In general, lymphocytopenia (a low lymphocyte count) occurs because:
A combination of these factors also may cause a low lymphocyte count.
Many diseases, conditions, and factors can lead to a low lymphocyte count. These conditions can be acquired or inherited. "Acquired" means you aren't born with the condition, but you develop it. "Inherited" means your parents passed the gene for the condition on to you.
Exactly how each disease, condition, or factor affects your lymphocyte count isn't known. Some people have low lymphocyte counts with no underlying cause.
Many acquired diseases, conditions, and factors can cause lymphocytopenia. Examples include:
Certain inherited diseases and conditions can lead to lymphocytopenia. Examples include DiGeorge anomaly, Wiskott-Aldrich syndrome, severe combined immunodeficiency syndrome, and ataxia-telangiectasia. These inherited conditions are rare.