RNA enzymes-ribozymes-are being developed as treatments for a variety of di
seases ranging from inborn metabolic disorders to viral infections and acqu
ired diseases such as cancer. Ribozymes can be used both to downregulate an
d to repair pathogenic genes. In some instances, short-term exogenous deliv
ery of stabilized RNA is desirable, but many treatments will require viral-
mediated delivery to provide long-term expression of the therapeutic cataly
st. Current gene therapy applications employ variations on naturally occurr
ing ribozymes, but in vitro selection has provided new RNA and DNA catalyst
s, and research on trans-splicing and RNase P has suggested ways to harness
the endogenous ribozymes of the cell for therapeutic purposes.