SYK(spleen tyrosine kinase) is a key regulator of signal transduction events,apoptosis and orderly cell cycle progression in B-lineage lymphoid cells. Although SYK has not been linked to a human disease, defective expression of the closely related T-cell tyrosine kinase ZAP-70 has been associated with severe combined immunodeficiency(PMID:11494125). This protein has 2 isoforms produced by alternative splicing.