Wild-type transthyretin amyloidosis as a cause of heart failure with preserved ejection fraction.

AIMS: Heart failure with preserved ejection fraction (HFpEF) is a heterogeneous clinical syndrome with multiple underlying causes. Wild-type transthyretin (TTR) amyloidosis (ATTRwt) is an underdiagnosed cause of HFpEF that might benefit from new specific treatments. ATTRwt can be diagnosed non-invasively by (99m)Tc-3,3-diphosphono-1,2-propanodicarboxylic acid ((99m)Tc-DPD) scintigraphy. We sought to determine the prevalence of ATTRwt among elderly patients admitted due to HFpEF. METHODS AND RESULTS: We prospectively screened all consecutive patients ≥60 years old admitted due to HFpEF [left ventricular (LV) ejection fraction ≥50%] with LV hypertrophy (≥12 mm). All eligible patients were offered a (99m)Tc-DPD scintigraphy. The study included 120 HFpEF patients (59% women, 82 ± 8 years). A total of 16 patients (13.3%; 95% confidence interval: 7.2-19.5) showed a moderate-to-severe uptake on the (99m)Tc-DPD scintigraphy. All patients with a positive scan underwent genetic testing of the TTR gene, and no mutations were found. An endomyocardial biopsy was performed in four patients, confirming ATTRwt in all cases. There were no differences in age, gender, hypertension, diabetes, coronary artery disease, or atrial fibrillation between ATTRwt patients and patients with other HFpEF forms. Although patients with ATTRwt exhibited higher median N-terminal pro-brain natriuretic peptide (6467 vs. 3173 pg/L; P = 0.019), median troponin I (0.135 vs. 0.025 µg/L; P < 0.001), mean LV maximal wall thickness (17 ± 3.4 vs. 14 ± 2.5 mm; P = 0.001), rate of pericardial effusion (44 vs. 19%; P = 0.047), and rate of pacemakers (44 vs. 12%; P = 0.004), clinical overlap between ATTRwt and other HFpEF forms was high. CONCLUSION: ATTRwt is an underdiagnosed disease that accounts for a significant number (13%) of HFpEF cases. The effect of emerging TTR-modifying drugs should be evaluated in these patients.

Cardiac dysfunction in mitochondrial disease. Clinical and molecular features.

BACKGROUND: Mitochondrial disorders (MD) are multisystem diseases that arise as a result of dysfunction of the oxidative phosphorylation system. The predominance of neuromuscular manifestations in MD could mask the presence of other clinical phenotypes such as cardiac dysfunction. Reported here is a retrospective study, the main objective of which was to characterize the clinical and molecular features of a cohort of patients with cardiomyopathy and MD. METHODS AND RESULTS: Hospital charts of 2,520 patients, evaluated for presumed MD were reviewed. The clinical criterion for inclusion in this study was the presence of a cardiac disturbance accompanied by a mitochondrial dysfunction. Only 71 patients met this criterion. The mitochondrial genome (mtDNA) could be sequenced only in 45 and the pathogenicity of 2 of the found changes was investigated using transmitochondrial cybrids. Three nucleotide changes in mtDNA that may be relevant and 3 with confirmed pathogenicity were identified but no mutations were found in the 13 nuclear genes analyzed. CONCLUSIONS: The mtDNA should be sequenced in patients with cardiac dysfunction accompanied by symptoms suggestive of MD; databases should be carefully and periodically screened to discard mitochondrial variants that could be associated with MD; functional assays are necessary to classify mitochondrial variants as pathogenic or polymorphic; and additional efforts must be made in order to identify nuclear genes that can explain some as yet uncharacterized molecular features of mitochondrial cardiomyopathy.

Mitochondrial haplogroups associated with end-stage heart failure and coronary allograft vasculopathy in heart transplant patients.

