👤 Marco Di Paolo

Sudden unexplained death (SUD) refers to cases of sudden death where autopsy fails to identify any cardiac or extracardiac underlying cause. Guideline-directed standard genetic testing identifies a disease-causing mutation in less than one-third of cases of SUD. Conversely, whole exome sequencing (WES) may provide the key to solve most cases of SUD even after several years from the subject's death. We report on a case of sudden unexpected death of a 37-year-old male, with inconclusive autopsy conducted 14 years ago. A recent reevaluation through WES was performed on DNA extracted from left ventricular samples. A multiple step process including several "in silico" tools was applied to identify potentially pathogenic variants. Data analysis was based on a 562 gene panel, including 234 candidate genes associated with sudden cardiac death or heart diseases, with the addition of 328 genes highly expressed in the heart. WebGestalt algorithms were used for association enrichment analysis of all genes with detected putative pathogenic variants. WES analysis identified four potentially pathogenic variants: RYR2:c.12168G>T, TTN:c.11821C>T (rs397517804), MYBPC3:c.1255C>T (rs368770848), and ACADVL:c.848T>C (rs113994167). WebGestalt algorithms indicated that their combination holds an unfavorable arrhythmic susceptibility which conceivably caused the occurrence of the events leading to our subject's sudden death. Associating WES technique with online prediction algorithms may allow the recognition of genetic mutations potentially responsible for otherwise unexplained deaths. Show less

Cellular mechanisms that mediate steatohepatitis, an increasingly prevalent condition in the Western world for which no therapies are available, are poorly understood. Despite the fact that its synthetic agonists induce fatty liver, the liver X receptor (LXR) transcription factor remains a target of interest because of its anti-atherogenic, cholesterol removal, and anti-inflammatory activities. Here we show that tetratricopeptide repeat domain protein 39B (Ttc39b, C9orf52) (T39), a high-density lipoprotein gene discovered in human genome-wide association studies, promotes the ubiquitination and degradation of LXR. Chow-fed mice lacking T39 (T39(-/-)) display increased high-density lipoprotein cholesterol levels associated with increased enterocyte ATP-binding cassette transporter A1 (Abca1) expression and increased LXR protein without change in LXR messenger RNA. When challenged with a high fat/high cholesterol/bile salt diet, T39(-/-) mice or mice with hepatocyte-specific T39 deficiency show increased hepatic LXR protein and target gene expression, and unexpectedly protection from steatohepatitis and death. Mice fed a Western-type diet and lacking low-density lipoprotein receptor (Ldlr(-/-)T39(-/-)) show decreased fatty liver, increased high-density lipoprotein, decreased low-density lipoprotein, and reduced atherosclerosis. In addition to increasing hepatic Abcg5/8 expression and limiting dietary cholesterol absorption, T39 deficiency inhibits hepatic sterol regulatory element-binding protein 1 (SREBP-1, ADD1) processing. This is explained by an increase in microsomal phospholipids containing polyunsaturated fatty acids, linked to an LXRα-dependent increase in expression of enzymes mediating phosphatidylcholine biosynthesis and incorporation of polyunsaturated fatty acids into phospholipids. The preservation of endogenous LXR protein activates a beneficial profile of gene expression that promotes cholesterol removal and inhibits lipogenesis. T39 inhibition could be an effective strategy for reducing both steatohepatitis and atherosclerosis. Show less

Myotubular myopathy (MTM) is a devastating pediatric neuromuscular disorder of phosphoinositide (PIP) metabolism resulting from mutations of the PIP phosphatase MTM1 for which there are no treatments. We have previously shown phosphatidylinositol-3-phosphate (PI3P) accumulation in animal models of MTM. Here, we tested the hypothesis that lowering PI3P levels may prevent or reverse the MTM disease process. To test this, we targeted class II and III PI3 kinases (PI3Ks) in an MTM1-deficient mouse model. Muscle-specific ablation of Pik3c2b, but not Pik3c3, resulted in complete prevention of the MTM phenotype, and postsymptomatic targeting promoted a striking rescue of disease. We confirmed this genetic interaction in zebrafish, and additionally showed that certain PI3K inhibitors prevented development of the zebrafish mtm phenotype. Finally, the PI3K inhibitor wortmannin improved motor function and prolonged lifespan of the Mtm1-deficient mice. In all, we have identified Pik3c2b as a genetic modifier of Mtm1 mutation and demonstrated that PIK3C2B inhibition is a potential treatment strategy for MTM. In addition, we set the groundwork for similar reciprocal inhibition approaches for treating other PIP metabolic disorders and highlight the importance of modifier gene pathways as therapeutic targets. Show less