A nonhereditary form of systemic amyloidosis associated with wild-type transthyretin causes heart involvement predominantly in elderly men (systemic senile amyloidosis, or SSA). However, hereditary transthyretin-related amyloidosis (ATTR) is the most frequent form of familial systemic amyloidosis, a group of severe diseases with variable neurological and organ involvement. ATTR remains a challenging and widely underdiagnosed condition, owing to its extreme phenotypic variability: the clinical spectrum of the disease ranges from an almost exclusive neurologic involvement to a strictly cardiac presentation. Such heterogeneity principally results from differential effects of the various reported transthyretin mutations, the geographic region the patient is from and, in the case of the most common mutation, Val30Met, whether or not large foci of cases occur (endemic versus nonendemic aggregation). Genetic or environmental factors (such as age, sex, and amyloid fibril composition) also contribute to the heterogeneity of ATTR, albeit to a lesser extent. The existence of exclusively or predominantly cardiac phenotypes should lead clinicians to consider the possibility of ATTR in all patients who present with an unexplained increase in left ventricular wall thickness at echocardiography. Assessment of such patients should include an active search for possible red flags that can point to the correct final diagnosis.

The clinical spectrum of ATTRwt is heterogeneous and differs from the classic phenotype: women are affected in a significant proportion; asymmetric LV hypertrophy and impaired LVEF are not rare and only a minority have low QRS voltages. Clinicians should be aware of the broad clinical spectrum of ATTRwt to correctly identify an entity for which a number of disease-modifying treatments are under investigation.

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A clinically relevant subset of Caucasian ATTR patients present with an exclusively cardiac phenotype, mimicking HCM or SSA. Echocardiographic and ECG findings are useful to differentiate ATTR from HCM but not from SSA. The role of liver transplantation in these patients should be reconsidered.

Cardiac amyloidosis (CA) is often misdiagnosed because of both physician-related and disease-related reasons including: fragmented knowledge among different specialties and subspecialties, shortage of centres and specialists dedicated to disease management, erroneous belief it is an incurable disease, rarity of the condition, intrinsic phenotypic heterogeneity, genotypic heterogeneity in transthyretin-related forms and the necessity of target organ tissue histological diagnosis in the vast majority of cases. Pitfalls, incorrect beliefs and deceits challenge not only the path to the diagnosis of CA but also the precise identification of aetiological subtype. The awareness of this condition is the most important prerequisite for the management of the risk of underdiagnoses and misdiagnosis. Almost all clinical, imaging and laboratory tests can be misinterpreted, but fortunately each of these diagnostic steps can also offer diagnostic "red flags" (i.e. highly suggestive findings that can foster the correct diagnostic suspicion and facilitate early, timely diagnosis). This is especially important because outcomes in CA are largely driven by the severity of cardiac dysfunction and emerging therapies are aimed at preventing further amyloid deposition.

The clinical phenotype of familial ATTR amyloidosis depends to some extent on the particular mutation, but differences exist also within mutations. We have previously described that two types of amyloid fibril compositions exist among Swedish ATTRV30M amyloidosis patients, one consisting of a mixture of intact and fragmented ATTR (type A) and one consisting of mainly intact ATTR (type B). The fibril types are correlated to phenotypic differences. Patients with ATTR fragments have a late onset and develop cardiomyopathy, while patients without fragments have an early onset and less myocardial involvement. The present study aimed to determine whether this correlation between fibril type and phenotype is valid for familial ATTR amyloidosis in general. Cardiac or adipose tissues from 63 patients carrying 29 different TTR non-V30M mutations as well as 13 Japanese ATTRV30M patients were examined. Fibril type was determined by western blotting and compared to the patients' age of onset and degree of cardiomyopathy. All ATTR non-V30M patients had a fibril composition with ATTR fragments, except two ATTRY114C patients. No clear conclusions could be drawn about a phenotype to fibril type correlation among ATTR non-V30M patients. In contrast, Japanese ATTRV30M patients showed a similar correlation as previously described for Swedish ATTRV30M patients. This study shows that a fibril composition with fragmented ATTR is very common in ATTR amyloidosis, and suggests that fibrils composed of only full-length ATTR is an exception found only in a subset of patients.

