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Severe combined immunodeficiency in a child with a healthy adenosine deaminase deficient mother
Insights
Adenosine deaminase (ADA) deficiency in a child with SCID presented unusual normal thymus histology. Low ADA activity in family members suggests it may be compatible with good immune function.
Area of Science:
- Immunology
- Biochemistry
- Genetics
Background:
- Severe-combined immunodeficiency (SCID) is a group of rare genetic disorders characterized by profound defects in the immune system.
- Adenosine deaminase (ADA) deficiency is a cause of SCID, leading to accumulation of toxic metabolites that impair lymphocyte development and function.
- This study focuses on a unique case of ADA deficient SCID with unusual clinical and immunological findings.
Purpose of the Study:
- To investigate the immunological and biochemical characteristics of an infant with ADA deficient SCID.
- To analyze the ADA activity and phenotype in the affected child and family members.
- To explore the correlation between residual ADA activity and immune function in individuals with partial ADA deficiency.
Main Methods:
- Clinical assessment and immunological evaluation of the patient, including thymic histology and lymphocyte function assays.
- Biochemical analysis of adenosine deaminase (ADA) activity in erythrocytes and lymphocytes.
- Starch gel electrophoresis for ADA phenotype determination.
- Measurement of ATP, dATP, and deoxyadenosine levels.
Main Results:
- The patient presented with ADA deficient SCID but had normal thymic histology and functional thymocytes.
- ADA activity was undetectable in the child's thymocytes.
- Family studies revealed varying levels of ADA activity, with the mother having significantly reduced ADA activity but preserved immune function.
- Elevated deoxyadenosine excretion was observed in the mother, but at lower levels than typically seen in ADA deficient SCID.
Conclusions:
- The findings challenge the conventional understanding of ADA deficiency pathogenesis, suggesting that normal thymic histology can occur in ADA deficient SCID.
- Partial ADA deficiency, even with low enzyme activity in key immune cells, may be compatible with sustained immune function and longevity.
- This case highlights the complexity of ADA deficiency and the potential for compensatory mechanisms in maintaining immune homeostasis.
Abstract:
We investigated adenosine deaminase (ADA) deficient severe-combined immunodeficiency (SCID) in an 8-month-old child with ADA deficient mother. The ADA deficiency in the child was unusual in that the thymic histology was normal. In addition, the thymocytes formed E-rosettes with sheep erythrocytes and were stimulated by T-cell mitogens. ADA activity could not be detected in the child's thymocytes. Studies on the family indicated that the father had about one-half of the normal erythrocyte ADA activity. All the family members with detectable ADA activity appeared to have, according to starch gel electrophoresis of erythrocyte lysates, the common ADA-1 phenotype; however, rigorous identification of phenotype was not possible in this study. The mother had less than 1% of normal ADA activity in both erythrocyte and lymphocyte extracts, but her whole peripheral blood lymphocytes demonstrated about 6% of normal activity. Normal concentrations of ATP and small amounts of dATP were found in the mother's erythrocytes. Deoxyadenosine excretion in her urine was elevated and approximately 5-10% of that excreted by individuals with ADA deficient SCID. These studies suggest that low amounts of ADA activity in erythrocytes and blood lymphocytes of certain individuals may be compatible with good immune function and longevity.