Multiple sclerosis and birth order

Abstract

- The relation between birth order and risk of multiple sclerosis (MS) was studied among MS patients in Israel. The evaluation was both by case-control study and comparison of expected and observed birth order in Israel-born patients. Results showed an excess of first-born and a low birth order among MS patients. Conversely, in MS patients born abroad but who developed the disease in Israel, MS was connected with an excess of last-born and high birth order. These contradictory results could not be explained by bias of case selection, difference in age, or changes in family size with time, and could indicate that different etiological factors are responsible for MS in distinct populations.