Presented by Kathy Grange, M.D. - Columbia, MO
Chromosomes are made of genes and contain DNA. The location of the genes is random, and the MSUD genes are located on many different chromosomes. Mutations (inborn errors) occur when there are deletions of base pairs, insertions, or wrong combinations. In a mutation, there may be no enzyme where there should be, or an abnormal enzyme. The abnormalities are what usually causes metabolic disorders.
Mennonites are homozygous (the same mutation exists on both genes). Non-Mennonites have a good probability of being compound heterozygous, one mutation from the mother and one from the father. MSUD is more complicated than other genetic disorders due to so many mutations.
Gene therapy requires locating and isolating the mutated gene. Family members can be tested for carrier status if the mutation is known. The mutation in Mennonites is known.
There are currently two methods of gene therapy÷injection of "fixed" genes into cells and viral mediated transfers. Direct injection is tricky and requires the removal of tissue from the source, injection and growth in a cell culture, and placement back into the source. With viral mediated transfers, it is necessary to prevent the virus from acting on its own (for example, a virus can insert itself in the wrong place and cause problems).
Researchers have successfully done viral mediated transfers in a beaker for MSUD. The next step is to try it on cows known to have MSUD. There are still questions as to how long the enzymes will remain active once the person has been "cured." It may be long term, or there may be periodic doses required, or it may be a supplement to diet.
DNA review and update
- Written by Joyce Brubacher