AIMS: Mitochondrial haplogroups are known to influence individual predisposition to a wide spectrum of metabolic and degenerative diseases, including ischaemic cardiovascular diseases. We have examined the influence of the mitochondrial DNA (mtDNA) background on the development of human end-stage heart failure (HF) in patients undergoing heart transplantation. The influence of mtDNA haplogroups on the incidence of transplant-related complications, mainly cardiac allograft vasculopathy (CAV), and on post-transplant survival was also studied. METHODS AND RESULTS: The most common mitochondrial haplogroups in European populations were genotyped in 450 heart transplant recipients, 248 heart transplant donors, and 206 healthy controls. Mitochondrial haplogroups were determined by PCR amplification of short mtDNA fragments, followed by restriction fragment length polymorphism analysis. After adjustment for age and sex the frequency of haplogroup H was significantly higher in heart transplant recipients than in controls [OR: 1.86 (95% confidence intervals, CI: 1.27-2.74), P= 0.014], and in heart donors [OR: 1.47 (95% CI: 0.99-2.19), P= 0.032]. Likewise, haplogroup Uk was found significantly more frequently among CAV patients than in non-CAV heart allograft recipients [OR: 4.1 (95% CI: 1.51-11.42), P= 0.042]. Finally, heart donor haplogroups had no influence on the morbidity or mortality after heart transplantation. CONCLUSIONS: Mitochondrial haplogroups behave like risk factors for the progress to end-stage HF in a Spanish cardiac transplant population. Mitochondrial DNA variants may have some influence on the appearance of cardiac transplant complications.

Clinical profile and outcome of cardiac amyloidosis in a Spanish referral center.

INTRODUCTION AND OBJECTIVES: Cardiac amyloidosis (CA) is produced by amyloid fiber deposition in the myocardium. The most frequent forms are those caused by light chains (AL) and transthyretin (ATTR). Our objective was to describe the diagnosis, treatment and outcomes of CA in a specialized Spanish center. METHODS: We included all patients diagnosed with CA in Hospital Universitario Puerta de Hierro Majadahonda from May 2008 to September 2018. We analyzed their clinical characteristics, outcomes, and survival. RESULTS: We included 180 patients with CA, of whom 64 (36%) had AL (50% men; mean age, 65±11 years) and 116 had ATTR (72% men; mean age 79±11 years; 18 with hereditary ATTR). The most common presentation was heart failure in both groups (81% in AL and 45% in ATTR, P <.01). Other forms of presentation in ATTR patients were atrial arrhythmias (16%), conduction disorders (6%), and incidental finding (6%); 70 patients (40%), had a previous alternative cardiac diagnosis. Diagnosis was noninvasive in 75% of ATTR patients. Diagnostic delay was higher in ATTR (2.8±4.3 vs 0.6±0.7 years, P <.001), but mortality was greater in AL patients (48% vs 32%, P=.028). Independent predictors of mortality were AL subtype (HR, 6.16; 95%CI, 1.56-24.30; P=.01), female sex (HR, 2.35; 95%CI, 1.24-4.46; P=.01), and NYHA functional class III-IV (HR, 2.07; 95%CI, 1.11-3.89; P=.02). CONCLUSIONS: CA is a clinical challenge, with wide variability in its presentation depending on the subtype, leading to diagnostic delay and high mortality. Improvements are needed in the early diagnosis and treatment of these patients.

[Mitochondrial DNA depletion and POLG mutations in a patient with sensory ataxia, dysarthria and ophthalmoplegia]. / Depleción del ácido desoxirribonucleico mitocondrial y mutaciones de POLG en un paciente con neuropatía sensorial atáxica, disartria y oftalmoplejía.

