Major histocompatibility complex class II deficiency

This code represents a rare primary immunodeficiency characterized by a severe defect in the expression of MHC class II molecules on antigen-presenting cells. This deficiency leads to impaired T-cell activation and subsequent severe combined immunodeficiency (SCID)-like symptoms, making affected individuals highly susceptible to opportunistic infections.

Use this code for patients diagnosed with major histocompatibility complex class II deficiency, often presenting in infancy with recurrent, severe bacterial, viral, and fungal infections. Documentation should clearly state the diagnosis, typically confirmed by genetic testing or flow cytometry demonstrating absent or reduced MHC class II expression.

• Ensure documentation specifies "class II" deficiency to differentiate from other MHC-related disorders.
• This is a primary immunodeficiency; do not confuse it with secondary immune deficiencies.
• Sequence this code as the primary diagnosis when it is the reason for the encounter.