The present invention relates to methods for determining predisposition to a manifestation of immune system related diseases, in particular infections, associated with a mutation in the human MASP-2 gene. The invention also features oligonucleotides, polypeptides, peptide fragments and antibodies which are used in the above methods as well as for the manufacture of a medicament for treatment of a disease associated with pathological activity of the lectin-complement pathway. Moreover, the invention provides a series of gene therapy vectors and a kit for diagnosis of the disease associated with a mutation in the human MASP-2 gene.