Normal and mutant human adenosine deaminase genes.

Area of Science:

• Biochemistry
• Immunology
• Genetics

Background:

• Adenosine deaminase (ADA) deficiency is a genetic cause of severe combined immunodeficiency (SCID).
• Accumulation of deoxyadenosine due to ADA deficiency is toxic to lymphoid cells, impairing immune function.
• Complete ADA deficiency results in a lack of both B- and T-lymphocyte function.

Purpose of the Study:

• To analyze B-lymphoblast cell lines from ADA-deficient patients at multiple molecular levels.
• To identify the types and locations of mutations responsible for ADA deficiency.
• To understand the molecular basis of ADA deficiency and its impact on immune function.

Main Methods:

• Blot hybridization and S1 nuclease analysis to assess ADA messenger RNA (mRNA) abundance and size.
• Sequence analysis of ADA complementary DNAs (cDNAs) to identify point mutations.
• Expression analysis to correlate mutations with ADA catalytic activity.
• Analysis of gene deletions and mRNA splicing defects.

Main Results:

• Most ADA-deficient cell lines possess ADA mRNA of normal size and abundance.
• The majority of mutations are single base changes leading to altered amino acid sequences and reduced ADA activity.
• Some cell lines exhibit mutations affecting mRNA processing, including exon deletions and large gene deletions.
• Mutations in partial ADA deficiency appear to affect protein stability, but specific mutations remain undefined.

Conclusions:

• Point mutations are the primary cause of ADA deficiency, leading to reduced enzyme activity and immunodeficiency.
• Aberrant mRNA splicing and gene deletions also contribute to ADA deficiency.
• Further research is needed to define the specific mutations causing partial ADA deficiency.