HMBS Deficiency, Long-Term ROS Damage and Biochemical Follow-Up Strategies

HMBS deficiency and acute intermittent porphyria (AIP) represent a metabolic paradigm for studying the interactions between enzyme defects, biochemical regulation, and oxidative stress. Hydroxymethylbilane synthase (HMBS) deficiency reduces metabolic flux in the heme biosynthetic pathway, leading to the accumulation of δ-aminolevulinic acid (ALA) and porphobilinogen (PBG). These precursors, particularly ALA, generate reactive oxygen species (ROS) through autooxidation, which causes mitochondrial damage, lipid and protein oxidation, and imAIPred neuronal signaling. The incomplete penetrance of the disease highlights the importance of genetic, epigenetic, and environmental factors in modulating the critical (threshold) metabolic detoxification capacity, explaining why many genetic carriers appear asymptomatic or exhibit only subacute symptoms. Recurrent (or even chronic in the most resistant cases) accumulation of ROS leads to distributed, chronic and degenerative multisystem damage, with sensorimotor neuropathies, autonomic and enteric nervous system dysfunction, gastroparesis, intestinal microcirculatory alterations, glomerular and tubular damage, myocardial fibrosis, hepatic steatosis, and retinopathy. These alterations manifest clinically slowly and often silently, accumulating until symptoms become detectable only in advanced stages. Integrated laboratory assessment of porphyrin precursors, redox status, and organ biomarkers allows for the identification of subclinical metabolic instability, providing a molecular basis for the management of chronic symptoms and targeted preventive strategies. The dynamic biochemical approach transcends the episodic view of AIP, allowing for monitoring clinical latency, subacute phases, post-crisis relapses, and the progression of chronicity, guiding interventions aimed at modulating metabolic flux, reducing oxidative stress, and preserving organ function.