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Maternal thyroid-blocking immunoglobulins in congenital hypothyroidism
R S Brown1, P Keating, E Mitchell
1Department of Pediatrics, University of Massachusetts Medical School, Worcester 01655.
Summary
Maternal thyroid-blocking antibodies are not common in babies with congenital hypothyroidism (CH). However, TSH binding inhibitory immunoglobulin G (IgG) testing can screen for these antibodies, which are linked to primary myxedema.
Area of Science:
- Endocrinology
- Immunology
- Reproductive Medicine
Background:
- Congenital hypothyroidism (CH) affects newborns, and maternal factors are investigated.
- Thyroid-specific autoantibodies can influence thyroid function.
- The role of maternal immunoglobulin G (IgG) in CH requires further clarification.
Purpose of the Study:
- To investigate the presence and role of maternal thyroid-blocking immunoglobulin G (IgG) in infants with congenital hypothyroidism (CH).
- To compare antibody activity in mothers of CH infants with mothers of infants with transient CH and healthy controls.
- To assess the diagnostic utility of TSH binding inhibitory IgG as a screening test.
Main Methods:
- Evaluated 24 mothers of CH infants for immunoglobulins (Igs) inhibiting TSH binding and blocking FRTL-5 cell growth/function.
- Compared results with 2 mothers of infants with transient CH (primary myxedema) and normal controls.
- Verified antibody activity using cell counts, Staphylococcal protein-A absorption, and idiotype analysis.
Main Results:
- Only one mother of a CH infant had potent TSH binding inhibitory, growth inhibitory, and function inhibitory IgGs; she was hypothyroid with atrophic thyroiditis.
- Both mothers with known primary myxedema had blocking IgGs.
- Thyroid-blocking activity assays showed similar half-maximal inhibition, suggesting a single antibody population in primary myxedema.
- No correlation was found between blocking IgGs and antimicrosomal antibody titers.
- Maternal thyroid-blocking IgGs interacting with the TSH receptor were not implicated in most sporadic CH cases.
Conclusions:
- Maternal thyroid-blocking immunoglobulin G (IgG) is unlikely to be a significant factor in most cases of sporadic congenital hypothyroidism (CH).
- TSH binding inhibitory IgG determination is a sensitive screening method for detecting TSH receptor-blocking antibodies, unlike antimicrosomal antibodies.