title: Adenosine deaminase deficiency with mosaicism for a "second-site suppressor" of a splicing mutation: decline in revertant T lymphocytes during enzyme replacement therapy.
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 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.
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Francisco X
authors.initials: FX
authors.lastname: Arredondo-Vega
authors.forename: Ines
authors.initials: I
authors.lastname: Santisteban
authors.forename: Eva
authors.initials: E
authors.lastname: Richard
authors.forename: Pawan
authors.initials: P
authors.lastname: Bali
authors.forename: Majed
authors.initials: M
authors.lastname: Koleilat
authors.forename: Michael
authors.initials: M
authors.lastname: Loubser
authors.forename: Abdulaziz
authors.initials: A
authors.lastname: Al-Ghonaium
authors.forename: Mariam
authors.initials: M
authors.lastname: Al-Helali
authors.forename: Michael S
authors.initials: MS
authors.lastname: Hershfield
mesh_terms: D000243:Adenosine Deaminase / Q000008:administration & dosage / Q000172:deficiency* / Q000235:genetics; D000293:Adolescent; D001483:Base Sequence; D002675:Child, Preschool; D004252:DNA Mutational Analysis; D005192:Family Health; D005260:Female; D016153:Genes, Suppressor; D005838:Genotype; D006801:Humans; D007223:Infant; D008297:Male; D009030:Mosaicism / Q000235:genetics*; D009154:Mutation; D022821:RNA Splice Sites / Q000235:genetics*; D012529:Saudi Arabia; D016511:Severe Combined Immunodeficiency / Q000209:etiology / Q000235:genetics; D013601:T-Lymphocytes / Q000166:cytology / Q000201:enzymology
chemical_list: D022821:RNA Splice Sites; D000243:Adenosine Deaminase