This gene is responsible for the potassium channel beta subunit MiRP1 which generates the potassium current IKr, and variant 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 the gene 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. The product of this gene is an auxiliary beta-subunit (NaVβ4) forming cardiac sodium channels, variants in which increase the late sustained sodium current. LQT13 is caused by variants in GIRK4, a protein involved in the parasympathetic modulation of the heart. Clinically, the patients are characterized by only modest QT prolongation, but an increased propensity for atrial arrhythmias. LQT14, LQT15 and LQT16 are caused by variants in the genes responsible for calmodulin (CALM1, CALM2, and CALM3 respectively).
In cases where a patient presents SIgAD and another condition which is treatable with IVIG, then a physician may treat the other condition with IVIG. The use of IVIG to treat SIgAD without first demonstrating an impairment of specific antibody formation is not recommended. Prognosis
Prognosis is excellent, although there is an association with autoimmune disease. Of note, selective IgA deficiency can complicate the diagnosis of one such condition, celiac disease, as the deficiency masks the high levels of certain IgA antibodies usually seen in celiac disease.As opposed to the related condition CVID, selective IgA deficiency is not associated with an increased risk of cancer.Patients with Selective IgA deficiency rarely have severe reactions to blood transfusions. Although Selective IgA deficiency is common, severe reactions to blood transfusions are very rare. People with selective IgA deficiency do not require special blood products unless they have a history of a severe allergic reaction to a blood transfusion. Epidemiology
Prevalence varies by population, but is on the order of 1 in 100 to 1 in 1000 people, making it relatively common for a genetic disease. SIgAD occurs in 1 in 39 to 1 in 57 people with celiac disease. This is much higher than the prevalence of selective IgA deficiency in the general population. It is also significantly more common in those with type 1 diabetes.It is more common in males than in females. See also
B cell deficiency

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