The biophysical characterization of the first SCN5A mutation R1512W identified in Chinese sudden unexplained nocturnal death syndrome

Abstract

Increasing evidence observed in clinical phenotypes show that abrupt breathing disorders during sleep may play an important role in the pathogenesis of sudden unexplained nocturnal death syndrome (SUNDS). The reported Brugada syndrome causing mutation R1512W in cardiac sodium channel α subunit encoded gene SCN5A, without obvious loss of function of cardiac sodium channel in previous in vitro study, was identified as the first genetic cause of Chinese SUNDS by us. The R1512W carrier was a 38-year-old male SUNDS victim who died suddenly after tachypnea in nocturnal sleep without any structural heart disease. To test our hypothesis that slight acidosis conditions may contribute to the significant loss of function of mutant cardiac sodium channels underlying SUNDS, the biophysical characterization of SCN5A mutation R1512W was performed under both extracellular and intracellular slight acidosis at pH 7.0. The cDNA of R1512W was created using site-directed mutagenesis methods in the pcDNA3 plasmid vector. The wild type (WT) or mutant cardiac sodium channel R1512W was transiently transfected into HEK293 cells. Macroscopic voltage-gated sodium current (INa) was measured 24 hours after transfection with the whole-cell patch clamp method at room temperature in the HEK293 cells. Under the baseline conditions at pH 7.4, R1512W (−175 ± 15 pA/pF) showed about 30% of reduction in peak INa compared to WT (−254 ± 23 pA/pF, P < 0.05). Under the acidosis condition at pH 7.0, R1512W (−130 ± 17 pA/pF) significantly decreased the peak INa by nearly 50% compared to WT (−243 ± 23 pA/pF, P < 0.005). Compared to baseline condition at pH 7.4, the acidosis at pH 7.0 did not affect the peak INa in WT (P > 0.05) but decreased peak INa in R1512W (P < 0.05). This initial functional study for SCN5A mutation in the Chinese SUNDS victim revealed that the acidosis aggravated the loss of function of mutant channel R1512W and suggested that nocturnal sleep disorders-associated slight acidosis may trigger the lethal arrhythmia underlying the sudden death of SUNDS cases in the setting of genetic defect.

An East Asian Common Variant Vinculin P.Asp841His Was Associated With Sudden Unexplained Nocturnal Death Syndrome in the Chinese Han Population

“…In this study, we identified, once again, that breathing‐disorder–related acidosis plays a crucial role for VCL‐D841H in aggravating SCN5A loss of function. All these findings strongly implicate the possible important contribution of sleep respiratory disorders in the occurrence of SUNDS …”

“…Plant et al previously reported that sleep respiratory abnormality‐associated intracellular acidosis significantly increased the late I Na caused by the sudden infant death syndrome susceptibility SCN5A common variant, S1103Y, in blacks. Recently, the SCN5A mutation, R1512W, found in a Chinese SUNDS victim with sudden nocturnal tachypnea before death was identified to show obvious SCN5A loss of function only under acidosis conditions . In this study, we identified, once again, that breathing‐disorder–related acidosis plays a crucial role for VCL‐D841H in aggravating SCN5A loss of function.…”

“…Recently, the SCN5A mutation, R1512W, found in a Chinese SUNDS victim with sudden nocturnal tachypnea before death was identified to show obvious SCN5A loss of function only under acidosis conditions. 33 In this study, we identified, once again, that breathingdisorder-related acidosis plays a crucial role for VCL-D841H in aggravating SCN5A loss of function. All these findings strongly implicate the possible important contribution of sleep respiratory disorders in the occurrence of SUNDS.…”

“…All these findings strongly implicate the possible important contribution of sleep respiratory disorders in the occurrence of SUNDS. 7,30,31,33…”

Sudden Unexplained Nocturnal Death Syndrome: The Hundred Years' Enigma

“…37 Using the whole-cell patch clamp method, we proved that intracellular and extracellular acidosis significantly decreases wild or mutant sodium currents in vitro co-expression systems. 38,39…”