Absence of C9ORF72 expanded or intermediate repeats in autopsy-confirmed Parkinson's disease.

BACKGROUND: We have reported that intermediate repeat lengths of the C9ORF72 repeat are a risk factor for Parkinson's disease (PD) in a clinically diagnosed data set. Because 10% to 25% of clinically diagnosed PD have different diagnoses upon autopsy, we hypothesized that this may reflect phenotypic heterogeneity or concomitant pathology of other neurodegenerative disorders. METHODS: We screened 488 autopsy-confirmed PD cases for expansion haplotype tag rs3849942T. In 196 identified haplotype carriers, the C9ORF72 repeat was genotyped using the repeat-primed polymerase chain reaction assay. RESULTS: No larger (intermediate or expanded) repeats were found in these autopsy-confirmed PD samples. This absence of larger repeats is significantly different from the frequency in clinically diagnosed datasets (P = 0.002). CONCLUSIONS: Our results suggest that expanded or intermediate C9ORF72 repeats in clinically diagnosed PD or parkinsonism might be an indication of heterogeneity in clinically diagnosed PD cases. Further studies are needed to elucidate the potential contribution of the C9ORF72 repeat to autopsy-confirmed PD.

Whole exome sequencing of rare variants in EIF4G1 and VPS35 in Parkinson disease.

OBJECTIVE: Recently, vacuolar protein sorting 35 (VPS35) and eukaryotic translation initiation factor 4 gamma 1 (EIF4G1) have been identified as 2 causal Parkinson disease (PD) genes. We used whole exome sequencing for rapid, parallel analysis of variations in these 2 genes. METHODS: We performed whole exome sequencing in 213 patients with PD and 272 control individuals. Those rare variants (RVs) with <5% frequency in the exome variant server database and our own control data were considered for analysis. We performed joint gene-based tests for association using RVASSOC and SKAT (Sequence Kernel Association Test) as well as single-variant test statistics. RESULTS: We identified 3 novel VPS35 variations that changed the coded amino acid (nonsynonymous) in 3 cases. Two variations were in multiplex families and neither segregated with PD. In EIF4G1, we identified 11 (9 nonsynonymous and 2 small indels) RVs including the reported pathogenic mutation p.R1205H, which segregated in all affected members of a large family, but also in 1 unaffected 86-year-old family member. Two additional RVs were found in isolated patients only. Whereas initial association studies suggested an association (p = 0.04) with all RVs in EIF4G1, subsequent testing in a second dataset for the driving variant (p.F1461) suggested no association between RVs in the gene and PD. CONCLUSIONS: We confirm that the specific EIF4G1 variation p.R1205H seems to be a strong PD risk factor, but is nonpenetrant in at least one 86-year-old. A few other select RVs in both genes could not be ruled out as causal. However, there was no evidence for an overall contribution of genetic variability in VPS35 or EIF4G1 to PD development in our dataset.

Interaction between troponin and myosin enhances contractile activity of myosin in cardiac muscle.

Ca(2+) signaling in striated muscle cells is critically dependent upon thin filament proteins tropomyosin (Tm) and troponin (Tn) to regulate mechanical output. Using in vitro measurements of contractility, we demonstrate that even in the absence of actin and Tm, human cardiac Tn (cTn) enhances heavy meromyosin MgATPase activity by up to 2.5-fold in solution. In addition, cTn without Tm significantly increases, or superactivates sliding speed of filamentous actin (F-actin) in skeletal motility assays by at least 12%, depending upon [cTn]. cTn alone enhances skeletal heavy meromyosin's MgATPase in a concentration-dependent manner and with sub-micromolar affinity. cTn-mediated increases in myosin ATPase may be the cause of superactivation of maximum Ca(2+)-activated regulated thin filament sliding speed in motility assays relative to unregulated skeletal F-actin. To specifically relate this classical superactivation to cardiac muscle, we demonstrate the same response using motility assays where only cardiac proteins were used, where regulated cardiac thin filament sliding speeds with cardiac myosin are >50% faster than unregulated cardiac F-actin. We additionally demonstrate that the COOH-terminal mobile domain of cTnI is not required for this interaction or functional enhancement of myosin activity. Our results provide strong evidence that the interaction between cTn and myosin is responsible for enhancement of cross-bridge kinetics when myosin binds in the vicinity of Tn on thin filaments. These data imply a novel and functionally significant molecular interaction that may provide new insights into Ca(2+) activation in cardiac muscle cells.