Glutaric aciduria type 1 (GA1) is an inborn error of lysine degradation characterized by a specific encephalopathy that is caused by toxic accumulation of lysine degradation intermediates. Substrate reduction through inhibition of DHTKD1, an enzyme upstream of the defective glutaryl-CoA dehydrogenase, has been investigated as a potential therapy, but revealed the existence of an alternative enzymatic source of glutaryl-CoA. Here we show that loss of DHTKD1 in GCDH-deficient HEK-293 cells leads

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... o a 2-fold decrease in the established GA1 clinical biomarker glutarylcarnitine, and demonstrate that OGDH is responsible for this remaining glutarylcarnitine production. We furthermore show that DHTKD1 interacts with OGDH, DLST and DLD to form a hybrid α-ketoglutaric and α-ketoadipic acid dehydrogenase complex. In summary, α-ketoadipic acid is an in vivo substrate for DHTKD1, but also OGDH. The classic α-ketoglutaric dehydrogenase complex can exist as a previously undiscovered hybrid containing DHTKD1 displaying improved kinetics towards α-ketoadipic acid.