Clinical Penetrance of the Transthyretin V122I Variant in Older Black Patients With Heart Failure: The SCAN-MP (Screening for Cardiac Amyloidosis With Nuclear Imaging in Minority Populations) Study

Navigating the penetrance and phenotypic spectrum of inherited cardiomyopathies

Inherited cardiomyopathies are genetic diseases that can lead to heart failure and sudden cardiac death. These conditions tend to run in families, following an autosomal dominant pattern where first-degree relatives have a 50% chance of carrying the pathogenic variant. Despite significant advancements and increased accessibility of genetic testing, accurately predicting the phenotypic expression of these conditions remains challenging due to the inherent variability in their clinical manifestations and the incomplete penetrance observed. This poses challenges in providing patient care and effectively communicating the potential risk of future disease to patients and their families. To address these challenges, this review aims to synthesize the available evidence on penetrance, expressivity, and factors influencing disease expression to improve communication and risk assessment for patients with inherited cardiomyopathies and their family members.

Unlocking Diversity in Cardiovascular Clinical Research: Lessons from the Screening for Cardiac Amyloidosis With Nuclear Imaging in a Minority Populations Study

BACKGROUND

The Screening for Cardiac Amyloidosis with Nuclear Imaging in Minority Populations study seeks to determine the prevalence of transthyretin cardiac amyloidosis (ATTR-CA) among older Black or Caribbean Hispanic individuals with heart failure and an increased wall thickness. We noticed varied recruitment percentages across the recruiting sites and sought to determine the factors associated with greater percentage enrollment of eligible participants.

METHODS

The percentage of enrolled to eligible participants was calculated across study sites. Baseline demographic and clinical characteristics, health literacy, trust in providers, perceived discrimination, area deprivation index (ADI) and English proficiency were compared by site using Kruskal-Wallis's test or one-way ANOVA for continuous variables and the Chi-Square test or Fisher's exact test for categorical variables. Wilcoxon rank sum and Chi-Square tests, with multiple comparisons correction using the false discovery rate (FDR) method, were used as post-hoc analysis when results were statistically significant.

RESULTS

Among the four recruiting sites, Boston Medical Center, Columbia University Irving Medical Center, Harlem Hospital and Yale University, which employed different recruitment approaches, the percentage of participants enrolled among eligible participants differed, with the highest rate at Harlem Hospital (n=149 of 310, 48%), followed by Yale University (n=27 of 67, 40%), Boston University (n=247 of 655, 38%), and Columbia University (n=137of 442, 32%), p <0.01. Direct recruitment by the primary cardiovascular care team providing clinical care was associated with higher percent enrolled across sites as were higher education levels and English proficiency. Enrollment differences across sites were not associated with the number of chronic diseases, physician trust, perceived discrimination, or health literacy.

CONCLUSIONS

Recruitment of eligible under-represented minorities (URMs) in SCAN-MP was associated with approaches employed in recruitment, including direct initial contact by the primary cardiovascular care team providing the potential participant's clinical care. Such data may help improve approaches to more successful recruitment of URMs in clinical research.

Cardiac Amyloidosis Due to Transthyretin Protein: A Review

Importance

Systemic amyloidosis from transthyretin (ATTR) protein is the most common type of amyloidosis that causes cardiomyopathy.

Observations

Transthyretin (TTR) protein transports thyroxine (thyroid hormone) and retinol (vitamin A) and is synthesized predominantly by the liver. When the TTR protein misfolds, it can form amyloid fibrils that deposit in the heart causing heart failure, heart conduction block, or arrhythmia such as atrial fibrillation. The biological processes by which amyloid fibrils form are incompletely understood but are associated with aging and, in some patients, affected by inherited variants in the TTR genetic sequence. ATTR amyloidosis results from misfolded TTR protein deposition. ATTR can occur in association with normal TTR genetic sequence (wild-type ATTR) or with abnormal TTR genetic sequence (variant ATTR). Wild-type ATTR primarily manifests as cardiomyopathy while ATTR due to a genetic variant manifests as cardiomyopathy and/or polyneuropathy. Approximately 50 000 to 150 000 people in the US have heart failure due to ATTR amyloidosis. Without treatment, heart failure due to ATTR amyloidosis is associated with a median survival of approximately 5 years. More than 130 different inherited genetic variants in TTR exist. The most common genetic variant is Val122Ile (pV142I), an allele with an origin in West African countries, that is present in 3.4% of African American individuals in the US or approximately 1.5 million persons. The diagnosis can be made using serum free light chain assay and immunofixation electrophoresis to exclude light chain amyloidosis combined with cardiac nuclear scintigraphy to detect radiotracer uptake in a pattern consistent with amyloidosis. Loop diuretics, such as furosemide, torsemide, and bumetanide, are the primary treatment for fluid overload and symptomatic relief of patients with ATTR heart failure. An ATTR-directed therapy that inhibited misfolding of the TTR protein (tafamidis, a protein stabilizer), compared with placebo, reduced mortality from 42.9% to 29.5%, reduced hospitalizations from 0.7/year to 0.48/year, and was most effective when administered early in disease course.

Conclusions and Relevance

ATTR amyloidosis causes cardiomyopathy in up to approximately 150 000 people in the US and tafamidis is the only currently approved therapy. Tafamidis slowed progression of ATTR amyloidosis and improved survival and prevented hospitalization, compared with placebo, in people with ATTR-associated cardiomyopathy.

Advances in the diagnosis and treatment of transthyretin amyloid cardiomyopathy

Transthyretin amyloid cardiomyopathy (ATTR-CM) is an underrecognized cause of heart failure (HF). ATTR-CM can lead to a number of cardiovascular manifestations including HF, rhythm disturbances, and valvular disease that ultimately limit quality of life and prognosis. Due to advances in diagnostic modalities and therapeutic options, the prevalence of ATTR-CM is rising. There are several classes of medications under active investigation, though most therapies are most efficacious if instituted early on in the disease course. As such, early clinical recognition and prompt diagnosis are crucial to improving disease related outcomes. In this review, we highlight clinical manifestations of ATTR-CM as well as contemporary diagnostic and treatment approaches to the disease.

Practical Guidance for the Use of Patisiran in the Management of Polyneuropathy in Hereditary Transthyretin-Mediated Amyloidosis

Variant transthyretin amyloidosis (ATTRv) is an autosomal dominant inherited genetic disorder that affects 5000-10,000 people worldwide. It is caused by mutations in the transthyretin (TTR) gene and results in amyloid deposition in a variety of organs due to abnormal accumulation of TTR protein fibrils. Although this is a multisystem disorder, the heart and peripheral nerves are the preferentially affected organs. Over 150 TTR gene mutations have been associated with this disease and the clinical phenotype can vary significantly. Severe forms of the disorder can be fatal. Fortunately, the oligonucleotide-based therapy era has resulted in the development of several novel treatment options. Patisiran is a small interfering RNA (siRNA) encapsulated in a lipid nanoparticle that targets both mutant and wild-type TTR and results in significant reductions of the TTR protein in the serum and in tissue deposits. Patisiran has been approved for treatment of adults with polyneuropathy due to hereditary TTR-mediated amyloidosis in both the United States (US) and European Union (EU). In this review, we will discuss the development of patisiran, the clinical trials that lead to treatment approval, and provide guideline parameters for use in clinical practice.  .