Immunoglobulin Family Genes encode structurally-related Immunoglobulin Family Proteins containing one, or more, 100-aa Immunoglobulin domain that includes a conserved intradomain disulfide bond and may be involved in protein-protein or protein-ligand interactions. Immunoglobulin Family members include hundreds of functionally diverse proteins, such as Immunoglobulins, the muscle kinase titin, and receptor tyrosine kinases. (NCI) [ ]