Mitochondria-DNA-Test: Grandmother (Mother’s side) with Grandsons or Granddaughters

S. is from Thailand and as a young child was adopted by a family in the USA. S. has no documentation concerning his biological parents. He found out, from a clergyman who had worked in Thailand that his biological mother had died a long while ago. The clergyman said that his grandmother (mother’s side) was still alive and that it would be possible to make contact with her. S. wanted confirmation that this really was his biological grandmother. A Mitochondria-DNA-test makes this possible because if S. is this lady’s grandchild, they would both have the same Mitochondria-DNA.