Coarctation of the aorta and turner syndrome; is there a common relationship?

Yes. All patients with known turner's syndrome are screened for this, in fact.
Syndrome = collectn. The idea of grouping findings together as syndromes allows physicians to have an understanding of what "silent" defects to look for in an infant presenting with distinctive features. The coarctation is much more common in turner syndrome kids than the regular population & may not be obvious on general exam. When chromosomes have mistakes, they can effect any body part & this is an important one.