Adenosine deaminase deficiency with mosaicism for a "second-site suppressor" of a splicing mutation: decline in revertant T lymphocytes during enzyme replacement therapy.
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.
Arredondo-Vega
Francisco X
FX
Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA.
Santisteban
Ines
I
Richard
Eva
E
Bali
Pawan
P
Koleilat
Majed
M
Loubser
Michael
M
Al-Ghonaium
Abdulaziz
A
Al-Helali
Mariam
M
Hershfield
Michael S
MS
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
D022821:RNA Splice Sites; D000243:Adenosine Deaminase