New mutations in C1GALT1C1 in individuals with Tn positive phenotype

Summary Tn polyagglutination results from inactivating mutations in C1GALT1C1, an X‐borne gene encoding a core 1 β3‐galactosyltransferase‐specific molecular chaperone (cosmc) required for the functioning of T‐synthase (β 1,3‐galactosyltransferase), a glycosyltransferase essential for the correct biosynthesis of O‐glycans. This study found novel inactivating mutations (Glu152Lys, Ser193Pro and Met1Ile) in the coding sequence of C1GALT1C1 in three Tn positive individuals and a complete lack of C1GALT1C1 cDNA expression was observed in an additional Tn positive individual. In addition, expression of ST6GALNAC1, which encodes (α‐N‐acetyl‐neuraminyl‐2,3‐β‐galactosyl‐1, 3)‐N‐acetylgalactosaminide α‐2,6‐sialyltransferase 1 and gives rise to sialyl‐Tn antigen, was present at comparable levels in normal and Tn‐positive human erythroblasts. Expression studies of wild‐type and Tn positive C1GALT1C1 cDNA in the Jurkat cell line confirmed that the amino acid substitutions observed in Tn are inactivating. Analysis of the transcriptome of cultured normal and Tn positive erythroblasts revealed numerous differences in gene expression. Reduced transcript levels for fatty acid binding protein 5 (FABP5) and plexin D1 (PLXND1), and increased levels for aquaporin 3 (AQP3) were confirmed by quantitative real‐time polymerase chain reaction. These data show that alteration of O‐glycan structures resulting from T‐synthase deficiency is accompanied by altered expression of a wide variety of genes in erythroid cells.