Pseudomonas pseudomallei and sudden unexplained death in Thai construction workers

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

Background

We have identified the cardiomyopathy‐susceptibility gene vinculin (VCL) mutation M94I may account for a sudden unexplained nocturnal death syndrome (SUNDS) case. We addressed whether VCL common variant D841H is associated with SUNDS.

Methods and Results

In 8 of 120 SUNDS cases, we detected an East Asian common VCL variant p.Asp841His (D841H). Comparing the H841 allele frequency of the general population in the local database (15 of 1818) with SUNDS victims (10 of 240) gives an odds ratio for SUNDS of 5.226 (95% CI, 2.321, 11.769). The VCL‐D841H variant was engineered and either coexpressed with cardiac sodium channel (SCN5A) in HEK293 cells or overexpressed in human induced pluripotent stem‐cell–derived cardiomyocytes to examine its effects on sodium channel function using the whole‐cell patch‐clamp method. In HEK293 cells, under physiological pH conditions (pH 7.4), D841H caused a 29% decrease in peak I_Na amplitude compared to wild type (WT), whereas under acidotic conditions (pH 7.0), D841H decreased further to 43% along with significant negative shift in inactivation compared to WT at pH 7.4. In induced pluripotent stem‐cell‐derived cardiomyocytes, similar effects of D841H on I_Na were observed. VCL colocalized with SCN5A at the intercalated disk in human cardiomyocytes. VCL was also confirmed to directly interact with SCN5A, and VCL‐D841H did not disrupt the association of VCL and SCN5A.

Conclusions

A VCL common variant was genetically and biophysically associated with Chinese SUNDS. The aggravation of loss of function of SCN5A caused by VCL‐D841H under acidosis supports that nocturnal sleep respiratory disorders with acidosis may play a key role in the pathogenesis of SUNDS.

Vinculin variant M94I identified in sudden unexplained nocturnal death syndrome decreases cardiac sodium current

Sudden unexplained nocturnal death syndrome (SUNDS) remains an autopsy negative disorder with unclear etiology. Vinculin (VCL) was linked to sudden arrhythmia death in VCL knockout mice prior to the appearance of cardiomyopathy. We hypothesized VCL mutations underlie risk for SUNDS. A rare heterozygous variant VCL-M94I was found in a SUNDS victim who suffered sudden nocturnal tachypnea and lacked pathogenic variants in known arrhythmia-causing genes. VCL was identified to interact with SCN5A in vitro/vivo. The VCL-M94I was co-expressed with the cardiac sodium channel in HEK293 cells and also overexpressed in induced pluripotent stem cells derived cardiomyocytes (iPSCs-CM). In HEK293 cells with pH 7.4, VCL-M94I caused ~30% decrease in peak sodium current (I_Na) amplitude compared to WT; under acidotic conditions (pH 7.0) typically found with hypoxia during sleep apnea, M94I resulted in 37% reduction in peak I_Na compared to WT and the combination of VCL-M94I and pH 7.0 decreased peak I_Na by ~56% compared to WT at pH 7.4. In iPSCs-CM, similar effects of M94I on reduction of peak I_Na were observed. This study initially shows both physical and functional interaction between VCL and cardiac sodium channel, and suggests an important role for respiratory acidosis in triggering the fatal arrhythmia underlying SUNDS.

Does Sudden Unexplained Nocturnal Death Syndrome Remain the Autopsy-Negative Disorder: A Gross, Microscopic, and Molecular Autopsy Investigation in Southern China

OBJECTIVE

To look for previously unrecognized cardiac structural abnormalities and address the genetic cause for sudden unexplained nocturnal death syndrome (SUNDS).

METHODS

Data for 148 SUNDS victims and 444 controls (matched 1:3 on sex, race, and age of death within 1 year) were collected from Sun Yat-sen University from January 1, 1998, to December 31, 2014, to search morphological changes. An additional 17 patients with Brugada syndrome (BrS) collected from January 1, 2006, to December 31, 2014, served as a comparative disease cohort. Target-captured next-generation sequencing for 80 genes associated with arrhythmia/cardiomyopathy was performed in 44 SUNDS victims and 17 patients with BrS to characterize the molecular spectrum.

RESULTS

The SUNDS victims had slight but statistically significant increased heart weight and valve circumference compared with controls. Twelve of 44 SUNDS victims (SCN5A, SCN1B, CACNB2, CACNA1C, AKAP9, KCNQ1, KCNH2, KCNJ5, GATA4, NUP155, ABCC9) and 6 of 17 patients with BrS (SCN5A, CACNA1C; P>.05) carried rare variants in primary arrhythmia-susceptibility genes. Only 2 of 44 SUNDS cases compared with 5 of 17 patients with BrS hosted a rare variant in the most common BrS-causing gene, SCN5A (P=.01). Using the strict American College of Medical Genetics guideline-based definition, it was found that only 2 of 44 (KCNQ1) SUNDS and 3 of 17 (SCN5A) patients with BrS hosted a "(likely) pathogenic" variant. Fourteen of 44 SUNDS cases with cardiomyopathy-related variants had a subtle but significantly decreased circumference of cardiac valves, and tended to die on average 5 to 6 years younger compared with the remaining 30 cases (P=.02).

CONCLUSION

We present the first comprehensive autopsy evidence that SUNDS victims may have concealed cardiac morphological changes. SUNDS and BrS may result from different molecular pathological underpinnings. The distinct association between cardiomyopathy-related rare variants and SUNDS warrants further investigation.

Sudden unexpected nocturnal deaths among Thai immigrant workers in Singapore. The possible role of toxigenic bacteria

Sudden Unexpected Nocturnal Deaths (SUND) occur in young, apparently healthy immigrant workers from Thailand, the Philippines and Bangladesh living among ex-patriot labour forces in countries such as Singapore and Saudi Arabia. Several factors associated with these deaths are similar to those observed for Sudden Infant Death Syndrome (SIDS): sleep related and mainly nocturnal occurrence; no prodromal illnesses other than mild respiratory tract infection; exposure to cigarette smoke; absence of invasive microorganisms at autopsy. The hypotheses proposed to explain these deaths in adults are examined. Based on our studies of the role toxigenic bacteria might play in some cases of SIDS, we suggest a new approach to the investigation of SUND.

Sudden unexplained death syndrome--a new manifestation in melioidosis?

The indirect haemagglutination (IHA) test using sensitized turkey erythrocytes and the indirect immunofluorescence assay (IgM-IFA) was confirmed to be sensitive in the detection of a recent or current Pseudomonas pseudomallei infection in 19 culture-confirmed Singapore melioidosis patients. All were found to have antibody titres from 4 to 32768 in the IHA test and 10 to 320 in the IgM-IFA test. When these tests were employed on sera from 16 immigrant Thai construction workers who died of sudden unexplained death syndrome (SUDS) and 73 healthy Thai fellow workers, 93.8% and 68.8% of SUDS cases had IHA titre of greater than or equal to 4 and IgM-IFA titre of greater than or equal to 10 respectively, in contrast to 39.7% and 12.3% found among healthy Thai workers. These data indicate that at the time of death, most of the SUDS patients had an active infection with P. pseudomallei, possibly resulting from reactivation of a latent infection. The aetiological role of P. pseudomallei as the major cause of SUDS is discussed.