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Genetic and molecular definition of complementation group D in MHC class II deficiency
M C Fondaneche1, J Villard, W Wiszniewski
1INSERM U429, Hôpital Necker-Enfants Malades, 149 rue de Sèvres, 15015 Paris, France. Geneva, Switzerland, Department of Pediatrics,
Insights
Mutations in the RFXAP gene cause a significant portion of MHC class II deficiency, specifically in complementation group D. This study classifies new patients and confirms RFXAP as the primary cause of group D defects.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- MHC class II deficiency is a severe immunodeficiency characterized by defects in the coordinate expression of MHC class II genes.
- Four complementation groups (A, B, C, D) have been identified in cell lines with MHC class II deficiency.
- Complementation group D was historically represented by a single mutant cell line (6.1.6), with the causative gene, RFXAP, identified more recently.
Purpose of the Study:
- To classify new patients with MHC class II deficiency into the established complementation groups.
- To investigate the role of the RFXAP gene in complementation group D defects.
- To analyze the mutational spectrum of RFXAP in patients with MHC class II deficiency.
Main Methods:
- Cell fusion experiments were performed with new patient-derived cell lines.
- Complementation analysis was used to assign patients to groups A, B, C, or D.
- Transfection with RFXAP cDNA was used to assess functional correction of MHC class II expression.
- Mutation analysis of the RFXAP coding region was conducted on patient samples.
Main Results:
- The majority of newly classified patients were assigned to complementation groups A, B, and D; no new complementation groups were identified.
- Five unrelated families were classified into complementation group D, and nine into groups A and B.
- Transfection with RFXAP cDNA fully corrected MHC class II expression in cells from group D patients.
- Mutations in the RFXAP coding region were identified in all tested group D patients, with recurrent mutations observed.
Conclusions:
- RFXAP mutations are a significant cause of MHC class II deficiency, particularly in complementation group D.
- The study successfully classified new patients, reinforcing the existing complementation group framework.
- The identification of recurrent RFXAP mutations suggests potential founder effects or mutational hotspots in certain populations.
Abstract:
Four complementation groups, A, B, C and D, have been described among cell lines defective in the coordinate expression of MHC class II genes. These include cell lines established from patients affected with MHC class II deficiency and experimentally generated mutant cell lines. Group D, in contrast to the other groups, was for a long time represented only by the 6.1.6 mutant cell line. The gene responsible for the defect in this group, RFXAP , recently was cloned and found to be mutated in the 6.1.6 cell line and in three patients. Here we report fusion experiments in several new HLA class II-deficient patients, completing the classification of the majority of known patients into the four complementation groups. Patients from five unrelated families were classified in complementation group D, while nine others fall into complementation groups A and B. None of the patients defined a new complementation group. Full correction of MHC class II expression was obtained in cells from patients belonging to group D by transfection with the RFXAP cDNA. The RFXAP coding region was found to be mutated in all patients. Mutations were found to be recurrent since only three different mutations have been found in the eight unrelated families reported to date.