There is no objection whatsoever in the Islamic religion for a man to marry any of his relatives except those forbidden for marriage whom Allah mentioned in surat an-Nisaa’ (4: 23) Thus, when Allah mentioned for us the relatives to whom marriage is forbidden, we then come to know that there is no objection for the remainder of the family relations. However, it is a good practice to have a blood test before marriage. If one suspects some hereditary disease or any other problem then he/she should seek the advice of a medical expert in this field.