Congenital insensitivity to pain | |
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Specialty | Neurology |
Congenital insensitivity to pain (CIP), also known as congenital analgesia, is one or more extraordinarily rare conditions in which a person cannot feel (and has never felt) physical pain. [1] The conditions described here are separate from the HSAN group of disorders, which have more specific signs and cause. Because feeling physical pain is vital for survival, CIP is an extremely dangerous condition. [1] It is common for people with the condition to die in childhood due to injuries or illnesses going unnoticed. [1] [2] Burn injuries are among the more common injuries. [2]
For people with this disorder, cognition and sensation are otherwise normal; for instance, patients can still feel discriminative touch (though not always temperature [3] ), and there are generally no detectable physical abnormalities.
Because children and adults with the disorder cannot feel pain, they may not respond to problems, thus being at a higher risk of more severe diseases. Children with this condition often sustain oral cavity damage both in and around the oral cavity (such as having bitten off the tip of their tongue) or fractures to bones. [2] Unnoticed infections and corneal damage due to foreign objects in the eye are also seen. [2] [4]
There are generally two types of non-response exhibited: [1] [4]
It may be that the condition is caused by increased production of endorphins in the brain.[ citation needed ] In this case, naloxone may be a treatment, but it does not always work. [5] In all cases, this disorder can be in the voltage-gated sodium channel SCN9A (Nav1.7). [6] Patients with such mutations are congenitally insensitive to pain and lack other neuropathies. There are three mutations in SCN9A: W897X, located in the P-loop of domain 2; I767X, located in the S2 segment of domain 2; and S459X, located in the linker region between domains 1 and 2. This results in a truncated non-functional protein. Nav1.7 channels are expressed at high levels in nociceptive neurons of the dorsal root ganglia. As these channels are likely involved in the formation and propagation of action potentials in such neurons, it is expected that a loss of function mutation in SCN9A leads to abolished nociceptive pain propagation. [7] [8]
PRDM12 gene is normally switched on during the development of pain-sensing nerve cells. People with homozygous mutations of the PRDM12 gene experience congenital insensitivity to pain (CIP). [9] [10]
A heterozygous microdeletion in the FAAH-OUT pseudogene of the fatty acid amide hydrolase (FAAH) chromosomal region that is expressed in the brain and dorsal root ganglia together with a common hypomorphic single nucleotide polymorphism in the FAAH gene was identified as the presumptive cause of congenital analgesia in a woman named Jo Cameron. She experienced lifelong insensitivity to pain and was oblivious to cuts and burns, did not experience pain during childbirth, did not experience pain from degeneration of a hip that required hip replacement surgery, and did not require analgesics for postoperative pain. Furthermore, she exhibited expedited wound healing and reduced scarring, could not sense heat from chili peppers, did not experience depression, fear, and anxiety and lacked a normal fear response to erratic and aggressive behaviour. However, Cameron also experienced slight memory impairment (was prone to losing the trail of thought while speaking, and experienced some forgetfulness), and could not experience thrill ("adrenaline rush"). [11] [12]
Another gene implicated in human pain insensitivity is ZFHX2, which encodes zinc finger homeobox 2. A 2018 study analysed six members of a family with inherited pain insensitivity and identified a "novel point mutation in ZFHX2, encoding a putative transcription factor expressed in small diameter sensory neurons", as the cause. As a therapeutic application, the study further discuses how "the ZFHX2 variant and downstream regulated genes associated with a human pain-insensitive phenotype are ... potential novel targets for the development of new analgesic drugs". [13]
Developmental disabilities such as autism can include varying degrees of pain insensitivity as a sign. [14] However, since these disorders are characterized by dysfunction of the sensory system in general, autism is not in itself an indicator of congenital insensitivity to pain.
The opioid antagonist naloxone allowed a woman with congenital insensitivity to pain to experience it for the first time. [15] Similar effects were observed in Nav1.7 null mice treated with naloxone. [15] As such, opioid antagonists like naloxone and naltrexone may be effective in treating the condition. [15]
It has been estimated to have a worldwide incidence of approximately 1 in every 125 million births. [16]
Congenital insensitivity to pain is found at an abnormally high frequency in Vittangi, a village in Kiruna Municipality in northern Sweden, where nearly 40 cases have been reported. [17]
Spinal muscular atrophies (SMAs) are a genetically and clinically heterogeneous group of rare debilitating disorders characterised by the degeneration of lower motor neurons and subsequent atrophy (wasting) of various muscle groups in the body. While some SMAs lead to early infant death, other diseases of this group permit normal adult life with only mild weakness.
Opioid use disorder (OUD) is a substance use disorder characterized by cravings for opioids, continued use despite physical and/or psychological deterioration, increased tolerance with use, and withdrawal symptoms after discontinuing opioids. Opioid withdrawal symptoms include nausea, muscle aches, diarrhea, trouble sleeping, agitation, and a low mood. Addiction and dependence are important components of opioid use disorder.
Erythromelalgia or Mitchell's disease is a rare vascular peripheral pain disorder in which blood vessels, usually in the lower extremities or hands, are episodically blocked, then become hyperemic and inflamed. There is severe burning pain and skin redness. The attacks are periodic and are commonly triggered by heat, pressure, mild activity, exertion, insomnia or stress. Erythromelalgia may occur either as a primary or secondary disorder. Secondary erythromelalgia can result from small fiber peripheral neuropathy of any cause, polycythemia vera, essential thrombocythemia, hypercholesterolemia, mushroom or mercury poisoning, and some autoimmune disorders. Primary erythromelalgia is caused by mutation of the voltage-gated sodium channel α-subunit gene SCN9A.
