Oral lesions in linear immunoglobulin A (IgA) bullous dermatosis (LAD). This is a rare autoimmune disease that leads to blistering of the skin and mucous membranes. It is caused by the immune system attacking the proteins that hold skin cells together at the junction between the epidermis and dermis. LAD is characterised by a linear band of IgA molecules at this junction. In most cases the cause is not known, but in some cases it is drug-induced. Treatment involves corticosteroids or immunosuppressants.