What is consanguinity?

Consanguinity refers to when a couple are blood relatives (they share an ancestor). An example is a when a couple are first cousins. Consanguinity is quite common in many cultures.
 

If a couple are consanguineous (related) their children have a higher chance of being affected by autosomal recessive genetic disorders. These only occur if a child has a mutation (change) in both copies of a particular gene pair.
 

What are the risks of consanguinity?

Factors and non-genetic variables due to consanguinity are known to influence childhood health including maternal age (age of the mother at the time of delivery of child), social conditions, education, birth order, and birth intervals.
 

A number of factors are extremely important to consider regarding the impact of consanguinity on child health:

• Gender (disability prevalence is higher in boys);
• Age (the cohort effect);
• Socioeconomic status;
• Maternal age and education;
• Birth order and birth intervals.

Rates of Foetal Loss

• Loss due to genetic disorders or other causes may occur early in pregnancy.

Birth outcomes

• Still births are more common in consanguineous couples.

Deaths in neonatal period and infancy

• There's an excess of 1.1 per cent of deaths in first cousin pregnancy both in infancy and in the neonatal period.

Birth defects

• Congenital disorders;
• Deafness - there's increased incidence of both syndromic and non-syndromic hearing loss with consanguinity;
• Visual impairment - consanguinity-associated blindness is less frequent than deafness but retinitis pigmentosa and congenital cataracts have been associated with consanguinity.

Congenital heart disease - Elevated rates

Other variable reports of other congenital cardiac abnormalities include coarctation, transposition of the great arteries, tetralogy of fallot and pulmonary atresia.

Other defects

• Neural tube defects have been suggested to be more common however, this could be related to a variety of factors;
• Rare metabolic conditions such as lysosomal storage disorders and cerebral lipoidoses may be more common.

Blood disorders

• Increased prevalence of α- and ß-thalassaemia, rare complex haemoglobinopathies (inherited blood disorders) and other haematological disorders such as leukaemia, are seen with consanguinity.

Developmental delay

• Severe, or mild, intellectual and developmental delays have higher prevalence in consanguineous unions. 

It should be highlighted that consanguineous marriage is not restricted to specific religions or population groups and consanguinity does not cause genetic disorders.