BACKGROUND AND OBJECTIVE: A broad spectrum of clinical disorders is produced by mutations in the DNA polymerase gamma mitochondrial (POLG) gene which are associated with altered mitochondrial DNA (mtDNA) integrity. The majority of disorders characterized by multiple mtDNA deletions present with progressive external ophthalmoplegia, though this feature is not usually found in syndromes caused by mtDNA depletion. We report on a patient having the clinical triad of sensory ataxic neuropathy, dysarthria and ophthalmoplegia (SANDO), POLG mutations and reduced muscle mtDNA content. PATIENT AND METHODS: The patient presented with sensory ataxic neuropathy, dysarthria and ophthalmoplegia. Diagnosis was established by using histological and genetic procedures (nerve biopsy, mtDNA molecular analysis in skeletal muscle and mutation screening in the POLG gene). RESULTS: Sural nerve biopsy showed marked loss of large myelinated fibers. Skeletal muscle analysis revealed multiple mtDNA deletions, a marked decrease in mtDNA copy number and pathogenic mutations in the POLG gene. CONCLUSIONS: POLG mutations must be considered in all patients with the cardinal findings of the SANDO phenotype, without taking into account the type of abnormalities encountered in the mitochondrial genome.

Clinical characteristics and determinants of the phenotype in TMEM43 arrhythmogenic right ventricular cardiomyopathy type 5.

BACKGROUND: Arrhythmogenic right ventricular cardiomyopathy type V (ARVC-5) is the most aggressive heterozygous form of ARVC. It is predominantly caused by a fully penetrant mutation (p.S358L) in the nondesmosomal gene TMEM43-endemic to Newfoundland, Canada. To date, all familial cases reported worldwide share a common ancestral haplotype. It is unknown whether the p.S358L mutation by itself causes ARVC-5 or whether the disease is influenced by genetic or environmental factors. OBJECTIVE: The purpose of this study was to examine the phenotype, clinical course, and the impact of exercise on patients with p.S358L ARVC-5 without the Newfoundland genetic background. METHODS: We studied 62 affected individuals and 73 noncarriers from 3 TMEM43-p.S358L Spanish families. The impact of physical activity on the phenotype was also evaluated. RESULTS: Haplotype analysis revealed that the 3 Spanish families were unrelated to patients with ARVC-5 with the Newfoundland genetic background. Two families shared 10 microsatellite markers in a 4.9 cM region surrounding TMEM43; the third family had a distinct haplotype. The affected individuals showed a 38.7% incidence of sudden cardiac death, which was higher in men. Left ventricular involvement was common, with 40% of mutation carriers showing a left ventricular ejection fraction of <50%. Compared with noncarriers, the R-wave voltage in lead V3 was lower (3.2 ± 2.8 mV vs 7.5 ± 3.6 mV; P < .001) and QRS complex in right precordial leads wider (104.7 ± 24.0 ms vs 88.2 ± 7.7 ms; P = .001). A history of vigorous exercise showed a trend toward more ventricular arrhythmias only in women (P = .053). CONCLUSION: ARVC-5 is associated with a high risk of sudden cardiac death and characteristic clinical and electrocardiographic features irrespective of geographical origin and genetic background. Our data suggest that, as in desmosomal ARVC, vigorous physical activity could aggravate the phenotype of TMEM43 mutation carriers.

OPA1 mutations induce mitochondrial DNA instability and optic atrophy 'plus' phenotypes.

Mutations in OPA1, a dynamin-related GTPase involved in mitochondrial fusion, cristae organization and control of apoptosis, have been linked to non-syndromic optic neuropathy transmitted as an autosomal-dominant trait (DOA). We here report on eight patients from six independent families showing that mutations in the OPA1 gene can also be responsible for a syndromic form of DOA associated with sensorineural deafness, ataxia, axonal sensory-motor polyneuropathy, chronic progressive external ophthalmoplegia and mitochondrial myopathy with cytochrome c oxidase negative and Ragged Red Fibres. Most remarkably, we demonstrate that these patients all harboured multiple deletions of mitochondrial DNA (mtDNA) in their skeletal muscle, thus revealing an unrecognized role of the OPA1 protein in mtDNA stability. The five OPA1 mutations associated with these DOA 'plus' phenotypes were all mis-sense point mutations affecting highly conserved amino acid positions and the nuclear genes previously known to induce mtDNA multiple deletions such as POLG1, PEO1 (Twinkle) and SLC25A4 (ANT1) were ruled out. Our results show that certain OPA1 mutations exert a dominant negative effect responsible for multi-systemic disease, closely related to classical mitochondrial cytopathies, by a mechanism involving mtDNA instability.

