Find information on thousands of medical conditions and prescription drugs.

Long QT Syndrome

The long QT syndrome (LQTS) is a heart disease in which there is an abnormally long delay between the electrical excitation (or depolarization) and relaxation (repolarization) of the ventricles of the heart. It is associated with syncope (loss of consciousness) and with sudden death due to ventricular arrhythmias. Arrhythmias in individuals with LQTS are often associated with exercise or excitement. The cause of sudden cardiac death in individuals with LQTS is ventricular fibrillation. more...

Home
Diseases
A
B
C
D
E
F
G
H
I
J
K
L
Amyotrophic lateral...
Bardet-Biedl syndrome
Labyrinthitis
Lafora disease
Landau-Kleffner syndrome
Langer-Giedion syndrome
Laryngeal papillomatosis
Laryngomalacia
Lassa fever
LCHAD deficiency
Leber optic atrophy
Ledderhose disease
Legg-Calvé-Perthes syndrome
Legionellosis
Legionnaire's disease
Leiomyoma
Leiomyosarcoma
Leishmaniasis
Lemierre's syndrome
Lennox-Gastaut syndrome
Leprechaunism
Leprophobia
Leprosy
Leptospirosis
Lesch-Nyhan syndrome
Leukemia
Leukocyte adhesion...
Leukodystrophy
Leukomalacia
Leukoplakia
LGS
Li-Fraumeni syndrome
Lichen planus
Ligyrophobia
Limb-girdle muscular...
Limnophobia
Linonophobia
Lipodystrophy
Lipoid congenital adrenal...
Liposarcoma
Lissencephaly
Lissencephaly syndrome...
Listeriosis
Liticaphobia
Liver cirrhosis
Lobster hand
Locked-In syndrome
Loiasis
Long QT Syndrome
Long QT syndrome type 1
Long QT syndrome type 2
Long QT syndrome type 3
LSA
Lung cancer
Lupus erythematosus
Lyell's syndrome
Lygophobia
Lyme disease
Lymphangioleiomyomatosis
Lymphedema
Lymphoma
Lymphosarcoma
Lysinuric protein...
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
Medicines

Individuals with LQTS have a prolongation of the QT interval on the ECG. The Q point on the ECG corresponds to the beginning of ventricular depolarization while the T point corresponds to the beginning of ventricular repolarization. The QT interval is measured from the Q point to the end of the T wave. While many individuals with LQTS have persistent prolongation of the QT interval, some individuals do not always show the QT prolongation; in these individuals, the QT interval may prolong with the administration of certain medications.

Genetics

The two most common types of LQTS are genetic and drug-induced. Genetic LQTS can arise from mutation to one of several genes. These mutations tend to prolong the duration of the ventricular action potential (APD), thus lengthening the QT interval. LQTS can be inherited in an autosomal dominant or an autosomal recessive fashion. The autosomal recessive forms of LQTS tend to have a more severe phenotype, with some variants having associated syndactyly or congenital neural deafness. A number of specific genes loci have been identified that are associated with LQTS. Following is a list of the most common mutations:

  • LQT1 - mutations to the alpha subunit of the slow delayed rectifier potassium channel (KvLQT1 or KCNQ1). The current through the heteromeric channel (KvLQT1+minK) is known as IKs. This mutation is thought to cause LQT by reducing the amount of repolarizing action potential current that prolongs action potential duration (APD). These mutations tend to be the most common yet least severe.
  • LQT2 - mutations to the alpha subunit of the fast delayed rectifier potassium channel (HERG + miRP). Current through this channel is known as IKr. This phenotype is also probably caused by a reduction in repolarizing current.
  • LQT3 - mutations to the alpha subunit of the sodium channel (SCN5A). Current through is channel is commonly referred to as INa. Depolarizing current through the channel late in the action potential is thought to prolong APD. The late current is due to failure of the channel to remain inactivated and hence enter a bursting mode in which significant current can enter when it should not. These mutations are more lethal but less common.
  • LQT4 - mutations in an anchor protein Ankyrin B which anchors the ion channels in the cell. Very rare.
  • LQT5 - mutations in the beta subunit MinK which coassembles with KvLQT1.
  • LQT6 - mutations in the beta subunit MiRP1 which coassembles with HERG.
  • LQT7 - mutations in the potassium channel KCNJ2 which leads to Andersen-Tawil syndrome.
  • LQT8 - mutations in the calcium channel Cav1.2 encoded by the gene CACNA1c leading to Timothy's syndrome

Other mutations affect the beta subunits ion channels. For example LQT6 affects minK (aka KCNE1) which is the beta subunit that coassembles with KCNQ1 to form IKs channels.

Read more at Wikipedia.org


[List your site here Free!]


Kvlqt1 And Scn5a Gene Mutation Testing In A Long-Qt Syndrome Family Of Singapore - Abstract
From CHEST, 10/1/00 by Dong Ling Liu

Dong Ling Liu, MD,PhD(*); Ming Yan MD,PhD; Wuxiang Liao, PhD and Yean Leng Lim, MD,PhD. Cardiac Research Laboratory, National Heart Centre, Outram Road, Singapore and Department of Obstetrics and Gynaecology, National University of Singapore, Kent Ridge, Singapore.

PURPOSE: Long QT (LQT) syndrome is a cardiac disorder that causes sudden death from ventricular tachyarrhythmias. Four LQT genes have been identified: KVLQT1 (LQT1, a cardiac potassium channel subunit gene), HERG (LQT2, a cardiac potassium channel gene), SCN5A (LQT3, a cardiac sodium channel gene) and Mink (LQT5, a cardiac potassium channel subunit gene). The aim of this study is to identify whether there are the mutations of KVLQT1 and SCN5A in a long-QT syndrome family in Singapore.

METHODS: We investigated the mutations of KVLQT1 and SCN5A genes by using polymerase chain reaction (PCR), restriction endonuclease analysis and gene sequencing in a LQT syndrome family in Singapore. Approval to use the blood samples was given by ethics Committee of Singapore General Hospital. The blood samples were obtained from a LQT syndrome family involved in 11 cases who three of them are LQT patients. 8 health people are as a control group. Genomic DNA was isolated from peripheral blood leukocytes. Oligonucleotide primer pairs were used to amplify to KVLQT1 pre-S6 and the SCN5A-coding region (exons 23 and 28) respectively. The restriction endonucleases (Hha I, Sty I and HgaI) and gene sequencing have been used to define KVLQT1 and SCN5A mutations respectively.

RESULTS: The results showed that the 195bp PCR products were cleaved into 129bp and 66bp fragments by using Hha I restriction endonuclease and the mutation point of A212E of KVLQT1 was not detected in the family. This was confirmed by gene sequencing. The mutation points at T1620M of the exons 28 and the codon 1397 of exon 23 of SCN5A were not found by using HagI and StyI restriction endonuclease and gene sequencing in the LQT syndrome family.

CONCLUSION: The mutation points of A212E of KVLQT1, T1620M of exons 28 and the codon 1397 of exon 23 of SCN5A were not detected in a LQT family of Singapore.

CLINICAL IMPLICATIONS: The molecular genetic testing may provide a diagnosis of or indication of risk for patients and relatives.

COPYRIGHT 2000 American College of Chest Physicians
COPYRIGHT 2001 Gale Group

Return to Long QT Syndrome
Home Contact Resources Exchange Links ebay