AIDS

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> acquired **immune deficiency** syndrome
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According to [wikipedia](https://en.wikipedia.org/wiki/HIV/AIDS),

Caused by infection with the human immunodeficiency virus (HIV).Following initial infection, a person may not notice any symptoms or may experience a brief period of influenza-like illness. As the infection progresses, it **interferes more with the immune system**, increasing the risk of common infections like tuberculosis, as well as other opportunistic infections, and tumors that rarely affect people who have working immune systems.

SCID

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> Severe combined **immunodeficiency**
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According to [wikipedia](https://en.wikipedia.org/wiki/Severe_combined_immunodeficiency),

.....is a genetic disorder characterized by the disturbed development of functional T cells and B cells caused by numerous genetic mutations that result in heterogeneous clinical presentations. SCID involves defective antibody response due to either direct involvement with B lymphocytes or through improper B lymphocyte activation due to non-functional T-helper cells. Consequently, both "arms" (B cells and T cells) of the adaptive **immune system are impaired** due to a defect in one of several possible genes. SCID is the most severe form of primary **immunodeficiencies**, and there are now at least nine different known genes in which mutations lead to a form of SCID.

Both the diseases affect the immune system of the human body. So, why they are classified as different disease? What is the property that differentiates the diseases?