Adenosine deaminase deficiency

The last SCID we talked about was caused by part of the IL-2 receptor not working. here, adenosine deaminase (ADA) is deficient. ADA is present in all cells as part of a salvage pathway to recycle adenine. interestingly, when you have a deficiency of this, the two cells that get sick are B cells and T cells and not other cells in the body.

Elements of the case

• female patient who began to get sick with multiple infections, including Candida, before one year of age

• mother’s antibodies should be able to protect the child for about six months. if you see multiple infections immediately after mom’s antibodies are scheduled to begin wearing off (say, just before one year of age), you really should think about a congenital immunological disorder

• family history of SCID in a brother

• no thymus on chest X-ray

• very low lymphocyte counts. no response to phytohemagglutinin, which usually stimulates T cells to divide. other such plant-derived molecules are concanavalin A and pokeweed mitogen

• no ADA in red cells

• cured with a bone marrow transplant from brother (not the brother who also has SCID, ha ha…well anyway it was pretty funny when he said it)

Principles to understand

• both T and B cells that lack ADA are poisoned by deoxyadenosine

• other cell types are not as sensitive as lymphocytes

• T and B cell functions are important for infections with bacteria, viruses, funguses (I didn’t know “funguses” was a word)

  • T cells are important to combat viral and fungal infections

  • B cells are important to combat bacterial infections

• basics of bone marrow or, preferably, stem cell transplantation

• ADA is autosomal

Degradation of nucleic acids

• normally, nucleic acids are metabolized to uric acid. we observe this when we administer chemotherapy and see an increase in uric acid excretion because so many cells are being killed

• adenosine deaminase deficiency will lead to T and B cell death

Category: Pathology Notes