A Novel Mechanism for Human Cardiac Ankyrin-B Syndrome due to Reciprocal Chromosomal Translocation.

BACKGROUND: Cardiac rhythm abnormalities are a leading cause of morbidity and mortality in developed countries. Loss-of-function variants in the ANK2 gene can cause a variety of cardiac rhythm abnormalities including sinus node dysfunction, atrial fibrillation and ventricular arrhythmias (called the "ankyrin-B syndrome"). ANK2 encodes ankyrin-B, a molecule critical for the membrane targeting of key cardiac ion channels, transporters, and signalling proteins. METHODS AND RESULTS: Here, we describe a family with a reciprocal chromosomal translocation between chromosomes 4q25 and 9q26 that transects the ANK2 gene on chromosome 4 resulting in loss-of-function of ankyrin-B. Select family members with ankyrin-B haploinsufficiency due to the translocation displayed clinical features of ankyrin-B syndrome. Furthermore, evaluation of primary lymphoblasts from a carrier of the translocation showed altered levels of ankyrin-B as well as a reduced expression of downstream ankyrin-binding partners. CONCLUSIONS: Thus, our data conclude that, similar to previously described ANK2 loss-of-function "point mutations", large chromosomal translocations resulting in ANK2 haploinsufficiency are sufficient to cause the human cardiac ankyrin-B syndrome. The unexpected ascertainment of ANK2 dysfunction via the discovery of a chromosomal translocation in this family, the determination of the familial phenotype, as well as the complexities in formulating screening and treatment strategies are discussed.

Expression and function of the Scn5a-encoded voltage-gated sodium channel NaV 1.5 in the rat jejunum.

BACKGROUND: The SCN5A-encoded voltage-gated sodium channel NaV 1.5 is expressed in human jejunum and colon. Mutations in NaV 1.5 are associated with gastrointestinal motility disorders. The rat gastrointestinal tract expresses voltage-gated sodium channels, but their molecular identity and role in rat gastrointestinal electrophysiology are unknown. METHODS: The presence and distribution of Scn5a-encoded NaV 1.5 was examined by PCR, Western blotting and immunohistochemistry in rat jejunum. Freshly dissociated smooth muscle cells were examined by whole cell electrophysiology. Zinc finger nuclease was used to target Scn5a in rats. Lentiviral-mediated transduction with shRNA was used to target Scn5a in rat jejunum smooth muscle organotypic cultures. Organotypic cultures were examined by sharp electrode electrophysiology and RT-PCR. KEY RESULTS: We found NaV 1.5 in rat jejunum and colon smooth muscle by Western blot. Immunohistochemistry using two other antibodies of different portions of NaV 1.5 revealed the presence of the ion channel in rat jejunum. Whole cell voltage-clamp in dissociated smooth muscle cells from rat jejunum showed fast activating and inactivating voltage-dependent inward current that was eliminated by Na(+) replacement by NMDG(+) . Constitutive rat Scn5a knockout resulted in death in utero. NaV 1.5 shRNA delivered by lentivirus into rat jejunum smooth muscle organotypic culture resulted in 57% loss of Scn5a mRNA and several significant changes in slow waves, namely 40% decrease in peak amplitude, 30% decrease in half-width, and 7 mV hyperpolarization of the membrane potential at peak amplitude. CONCLUSIONS & INFERENCES: Scn5a-encoded NaV 1.5 is expressed in rat gastrointestinal smooth muscle and it contributes to smooth muscle electrophysiology.