Adenosine deaminase deficiency with mosaicism for a “second-site suppressor” of a splicing mutation: decline in revertant T lymphocytes during enzyme replacement …

FX Arredondo-Vega, I Santisteban… - Blood, The Journal …, 2002 - ashpublications.org
FX Arredondo-Vega, I Santisteban, E Richard, P Bali, M Koleilat, M Loubser, A Al-Ghonaium…
Blood, The Journal of the American Society of Hematology, 2002ashpublications.org
Abstract Four patients from 3 Saudi Arabian families had delayed onset of immune
deficiency due to homozygosity for a novel intronic mutation, g. 31701T> A, in the last splice
acceptor site of the adenosine deaminase (ADA) gene. Aberrant splicing mutated the last 4
ADA amino acids and added a 43-residue “tail” that rendered the protein unstable. Mutant
complementary DNA (cDNA) expressed in Escherichia coli yielded 1% of the ADA activity
obtained with wild-type cDNA. The oldest patient, 16 years old at diagnosis, had greater …
Abstract
Four patients from 3 Saudi Arabian families had delayed onset of immune deficiency due to homozygosity for a novel intronic mutation, g.31701T>A, in the last splice acceptor site of the adenosine deaminase (ADA) gene. Aberrant splicing mutated the last 4 ADA amino acids and added a 43-residue “tail” that rendered the protein unstable. Mutant complementary DNA (cDNA) expressed inEscherichia coli yielded 1% of the ADA activity obtained with wild-type cDNA. The oldest patient, 16 years old at diagnosis, had greater residual immune function and less elevated erythrocyte deoxyadenosine nucleotides than his 4-year-old affected sister. His T cells and Epstein-Barr virus (EBV) B cell line had 75% of normal ADA activity and ADA protein of normal size. DNA from these cells and his whole blood possessed 2 mutant ADA alleles. Both carried g.31701T>A, but one had acquired a deletion of the 11 adjacent base pair, g.31702-12, which suppressed aberrant splicing and excised an unusual purine-rich tract from the wild-type intron 11/exon 12 junction. During ADA replacement therapy, ADA activity in T cells and abundance of the “second-site” revertant allele decreased markedly. This finding raises an important issue relevant to stem cell gene therapy.
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