Genetic aspects of pain and its variability in the human population

The sensation of pain is common to both animals and human beings. Its threshold, intensity, tolerability, and characteristics are variable and depend on ethnicity, gender, stress exposure, co-existing mental disorders, such as depression or anxiety, social and economical background, as well as on genetic factors. It is estimated that about 5 and 20 percent of population suffer from acute and chronic pain, respectively, which results in the search for medical advice in healthcare facilities, and causes great expenses in health care budgets worldwide. Research aimed at identifying the causative agents of pain syndromes include single nucleotidepolymorphism (SNP), family history studies, twin siblings' genetic diversity studies, and recently, also a genome-wide association study (GWAS). Clinical syndromes of derangement of pain sensation are generally caused by single gene mutations (e.g. erythromelalgia and paroxysmal extreme pain disorder caused by mutations of SCN9A), but can also be associated with multiple gene mutations, as happens in migraine, fibromyalgia or hereditary sensory and autonomic neuropathies. Structural changes of proteins caused by gene mutations involve various cellular element, such as ion channels, receptors, scaffolding proteins, enzymes, transporting proteins, eventually leading to numerous clinical entities in which pain or its lack remain the leading symptoms. The sensation of pain is initiated by a stimulus, which activates the free nerve endings via chemical mediators, and the mechanical stimuli is then transmitted to the brain along the neurons and spinal tracts. Synaptic neurotransmitters and cell structures take part in this process and eventually affect the intensity of pain sensation.