DNA molecules optimized sequences that encode the IA-2IC antigen, RNA molecules, expression vectors, transformed cells, method of preparing the IA-2IC antigen, polypeptide of the human IA-2IC antigen, and in vitro procedure and kit for the diagnosis of autoimmune diabetes

Otimized DNA molecules that encode human IA-2ic, wherein at least one of the codons starting at positions 2747 and 2816 of the complete IA-2 gene is CGT. Said molecules are useful for detecting insulin-dependent (type 1) diabetes mellitus, and may be fused to auxiliary proteins or peptides (for example, His-tag). RNA molecules encoded by the optimized DNA molecules, expression vectors comprising the optimized DNA molecules and cells transformed with said DNA molecules (particularly Escherichia coli cells). Also a method of producing human IA-2ic antigen that comprises growing cells transformed with the said optimized nucleic acid molecules under conditions suitable for producing said protein, the polypeptide obtained through that procedure, and an in vitro diagnostic method and a diagnostic kit using it.