Mitochondrial DNA depletion syndrome due to mutations in the RRM2B gene.

Mitochondrial DNA depletion syndrome (MDS) is characterized by a reduction in mtDNA copy number and has been associated with mutations in eight nuclear genes, including enzymes involved in mitochondrial nucleotide metabolism (POLG, TK2, DGUOK, SUCLA2, SUCLG1, PEO1) and MPV17. Recently, mutations in the RRM2B gene, encoding the p53-controlled ribonucleotide reductase subunit, have been described in seven infants from four families, who presented with various combinations of hypotonia, tubulopathy, seizures, respiratory distress, diarrhea, and lactic acidosis. All children died before 4 months of age. We sequenced the RRM2B gene in three unrelated cases with unexplained severe mtDNA depletion. The first patient developed intractable diarrhea, profound weakness, respiratory distress, and died at 3 months. The other two unrelated patients had a much milder phenotype and are still alive at ages 27 and 36 months. All three patients had lactic acidosis and severe depletion of mtDNA in muscle. Muscle histochemistry showed RRF and COX deficiency. Sequencing the RRM2B gene revealed three missense mutations and two single nucleotide deletions in exons 6, 8, and 9, confirming that RRM2B mutations are important causes of MDS and that the clinical phenotype is heterogeneous and not invariably fatal in infancy.

Association of novel POLG mutations and multiple mitochondrial DNA deletions with variable clinical phenotypes in a Spanish population.

BACKGROUND: Both dominant and recessive mutations were reported in the gene encoding the mitochondrial (mt) DNA polymerase gamma (POLG) in patients with progressive external ophthalmoplegia (PEO). Phenotypes other than PEO were recently documented in patients with mutations in the POLG gene. OBJECTIVE: To screen patients with mitochondrial disease and multiple mtDNA deletions in muscle for mutations in the coding regions of the POLG, PEO1, and SLC25A4 genes. DESIGN: To identify the underlying molecular defect in a group of patients with multiple mtDNA deletions comparing their molecular genetic findings with those of healthy controls. PATIENTS: Twenty-four patients (16 men and 8 women) diagnosed with mitochondrial disease and having multiple mtDNA deletions in muscle by Southern blot analysis. Thirteen patients had PEO; 2 had PEO alone, 4 had PEO and myopathy, and 5 had PEO and multisystem involvement. Four patients had multisystem disease without PEO. The remaining 9 patients had isolated myopathy. DNA from 100 healthy individuals was also studied. RESULTS: No mutation was identified in the PEO1 or SLC25A4 genes. Nine POLG mutations were observed in 6 of 24 patients. Four novel mutations were detected and mapped in the linker region (M603L) and in the pol domain of the enzyme (R853W; D1184N; R1146C). Five patients with PEO had mutations: 2 were compound heterozygotes, 1 was homozygous, and another showed a mutation in a single allele. The remaining patient also showed a sole mutation and had an unusual phenotype lacking ocular involvement. CONCLUSIONS: POLG molecular defects were found in 25% of our patients with multiple mtDNA deletions and mitochondrial disease. The uncommon phenotype found in 1 of these patients stresses the clinical variability of patients harboring POLG mutations. Molecular studies in the POLG gene should be addressed in patients with mitochondrial disease, particularly in those with PEO, and multiple mtDNA deletions.

Comparative analysis of the pathogenic mechanisms associated with the G8363A and A8296G mutations in the mitochondrial tRNA(Lys) gene.

