And another way to remember the NADH and FADH2 synthesis location on the cycle is to notice how the enzymes are all dehydrogenases, and if you just memorize succinate dehydrogenase is the one that makes FADH2, then the rest make NADH !! Over all great series though man.
For FADH deficiency, see Vitamin B2 deficiency
Mnemonic
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NAD NAD GAH FAH NAH → NAD (1st NADH: Isocitrate dehydrogenase) → NAD (2nd NADH: α-Ketoglutarate dehydrogenase, thiamine-dependent t) → GAH (GTP: Succinyl-CoA synthetase; “G” for GTP, “AH” sounds like the “high-energy” thioester hydrolysis) → FAH (FADH₂: Succinate dehydrogenase; “F” for FAD/FADH₂) → NAH (3rd NADH: Malate dehydrogenase)