In addition to rapid signaling, electrical activity provides important cues to developing neurons. Electrical activity relies on the function of several different types of voltage-gated ion channels. Whereas voltage-gated Ca2+ channel activity regulates several aspects of neuronal differentiation, much less is known about developmental roles of voltage-gated Na+ channels, essential mediators of electrical signaling. Here, we focus on the zebrafish Na+ channel isotype, Nav1.6a,which is encoded by the scn8a gene. A restricted set of spinal neurons, including dorsal sensory Rohon-Beard cells, two motoneuron subtypes with different axonal trajectories, express scn8a during embryonic development. CaP, an early born primary motoneuron subtype with ventrally projecting axons expresses scn8a, as does a class of secondary motoneurons with axons that project dorsally. To test for developmental roles of scn8a, we knocked down Nav1.6a protein using antisense morpholinos. Na+ channel protein and current amplitudes were reduced in neurons that express scn8a. Furthermore,Nav1.6a knockdown altered axonal morphologies of some but not all motoneurons. Dorsally projecting secondary motoneurons express scn8aand displayed delayed axonal outgrowth. By contrast, CaP axons developed normally, despite expression of the gene. Surprisingly, ventrally projecting secondary motoneurons, a population in which scn8a was not detected,displayed aberrant axonal morphologies. Mosaic analysis indicated that effects on ventrally projecting secondary motoneurons were non cell-autonomous. Thus,voltage-gated Na+ channels play cell-autonomous and non cell-autonomous roles during neuronal development.

Whereas it is known that voltage-gated calcium channels play important roles during development, potential embryonic roles of voltage-gated sodium channels have received much less attention. Voltagegated sodium channels consist of pore-forming ␣-subunits (Na v 1) and auxiliary ␤-subunits. Here, we report the embryonic and larval expression patterns for all eight members of the gene family (scna) coding for zebrafish Na v 1 proteins. We find that each scna gene displays a distinct expression pattern that is temporally and spatially dynamic during embryonic and larval stages. Overall, our findings indicate that scna gene expression occurs sufficiently early during embryogenesis to play developmental roles for both muscle and nervous tissues.

The transaminases alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are markers of hepatocellular injury but are highly concentrated in muscle cells. Consequently, muscular dystrophies such as Duchenne muscular dystrophy, lead to hypertransaminasemia. Elevation in ALT and AST is most striking during the early stages of disease, before onset of or when only subtle signs of muscle disease are present. Thus, the incidental finding of elevated ALT/AST may be the presenting sign of muscle disease in many children and provides an opportunity for early diagnosis. Many physicians, however, pursue extensive workup for liver disease in children who present with the incidental finding of elevated ALT/AST. This results in delayed diagnosis and initiation of treatment and increased expense and may lead to unnecessary invasive procedures. We report 12 patients with muscle disease who presented with a variety of symptoms and were found to have an incidental finding of elevated ALT/AST. We propose a rapid screening process for evaluating children with the incidental finding of elevated ALT/ AST to shorten the time to diagnosis of muscle disease. (J Am Board Fam Med 2012;25:536 -540.)

SUMMARYIt is commonly thought that differentiated neurons do not give rise to new cells, severely limiting the potential for regeneration and repair of the mature nervous system. However, we have identified cells in zebrafish larvae that first differentiate into dorsal root ganglia sensory neurons but later acquire a sympathetic neuron phenotype. These transdifferentiating neurons are present in wild-type zebrafish. However, they are increased in number in larvae that have a mutant voltage-gated sodium channel gene, scn8aa. Sodium channel knock-down promotes migration of differentiated sensory neurons away from the ganglia. Once in a new environment, sensory neurons transdifferentiate regardless of sodium channel expression. These findings reveal an unsuspected plasticity in differentiated neurons that points to new strategies for treatment of nervous system disease.

Objective:To determine the health care costs associated with pediatric multiple sclerosis (MS).Methods:We performed a retrospective analysis of all patients with MS 18 years of age or younger who were diagnosed or treated between 2002 and 2012 in a population-based cohort. Demographics and health care costs were extracted from the Intermountain Healthcare Enterprise Data Warehouse. Patients were divided into high-cost (>84th percentile) and low-cost groups and differences in health care utilization between the groups were analyzed.Results:Fifty-seven pediatric patients with MS were identified. Health care costs for the cohort totaled more than $1.5 million over the 10-year period, with the top 16th percentile of patients contributing nearly two-thirds. Outpatient visits represented the majority of health care encounters and expenditures, accounting for 83.1% of total costs. Costs per encounter were highest for inpatient stays, averaging $2,924 per stay.Conclusions:The burden of health care expenses for pediatric patients with MS is significant. Expenditures related to outpatient visits were the largest contributor to costs, but inpatient stays were the most costly per encounter. A small proportion of patients incurred the bulk of costs and spent significantly more time receiving care compared to the majority of patients. Avoidance of inpatient treatment and efficient outpatient management are potential areas for health care cost reduction and improvement in care.