Mitochondrial β-oxidation of long chain fatty acyl-CoAs is well recognized as a primary metabolic pathway for maintenance of energy homeostasis and body temperature. However, it also recycles carbons from many long chain fatty acids for lipid synthesis. Little is known about the mechanistic role of the latter in the pathogenesis of symptoms in genetic defects of β-oxidation, and its derangement may in part explain the features of disorders such as neurological dysfunction or acute respiratory distress syndrome that respond poorly to treatment with alternative energy sources.

Very long chain acyl-CoA dehydrogenase (VLCAD) is the dominant long chain acyl-CoA dehydrogenase (ACAD) in energy generation in human muscle and the heart. In contrast, this study provides evidence that ACAD9 and long chain acyl-CoA dehydrogenase (LCAD) more likely function in lipid recycling and synthesis in human brain and lung, respectively, supported by their unique substrate utilization and tissue distribution pattern. Furthermore, we have identified a new genetic deficiency of ACAD9 presenting with episodic liver failure and cardiomyopathy during otherwise mild illnesses, along with chronic neurologic dysfunction. This disorder represents the first in a b-oxidation enzyme primarily involved in lipid recycling or synthesis, revealing a new mechanism of pathogenesis in human disease.

Source(s) of Support

National Institutes of Health

Principal Investigator

Gerard Vockley, MD, PhD