High-resolution autoreactive epitope mapping and structural modeling of the 65 kDa form of human glutamic acid decarboxylase

The smaller isoform of the GABA-synthesizing enzyme, glutamic acid decarboxylase 65 (GAD65), is unusually susceptible to becoming a target of autoimmunity affecting its major sites of expression, GABA-ergic neurons and pancreatic β-cells. In contrast, a highly homologous isoform, GAD67, is not an autoantigen. We used homolog-scanning mutagenesis to identify GAD65-specific amino acid residues which form autoreactive B-cell epitopes in this molecule. Detailed mapping of 13 conformational epitopes, recognized by human monoclonal antibodies derived from patients, together with two and three-dimensional structure prediction led to a model of the GAD65 dimer. GAD65 has structural similarities to ornithine decarboxylase in the pyridoxal-5′-phosphate-binding middle domain (residues 201-460) and to dialkylglycine decarboxylase in the C-terminal domain (residues 461-585). Six distinct conformational and one linear epitopes cluster on the hydrophilic face of three amphipathic α-helices in exons 14-16 in the C-terminal domain. Two of those epitopes also require amino acids in exon 4 in the N-terminal domain. Two distinct epitopes reside entirely in the N-terminal domain. In the middle domain, four distinct conformational epitopes cluster on a charged patch formed by amino acids from three α-helices away from the active site, and a fifth epitope resides at the back of the pyridoxal 5′-phosphate binding site and involves amino acid residues in exons 6 and 11-12. The epitopes localize to multiple hydrophilic patches, several of which also harbor DR∗0401-restricted T-cell epitopes, and cover most of the surface of the protein. The results reveal a remarkable spectrum of human autoreactivity to GAD65, targeting almost the entire surface, and suggest that native folded GAD65 is the immunogen for autoreactive B-cells

Array-Based Karyotyping for Prognostic Assessment in Chronic Lymphocytic Leukemia: Performance Comparison of Affymetrix 10K2.0, 250K Nsp, and SNP6.0 Arrays

Specific chromosomal alterations are recognized as important prognostic factors in chronic lymphocytic leukemia (CLL). Array-based karyotyping is gaining acceptance as an alternative to the standard fluorescence in situ hybridization (FISH) panel for detecting these aberrations. This study explores the optimum single nucleotide polymorphism (SNP) array probe density for routine clinical use, presents clinical validation results for the 250K Nsp Affymetrix SNP array, and highlights clinically actionable genetic lesions missed by FISH and conventional cytogenetics. CLL samples were processed on low (10K2.0), medium (250K Nsp), and high (SNP6.0) probe density Affymetrix SNP arrays. Break point definition and detection rates for clinically relevant genetic lesions were compared. The 250K Nsp array was subsequently validated for routine clinical use and demonstrated 98.5% concordance with the standard CLL FISH panel. SNP array karyotyping detected genomic complexity and/or acquired uniparental disomy not detected by the FISH panel. In particular, a region of acquired uniparental disomy on 17p was shown to harbor two mutated copies of TP53 that would have gone undetected by FISH, conventional cytogenetics, or array comparative genomic hybridization. SNP array karyotyping allows genome-wide, high resolution detection of copy number and uniparental disomy at genomic regions with established prognostic significance in CLL, detects lesions missed by FISH, and provides insight into gene dosage at these loci