There are several types of severe combined immune deficiency (SCID). All patients lack both the cellular and humoral arms of the immune system and present in infancy with persistent severe viral, bacterial, protozoan or fungal infections along with rashes, diarrhea, poor wound healing, and failure-to-thrive. T-cell lymphopenia is characteristic of all forms of SCID, but the presence of B cells and NK cells is variable depending on the genes involved. In RAG1 or RAG2 deficiency, the typical circulating lymphocyte profile is T–B–NK+. This profile is distinct from the more common X-linked SCID, which most often has the profile T–B+NK–, as well as from ADA-deficient SCID which has the profile T–B–NK–.