| Channelopathy | |
|---|---|
 | |
| Sodium channel, implicated in channelopathies includingBrugada syndrome,Long QT syndrome,Dravet syndrome,Paramyotonia congenita | |
| Specialty | Medical genetics,Neuromuscular medicine,Cardiology |
| Symptoms | Dependent on type. Include:Syncope,muscle weakness,seizures,breathlessness |
| Complications | Dependent on type. Include:Sudden death |
| Causes | Genetic variants |
Channelopathies are a group of diseases caused by the dysfunction ofion channel subunits or their interactingproteins. These diseases can beinherited or acquired by other disorders, drugs, or toxins. Mutations ingenes encodingion channels, which impair channel function, are the most common cause of channelopathies.[1] There are more than 400 genes that encode ion channels, found in all human cell types and are involved in almost all physiological processes.[2] Each type of channel is a multimeric complex of subunits encoded by a number of genes. Depending where themutation occurs it may affect the gating, conductance, ion selectivity, or signal transduction of the channel.
Channelopathies can be categorized based on the organ system which they are associated with. In the cardiovascular system, the electrical impulse needed for each heartbeat is made possible by theelectrochemical gradient of each heart cell. Because the heartbeat is dependent on the proper movement of ions across the surface membrane, cardiac channelopathies make up a key group of heart diseases.[3]Long QT syndrome, the most common form of cardiac channelopathy, is characterized by prolonged ventricular repolarization, predisposing to a high risk of ventricular tachyarrhythmias (e.g., torsade de pointes), syncope, and sudden cardiac death.[1]
The channelopathies of humanskeletal muscle include hyper- and hypokalemic (high and low potassium blood concentrations)periodic paralysis,myotonia congenita andparamyotonia congenita.
Channelopathies affectingsynaptic function are a type ofsynaptopathy.
Mutations in genes encoding ion channels, which cause defects in channel function, are the most common cause of channelopathies.[1]
Acquired channelopathies are caused by acquired disorders, drug use, toxins, etc.[1]
The types in the following table are commonly accepted.[by whom?][citation needed] Channelopathies currently under research, likeKir4.1 potassium channel inmultiple sclerosis, are not included.
| Condition | Channel type |
|---|---|
| Bartter syndrome | various, by type |
| Brugada syndrome | various, by type |
| Catecholaminergic polymorphic ventricular tachycardia (CPVT) | Ryanodine receptor |
| Congenital hyperinsulinism | Inward-rectifier potassium ion channel |
| Cystic fibrosis | Chloride channel |
| Dravet syndrome | Voltage-gated sodium channel |
| Episodic ataxia | Voltage-gated potassium channel |
| Erythromelalgia | Voltage-gated sodium channel |
| Generalized epilepsy with febrile seizures plus | Voltage-gated sodium channel |
| Familial hemiplegic migraine | various |
| Associated with one particular disabling form offibromyalgia[4] | Voltage-gated sodium channel |
| Hyperkalemic periodic paralysis | Voltage-gated sodium channel |
| Hypokalemic periodic paralysis | Voltage-gated sodium channel or voltage-dependent calcium channel (calciumopathy) |
| Lambert–Eaton myasthenic syndrome | Voltage-gated calcium channel |
| Long QT syndrome main typeRomano-Ward syndrome | various, by type |
| Malignant hyperthermia | Ligand-gated calcium channel |
| Mucolipidosis type IV | Non-selective cation channel |
| Myotonia congenita | Voltage-dependent chloride channel |
| Neuromyelitis optica | Aquaporin-4 water channel |
| Neuromyotonia | Voltage-gated potassium channel |
| Nonsyndromic deafness | various |
| Paramyotonia congenita (aperiodic paralysis) | Voltage-gated sodium channel |
| Polymicrogyria (brain malformation) | Voltage-gated sodium channel,SCN3A[5]ATP1A3[6] |
| Retinitis pigmentosa (some forms) | Ligand-gated non-specific ion channels |
| Short QT syndrome | various potassium channels suspected |
| Temple–Baraitser syndrome | Voltage-gated potassium channel,KCNH1[7] |
| Timothy syndrome | Voltage-dependent calcium channel |
| Tinnitus | Voltage-gated potassium channel of the KCNQ family |
| Seizure | Voltage-dependent potassium channel[8][9] |
| Zimmermann–Laband syndrome, type1 | Voltage-gated potassium channel,KCNH1 |
Bothchannels andpumps are ion transporters which move ions across membranes. Channels move ions quickly, throughpassive transport, down electrical and concentration gradients (moving "downhilll"); whereas pumps move ions slowly, throughactive transport, building-up gradients (moving "uphill").[10] Historically the difference between the two seemed cut and dried; however, recent research has shown that in some ion transporters, it is not always clear whether it functions as a channel or a pump.[10]
Diseases involving ion pumps can produce symptoms similar to channelopathies, as they both involve the movement of ions across membranes.Brody disease (also known as Brody myopathy) includes symptoms similar tomyotonia congenita, including muscle stiffness and cramping after initiating exercise (delayed muscle relaxation). However, it is pseudo-myotonia as those with Brody disease have normalEMG.[11]
Due to similar symptoms, different genes for both channels and pumps can be associated with the same disease. For instance,polymicrogyria has been associated with the channel geneSCN3A[12] and the pump geneATP1A3,[6] among other genes that are not ion transporters.[13]
VIDEOChannel Surfing in Pediatrics by Carl E. Stafstrom, M.D., at the UW-Madison Health Sciences Learning Center.