Consanguinity means marriage or having children with a close biological relative, such as a first cousin or second cousin. In many communities around the world, consanguineous marriages are culturally accepted and can be common. While most children born to related parents are healthy, consanguinity is important in genetics because it increases the chance that both parents carry the same hidden genetic changes, which can raise the risk of certain inherited disorders in their children.
To understand why this happens, it helps to know that every person carries many genetic variants. Some variants are harmless, and some can cause disease. Many serious genetic conditions are “recessive,” which means a child must inherit two non-working copies of a gene—one from the mother and one from the father—for the condition to appear. If a person has only one non-working copy and the other copy works normally, they are usually healthy and may never know they carry that change. This is called being a “carrier.”
In families, relatives share more DNA than unrelated individuals because they come from the same ancestors. For example, first cousins often share a portion of their genetic material through their shared grandparents. This increases the chance that both partners inherited the same recessive gene change from a common ancestor. When both parents carry the same recessive variant, there is a higher likelihood that a child could inherit both copies and be affected by the genetic condition.
This is why consanguinity is linked to a higher risk of autosomal recessive disorders, including some rare metabolic conditions, neurodevelopmental disorders, hearing loss, and certain blood or immune disorders. These conditions may not have been seen in the family for generations because carriers are healthy, and the disorder only appears when two carriers have a child together. Sometimes, families may notice repeated miscarriages, infant deaths, developmental delay, or similar health problems in multiple children, which can be clues pointing toward a recessive genetic condition.
Consanguinity can also increase the chance that a child inherits longer stretches of identical DNA from both parents, a concept known as “homozygosity.” This matters because it increases the likelihood that rare harmful variants become paired together. In genetic testing, this pattern can sometimes help doctors identify the cause of a child’s condition more quickly, especially when whole exome sequencing or whole genome sequencing is used.
It is important to remember that consanguinity does not mean a couple will definitely have an affected child. It only changes the probability by increasing the chance that both parents carry the same recessive variant. Many consanguineous couples have healthy children, especially when there is no known family history of genetic disease. However, the overall population risk is higher compared to unrelated couples, which is why genetic counseling can be helpful before pregnancy or early in pregnancy.
The most practical and empowering step for couples who are related is to consider carrier screening and genetic counseling. Testing – for example on a whole genome sequencing can identify whether both partners carry variants in the same gene that could affect a child. If a shared risk is found, families can discuss options such as early diagnosis, pregnancy monitoring, newborn screening, or reproductive choices depending on their values and medical advice. With the right information and support, families can make confident decisions and improve the chances of early detection and timely treatment when needed.
