       Document 0181
 DOCN  M9460181
 TI    Correct splicing despite mutation of the invariant first nucleotide of a
       5' splice site: a possible basis for disparate clinical phenotypes in
       siblings with adenosine deaminase deficiency.
 DT    9408
 AU    Arredondo-Vega FX; Santisteban I; Kelly S; Schlossman CM; Umetsu DT;
       Hershfield MS; Department of Medicine, Duke University Medical Center,
       Durham,; NC 27710.
 SO    Am J Hum Genet. 1994 May;54(5):820-30. Unique Identifier : AIDSLINE
       MED/94234148
 AB    Adenosine deaminase (ADA) deficiency usually causes severe combined
       immune deficiency in infancy. Milder phenotypes, with delayed or late
       onset and gradual decline in immune function, also occur and are
       associated with less severely impaired deoxyadenosine (dAdo) catabolism.
       We have characterized the mutations responsible for ADA deficiency in
       siblings with striking disparity in clinical phenotype. Erythrocyte dAdo
       nucleotide pool size, which reflects total residual ADA activity, was
       lower in the older, more mildly affected sib (RG) than in her younger,
       more severely affected sister (EG). Cultured T cells, fibroblasts, and B
       lymphoblasts of RG had detectable residual ADA activity, while cells of
       EG did not. ADA mRNA was undetectable by northern analysis in these
       cells of both patients. Both sibs were found to be compound
       heterozygotes for the following novel splicing defects: (1) a G+1-->A
       substitution at the 5' splice site of IVS 2 and (2) a complex 17-bp
       rearrangement of the 3' splice site of IVS 8, which inserted a run of
       seven purines into the polypyrimidine tract and altered the reading
       frame of exon 9. PCR-amplified ADA cDNA clones with premature
       translation stop codons arising from aberrant pre-mRNA splicing were
       identified, which were consistent with these mutations. However, some
       cDNA clones from T cells of both patients and from fibroblasts and
       Epstein-Barr virus (EBV)-transformed B cells of RG, were normally
       spliced at both the exon 2/3 and exon 8/9 junctions. A normal coding
       sequence was documented for clones from both sibs. The normal cDNA
       clones did not appear to arise from either contamination or PCR
       artifact, and mosaicism seems unlikely to have been involved. These
       findings suggest (1) that a low level of normal pre-mRNA splicing may
       occur despite mutation of the invariant first nucleotide of the 5'
       splice donor sequence and (2) that differences in efficiency of such
       splicing may account for the difference in residual ADA activity, immune
       dysfunction, and clinical severity in these siblings.
 DE    Adenosine Deaminase/*DEFICIENCY/*GENETICS/METABOLISM  Base Sequence
       Case Report  Cell Line  Cells, Cultured  Child, Preschool
       DNA/CHEMISTRY/GENETICS  DNA Primers  Exons  Female
       Fibroblasts/ENZYMOLOGY  Heterozygote Detection  Human  Infant  Molecular
       Sequence Data  Nuclear Family  Phenotype  *Point Mutation  Polymerase
       Chain Reaction  *RNA Splicing  RNA, Messenger/ANALYSIS  Severe Combined
       Immunodeficiency/ENZYMOLOGY/*GENETICS  Support, Non-U.S. Gov't  Support,
       U.S. Gov't, P.H.S.  T-Lymphocytes/ENZYMOLOGY  JOURNAL ARTICLE

       SOURCE: National Library of Medicine.  NOTICE: This material may be
       protected by Copyright Law (Title 17, U.S.Code).

