Variants causing a reduction in the early peak current can cause Brugada syndrome and cardiac conduction disease, while other variants have been associated with dilated cardiomyopathy. Some variants which affect both the early and late sodium current can cause overlap syndromes which combine aspects of both LQT3 and Brugada syndrome. Rare Romano–Ward subtypes (LQT4-6 and LQT9-16)
LQT5 is caused by variants in the KCNE1 gene responsible for the potassium channel beta subunit MinK. This subunit, in conjunction with the alpha subunit encoded by KCNQ1, is responsible for the potassium current IKs which is decreased in LQTS. LQT6 is caused by variants in the KCNE2 gene responsible for the potassium channel beta subunit MiRP1 which generates the potassium current IKr. Variants that decrease this current have been associated with prolongation of the QT interval. However, subsequent evidence such as the relatively common finding of variants in the gene in those without long QT syndrome, and the general need for a second stressor such as hypokalaemia to be present to reveal the QT prolongation, has suggested that this gene instead represents a modifier to susceptibility to QT prolongation. Some therefore dispute whether variants in KCNE2 are sufficient to cause Romano-Ward syndrome by themselves.LQT9 is caused by variants in the membrane structural protein, caveolin-3. Caveolins form specific membrane domains called caveolae in which voltage-gated sodium channels sit. Similar to LQT3, these caveolin variants increase the late sustained sodium current, which impairs cellular repolarization.LQT10 is an extremely rare subtype, caused by variants in the SCN4B gene.
squatting down, walking up or down stairs, looking out of the window of a moving car or train). Vertigo is called height vertigo when the sensation of vertigo is triggered by heights. Height vertigo is caused by a conflict between vision, vestibular and somatosensory senses. This occurs when vestibular and somatosensory systems sense a body movement that is not detected by the eyes. More research indicate that this conflict leads to both motion sickness and anxiety. Causes
Traditionally, acrophobia has been attributed, like other phobias, to conditioning or a traumatic experience. Recent studies have cast doubt on this explanation. Individuals with acrophobia are found to be lacking in traumatic experiences. Nevertheless, this may be due to the failure to recall the experiences, as memory fades as time passes. To address the problems of self report and memory, a large cohort study with 1000 participants was conducted from birth; the results showed that participants with less fear of heights had more injuries because of falling.