What’s the genetic disease risk for children of related couples?

In 2012 The Conversation had an article about cousin marriage:

Marriages between people who are related is more common than you might think. Unlike what many people think, their offspring are not doomed to birth defects or medical problems.

In fact, unless they both carry the same gene mutation, the couple’s chance of having a healthy child is almost as high as any other couple. Let’s examine why, through the story of one couple.

*******************************************************************************************

Without a family history of an autosomal recessive condition, Maria and Max have an 8% chance of having a child diagnosed with a problem after birth. In other words, their chance of having a healthy baby is greater than 90%, a figure that most people find quite reassuring.

This figure is not too different to the general population risk of having a baby with a birth defect. Most related couples accept this risk and focus instead on general measures to have a healthy baby, such as taking folate, losing weight, and reducing their intake of alcohol and cigarettes.