On the C57BL/6J congenic background, tremulous heterozygotes have no outward phenotype at 3 weeks of age. However, a whole body tremor that is visible at rest, and weight loss with ataxia begin to present as early as four weeks of age. The cachexia and ataxia progress rapidly and all heterozygotes die by eight weeks of age on this genetic background. On a segregating stock background (Stock No. 017338) survival is somewhat improved.
The tremulous mutation arose spontaneously in (C57BL/6J x CBA/J)F1 hybrid at The Jackson Laboratory in 2006. This dominant mutation is maintained by breeding heterozygous ovarian transplant hosts. It was backcrossed to C57BL/6J for four generations then outcrossed once to CAST/EiJ before being backcrossed again to C57BL/6J for eight more generations by March, 2014.