Aging of transgenic mice that overexpress the London mutant of amyloid precursor protein (APP/V717I) (Moechars et al., 1999a) was now demonstrated not to affect the normalized levels of alpha- or beta-cleaved secreted APP nor of the beta-C-terminal stubs. This indicated that aging did not markedly disturb either alpha- or beta-secretase cleavage of APP and failed to explain the origin of the massive amounts of amyloid peptides Abeta40 and Abeta42, soluble and precipitated as amyloid plaques in the brain of old APP/V717I transgenic mice. We tested the hypothesis that aging acted on presenilin1 (PS1) to affect gamma-secretase-mediated production of amyloid peptides by comparing aged APP/V717I transgenic mice to double transgenic mice coexpressing human PS1 and APP/V717I. In double transgenic mice with mutant (A246E) but not wild-type human PS1, brain amyloid peptide levels increased and resulted in amyloid plaques when the mice were only 6-9 months old, much earlier than in APP/V717I transgenic mice (12-15 months old). Mutant PS1 increased mainly brain Abeta42 levels, whereas in aged APP/V717I transgenic mice, both Abeta42 and Abeta40 increased. This resulted in a dramatic difference in the Abeta42/Abeta40 ratio of precipitated or plaque-associated amyloid peptides, i.e., 3.11+/-0.22 in double APP/V717I x PS1/A246E transgenic mice compared with 0.43 +/- 0.07 in aged APP/V717I transgenic mice, and demonstrated a clear difference between the effect of aging and the effect of the insertion of a mutant PS1 transgene. In conclusion, we demonstrate that aging did not favor amyloidogenic over nonamyloidogenic processing of APP, nor did it exert a mutant PS1-like effect on gamma-secretase. Therefore, the data are interpreted to suggest that parenchymal and vascular accumulation of amyloid in aging brain resulted from failure to clear the amyloid peptides rather than from increased production.
Purpose of the Study: Conventional heart rate variability (HRV) parameters in long QT syndrome (LQTS) have only been studied in small cohorts and results were conflicting. Therefore we evaluated HRV parameters in a large cohort of genotyped LQTS patients. Methods: We included 68 LQTS patients (22 LQT1, 39 LQT2 and 7 LQT3) and 55 controls comprised of 31 genotype negative family members of LQTS probands and 24 additional controls to balance the groups. All individuals underwent 2 channel 24 hour holter recordings with HRV analysis (Synescope, ELA medical). Parameters were assessed both over 24 hours and during daytime (8AM-9 PM) and nighttime (11PM-6AM) separately. The included parameters were both time domain measures (SDNN, SDANN, RMSSD, SDNN index and PNN50) and frequency domain measures of HRV (normalized high frequency (HFn) and low frequency (LFn) power). LQTS patients and controls were compared using a unpaired student T-test. LQT1 and LQT2 were compared with controls using One-way ANOVA. Patients with LQT3 were not included in this genotype analysis since the low number of patients (N = 7). Summary of Results: LQTS patients were more often treated with beta-blockers (37% versus 20%; p = 0.04), while age and gender were comparable. RMSSD (52 ± 31 ms versus 39 ± 19 ms; p = 0.008), PNN50 (18 ± 15 % versus 11 ± 9 %; p = 0.004), SDNN (157 ± 47 ms versus 141 ± 36 ms; p = 0.03) and HFn (27 ± 12 ms versus 22 ± 10 ms; p = 0.01) were significantly increased, while LFn (60 ± 12 ms versus 66 ± 10 ms; p = 0.006) was significantly reduced during 24 hour measurements in LQTS compared to controls. These observations remained significant during daytime, but during nighttime this was only true for RMSSD, PNN50 and HFn. Subgroup analysis revealed that the difference for RMSSD, PNN50, SDNN and LFn remained significant in the LQT2 patients, but not in the LQT1 patients compared to controls. There was no difference in any of the HRV parameters in the LQTS patients taking beta-blockers (N = 25) compared to those that did not (N = 43). Since there were only 8 symptomatic LQTS patients in this cohort, evaluation of the value in risk stratification was not feasible. Conclusion: Patients with LQTS, and especially LQT2, showed a modulation of the autonomic tone of the sinus node. Whether these markers can help in risk stratification should be evaluated in a cohort with more symptomatic patients.
Mutations in the cardiac sodium channel, SCN5A, have been associated with one type of long-QT syndrome, with isolated cardiac conduction defects and Brugada syndrome. The sodium channelopathies exhibit marked variation in clinical phenotypes. The mechanisms underlying the phenotypical diversity, however, remain unknown. Exonic SCN5A mutations can be detected in 20% of Brugada syndrome patients.An intronic mutation (c.4810+3_4810+6dupGGGT) in the SCN5A gene, located outside the consensus splice site, was detected in this study in a family with a highly variable clinical phenotype of Brugada syndrome and/or conduction disease and in a patient with Brugada syndrome. The mutation was not found in a control panel of 100 (200 alleles) ethnically matched normal control subjects. We provide in vivo and in vitro evidence that the mutation can disrupt the splice donor site, activate a cryptic splice site, and create a novel splice site. Notably, our data show that normal transcripts can be also derived from the mutant allele.This is the first report of an unconventional intronic splice site mutation in the SCN5A gene leading to cardiac sodium channelopathy. We speculate that its phenotypical diversity might be determined by the ratio of normal/abnormal transcripts derived from the mutant allele.
We present a new mutation in KCNH2 (c.2038delG) resulting in a frameshift and premature truncation of the IKr channel protein in a large LQTS family with several sudden death cases. This mutation was initially missed by mutation scanning with DHPLC due to allelic dropout and only retrieved after repeat genetic testing with targeted capture and massive parallel sequencing. There was full penetrance of this mutation, only if an individualized QT correction derived from 24-hour Holter data was used. This case again underscores the importance of repeat genetic testing in robust cases of LQTS that remained genotype negative with mutation scanning techniques.
