Abstract 2968: Postmortem Genetic Testing of the GPD1-L-Encoded Glycerol-3-Phosphate Dehydrogenase 1-Like Protein in Sudden Infant Death Syndrome

Introduction: Approximately 10 – 15% of sudden infant death syndrome (SIDS) may be caused by cardiac channelopathies including Brugada syndrome (BrS). Type 1 BrS (BrS1), due to mutations in the SCN5A-encoded sodium channel, accounts for approximately 20% of BrS. Recently, a novel mutation in glycerol-3-phosphate dehydrogenase 1-like (GPD1-L) disrupted trafficking of SCN5A in a multi-generational family with BrS. We hypothesized that mutations in GPD1-L may be responsible for some cases of SIDS. Methods: Using DHPLC and direct DNA sequencing, we performed comprehensive open reading frame/splice site mutational analysis of GPD1-L on genomic DNA extracted from necropsy tissue of 228 anonymous cases of SIDS (86 females, 142 males, average age = 3 + 2 months, range 6 hours to 12 months). Results: Three putative, SIDS-associated GPD1-L missense mutations, E83K, I124V, and R273C, were discovered in a three-month-old white male, a five-week-old white female, and a one-month-old white male, respectively. All mutations occurred in highly conserved residues and were absent in 600 reference alleles. Compared to wild type GPD1-L, GPD1-L mutations co-expressed with SCN5A in heterologous HEK cells produced a 60% reduction in peak sodium current density (p<0.004). Adenovirus-mediated gene transfer of the E83K-GPD1-L mutation into neonatal mouse myocytes markedly attenuated the sodium current as well (p<0.01). These decreases in current density are consistent with sodium channel loss-of-function diseases like BrS. Conclusion: This study is the first to report mutations in GPD1-L as a pathogenic cause for a small subset (~1%) of SIDS via a secondary loss-of-function mechanism whereby perturbations in GPD1-L precipitate a marked decrease in the peak sodium current and a potentially lethal, BrS-like pro-arrhythmic substrate.