Are the biological risks of having children with your cousin real or exaggerated?

Yes and no.

I think the risk factors are increased with the parents' medical history more than their actual relationship (in terms of being relatives). For example, let's say two people with "sickle cell trait" (who are not related in any way) get married and have children. Then there is a 25% chance that each child will have sickle cell, which is a lifelong inherited disease. In this case, both parents lead a normal life because they have the trait of the disease, but not the actual disease, but their children may have the actual disease and suffer. On the other hand, if totally healthy cousins get married, then there is a zero percent chance that their children will have sickle cell (I'm just using this disease as an example). Moreover, if someone with sickle cell marries his cousin who does not have sickle cell or sickle cell trait, then all the children will inherit the trait but will not be sick. In other words, this case is much better than two strangers who both have the trait getting married.

Of course, I don't deny that if a certain genetic disorder runs in the family, the children's risk factor increases significantly. But the sole reason for risk factors is NOT only present when parents are cousins. As a matter of fact, the risk factor may be higher for couples who are not relatives (just like in the example I gave above). That's why couples should test themselves for compatibility before deciding to have children.

Edit: As for the answer which said that the children may have two sets or arms or no sets of arms – that's not true at all. That's not how genes split up when the baby is formed. Each parent gives 50% of the genes regardless of whether the parents are relatives or not. Being a Muslim, I come for a society where it is very common for cousins to get married. Although I personally am not in favor of this, I have not seen any problems in regards of having babies with deformity. The only problems I have witnessed are due to genetic illnesses such as the one I displayed above. Nowadays, people in my society are more educated and almost every couple take tests before getting married (whether they are cousins or not).

There are risks. The risks aren't as serious if brothers and sisters were to procreate, but the risks are still there. 1st cousins share many genes...their parents are brother and sister after all. Lets say that these 2 cousins shared 25% of their dna...well, that 25% can mean the difference between a healthy, normal child and a mentally retarded child. The risk is definitally increased if certain illnesses run through the family. Lets say a there's a certain illness that runs through the family, and it's a recessive gene. Both the parents have a dominant gene that keeps it from showing up in them. But their child has an increased chance that he/she will get both recessive genes, therefore getting the disease.

the only problem with having children with one's cousin is the genetics when a child is first created. when the sperm penetrates the egg, the DNA they both carry binds to each other making a complete genetic code. the problem is that the codes between cousins is so close that you'll probably have double of certain parts of the code. when that happens they will either cancel each other out or will both be integrated into the code. this means that the child could end up with, for example, 2 sets or no arms.

The risks are real. A couple of my relatives are either disabled or sterile as a result of their parents being first cousins. It really isn't a good idea, as the chance of recessive genetic traits being expressed increases.

They aren't exxagerated.

There's too many of the same genes and it completely screws everything up as the baby develops.

^Worst case scenerio I suppose.

http://en.wikipedia.org/wiki/Inbreeding