Thanks for writing in.
I am a medical specialist with additional degree in cardiology. I read your question with diligence.
BLOOD RELATED marriages are called consanguineous marriages — sanguine meaning blood.
Around the globe consanguineous marriages have been practised by many societies from time immemorial. It is widely practiced in Asia, North Africa, Switzerland, Middle East, some parts of China, Japan and fishermen communities in Europe and America. One in two rural marriages in Tamil Nadu and Andhra Pradesh (States of India) are consanguineous.
What type of marriages are consanguineous marriages? When you marry biologically related or blood relatives then it is consanguineous marriage. Most commonly in our part of the world, first cousins — uncle's son marries auntie's daughter or vice versa.
However another type of marriage is where maternal uncle marries his niece (sister's daughter). Theoretical risk of having a genetic defect child is higher in the latter type of marriage than the former. Most of us do not even recognize the pros and cons of such marriages.
While assessing the consequence of consanguineous against non-consanguineous (non-blood related) marriages in health and disease, several scientific studies have shown that consanguinity leads to death of infants before, during or immediately after birth, increased incidence of birth defects, genetic diseases including blinding disorders, blood cancer (acute lymphocytic leukemia
), breathing problems for children at birth (apnea), increased susceptibility to disease etc.
Some scientists contradict these studies and state that other biological factors could be accountable for the results and not consanguinity alone.
In one landmark study it was shown that consanguinity could increase the incidence of many blinding disorders like retinitis pigmentosa
, Leber congenital amaurosis
, Lawrence-Moon-Bardet-Biedl syndrome, Stargardt disease
, Usher syndrome
etc (Consanguinity and Ocular Genetic Diseases in South India: Analysis of a Five-year study. Community Genetics: 2002:5:180-185). Consanguinity could increase the risk of inheriting any one of the 4968 (autosomal recessive) genetic diseases that could affect any part of the body from head to foot.
Some animal studies have shown that inbreeding or consanguinity could enhance longevity. It has been proved beyond doubt that consanguineous marriages farther than second cousins would not result in major genetic diseases.
can predict some of these diseases and with doctor's opinion a decision for abortion can be taken. Or children can be adopted.
As far as blood group is concerned you are confusing the issue when Rh-ve mother carries Rh+ fetus that can happen in normal marriages also. You can get blood group checked. Also, to the extent possible, genes for autosomal recessive diseases should be checked. For both parents having recessive genes are bound to give the disease to offspring. Again this can happen in unrelated partners getting married so have no fear of consulting a genetics specialist
With Best Wishes.
Dr Anil Grover, Cardiologist
M.B.;B.S, M.D. (Internal Medicine) D.M.(Cardiology)