[This is an old post from Tumblr, originally posted in July 2014. The link to the website referenced no longer works, but the information was from there and you can find those facts elsewhere too.]
I’m not an expert on this topic, but I will share some basic information I found while reading up on it. If you’ve done your research then you will most likely know these things already.
According to http://www.talkinggenetics.co.uk (a Health Care service that supports consanguineous couples and families) one of the most common problems that consanguineous couples may run into when it comes to making a family, is that of Autosomal Recessive Inheritance. Autosomal means that it can affect both female and male children.
If you follow this link and click on the first picture to the right of the page, you will be led through a video which will explain in a simplified form how this type of gene transfer works, and what are the chances of having a child with a genetic disorder.
According to studies done on this subject, the chances of having a child with a genetic defect for a cousin couple is double the risk for a non-related couple. But the risk, to begin with, is not large, and studies have shown that cousin couples have a 93% chance of having healthy children.
Having a higher risk of passing on health issues does not necessarily mean you will encounter problems, as the risks for cousin couples are not significantly higher than that between any two, un-related people. The reason that there is a risk at all is because a couple that are related would share more genes (that are likely to be the same type of recessive gene) than those who are unrelated, since they will have received these genes from the same family tree. And if the child gets a faulty gene from each parent, this is when it may affect their offspring. There is a 25 percent chance of this happening, but only IF the parents are both carriers of the same kind of bad gene.
Since so much of this is dependent on your individual genetics and the health history of your shared ancestry, it is important to seek out genetic counseling to help you make an informed decision on what’s right for you.
This process would involve obtaining a medical history of your family (including identifying any diseases that run in the bloodline), considering patterns of inheritance of a specific condition that may suggest the chance of a recurrence down the line, genetic testing (by blood samples), as well as finding resources (for both emotional support & self-education).
Since the Internet is full of unreliable and conflicting information, the best way to get an accurate assessment of your options is to go to a professional genetic councilor. Since cousin marriages are common in certain cultures, there will always be services available for people in these kinds of relationships. The best thing about those services is that they are non-directive, which means that the third party will listen to their clients’ concerns and views, guiding the clients to evaluate their own needs and make their own decisions based on the facts, without bias.
I’d also like to add that I know someone who is in a cousin marriage. They have three children together, who are all healthy. The wife must’ve been in her 30s and the husband in his 40s when they had their third child, but this child is as healthy as the first two, who they had years before her.