LQT1 accounts

LQT1 accounts for about half of the patients
with long-QT syndrome. The gene for LQT2 encodes
a 1195-amino-acid transmembrane protein
responsible for the other major potassium
channel that participates in phase 3 repolarization
(HERG stands for (human-ether-r-go-gorelated
gene, a Drosophila homologue). LQT3, a
sodium channel protein, consists of four subunits,
each containing six transmembrane
domains and a number of phosphate-binding
sites. Homozygosity for LQT1 (KVLQT1 gene) or
LQT5 (KCNE1 gene) causes a form of long-QT
syndrome associated with deafness, the Jervell
and Lange-Nielsen syndrome. (Figure adapted
from Ackerman and Clapham, 1997.) It is important
to distinguish the different types because
the choice of medication differs.