Two mutations (G8363A and A8296G) in the mtDNA (mitochondrial DNA) tRNA(Lys) gene have been associated with severe mitochondrial diseases in a number of reports. Their functional significance, however, remains unknown. We have already shown that homoplasmic cybrids harbouring the A8296G mutation display normal oxidative phosphorylation, although the possibility of a subtle change in mitochondrial respiratory capacity remains an open issue. We have now investigated the pathogenic mechanism of another mutation in the tRNA(Lys) gene (G8363A) by repopulating an mtDNA-less human osteosarcoma cell line with mitochondria harbouring either this genetic variant alone or an unusual combination of the two mutations (A8296G+G8363A). Cybrids homoplasmic for the single G8363A or the A8296G+G8363A mutations have defective respiratory-chain enzyme activities and low oxygen consumption, indicating a severe impairment of the oxidative phosphorylation system. Generation of G8363A cybrids within a wild-type or the A8296G mtDNA genetic backgrounds resulted in an important alteration in the conformation of the tRNA(Lys), not affecting tRNA steady-state levels. Moreover, mutant cybrids have an important decrease in the proportion of amino-acylated tRNA(Lys) and, consequently, mitochondrial protein synthesis is greatly decreased. Our results demonstrate that the pathogenicity of the G8363A mutation is due to a change in the conformation of the tRNA that severely impairs aminoacylation in the absence of changes in tRNA stability. The only effect detected in the A8296G mutation is a moderate decrease in the aminoacylation capacity, which does not affect mitochondrial protein biosynthesis.

Parkinsonism, cognitive deficit and behavioural disturbance caused by a novel mutation in the polymerase gamma gene.

Polymerase γ (POLG) is the enzyme responsible for the replication and maintenance of mitochondrial DNA (mtDNA). Mutations in the POLG1 gene can lead to mitochondrial dysfunction, producing a wide range of neurological and non-neurological phenotypes. Neurological manifestations include ataxia, muscular weakness, epilepsy, progressive external ophthalmoplegia (PEO), ptosis, neuropathy, psychiatric disorders and, more rarely, parkinsonism. We present the case of an 80-year old female patient with a history of PEO, ptosis, childish behaviour, obsessive disorder, cognitive decline, and parkinsonism. A comprehensive study showed striatal dopamine deficiency on DaT Scan and ragged red fibres as evidenced by Gomori staining in a biopsy of the biceps brachii. Multiple deletions of mtDNA were detected, and sequencing of the POLG1 gene identified a novel substitution, 2834A>T, in exon 18, changing the p.His945Leu amino acid. In silico analysis using PolyPhen-2 (http://genetics.bwh.hardvard.edu/pph2/) predicted that this change is probably damaging, with a score of 1.0 (0-1).

The A8296G mtDNA mutation associated with several mitochondrial diseases does not cause mitochondrial dysfunction in cybrid cell lines.

Transmitochondrial cybrid cell lines homoplasmic for the A8296G mtDNA transition, a mutation associated with several mitochondrial diseases, have a normal oxidative phosphorylation function, as shown by oxygen consumption, lactate production, respiratory enzyme activities, and growth using galactose as the only source of energy. The synthesis of mitochondrial proteins is also similar in mutant and wild-type cybrids. Our results suggest that the A8296G mutation is a polymorphism and reinforce the necessity of performing functional studies to assess the pathogenicity of mtDNA mutations.

Apolipoprotein E, angiotensin-converting enzyme and alpha-1-antichymotrypsin genotypes are not associated with post-stroke dementia.

