•   Idiopathic, haemoglobinopathies (e.g., sickle cell anaemia, thalassemia and leukaemia)  •   Illicit drugs (e.g., cocaine and cannabis)  •   Medications11 (e.g., antipsychotics, antidepressants, intracavernosal PGE-1 injections, PDE-5 inhibitors, anticoagulants and alpha-blockers)  •   Pelvic malignancy, neurological disorders (e.g., cauda equina and spinal cord injury)  •   Infections (e.g., SARS-CoV-2)12  •   Toxins (e.g., black widow spider bite, scorpion sting and carbon monoxide poisoning)  •   Metabolic disorders (e.g., amyloidosis). Here, PDE5A is linked to carbon monoxide poisoning.