X-linked severe combined immunodeficiency (X-SCID)

X-linked severe combined immunodeficiency (X-SCID) is a genetic disorder where boys have a defective gene on the X chromosome that impairs their immune system. This defect prevents the development of functional T and B lymphocytes, critical cells that fight infections. As a result, affected individuals are extremely vulnerable to infections from bacteria, viruses, and fungi that healthy people can usually resist. X-SCID is usually inherited from carrier mothers and typically manifests early in life, requiring treatments like bone marrow transplants to restore immune function and prevent life-threatening infections.