Aims We aimed to assess carpal tunnel syndrome (CTS) prevalence in transthyretin (TTR)‐related and light‐chain amyloidosis (AL), comparing it to the general population, adjusted for age and gender. In TTR‐related amyloidosis (ATTR) we investigated (i) CTS prevalence in relation to genotype, cardiac amyloidosis (CA), age and gender; (ii) CTS role as an incremental risk factor for CA; (iii) temporal relationship between CTS and CA; and (iv) CTS prognostic role. Methods and results Data from 538 subjects (166 hereditary ATTR, 107 wild‐type ATTR, 196 AL amyloidosis, and 69 TTR mutation carriers; 64% male, median age 62.4 years), evaluated at our centre (Bologna, Italy), were analysed and compared to a published cohort of 14.9 million people, in which incidence rates of CTS had been estimated. CTS prevalence was highest in ATTR patients with CA (20.3% vs. 4.1% in the general population), while it was comparable to the general population when CA was absent and in AL patients. CTS standardized incidence rates were markedly elevated in ATTR males in the eighth decade of life (13.08 in hereditary ATTR, 15.5 in wild‐type ATTR). The risk of developing CA was greater in ATTR patients with CTS; the probability of having CTS was highest 5–9 years prior to CA diagnosis. CTS was an independent mortality risk factor in ATTR. Conclusions Compared to general population the adjusted prevalence of CTS is higher among elderly men with ATTR; CTS is a prognostic marker in ATTR, independently of cardiac involvement, and precedes CA diagnosis by 5–9 years. The awareness of this association and time delay offers the possibility of an early pre‐clinical ATTR‐CA diagnosis.

Background: Truncating variants in the TTN gene (TTNtv) are the commonest cause of heritable dilated cardiomyopathy. This study aimed to study the phenotypes and outcomes of TTNtv carriers. Methods: Five hundred thirty-seven individuals (61% men; 317 probands) with TTNtv were recruited in 14 centers (372 [69%] with baseline left ventricular systolic dysfunction [LVSD]). Baseline and longitudinal clinical data were obtained. The primary end point was a composite of malignant ventricular arrhythmia and end-stage heart failure. The secondary end point was left ventricular reverse remodeling (left ventricular ejection fraction increase by ≥10% or normalization to ≥50%). Results: Median follow-up was 49 (18–105) months. Men developed LVSD more frequently and earlier than women (45±14 versus 49±16 years, respectively; P =0.04). By final evaluation, 31%, 45%, and 56% had atrial fibrillation, frequent ventricular ectopy, and nonsustained ventricular tachycardia, respectively. Seventy-six (14.2%) individuals reached the primary end point (52 [68%] end-stage heart failure events, 24 [32%] malignant ventricular arrhythmia events). Malignant ventricular arrhythmia end points most commonly occurred in patients with severe LVSD. Male sex (hazard ratio, 1.89 [95%CI, 1.04–3.44]; P =0.04) and left ventricular ejection fraction (per 10% decrement from left ventricular ejection fraction, 50%; hazard ratio, 1.63 [95%CI, 1.30–2.04]; P <0.001) were independent predictors of the primary end point. Two hundred seven of300 (69%) patients with LVSD had evidence of left ventricular reverse remodeling. In a subgroup of 29 of74 (39%) patients with initial left ventricular reverse remodeling, there was a subsequent left ventricular ejection fraction decrement. TTNtv location was not associated with statistically significant differences in baseline clinical characteristics, left ventricular reverse remodeling, or outcomes on multivariable analysis ( P =0.07). Conclusions: TTNtv is characterized by frequent arrhythmia, but malignant ventricular arrhythmias are most commonly associated with severe LVSD. Male sex and LVSD are independent predictors of outcomes. Mutation location does not impact clinical phenotype or outcomes.