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Almost 1 billion people practice consanguineous marriage, with more in parts of the Middle East, North Africa, and South Asia. Pakistanis have the highest blood relative marriage rate at 65%. Married blood relatives often increase the genetic risk in their babies. When two individuals pass the same genes to their baby, it can often lead to congenital disorders, developmental delays, and other genetic problems.
What is Consanguinity?
Consanguinity refers to marriage or union between individuals who are biologically related and share a common ancestor. The most common degrees of blood relatives' marriage include first cousins, who share grandparents; second cousins, who share great-grandparents; uncle-niece or aunt-nephew (sibling and sibling's children); and double-first cousins (children of two siblings)
First cousins share 12.5% genes, so their kids have almost 6.25% common genes, and second cousins share 3.1% genes. Though these may look like a small number, even a little shared genetics can cause an effect on the baby.
Genetic Basics
Parents share 23 chromosomes in their baby, and each chromosome contains genes. These genes carry traits and disorders within their family. These genes contain recessive and dominant genes.
Dominant genes need one copy to be expressed. But recessive needs two copies to be expressed. One recessive copy does not express but stays silent. Most genetic disorders are recessive ones, which means that to pass a genetic disorder, two recessive genes have to merge. Healthy people often carry 3-5 recessive genes.
- Heterozygosity: It means carrying two different genes or alleles. One dominant and one recessive. Dominant masks the recessive ones.
- Homozygosity: It means having two identical alleles. It expresses either dominant or recessive traits.
When marrying blood relatives, the shared gene increases the odds of homozygosity, which increases the risk of inheriting recessive disorders.
Gene Mechanisms Behind Risk
When blood relatives have children, the shared family DNA can result in genetic disorders for babies. Most genetic disorders with consanguinity follow autosomal recessive inheritance. Each parent passes 23 chromosomes, and autosomes are the 22 non-sex chromosomes.
Each parent has one normal gene copy, and one receives a gene copy, but they mostly stay healthy because of the dominant gene. If a baby gets two recessive copies from both parents, it expresses and triggers the disorder. Blood relatives inherit DNA from the same ancestor, which increases the chances that both parents carry the same recessive copies. But in unrelated parents, the odds are low.
This process increases homozygosity, which is linked to metabolic disorders, congenital anomalies, neurodevelopmental conditions, thalassemia and cystic fibrosis.
Genetic Risks of Marrying Blood Relatives
Research confirms that marrying blood relatives increases the health challenges in their kids. Here are some common problems faced in consanguineous marriage.
Congenital Anomalies and Birth Defects
Children of close blood relatives face high risks of congenital anomalies, structural or functional birth defects. The risk of birth defects is 2-2.5 times higher than in unrelated parents. The common birth defects include heart defects, neural tube defects, cleft lip, and limb malformations.
Stullbirths
Consanguinity increases the risk of stillbirths and perinatal mortality. Risks are 1.5 to 2 times higher. Stillbirth often results from placental dysfunction, severe congenital anomalies that couldn't support survival, or genetic conditions. Neonatal death risks are high due to malformation.
Developmental Disorders
Kids show higher rates of developmental issues, including metabolic and neurological conditions. They show a high prevalence of brain or liver damage, intellectual disability, hearing loss, autism, and epilepsy.
Growth Outcomes
Consanguineous kids often face low birth weight, vulnerability to diseases, and nutritional deficits, which can lead to chronic genetic conditions.
How Repeated Consanguinity Across Generations Increases Risk
Marrying blood relatives increases the genetic risk. Repeated consanguinity across generations results in:
- Accumulation of Recessive Genes: These mutations accumulate, and when the affected children reproduce, it passes onto the next generation.
- Rising Homozygosity: Repeated Consanguinity increases homozygosity and reduces protective genetic variations, increasing the risk of developmental defects, reducing intellectual ability, and poor adaptation to stress.
- Inbreeding Depression: Inbreeding increases homozygosity, and it results in more infant and childhood mortality, reduced birth weight and growth, congenital anomalies, and lower cognitive performance.
- Impacts Health: Consanguinity also affects the overall health of the baby, reduces immune function, disrupts neurodevelopment, and reduces lifespan.
Consanguinity Across Cultures
About 10-29% of global marriages occur between blood relatives, with more in South Asian Middle East, and North Africa. In Pakistan, Kuwait, Qatar, the UAE, and Sudan, first-cousin marriages are more prominent. Consanguinity is more prominent among Muslim societies as Islamic norms accept it.
Benefits of Consanguineous Marriage
Despite the biological risk, marrying blood relations is still common because of social gains. Marrying cousins and close blood relatives strengthens bonds and reduces divorce rates. It also increases trust. Because they are from the family, the women’s honour can be protected.
Consanguineous marriage means the wealthy family can stay within the family. Because of the shared values and traditions, the marriage can be stable. Royal families practice consanguinity to retain power, wealth, and to safeguard their royal bloodline.
Marriage between blood relatives increases genetic risks for the babies because of the shared ancestry. When two recessive genes merge, it can express genetic disorders, stillbirths, developmental disabilities, infant mortality, increased congenital anomalies, and other long-term health challenges. Awareness is the first step to reducing the risks. Education about consanguinity helps people understand the risk from a scientific perspective.
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FAQs on Can Marrying a Relative Affect a Baby’s Health? What to Know
- Is there any problem in marrying the same blood group?
Marrying the same blood group doesn't cause any problems in marriage or child. The problem only arises when the mother and foetus have incompatibility in the Rh factor. If the mother is Rh-negative and the foetus is Rh-positive, this incompatibility can cause hemolytic disease in the baby. If both parents are Rh-negative or Rh-positive, there is no risk. - Does consanguinity affect longevity?
Consanguinity, that is, marrying blood relatives, reduces the kid’s longevity. The life expectancy of children of first cousins is reduced by over three years. It's mainly due to recessive genetic disorders. These kids from consanguinity also face a high risk of mortality, congenital anomalies, and disabilities.