The absence of TRECs in newborns is indicative of which condition?

The absence of T-cell receptor excision circles (TRECs) in newborns is primarily associated with severe combined immunodeficiency (SCID). TRECs are small DNA circles formed during the development of T cells in the thymus. In healthy individuals, the presence of TRECs indicates functional T-cell development, which is crucial for a robust immune response.

In cases of SCID, there is a profound defect in T-cell development, leading to significantly low or absent levels of both T cells and TRECs. This condition prevents the infant from developing a proper immune response, making them highly susceptible to infections. Screening for TRECs in newborns is, therefore, a critical diagnostic tool for identifying SCID early, allowing for timely interventions such as bone marrow transplantation.

The other conditions listed do not specifically correlate with TREC absence in newborns. Acquired immune deficiency syndrome (AIDS) is an infection rather than a genetic defect, and while congenital immunodeficiency can involve different mechanisms, it is not exclusively associated with absent TRECs like SCID is. The transitional immune response refers to the period around birth when maternal antibodies are being transferred and does not directly relate to TREC levels.