There is evidence that indicates the involvement of environmental and genetic factors in the pathogenesis of post-stroke dementia (PSD). In the present work, we examined different polygenic influences on the risk of PSD in a series of stroke patients. We studied 150 consecutive patients evaluated 3 months after suffering acute strokes. All patients were evaluated with a prospective standard protocol and genotyped for vascular disease-associated polymorphisms in the genes coding for apolipoprotein E (including apoE coding and apoE promoter polymorphisms), angiotensin-converting enzyme (ACE) and alpha-1-antichymotrypsin (ACT). Thirty-two cases (21.3%) resulted in dementia 3 months after the stroke. In patients with PSD, the frequency of apoE epsilon 4 (0.08), ACE-D (0.64), ACT-A (0.62) alleles and apoE gene promoter polymorphisms (-491/A, 0.88; -427/C, 0.02) was similar to that of patients without PSD (apoE epsilon 4: 0.10, p=0.79; ACE-D: 0.56, p=0.36; ACT-A: 0.51, p=0.21; -491/A: 0.86, p=1.00; -427/C: 0.08, p=0.29). Our data indicate that PSD is not associated with the genetic risk factors of vascular dementia (VD) that were studied, and that additional factors may contribute to the pathogenesis of PSD.

Co-occurrence of four nucleotide changes associated with an adult mitochondrial ataxia phenotype.

BACKGROUND: Mitochondrial DNA maintenance disorders are an important cause of hereditary ataxia syndrome, and the majority are associated with mutations in the gene encoding the catalytic subunit of the mitochondrial DNA polymerase (DNA polymerase gamma), POLG. Mutations resulting in the amino acid substitutions A467T and W748S are the most common genetic causes of inherited cerebellar ataxia in Europe. METHODS: We report here a POLG mutational screening in a family with a mitochondrial ataxia phenotype. To evaluate the likely pathogenicity of each of the identified changes, a 3D structural analysis of the PolG protein was carried out, using the Alpers mutation clustering tool reported previously. RESULTS: Three novel nucleotide changes and the p.Q1236H polymorphism have been identified in the affected members of the pedigree. Computational analysis suggests that the p.K601E mutation is likely the major contributing factor to the pathogenic phenotype. CONCLUSIONS: Computational analysis of the PolG protein suggests that the p.K601E mutation is likely the most significant contributing factor to a pathogenic phenotype. However, the co-occurrence of multiple POLG alleles may be necessary in the development an adult-onset mitochondrial ataxia phenotype.

The pathogenicity scoring system for mitochondrial tRNA mutations revisited.

Confirming the pathogenicity of mitochondrial tRNA point mutations is one of the classical challenges in the field of mitochondrial medicine. In addition to genetic and functional studies, the evaluation of a genetic change using a pathogenicity scoring system is extremely useful to discriminate between disease-causing mutations from neutral polymorphisms. The pathogenicity scoring system is very robust for confirming pathogenicity, especially of mutations that show impaired activity in functional studies. However, mutations giving normal results using the same functional approaches are disregarded, and this compromises the power of the system to rule out pathogenicity. We propose to include a new criterion in the pathogenicity scoring systems regarding mutations which fail to show any mitochondrial defect in functional studies. To evaluate this proposal we characterized two mutations, m.8296A>G and m.8347A>G, in the mitochondrial tRNA(L) (ys) gene (MT-TK) using trans-mitochondrial cybrid analysis. m.8347A>G mutation severely impairs oxidative phosphorylation, suggesting that it is highly pathogenic. By contrast, the behavior of cybrids homoplasmic for the m.8296A>G mutation is similar to cybrids containing wild-type mitochondrial DNA (mtDNA). The results indicate that including not only positive but also negative outcomes of functional studies in the scoring system is critical for facilitating the diagnosis of this complex group of diseases.

Leigh Syndrome and the Mitochondrial m.13513G>A Mutation: Expanding the Clinical Spectrum.

