Very-long-chain acyI-CoA dehydrogenase (VLCAD) catalyzes the first step of the mammalian mitochondrial fatty acid oxidation (FAO) spiral that generates energy in the heart and other highly oxidative tissues. Human recessive VLCAD deficiency produces phenotypes of early fatal cardiomyopathy and arrhythmias, infantile hypoketotic hypoglycemia and liver failure, sudden death in infancy (SIDS), and later episodic skeletal myopathy. Our first hypothesis is that VLCAD deficiency has a genotype-phenotype correlation that we will investigate (Aim 1) through molecular genetics, correlating with clinical phenotypes, and by studying the pathogenetics of some VLCAD mutations, particularly V243A that exists in patients discovered by newborn screening. Our second hypothesis is that VLCAD is essential for cardiac function both because of its enzymatic role, but also because VLCAD is required for transcriptional regulation of multiple genes. This will be investigated by characterizing the 20 bp long VLCAD enhancer we have isolated (Aim 2) and by characterizing VLCAD-deficient mice and their heterozygote littermates that exhibit the phenotypes of sudden death, late-onset obesity, development of tumors, and inducible arrhythmias and that die in response to fasting and exposure to cold. This characterization includes use of transgenic mice and cell transfections to examine VLCAD transcriptional regulation (Aim 2) and telemetry, invasive electrophysiology, microarray analysis, exercise testing, and dietary manipulation of VLCAD -/- and +/- animals (Aim 3). We will also create tissue-specific (heart, brown fat, liver, muscle) knockouts (Aim 4) to ascertain the relative contributions of these organs to phenotypes. We know that VLCAD -/- animals exhibit marked alterations in tissue gene expression by one day, a perinatal """"""""adaptive response"""""""". We hypothesize that this live-saving adaptive response creates differences in gene expression that are the substrate for the later pathologies of sudden death, arrhythmias, obesity, and tumorigenesis. This is, thus, a model of how polymorphisms or mutations in one gene modify expression of other later in life, leading to pathology. One highly induced gene in this genetic response is a novel protein, designated heart endothelin-related substance (HERS) that, based upon homology and expression data, we postulate functions in cardiac development and calcium metabolism. We will investigate its role by generating a HERS knockout in the last specific aim.