheral nerves appear to be the main targets of the TTR-related pathologic process. Without treatment, the prognosis is poor, with an average life expectancy of 7-11 years; however, in recent years, the development of new therapeutics has brought new hope to patients.
Here are five things to know about hereditary amyloidosis.
1. Diagnosis of hereditary amyloidosis requires a high level of suspicion.
The diagnosis of hATTR amyloidosis presents a significant challenge, particularly in nonendemic regions where a lack of family history and heterogeneity of clinical presentation can delay diagnosis by 4-5 years. A timely diagnosis requires clinicians to maintain a high index of suspicion, especially when evaluating patients with neuropathic symptoms. Early diagnosis is crucial to begin patients on recently available disease-modifying therapies that can slow the disease course. Failure to recognize is the major barrier to improved patient outcomes.
Confirming the diagnosis involves detecting amyloid deposits in tissue biopsy specimens from various possible sites, including the skin, nerves, myocardium, and others. However, the diagnosis can be challenging owing to the uneven distribution of amyloid fibrils, sometimes requiring multiple biopsies or alternative diagnostic approaches, such as TTR gene sequencing, to confirm the presence of an amyloidogenic pathogenic variant. Biopsy for hATTR amyloidosis is not required if imaging of the clinical phenotype and genetic testing are consistent.
Once diagnosed, the assessment of organ involvement is essential, using nerve conduction studies, cardiac investigations (eg, echocardiography, ECG, scintigraphy), ophthalmologic assessments, and complete renal function evaluations to fully understand the extent of disease impact.
2. Hereditary amyloidosis diseases are classified into two primary categories.
Hereditary amyloidosis represents a group of diseases caused by inherited gene mutations and is classified into two main types: ATTR (transthyretin-related) and non-TTR. Most cases of hereditary amyloidosis are associated with the TTR gene. Mutations in this protein lead to different forms of ATTR amyloidosis, categorized on the basis of the specific mutation involved, such as hATTR50M (genotype Val50Met), which is the most prevalent form.
ATTR mutations result in a variety of health issues, manifesting in three primary forms:
- Neuropathic ATTR (genotype Val50Met): Early symptoms include sensorimotor polyneuropathy of the legs, carpal tunnel syndrome, autonomic dysfunction, constipation/diarrhea, and impotence; late symptoms include cardiomyopathy, vitreous opacities, glaucoma, nephropathy, and CNS symptoms.
- Cardiac ATTR (genotype Val142Ile): This type is characterized by cardiomegaly, conduction block, arrhythmia, anginal pain, congestive heart failure, and sudden death.
- Leptomeningeal ATTR (genotype Asp38Gly): This is characterized by transient focal neurologic episodes, intracerebral and/or subarachnoid hemorrhages, dementia, ataxia, and psychosis.
Non-TTR amyloidoses are rarer than are ATTR variations and involve mutations in different genes that also have significant health impacts. These include proteins such as apolipoprotein AI, fibrinogen A alpha, lysozyme, apolipoprotein AII, gelsolin, and cystatin C. Each type contributes to a range of symptoms and requires individualized management approaches.
3. Heightened disease awareness has increased the recognized prevalence of hereditary amyloidosis.
hATTR amyloidosis has historically been recognized as a rare disease, with significant clusters in Portugal, Brazil, Sweden, and Japan and alongside smaller foci in regions such as Cyprus and Majorca. This disease›s variable incidence across Europe is now perceived to be on the rise. It is attributed to heightened disease awareness among healthcare providers and the broader availability of genetic testing, extending its recognized impact to at least 29 countries globally. The genetic landscape of hATTR amyloidosis is diverse, with over 140 mutations identified in the TTR gene. Among these, the Val50Met mutation is particularly notable for its association with large patient clusters in the endemic regions.
Morbidity and mortality associated with hATTR amyloidosis are significant, with an average lifespan of 7-11 years post diagnosis; however, survival rates can vary widely depending on the specific genetic variant and organ involvement. Early diagnosis can substantially improve outcomes; yet, for many, the prognosis remains poor, especially in cases dominated by cardiomyopathy. Genetics play a central role in the disease›s transmission, with autosomal-dominant inheritance patterns and high penetrance among carriers of pathogenic mutations. Research continues to uncover the broad spectrum of genetic variations contributing to hATTR amyloidosis, with ongoing studies poised to expand our understanding of its molecular underpinnings and potential treatment options.
4. The effect on quality of life is significant both in patients living with hATTR amyloidosis and their caregivers.
hATTR amyloidosis imposes a multifaceted burden on patients and their caregivers as the disease progresses. Symptoms range from sensorimotor impairment and gastrointestinal or autonomic dysfunction to heart failure, leading to significant health-related quality-of-life deficits. The systemic nature of hATTR amyloidosis significantly affects patients› lifestyles, daily activities, and general well-being, especially because it typically manifests in adulthood — a crucial time for occupational changes. The progression of hATTR amyloidosis exacerbates the challenges in maintaining employment and managing household chores, with symptomatic patients often unable to work and experiencing difficulties with absenteeism and presenteeism when they are able to work.
hATTR amyloidosis leads to physical, mental, occupational, and social limitations for patients, and it also places a considerable strain on their families and caregivers, who report poor mental health, work impairment, and a high time commitment (mean, 45.9 h/wk) to providing care.
5. There have been significant advancements in therapeutic options for early-stage hATTR amyloidosis.
After diagnosis, prompt initiation of treatment is recommended to delay the progression of hATTR amyloidosis; a multidisciplinary approach is essential, incorporating anti-amyloid therapy to inhibit further production and/or deposition of amyloid aggregates. Treatment strategies also include addressing symptomatic therapy and managing cardiac, renal, and ocular involvement. Although many therapies have been developed, especially for the early stages of hATTR amyloidosis, therapeutic benefits for patients with advanced disease remain limited.
Recent advancements in the treatment of hATTR amyloidosis have introduced RNA-targeted therapies including patisiran, vutrisiran, and eplontersen, which have shown efficacy in reducing hepatic TTR synthesis and the aggregation of misfolded monomers into amyloid deposits. These therapies, ranging from small interfering RNA formulations to antisense oligonucleotides, offer benefits in managing both cardiomyopathy and neuropathy associated with hATTR amyloidosis , administered through various methods, including intravenous infusions and subcutaneous injections. In addition, the stabilization of TTR tetramers with the use of drugs such as tafamidis and diflunisal has effectively prevented the formation of amyloidogenic monomers. Moreover, other investigational agents, including TTR stabilizers like acoramidis and tolcapone, as well as novel compounds that inhibit amyloid formation and disrupt fibrils, are expanding the therapeutic landscape for hATTR amyloidosis , providing hope for improved management of this complex condition.
Dr. Gertz is a professor and consultant in the Department of Hematology, Mayo Clinic, Rochester, Minnesota. He has disclosed the following relevant financial relationships: Received income in an amount equal to or greater than $250 from AstraZeneca, Ionis, and Alnylym.
A version of this article appeared on Medscape.com.