Some ethnic propensities for genetic diseases

Ethnic Group	Genetic Defect
African Americans	Sickle Cell Anemia
Central or Eastern Jews	Tay - Sachs disease
Italian, Greek, Middle Eastern	Thalassemia

-----http://www.americanpregnancy.org/gettingpregnant/geneticcounseling.html

EDIT:
Ashkenazi Jews have also a higher propensity for Cystic Fibrosis
http://www.ncbi.nlm.nih.gov/pubmed/10464623

EDIT:
http://spittoon.23andme.com/2012/05/22/the-uniqueness-of-ashkenazi-jewish-ancestry-is-important-for-health/