This invention provides a novel isolated polynucleotide sequence, called ADARP1 (adenosine deaminase related protein 1), that displays significant homology to the adenosine deaminase (ADA) gene. Also provided is the amino acid sequence of the ADARP1 polypeptide encoded by the polynucleotide of the invention. The RNA for this novel gene is found in variety of tissues, with higher levels observed in the heart, testes, and skeletal muscle compared with others tested. Based on amino acid sequence homology, the ADARP1 protein will likely display the catalytic activity characteristic of ADA. This newly found ADARP1 gene and its encoded product may be useful in the treatment of immunodeficiencies, including severe combined immunodeficiency disease (SCID) and other ADA deficiencies, treatment of male reproductive disorders, testicular disorders and musclo-skeletal disorders.