The mitochondrial DNA m.13513G>A mutation in the ND5 subunit gene is a frequent cause of Leigh syndrome. Patients harboring this mutation typically present with ptosis and cardiac conduction abnormalities, particularly Wolff-Parkinson-White syndrome, and have a late clinical onset, which contrasts with the typical infantile form. The authors describe a patient presenting with intrauterine growth retardation and visual impairment at 3 months of age, followed by infantile spasms, severe gastrointestinal dysmotility, and neurological regression. The patient had hyperlactacidemia and bilateral basal ganglia and brainstem lesions on MRI. Although he did not present cardiac conduction abnormalities, his mother had been diagnosed with Wolff-Parkinson-White syndrome. The m.13513G>A mutation was found in the patient's muscle and in several tissues of his mother. The present results expand the phenotype of Leigh syndrome associated with the m.13513G>A mutation, which should be suspected in patients with early-onset mitochondrial encephalopathy with infantile spasms or prominent gastrointestinal smooth muscle involvement.

Genetics in dilated cardiomyopathy.

Discoveries made during the last 20 years have revealed a genetic origin in many cases of dilated cardiomyopathy (DCM). Currently, over 40 genes have been associated with the disease. Mutations in DCM-causing genes induce the condition through a variety of different pathological pathways with complex and not completely understood mechanisms. Genes that encode for sarcomeric, cytoskeletal, nuclear membrane, dystrophin-associated glycoprotein complex and desmosomal proteins are the principal genes involved. In this review we discuss the most frequent DCM-causing genes. We propose a classification in which DCM genes are considered as being major or minor genes according to their mutation frequency and the available supporting evidence. The main phenotypic characteristics associated with each gene are discussed.

Mitochondrial tRNA valine as a recurrent target for mutations involved in mitochondrial cardiomyopathies.

The aim of this study was to identify the genetic defect in two patients having cardiac dysfunction accompanied by neurological symptoms, and in one case MRI evidence of cortical and cerebellar atrophy with hyperintensities in the basal ganglia. Muscle biopsies from each patient revealed single and combined mitochondrial respiratory chain deficiency. The complete mtDNA sequencing of both patients revealed two transitions in the mitochondrial tRNA(Val) gene (MT-TV) (m.1628C>T in Patient 1, and m.1644G>A in Patient 2). The functional and molecular analyses reported here suggest that the MT-TV gene should be routinely considered in the diagnosis of mitochondrial cardiomyopathies.

Desmosomal protein gene mutations in patients with idiopathic dilated cardiomyopathy undergoing cardiac transplantation: a clinicopathological study.

BACKGROUND: Idiopathic dilated cardiomyopathy (DCM) is the most frequent indication for orthotopic heart transplantation. It has been suggested that mutations in genes encoding desmosomal proteins, more typically associated with arrhythmogenic right ventricular cardiomyopathy, are a cause of DCM. OBJECTIVES: To determine the frequency of desmosomal protein gene mutations in heart transplant recipients and their families and to examine histopathological characteristics of explanted organs from mutation carriers. METHODS: 89 unrelated patients aged 47.9±13.5 years (80% male) transplanted for end-stage DCM underwent genetic screening of five desmosomal genes (PKP2, DSP, DSC2, DSG2 and JUP). The findings were correlated with clinical features and histological characteristics in explanted hearts. RESULTS: Pathogenic mutations were identified in 12 patients (13%). Five additional patients (6%) had genetic variants of unknown significance. The clinical phenotype of patients with pathogenic mutations was indistinguishable from that observed in patients without mutations. Evaluation of 76 relatives from 14 families with sequence variants (11 with pathogenic mutations and three with variants of unknown effect) identified 38 mutation carriers, four of whom had an overt DCM phenotype. Evidence of co-segregation of mutations with DCM phenotype was found in five families. Histological evaluation of explanted hearts did not show any specific features in patients with pathogenic mutations. CONCLUSIONS: Mutations in desmosomal genes are frequent in patients with advanced DCM undergoing cardiac transplantation. These findings emphasise the importance of familial evaluation and genetic counselling in patients with end-stage DCM and pose important challenges for current histopathological criteria for arrhythmogenic right ventricular cardiomyopathy.