Purpose: Ion channel activity is involved in several basic cellular behaviors that are integral to metastasis (e.g., proliferation, motility, secretion, and invasion), although their contribution to cancer progression has largely been ignored. The purpose of this study was to investigate voltagegated Na + channel (VGSC) expression and its possible role in human breast cancer. Experimental Design: Functional VGSC expression was investigated in human breast cancer cell lines by patch clamp recording. The contribution of VGSC activity to directional motility, endocytosis, and invasion was evaluated by in vitro assays. Subsequent identification of the VGSC a-subunit(s) expressed in vitro was achieved using reverse transcription-PCR, immunocytochemistry, and Western blot techniques and used to investigate VGSCa expression and its association with metastasis in vivo. Results:VGSC expression was significantly up-regulated in metastatic human breast cancer cells and tissues, and VGSC activity potentiated cellular directional motility, endocytosis, and invasion. Reverse transcription-PCR revealed that Na v 1.5, in its newly identified ''neonatal'' splice form, was specifically associated with strong metastatic potential in vitro and breast cancer progression in vivo. An antibody specific for this form confirmed up-regulation of neonatal Na v 1.5 protein in breast cancer cells and tissues. Furthermore, a strong correlation was found between neonatal Na v 1.5 expression and clinically assessed lymph node metastasis. Conclusions: Up-regulation of neonatal Na v 1.5 occurs as an integral part of the metastatic process in human breast cancer and could serve both as a novel marker of the metastatic phenotype and a therapeutic target.Breast cancer is the most common cancer of women and the second leading cause of female cancer mortality, accounting for about 10% of all cancer deaths in the western world (1, 2). To date, several breast cancer metastasis -associated genes have been identified both individually and in combination in microarray analyses (3, 4). These include oncogenes (e.g., ras and c-myc), cell cycle -associated markers (e.g., Ki67), adhesion molecules (e.g., E-cadherins), motility factors (e.g., hepatic growth factor), growth factors and their receptors (e.g., epidermal growth factor/Her-2 and fibroblast growth factor), and the well-established steroid hormones (e.g., estrogen and progesterone; refs. 3, 4). However, indirect measures of metastatic progression (including size of primary carcinoma, assessment of intratumoral vascular invasion, and lymph node involvement) remain the most widely used methods in clinical management. At present, although it is possible to detect micrometastases, approximately one third of women who seem disease-free at primary diagnosis eventually develop overt metastases (5, 6). Clinicians, therefore, require a more accurate diagnosis to predict the development of metastatic disease.Ion channels are major signaling molecules expressed in a wide range of tissues where they hav...

Summary Invertebrate model systems are powerful tools for studying human disease owing to their genetic tractability and ease of screening. We conducted a mosaic genetic screen of lethal mutations on the Drosophila X-chromosome to identify genes required for the development, function, and maintenance of the nervous system. We identified 165 genes, most of whose function has not been studied in vivo. In parallel, we investigated rare variant alleles in 1,929 human exomes from families with unsolved Mendelian disease. Genes that are essential in flies and have multiple human homologs were found to be likely to be associated with human diseases. Merging the human datasets with the fly genes allowed us to identify disease-associated mutations in six families and to provide insights into microcephaly associated with brain dysgenesis. This bidirectional synergism between fly genetics and human genomics facilitates the functional annotation of evolutionarily conserved genes involved in human health.

Charcot-Marie-Tooth (CMT) disease is a clinically and genetically heterogeneous distal symmetric polyneuropathy. Whole-exome sequencing (WES) of 40 individuals from 37 unrelated families with CMT-like peripheral neuropathy refractory to molecular diagnosis identified apparent causal mutations in ~45% (17/37) of families. Three candidate disease genes are proposed, supported by a combination of genetic and in vivo studies. Aggregate analysis of mutation data revealed a significantly increased number of rare variants across 58 neuropathy associated genes in subjects versus controls; confirmed in a second ethnically discrete neuropathy cohort, suggesting mutation burden potentially contributes to phenotypic variability. Neuropathy genes shown to have highly penetrant Mendelizing variants (HMPVs) and implicated by burden in families were shown to interact genetically in a zebrafish assay exacerbating the phenotype established by the suppression of single genes. Our findings suggest that the combinatorial effect of rare variants contributes to disease burden and variable expressivity.

Inherited peripheral neuropathies are frequent neuromuscular disorders known for their clinical and genetic heterogeneity. In 33 families, we identified 8 mutations in HINT1 (encoding histidine triad nucleotide-binding protein 1) by combining linkage analyses with next-generation sequencing and subsequent cohort screening of affected individuals. Our study provides evidence that loss of functional HINT1 protein results in a distinct phenotype of autosomal recessive axonal neuropathy with neuromyotonia.

Charcot-Marie-Tooth disease type 4C (CMT4C) is a childhood-onset demyelinating form of hereditary motor and sensory neuropathy associated with an early-onset scoliosis and a distinct Schwann cell pathology. CMT4C is inherited as an autosomal recessive trait and has been mapped to a 13-cM linkage interval on chromosome 5q23-q33. By homozygosity mapping and allele-sharing analysis, we refined the CMT4C locus to a suggestive critical region of 1.7 Mb. We subsequently identified mutations in an uncharacterized transcript, KIAA1985, in 12 families with autosomal recessive neuropathy. We observed eight distinct protein-truncating mutations and three nonconservative missense mutations affecting amino acids conserved through evolution. In all families, we identified a mutation on each disease allele, either in the homozygous or in the compound heterozygous state. The CMT4C gene is strongly expressed in neural tissues, including peripheral nerve tissue. The translated protein defines a new protein family of unknown function with putative orthologues in vertebrates. Comparative sequence alignments indicate that members of this protein family contain multiple SH3 and TPR domains that are likely involved in the formation of protein complexes.