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ADA SCID

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acorrigan's version from 2017-05-11 19:45

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Question Answer
What chromosomal region is the ADA gene located within?20q13.12
How many exons are there in the ADA gene?12, this was refuted and said to be 10
At what does ADA typically present?Within the first six months of life
What are the common presenting symptoms of ADA?Absent thymus, recurrent infections, failure to thrive, diarrhoea, skin rashes
What tests would typically be carried out to confirm a clinical suspicion of ADA?Routine blood tests show near absence of T-, B- and NK-lymphocytes. ADA enzyme assay in red cell lysates. Molecular testing to characterise the causative genetic variants.
What are the key indicators of ADA deficiency?High levels of deoxyATP in plasma. Low or absent ADA activity in red cell lysate assays. This could be masked in those who have recently had blood transfusions.
What is the mechanism underlying the depletion of lymphocytes in ADA deficiency?ADA is responsible for the irreversible deamination of adenosine and deoxyadenosine to inosine and deoxyinosine. ADA activity is highest in lymphocytes. Absence of ADA activity leads to the accumulation of highly toxic deoxyATP which leads to the destruction of lymphocytes and lymphoid tissue.
Why is early diagnosis important?With early treatment individuals with ADA SCID can live normal, healthy lives. Without treatment, infants rarely survive beyond 2 years of life.
How is ADA SCID treated?Bone marrow/stem cell transplantation from HLA matched donor has high sucess rate if done in the first 3 months. Gene therapy is currently at the trial stage and has shown some sucess but requires further work due to the development of leukaemia in some patients using a particular viral vector.
What is the most common cause of SCID?Mutation in the interleukin 2 receptor gamma, which is located on the X chromosome
What is the inheritance pattern for ADA SCID?Autosomal recessive
What is the risk of ADA SCID for a child of two carrier parents?25% affected, 50% unaffected carrier, 25% unaffected & not a carrier
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