Change in the amino acid sequence of a protein is called a mutation. Antibodies, also known as immunoglobulins, are proteins that are composed of multiple subunits; two heavy chains and two light chains. The function of the antibody will be deranged depending on what subunit is mutated. If there is mutation in the heavy chain, the antibody may lose the function to recognize antigens and may produce a non-specific kind of immune disorder. On the other hand, if light chains are mutated then there may be detachment of the light chains to the heavy chains and will pathologically be excreted in the urine (Bence-Jones proteinuria).