Consanguineous Marriages and Childhood Blindness
Ramesh Kekunnaya, MD, FRCS, Consultant Pediatric Ophthalmologist,
L V Prasad Eye Institute, Hyderabad
1.What is a Consanguineous Marriage?
The word “Consanguineous” comes from two Latin words “Con” meaning “With / Together” and “Sanguine” meaning “Blood”. It describes a relationship between two people who share an ancestor. Consanguineous marriages are common in many families especially among Muslims and Dravidian Hindus of Southern India. In these societies, marriages are often between a man and his parent’s sibling’s daughter. High occurrence of consanguineous marriages has been associated with low socioeconomic status, illiteracy, and rural residence. The reasons reported are primarily social. It is believed, that stronger family ties will be formed, financial and health uncertainties may be avoided, and the integrity of estates in land-owning families may be preserved.
2. Disease spectrum
Though most consanguineous couples can have normal healthy children, consanguinity has been reported as an important factor in the development of autosomal recessive diseases and congenital anomalies, including hydrocephalus, polydactyly, and bilateral cleft lip and cleft palate. The risk of birth defects in the offsprings of first cousin marriages has been estimated at 5–8% as compared to 2–3% in non-consanguineous marriages. Consanguinity has also been reported to contribute to reproductive hazards, child deaths, as well as spontaneous abortions and stillbirths. There have also been some reports in the literature with positive association between consanguinity, Down syndrome and various congenital heart defects.
The following eye diseases have been seen in children who are born to parents of consanguineous marriage:
- Congenital glaucoma
- Congenital Strabismus (Squint)
- Congenital Cataract
- Retinitis pigementosa and other hereditary retinal disorders.
- Ocular or oculocutaneos albinism
- Congenital birth defects like Uveal Coloboma. Etc.
All of the above can cause moderate to severe visual impairment or blindness. The important symptoms or signs to be noted are poor vision, non-development of eye contact with others, night blindness, intolerance to light (photophobia), enlarged eyeballs (Buphthalmos), crossed eyes (Squint) or shaking eyeballs (Nystagmus). These can directly or indirectly delay developmental milestones in a child’s life.
3. How are genetic diseases transferred?
The offspring of consanguineous relationships are at greater risk of certain genetic disorders. Autosomal recessive disorders occur in individuals who are homozygous for a particular recessive gene mutation. This means that they carry two copies (alleles) of the same gene. Except in certain rare circumstances (new mutations or uniparental disomy) both parents of an individual with such a disorder will be carriers of the gene. Such carriers are not affected and will not display any signs that they are carriers, and so may be unaware that they carry the mutated gene. As relatives share a proportion of their genes, it is much more likely that related parents will be carriers of an autosomal recessive gene, and therefore their children are at a higher risk of an autosomal recessive disorder. The extent to which the risk increases, depends on the degree of genetic relationship between the parents; so the risk is greater in relationships where the parents are close relatives, but for relationships between more distant relatives, such as second cousins, the risk is lower (although still greater than the general unrelated population).
4. Preventive aspects
Marriages between blood relatives should be avoided, as far as possible. Ancient Indian customs clearly state that a marriage within the same “Gotra” is a consanguineous marriage. The term Gotra broadly refers to people who are descendants in an unbroken male line from a common male ancestor. Such marriages may lead to gestational and genetic problems in the fetus. It has therefore been a common practice in Hindu households to ask the couples' Gotra during pre-marriage discussions. Couples of the same Gotra are advised not to marry. The advisers of this system say that this practice definitely helps in reducing gestational problems thereby ensuring a healthy progeny. One flaw in this system might be that the bride or groom’s mother’s maiden gotra is not taken into consideration. In today’s day and age, it might be a worth the while taking even this aspect into consideration prior to fixing up an alliance, in order to prevent any genetic overlap.
Couples with consanguineous marriages should go for prenatal genetic counseling in order to understand the risks for the fetus.
Prompt medical help must be sought if and when any ophthalmic or systemic abnormalities are detected. For example, conditions like congenital Cataract and Glaucoma can be surgically corrected if diagnosed & treated early on in life. Early intervention, low vision aids, and other rehabilitative measures, can aid in improving quality of vision in visually impaired children, thereby greatly improving their quality of life.
Public health programs with a multi-approach strategy involving educating people, increasing awareness about genetic consequences of consanguineous marriages, prenatal diagnosis and neonatal screening can be use to prevent consanguineous marriages.