Sodium Channelopathy Underlying Familial Sick Sinus Syndrome With Early Onset and Predominantly Male Characteristics

Background-Sick sinus syndrome (SSS) is a common arrhythmia often associated with aging or organic heart diseases but may also occur in a familial form with a variable mode of inheritance. Despite the identifcation of causative genes, including cardiac Na channel (SCN5A), the pathogenesis and molecular epidemiology of familial SSS remain undetermined primarily because of its rarity. Methods and Results-We genetically screened 48 members of 15 SSS families for mutations in several candidate genes and determined the functional properties of mutant Na channels using whole-cell patch clamping. We identifed 6 SCN5A mutations including a compound heterozygous mutation. Heterologously expressed mutant Na channels showed loss-of-function properties of reduced or no Na current density in conjunction with gating modulations. Among 19 family members with SCN5A mutations, QT prolongation and Brugada syndrome were associated in 4 and 2 individuals, respectively. Age of onset in probands carrying SCN5A mutations was signifcantly less (mean±SE, 12.4±4.6 years; n=5) than in SCN5A-negative probands (47.0±4.6 years; n=10; P<0.001) or nonfamilial SSS (74.3±0.4 years; n=538; P<0.001). Meta-analysis of SSS probands carrying SCN5A mutations (n=29) indicated profound male predominance (79.3%) resembling Brugada syndrome but with a considerably earlier age of onset (20.9±3.4 years). Conclusions-The notable pathophysiological overlap between familial SSS and Na channelopathy indicates that familial SSS with SCN5A mutations may represent a subset of cardiac Na channelopathy with strong male predominance and early clinical manifestations

Parenchymal destruction in asthma : Fixed airflow obstruction and lung function trajectory

Background: Fixed airflow obstruction (FAO) in asthma, particularly in nonsmokers, is generally believed to be caused by airway remodeling. However, parenchymal destruction may also contribute to FAO and longitudinal decline in forced expiratory volume in 1 second (FEV1). Objectives: To evaluate parenchymal destruction, we used emphysema indices, exponent D, and low-attenuation area percentage (LAA%) on computed tomography (CT), and test whether the parenchymal destruction and airway disease are independently associated with FAO and FEV1 decline in both smoking and nonsmoking asthma. Methods: Exponent D, LAA%, wall area percentage at segmental airways, and airway fractal dimension (AFD) in those with asthma were measured on inspiratory CT and compared to those in patients with chronic obstructive pulmonary disease (COPD). Results: Exponent D was lower and LAA% was higher in COPD (n = 42) and asthma with FAO (n = 101) than in asthma without FAO (n = 88). The decreased exponent D and increased LAA% were associated with FAO regardless of smoking status or asthma severity. In multivariable analysis, decreased exponent D and increased LAA% were associated with an increased odds ratio of FAO and decreased FEV1, irrespective of wall area percentage and airway fractal dimension. Moreover, decreased exponent D affected the longitudinal decline in FEV1 in those with severe asthma, independent of smoking status. Conclusions: Patients with asthma with FAO showed parenchymal destruction regardless of smoking status and asthma severity. Parenchymal destruction was associated with an accelerated FEV1 decline, suggesting the involvements of both airway and parenchyma in the pathophysiology of a subgroup of asthma