Some diseases are called multifactorial because they are due to the interaction between genetic events and environmental factors. These are common diseases, present in one in 50 or 100 in the population such as diabetes, hypertension, asthma, rheumatoid arthritis, Crohn's disease, some cancer and certain psychiatric illnesses like schizophrenia.
Why do we say that these diseases have a genetic component?
The most important argument is the existence of familial cases, with several people with the disease in different generations. Further study of twins that are genetically identical, shows that if one twin is affected with the disease the second is more likely to develop the disease than other siblings or fraternal twins. So although genetic factors are involved.
How Genoa are involved in each of these diseases? We do not yet know.
Does eye diseases been among multifactorial diseases?
In my family my father wore glasses and all my brothers (4). I wear them some twenty years ago . Today my wife whose father suffers eye disease wears glassses also .Now all our four children are with glasses.