Where a defect of an enzyme in the citric acid cycle decreases atp production

Given the Citric Acid Cycle or Kreb's Cycle or Tricarboxylic acid, an overall decrease in the ATP production in mitochondria can be caused by deficiency of succinyl coenzyme A synthethase).This enzyme act on the conversion of of the succinyl group to succinate. Decrease in ATP levels can be seen in the substrate-level phosphorylation of converting succinyl CoA to succinate.

No, the entire cycle will not be functional resulting to acidosis. The cells would choose to produce lactic acid as means of obtaining ATP. People with deficiency in succinyl CoA synthetase will have fatal infantile lactic acid acidosis.

With respect to the cycle products, there would be a decrease or no ATP present in mitochondria that is produced by TCA cycle. There would also be a decrease in NADH level and the same carbon dioxide level.

Production of ATP would decrease because of the deficiency of succinyl CoA synthetase. Upon the conversion of succinyl CoA to succinate, which is catalyze and act on by succinyl CoA synthetase, an associated production of ATP occurs.