G. Sruthi, B. Optom
Fellowship in Clinical Optometry, Aravind Eye Care System, Chennai, India
Consanguinity is a mixture of two words taken from the Latin language; “con” means similar, and “sanguineous” means blood. In clinical genetics, a consanguineous marriage is defined as a union between two individuals who are related as second cousins or closer in which the offspring of a consanguineous union is expected to inherit identical gene copies from both parents. Children born out of consanguineous unions may be at increased risk of acquiring genetic disorders because of the expression of autosomal recessive gene mutations inherited from a common ancestor in a homozygous state. The incidence of congenital malformations involving major systems of the body has been reported to be higher in consanguineous marriages, especially uncle-niece marriages compared to those between first cousins.
Grades of Consanguinity marriage
Figure 1: Grades of consanguinity marriage
(Image courtesy – https://sociovillage.wordpress.com/2016/09/28/consanguinity/)
The risk of severe birth defects varies, depending on both the kind of society in which the relationship exists, and the way studies measure a child’s health during the first few years of its life. The closer the biological relationship, the higher the chances for genetic disorders. First-degree relatives who are in a relationship have about a 30 percent risk of bearing a child with severe birth defects. The risk is about 2-3 percent in the third degree.
The most common causes of Consanguinity marriage are congenital anomalies, hearing and vision impairment, mental retardation or learning disability, Developmental delay, or failure to thrive inherited blood disorder, and unexplained neonatal or infant death in offspring. (1-3)
Table 1: Common ocular hereditary disorders with their common gene involved.
|Diseases||Description of the condition||Common Gene Involved|
|Congenital hereditary endothelial dystrophy (4)||
||27 Genes involved in this condition
|Xeroderma pigmentosum (6)||
|Oculocutaneous Albinism (7)||
||It is caused by a mutation in many genes.
|Axenfeld Rieger Syndrome (9)||
|Congenital Glaucoma (10-11)||
|Congenital / Developmental Cataract (12)||
||More than 100 genes responsible for cataract and associated conditions|
|Leber Congenital Amaurosis (13)||
||Frequently mutated genesis in LCA
|Retinitis pigmentosa (14)||
||Frequently mutated genesis in LCA
|Cone-rod dystrophy (15)||
|Familial exudative Vitreo-Retinopathy (16)||
|Familial exudative Vitreo-Retinopathy (16)||
|Vitelliform Dystrophy (17)||
|Optic Atrophy (18)||
Due to the sharing of genetic material from the common ancestor, the marriages between uncle, niece and first cousins result in genetic disorders in the offspring.
Table 2: How consanguinity results in hereditary diseases (19)
|Relationship||Average percentage of DNA shared|
|Parents to children||50|
|Brothers and sisters||50|
|Uncle and niece||25|
Genetic counselling and its importance
Genetic counselling is counselling a patient regarding genetics, risk factors and diseases caused by consanguinity. (20) It involves obtaining the family and medical history from the patient and referring the clinician and reviewing the medical records of the patient and family members. There are separate centres available for genetic counselling on consanguinity. Genetic counselling is critical and must be performed in a sensitive, caring, and sensible manner. The consanguineous couples must be referred to well before conception, especially when there is a family history of possible autosomal recessive conditions. They should be made to understand that nobody chooses to deliberately pass an illness to their offspring, and no one is to be blamed.
Goals of genetic counselling for consanguineous couples and their offspring
- Providing preconception reproductive options
- Improving pregnancy outcomes
- Reducing morbidity and mortality
- Knowledge about screening the new-borns.
Consanguinity is a common trend still followed in many countries. Thus, genetic counselling and Genetic Screening play an important role to control hereditary disorders. Parents especially those lacking formal education should get more awareness of consanguinity.
|Health is wealth
Instead of creating a wealthy environment
We can create a diseases free environment for our future generation
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- Rauniyar, D., & Das, A. V. (2022). Consanguinity and ocular disorders in India: Electronic medical records driven big data analytics. Indian Journal of Ophthalmology, 70(7), 2401-2407.
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- Kondo H. (2015). Complex genetics of familial exudative vitreoretinopathy and related pediatric retinal detachments. Taiwan journal of ophthalmology, 5(2), 56–62. https://doi.org/10.1016/j.tjo.2015.04.002
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- Consanguinity and Eye by Dr P Sundaresan and N Prasanthi [https://www.researchgate.net/profile/Arvind_Singh56/post/Do_you_think_marriage_within_blood_relations_may_be_harmful_to_the_children_or_next_generations/attachment/5aad01b0b53d2f0bba5895f9/AS%3A605138209218560%401521287600047/download/Consanguinity]
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