Final answer:
The provided material does not specify the second most common form of SCID, but it does note that the most common form is X-linked SCID. SCID leads to severe infections and ineffective vaccines, with treatments including bone marrow transplants or gene therapy.
Step-by-step explanation:
Second Most Common Form of SCID
The second most common form of Severe Combined Immunodeficiency (SCID) has not been specified in the provided material; however, it is known that the most common form is X-linked SCID. SCID is characterized by defects in both B-cell and T-cell responses, leading to severe opportunistic infections and a lack of immunological memory, rendering vaccines ineffective.
Treatments include bone marrow transplants, which can be risky, as evidenced by the case of David Vetter, and gene therapy, which offers promise for cases where transplants fail. SCID often results from an X-linked recessive mutation affecting B cell and T cell production.
Medical interventions for SCID, such as bone marrow transplants, come with complications like graft-versus-host disease. While bone marrow transplants replenish the immune system through the proliferative capabilities of hematopoietic stem cells, gene therapy offers an alternative by inserting nondefective genes directly into the patient's cells, eliminating the need for tissue matching.