The chain and its test points: a testable model linking sensory throughput, thiol reserve and copper delivery in post-COVID illness, fatigue and sensory hypersensitivity

Version 1.2 (25 September 2026): Four further test points are added — the redox switch at PTEN and ATM (gap G9, with predictions P11 and P12), copper accumulation as an acquired state (G10, with P13), the sulfate exit at the endothelial glycocalyx (G11, with P14), and the shared draw on the thiol pool by pathogens that cannot synthesise it (G12, with P15). With them the model closes into a circle a second time, now around copper: delivery of copper to ATP7A and ATP7B is co-regulated by the glutathione system, ATP7A loads extracellular superoxide dismutase SOD3 on the glycocalyx, and superoxide is the fourth link of the chain from which peroxynitrite is formed. The thiol pool therefore also carries the defence against the very species that consumes it. Also included: four reinforcements of existing predictions, a self-correction to gap 5 (the earlier wording was drawn too widely; the gap stands for two different and sharper reasons), the extension of the series to ten parts, a fifth study design covering three of the new predictions in a single blood draw, and twenty-six additional references. The sheet now states fifteen falsifiable predictions and twelve named gaps. Versions 1.0 and 1.1 remain citable under the same concept DOI. Version 1.1 (13 September 2026): The vitamin K cycle is added as an eighth test point (gap G8) with two new falsifiable predictions (P9, P10) and fourteen additional references. With it the model closes into a circle: peroxynitrite, the endpoint of the chain as described in version 1.0, acts through S-nitrosylation of thioredoxin-like domains on vitamin K reduction, and through undercarboxylated matrix Gla protein back onto calcium distribution, where the chain begins. A figure of the closed chain has been added to section 1. Version 1.0 remains citable under the same concept DOI.