Telomere length (ratio) and years since their child's
diagnosis with chronic illness.
Arguments
source
Epel, E.S., E.H. Blackburn, J. Lin, F.S. Dhabhar, N.E.
Adler, J.D. Morrow, and R.M. Cawthon. 2004. Accelerated
telomere shortening in response to life stress.
Proceedings of the National Academy of Sciences
(USA) 101: 17312-17315.