Assuntos
Pólipos Adenomatosos/patologia , DNA Glicosilases/genética , Neoplasias Duodenais/epidemiologia , Pólipos Adenomatosos/diagnóstico , Pólipos Adenomatosos/genética , Adulto , Idoso , Idoso de 80 Anos ou mais , Neoplasias Duodenais/diagnóstico , Neoplasias Duodenais/genética , Neoplasias Duodenais/patologia , Duodenoscopia/estatística & dados numéricos , Duodeno/diagnóstico por imagem , Duodeno/patologia , Feminino , Humanos , Mucosa Intestinal/diagnóstico por imagem , Mucosa Intestinal/patologia , Masculino , Pessoa de Meia-Idade , Prevalência , Estudos Prospectivos , Adulto JovemRESUMO
Familial adenomatous polyposis (FAP) is characterised by the development of hundreds to thousands of colorectal adenomas and results from inherited or somatic mosaic variants in the APC gene. Index patients with suspected FAP are usually investigated by APC coding region sequence and dosage analysis in a clinical diagnostic setting. The identification of an APC variant which is predicted to alter protein function enables predictive genetic testing to guide the management of family members. This report describes a 4-generation family with a phenotype consistent with FAP, but in which an APC variant had not been identified, despite testing. To explore this further, quantitative PCR (qPCR) was employed to assess APC transcription, demonstrating reduced levels of APC RNA. Next generation sequencing (NGS) identified the APC 5'UTR/ Exon 1 variant, c.-190 G>A, that had been reported previously in an another FAP family with APC allelic imbalance. Quantitative RNA studies and DNA sequencing of the APC promoters/ Exon 1 may be useful diagnostically for patients with suspected FAP when coding region variants cannot be identified.
Assuntos
Proteína da Polipose Adenomatosa do Colo/genética , Polipose Adenomatosa do Colo/genética , Mutação , Regiões Promotoras Genéticas , Regiões 5' não Traduzidas , Polipose Adenomatosa do Colo/diagnóstico , Proteína da Polipose Adenomatosa do Colo/metabolismo , Humanos , Linhagem , RNA Mensageiro/genética , RNA Mensageiro/metabolismoRESUMO
It has been six years since the first reported link between mutations in the cardiac ryanodine receptor Ca(2+) release channel (RyR2) and catecholaminergic polymorphic ventricular tachycardia (CPVT), a malignant stress-induced arrhythmia. In this time, rapid advances have been made in identifying new mutations, and in understanding how these mutations disrupt normal channel function to cause VT that frequently degenerates into ventricular fibrillation (VF) and sudden death. Functional characterisation of these RyR2 Ca(2+) channelopathies suggests that mutations alter the ability of RyR2 to sense its intracellular environment, and that channel modulation via covalent modification, Ca(2+)- and Mg(2+)-dependent regulation and structural feedback mechanisms are catastrophically disturbed. This review reconciles the current status of RyR2 mutation-linked etiopathology, the significance of mutational clustering within the RyR2 polypeptide and the mechanisms underlying channel dysfunction. We will also review new data that explores the link between abnormal Ca(2+) release and the resultant cardiac electrical instability in VT and VF, and how these recent developments impact on novel anti-arrhythmic therapies. Finally, we evaluate the concept that mechanistic differences between CPVT and other arrhythmogenic disorders may preclude a common therapeutic strategy to normalise RyR2 function in cardiac disease.
Assuntos
Arritmias Cardíacas/genética , Arritmias Cardíacas/fisiopatologia , Mutação , Canal de Liberação de Cálcio do Receptor de Rianodina/genética , Canal de Liberação de Cálcio do Receptor de Rianodina/fisiologia , Arritmias Cardíacas/terapia , Sinalização do Cálcio , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina , Proteínas Quinases Dependentes de Cálcio-Calmodulina/metabolismo , Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Eletrofisiologia , Humanos , Complexos Multiproteicos , Fosforilação , Canal de Liberação de Cálcio do Receptor de Rianodina/química , Taquicardia Ventricular/genética , Taquicardia Ventricular/fisiopatologia , Taquicardia Ventricular/terapiaRESUMO
Arrhythmogenic cardiac ryanodine receptor (RyR2) mutations are associated with stress-induced malignant tachycardia, frequently leading to sudden cardiac death (SCD). The causative mechanisms of RyR2 Ca2+ release dysregulation are complex and remain controversial. We investigated the functional impact of clinically-severe RyR2 mutations occurring in the central domain, and the C-terminal I domain, a key locus of RyR2 autoregulation, on interdomain interactions and Ca2+ release in living cells. Using high-resolution confocal microscopy and fluorescence resonance energy transfer (FRET) analysis of interaction between fusion proteins corresponding to amino- (N-) and carboxyl- (C-) terminal RyR2 domains, we determined that in resting cells, RyR2 interdomain interaction remained unaltered after introduction of SCD-linked mutations and normal Ca2+ regulation was maintained. In contrast, after channel activation, the abnormal Ca2+ release via mutant RyR2 was intrinsically linked to altered interdomain interaction that was equivalent with all mutations and exhibited threshold characteristics (caffeine >2.5 mmol/L; Ca2+ >150 nmol/L). Noise analysis revealed that I domain mutations introduced a distinct pattern of conformational instability in Ca2+ handling and interdomain interaction after channel activation that was absent in signals obtained from the central domain mutation. I domain-linked channel instability also occurred in intact RyR2 expressed in CHO cells and in HL-1 cardiomyocytes. These new insights highlight a critical role for mutation-linked defects in channel autoregulation, and may contribute to a molecular explanation for the augmented Ca2+ release following RyR2 channel activation. Our findings also suggest that the mutational locus may be an important mechanistic determinant of Ca2+ release channel dysfunction in arrhythmia and SCD.