A Novel RAC2 Mutation Causing Combined Immunodeficiency.

Area of Science:

• Genetics
• Immunology
• Molecular Biology

Background:

• Ras-related C3 botulinum toxin substrate 2 (RAC2) is vital for cell signaling and actin dynamics.
• Genetic RAC2 mutations typically cause primary immunodeficiency with complete penetrance.

Observation:

• A novel heterozygous missense mutation (c.44G>A, p.G15D) in RAC2 was identified in a Chinese family.
• The proband exhibited recurrent infections, bronchiectasis, and specific immunological defects, including low T cell counts and impaired neutrophil function.
• Family members with the same mutation showed variable phenotypes, from severe disease to mild defects, indicating incomplete penetrance.

Findings:

• The RAC2 mutation led to increased reactive oxygen species, impaired neutrophil actin polarization, and dysregulated T cell responses.
• Flow cytometry, qPCR, and whole-exome sequencing confirmed the mutation and associated immunological abnormalities.
• The study identified a RAC2 gain-of-function mutation with incomplete penetrance, broadening the clinical and genetic spectrum of RAC2-related disorders.

Implications:

• This research expands the understanding of RAC2's role in immunity and disease.
• It highlights the importance of considering RAC2 mutations in primary immunodeficiencies, even with incomplete penetrance.
• The findings underscore the complexity of genotype-phenotype correlations in genetic disorders.