Congenital insensitivity to pain with anhidrosis (CIPA) is a rare autosomal recessive disorder of the nervous system which prevents the feeling of pain or temperature and prevents a person from sweating. Cognitive disorders are commonly coincidental. CIPA is the fourth type of hereditary sensory and autonomic neuropathy (HSAN), and is also known as HSAN IV.
Fatty-acid amide hydrolase 1 (FAAH) is a member of the serine hydrolase family of enzymes. It was first shown to break down anandamide (AEA), an N-acylethanolamine (NAE) in 1993. In humans, it is encoded by the gene FAAH.
Small fiber peripheral neuropathy is a type of peripheral neuropathy that occurs from damage to the small unmyelinated and myelinated peripheral nerve fibers. These fibers, categorized as C fibers and small Aδ fibers, are present in skin, peripheral nerves, and organs. The role of these nerves is to innervate some skin sensations and help control autonomic function. It is estimated that 15–20 million people in the United States have some form of peripheral neuropathy.
Sodium voltage-gated channel alpha subunit 9 is a sodium ion channel that in humans is encoded by the SCN9A gene. It is usually expressed at high levels in two types of neurons: the nociceptive (pain) neurons at the dorsal root ganglion (DRG) and trigeminal ganglion; and sympathetic ganglion neurons, which are part of the autonomic (involuntary) nervous system.
Sodium channel, voltage-gated, type XI, alpha subunit also known as SCN11A or Nav1.9 is a voltage-gated sodium ion channel protein which is encoded by the SCN11A gene on chromosome 3 in humans. Like Nav1.7 and Nav1.8, Nav1.9 plays a role in pain perception. This channel is largely expressed in small-diameter nociceptors of the dorsal root ganglion and trigeminal ganglion neurons, but is also found in intrinsic myenteric neurons.
Sodium channel protein type 2 subunit alpha, is a protein that in humans is encoded by the SCN2A gene. Functional sodium channels contain an ion conductive alpha subunit and one or more regulatory beta subunits. Sodium channels which contain sodium channel protein type 2 subunit alpha are sometimes called Nav1.2 channels.
Hereditary sensory and autonomic neuropathy (HSAN) or hereditary sensory neuropathy (HSN) is a condition used to describe any of the types of this disease which inhibit sensation.
Hereditary sensory neuropathy, type II also known as HSN2 is a region of a parent protein which in humans is encoded by the WNK1 gene. It is a transcript variant of the WNK1 gene that is selectively expressed in nervous system tissues, and during development. Mutations in this exon of the WNK1 gene have been identified as causative in genetic neuropathy syndromes, and in inherited pain insensitivity.
Nav1.8 is a sodium ion channel subtype that in humans is encoded by the SCN10A gene.
Clinical neurochemistry is the field of neurological biochemistry which relates biochemical phenomena to clinical symptomatic manifestations in humans. While neurochemistry is mostly associated with the effects of neurotransmitters and similarly functioning chemicals on neurons themselves, clinical neurochemistry relates these phenomena to system-wide symptoms. Clinical neurochemistry is related to neurogenesis, neuromodulation, neuroplasticity, neuroendocrinology, and neuroimmunology in the context of associating neurological findings at both lower and higher level organismal functions.
Pain in invertebrates is a contentious issue. Although there are numerous definitions of pain, almost all involve two key components. First, nociception is required. This is the ability to detect noxious stimuli which evokes a reflex response that moves the entire animal, or the affected part of its body, away from the source of the stimulus. The concept of nociception does not necessarily imply any adverse, subjective feeling; it is a reflex action. The second component is the experience of "pain" itself, or suffering—i.e., the internal, emotional interpretation of the nociceptive experience. Pain is therefore a private, emotional experience. Pain cannot be directly measured in other animals, including other humans; responses to putatively painful stimuli can be measured, but not the experience itself. To address this problem when assessing the capacity of other species to experience pain, argument-by-analogy is used. This is based on the principle that if a non-human animal's responses to stimuli are similar to those of humans, it is likely to have had an analogous experience. It has been argued that if a pin is stuck in a chimpanzee's finger and they rapidly withdraw their hand, then argument-by-analogy implies that like humans, they felt pain. It has been questioned why the inference does not then follow that a cockroach experiences pain when it writhes after being stuck with a pin. This argument-by-analogy approach to the concept of pain in invertebrates has been followed by others.
Hereditary sensory and autonomic neuropathy type I or hereditary sensory neuropathy type I is a group of autosomal dominant inherited neurological diseases that affect the peripheral nervous system particularly on the sensory and autonomic functions. The hallmark of the disease is the marked loss of pain and temperature sensation in the distal parts of the lower limbs. The autonomic disturbances, if present, manifest as sweating abnormalities.
PR domain zinc finger protein 12 is a protein that in humans is encoded by the PRDM12 gene. This gene is normally switched on during the development of pain-sensing nerve cells. People with homozygous mutations of the PRDM12 gene experience congenital insensitivity to pain (CIP). PRMD12 is a part of a larger domain that mediate histone methyltransferases. Enzymes target gene promoters in order to control gene expression.
Zinc finger homeobox 2 is a protein that in humans is encoded by the ZFHX2 gene. It has been implicated in pain insensitivity.
The eradication or abolition of suffering is the concept of using biotechnology to create a permanent absence of involuntary pain and suffering in all sentient beings.
Marsili syndrome is an extremely rare genetic disorder which is characterized by symptoms similar to those reported on individuals with congenital insensitivity to pain with anhidrosis. It can be fatal if it goes unnoticed/undiagnosed.
Jo Cameron, also known as Patient PFS, is a Scottish woman who feels no pain and experiences little to no anxiety or other aspects of negative affect.