View source for LQT1

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{{Long QT Syndrome}}

{{CMG}}

==Overview==
LQT1 is the most common subtype of long QT syndrome. It is caused by a mutation on chromosome 11p15.5, which codes for the voltage-gated potassium channel, [[KvLQT1]]. The defect in the channel is what leads to the lengthened time of [[repolarization]] of the heart, leading to a prolonged [[QT interval]] seen on [[EKG]]. The severity and type of symptoms in LQT1 will vary based on where exactly the mutation is located, and whether it is a homozygous or heterozygous mutation.

==Long QT1 Syndrome==
{| class="wikitable"
| '''Type''' || '''OMIM''' || '''Mutation''' || '''Notes'''
 |- 
 | [[LQT1]] || {{OMIM2|192500}} || alpha subunit of the slow delayed rectifier potassium channel ([[KvLQT1]] or KCNQ1)  || The current through the heteromeric channel (KvLQT1 + minK) is known as I<sub>Ks</sub>.  These mutations often cause LQT by reducing the amount of repolarizing current that is required to terminate the action potential, leading to an increase in the action potential duration (APD).  These mutations tend to be the most common yet least severe. 
|}



LQT1 is the most common type of long QT syndrome, making up about 40 to 55 percent of all cases.  This variant will sometimes come to the attention of the cardiologist following a cardiac event during exercise like swimming. The LQT1 [[gene]] is {{gene|KCNQ1}} which has been isolated to[[chromosome]]11p15.5. KCNQ1 codes for the voltage-gated potassium channel [[KvLQT1]] that is highly expressed in the heart.  It is believed that the product of the KCNQ1 gene produces an alpha subunit that interacts with other proteins (particularly the minK beta subunit) to create the I<sub>Ks</sub> ion channel, which is responsible for the delayed potassium rectifier current of the [[cardiac action potential]].

Mutations to the KCNQ1 gene can be inherited in an [[autosomal dominant]] or an[[autosomal recessive]] pattern in the same family.  In the autosomal recessive mutation of this gene,[[homozygous]] mutations in KVLQT1 leads to severe prolongation of the QT interval (due to near-complete loss of the I<sub>Ks</sub> ion channel), and is associated with increased risk of ventricular arrhythmias and congenital deafness.  This variant of LQT1 is known as the [[Jervell and Lange-Nielsen syndrome]].

Most individuals with LQT1 show paradoxical prolongation of the QT interval with infusion of [[epinephrine]].  This can also unmark latent carriers of the LQT1 gene.

Many [[missense mutation]]s of the LQT1 gene have been identified.  These are often associated with a high risk percentage of symptomatic carriers and sudden death. Mutations that occur in the transmembrane region in the cells of affected persons, are more likely to lead to symptoms and manifestations such as [[syncope]], aborted [[cardiac arrest]] and [[sudden cardiac death]], when compared with mutations that occur in the C-terminal region.

==References==
{{Reflist|2}}

[[Category:Cardiology]]
[[Category:Electrophysiology]]