Clinical and functional spectrum of RAC2-related immunodeficiency.

Area of Science:

• Immunology
• Genetics
• Cell Biology

Background:

• Mutations in the Rho-family GTPase RAC2 are linked to severe combined immunodeficiency (SCID), leukocyte adhesion deficiency (LAD)-like disease, and combined immune deficiency (CID).
• Understanding the genotype-phenotype correlation in RAC2 mutations is crucial for diagnosing and managing these immune disorders.

Purpose of the Study:

• To investigate the spectrum of clinical presentations and molecular mechanisms associated with RAC2 mutations.
• To identify novel RAC2 variants and characterize their impact on immune cell function.

Main Methods:

• Clinical data from 54 patients across 37 families were analyzed, including 15 novel RAC2 missense mutations.
• Functional assays assessed downstream effector functions, including superoxide production, kinase binding, and protein stability.
• Confocal microscopy evaluated actin assembly, membrane ruffling, and macropinosome formation.

Main Results:

• RAC2 mutations resulted in a spectrum of immune dysfunction, categorized by disease presentation: neonatal SCID, infantile LAD-like disease, and CID.
• Constitutively active mutations caused SCID, dominant-negative mutations caused LAD-like disease, and dominant-activating mutations caused CID.
• Mutant RAC2 proteins showed aberrant functions, including altered actin assembly, protein localization, and superoxide production, with specific defects correlating to infection types.

Conclusions:

• RAC2 mutations lead to a diverse range of immune deficiencies, with the specific clinical phenotype determined by the mutation's effect on RAC2 activity.
• Functional assays are essential for understanding the consequences of RAC2 mutations, as no single assay fully captures the functional impact.
• Targeted investigation of RAC2 is important for diagnosing and potentially treating patients with unexplained immune dysregulation.