ancestry but also common among Latin-American, Middle Eastern populations, as well as those people of South European regions such as Turkey, Greece, and Italy Thalassemia, most prevalent in populations having Mediterranean ancestry, to the point that the disease's name is derived from Greek thalassa, "sea" Tay–Sachs disease, an autosomal recessive disorder most common among Ashkenazi Jews, French Canadians of Saguenay–Lac-Saint-Jean, Cajuns of Louisiana and Old Order Amish of Pennsylvania Hereditary hemochromatosis, most common among persons having Northern European ancestry, in particular those people of Celtic descent Hermansky–Pudlak syndrome, most common among Puerto Ricans Finnish heritage diseases, autosomal recessive diseases that are far more common among Finns Multifactorial polygenic diseases Many diseases differ in frequency between different populations. However, complex diseases are affected by multiple factors, including genetic and environmental. There is controversy over the extent to which some of these conditions are influenced by genes, and ongoing research aims to identify which genetic loci, if any, are linked to these diseases. "Risk is the probability that an event will occur. In epidemiology, it is most often used to express the probability that a particular outcome will occur following a particular exposure." Different populations are considered "high-risk" or "low-risk" groups for various diseases due to the probability of that particular population being more exposed to certain risk factors. Beyond genetic factors, history and culture, as well as current environmental and social conditions, influence a certain populations' risk for specific diseases. Disease progression Racial groups may differ in how a disease progresses. Different access to healthcare services, different living and working conditions influence how a disease progresses within racial groups. However, the reasons for these differences are multiple, and should not be understood a consequence of genetic differences between races, but rather as effects of social and environmental factors affecting. Prevention Genetics have been proven to be a strong predictor for common diseases such as cancer, cardiovascular disease (CVD), diabetes, autoimmune disorders, and psychiatric illnesses. Some geneticists have determined that "human genetic variation is geographically structured" and that different geographic regions correlate with different races. Meanwhile, others have claimed that the human genome is characterized by clinal changes across the globe, in relation with the "Out of Africa" theory and how migration to new environments cause changes in populations' genetics over time. Some diseases are more prevalent in some populations identified as races due to their common ancestry. Thus, people of African