Final answer:
The two main examples of Severe Combined Immunodeficiency (SCID) diseases are X-linked SCID, primarily affecting males, and Adenosine deaminase deficiency (ADA-SCID), affecting both genders.
Step-by-step explanation:
Severe Combined Immunodeficiency (SCID) is characterized by defects in B-cell and T-cell functions, which result in impaired antibody responses and cell-mediated immune responses.
The two main examples of SCIDs are X-linked SCID, which is the most common form and accounts for nearly half of all cases, typically found in males, and Adenosine deaminase deficiency (ADA-SCID), which affects both boys and girls and is caused by mutations in the enzyme adenosine deaminase. People with SCID are exceptionally vulnerable to infections and cannot develop immunological memory, rendering vaccines ineffective and potentially dangerous.