A method of diagnosing a disease or syndrome associated with disregulation of Neuregulin-4 (NRG-4), Aa novel ErbB-4 ligand, referred to herein as Neuregulin-4 (NRG-4)in a subject is disclosed. The method comprising: (a) obtaining a sample from a subject; (b) incubating the sample with at least one oligonucleotide or oligonucleotide analog of at least bases, said oligonucleotide or oligonucleotide analog capable of hybridizing to a portion of a polynucleotide strand encoding NRG-4 to thereby diagnosing the disease, condition or syndrome associated with disregulation of NRG-4.