The novel Passione, Globo, in 2010, addressed this issue: two young and only started dating sometime later discovered they were cousins. The author of the novel took the story forward - before marriage, decided to see a doctor to find out what the real risks of having a child with some genetic disease. The scene showed the general public a medical specialty little known and difficult to access for most of the population genetics. This bizarre story can also happen in real life and portrays very well what has long been said among the people about the inbreeding, but on which the laity have very little explanation to offer. So it is important that a similar situation to that people seek help from a geneticist, who evidently is the professional best suited to offer genetic counseling based on scientific data. In the care of these cases the geneticist will have to make a detailed study of each particular situation, reconstrundo judiciously data familiar to the end be able to reach a risk estimate that is most appropriate for a given consanguineous couple.

GENERAL RULE: Never expect a couple of cousins ​​to get pregnant then refer you to a geneticist! In doing so, it would lose the chance to be offered genetic counseling preemptively able to effectively help this couple to make a realistic and conscious reproductive planning.

Before attempting to explain better biological risks involved in a consanguineous marriage, it is advisable to understand who are the so called "inbred individuals." The word outbred ('con' + 'sanguine') originates from the Latin, meaning "of the same blood." And therefore are considered inbred those who have at least one common ancestor. The greater the degree of consanguinity (brothers, fathers and sons, first cousins, uncle and niece), the greater the chances of two individuals share the same recessive genes with which we are born. The recessive genes are "weak genes" and therefore must be present in a double dose to that trait or genetic disease that they determine to be present in the body. For example, assuming that having blue eyes are a recessive trait, it means that the child's eye blue is generated, it will be necessary that the gene is present twice in his body. Thus, for the blue eye is necessary to express the training the individual this recessive gene have a maternal origin and a paternal origin. The same reasoning used for some genetic disease called "autosomal recessive." For unrelated couples the chances that a disease related to these recessive genes in double happening is about 2%. However, on close relatives (cousins) the chances are greatly increased. It's easy to understand why. Like our brothers and cousins ​​share genes somehow similar to ours, in the union of two people with such levels of kinship, the chances of these recessive genes happen is great. See, if your mother inherited the recessive gene from his maternal grandparents, it is obvious that this could have happened to her maternal aunt and consequently you and your cousin can also inherit them, right? If you marry a first cousin, the chances that their future offspring manifest recessive genes in homozigoseaumentam in relation to a couple who have no kinship. Consanguineous marriages have taken place in most peoples since time Old Testament Bible. There are several couples of famous cousins, and among them we cite the case of Charles Darwin with his wife Emma Wedgwood, who had 10 healthy children, and some of these children succeed in their lives. Currently consanguineous marriages are more prevalent in communities originating from North Africa, the Middle East and much of Asia. Some desssas communities to encourage this type of union. English community in Pakistan is estimated that no less than 50-60% of marriages are consanguineous. Besides being one of consanguineous marriages a concern with recesivas and multifactorial disease in future offspring of the couple also weighs in the decision of this type of marriage the social stigma that it wont result in some communities. In the United States there is a certain taboo in relation to this type of marriage to the point where several states remain prohibitive laws still in force in relation to their achievement. Now this does not happen in the countries of Europe and several countries in Asia as noted earlier. WHAT ARE THE RISKS? Some diseases caused by recessive genes cause mental retardation, congenital deafness, bone dysplasia, blindness and metabolic disorders (fibrocystic disease of the pancreas and various inborn errors of metabolism). Geneticists believe that each of us is born with three to four recessive genes that are double, manifest a genetic disease in the offspring. The risk of any couple to conceive a child with a serious or lethal type cystic fibrosis or spina bifida is 3-4%, however, a couple of cousins ​​legitimate (first degree), no family history of ill persons allegedly caused by recessive genes this chance can increase to 6-8%. Even so, there would be a 92% chance that the offspring of the couple is normal.

Source: www.clinicagenetica.com.br