A Novel and Lethal De Novo LQT-3 Mutation in a Newborn with Distinct Molecular Pharmacology and Therapeutic Response

SCN5A encodes the alpha-subunit (Na(v)1.5) of the principle Na(+) channel in the human heart. Genetic lesions in SCN5A can cause congenital long QT syndrome (LQTS) variant 3 (LQT-3) in adults by disrupting inactivation of the Na(v)1.5 channel. Pharmacological targeting of mutation-altered Na(+) channels has proven promising in developing a gene-specific therapeutic strategy to manage specifically this LQTS variant. SCN5A mutations that cause similar channel dysfunction may also contribute to sudden infant death syndrome (SIDS) and other arrhythmias in newborns, but the prevalence, impact, and therapeutic management of SCN5A mutations may be distinct in infants compared with adults.Here, in a multidisciplinary approach, we report a de novo SCN5A mutation (F1473C) discovered in a newborn presenting with extreme QT prolongation and differential responses to the Na(+) channel blockers flecainide and mexiletine. Our goal was to determine the Na(+) channel phenotype caused by this severe mutation and to determine whether distinct effects of different Na(+) channel blockers on mutant channel activity provide a mechanistic understanding of the distinct therapeutic responsiveness of the mutation carrier. Sequence analysis of the proband revealed the novel missense SCN5A mutation (F1473C) and a common variant in KCNH2 (K897T). Patch clamp analysis of HEK 293 cells transiently transfected with wild-type or mutant Na(+) channels revealed significant changes in channel biophysics, all contributing to the proband's phenotype as predicted by in silico modeling. Furthermore, subtle differences in drug action were detected in correcting mutant channel activity that, together with both the known genetic background and age of the patient, contribute to the distinct therapeutic responses observed clinically.The results of our study provide further evidence of the grave vulnerability of newborns to Na(+) channel defects and suggest that both genetic background and age are particularly important in developing a mutation-specific therapeutic personalized approach to manage disorders in the young

Cystic fibrosis on the African continent

Cystic fibrosis (CF; OMIM 219700) is a life-shortening and costly autosomal recessive disease that has been most extensively studied in individuals of Caucasian descent. There is ample evidence, however, that it also affects other ethnicities. In Africa there have been several reports of CF, but there has been no concerted effort toward establishing the molecular epidemiology of this disease on the continent, which is the first step toward outlining a public health strategy to effectively address the needs of these patients. A literature search revealed reports from only 12 of the 54 African states on the molecular analysis of the mutations present in suspected CF patients, resulting in the identification of 79 mutations. Based on previous functional investigations, 39 of these cause CF, 10 are of varying clinical consequence, 4 have no associated evidence regarding whether they cause CF, 4 are synonymous, 5 are novel, and 21 are unique to Africa. We propose that CF be more thoroughly investigated on the continent to ensure that the public health needs of African CF patients—both those in Africa and those of African descent living elsewhere—are met.The University of Pretoria Vice-Chancellor’s Post-doctoral Research Programme, the Institute for Cellular and Molecular Medicine at the University of Pretoria and the Genomics Research Institute (a University of Pretoria Institutional Research Theme).2017-01-31hb2016Immunolog

Ultrastructural readout of functional synaptic vesicle pools in hippocampal slices based on FM dye labeling and photoconversion

Fast activity-driven turnover of neurotransmitter-filled vesicles at presynaptic terminals is a crucial step in information transfer in the CNS. Characterization of the relationship between the nanoscale organization of synaptic vesicles and their functional properties during transmission is currently of interest. Here we outline a procedure for ultrastructural investigation of functional vesicles in synapses from native mammalian brain tissue. FM dye is injected into the target region of a brain slice and upstream axons are electrically activated to stimulate vesicle turnover and dye uptake. In the presence of diaminobenzidine (DAB), photoactivation of dye-filled vesicles yields an osmiophilic precipitate that is visible in electron micrographs. When combined with serial-section electron microscopy, fundamental ultrastructure-function relationships of presynaptic terminals in native circuits are revealed. We outline the utility of this protocol for the 3D reconstruction of a recycling vesicle pool in CA3-CA1 synapses from an acute hippocampal slice and for the characterization of its anatomically defined docked pool. This protocol requires 6-7 d