INTRODUCTION:
Genetic disorders are still perceived as an uncommon event in our general population. However the literature reveals that every year an estimated 7.9 million children (6 percent of total births worldwide) are born with a serious birth defect of genetic or partially genetic origin. Additional hundreds of thousands more are born with serious birth defects of post-conception origin, including maternal exposure to environmental agents (teratogens) such as alcohol, rubella, syphilis and iodine deficiency that can harm a developing fetus.
The expression of various human traits depends on interaction between genes and environment i.e. genetic vs nongenetic (infections, teratogens) factors. Disorders caused due to mutation in a single gene can be due to influence of the environmental factors eg. cystic fibrosis and sickle cell disorder. Similarly infection with HIV-1 can led to genetic polymorphism.
As per data presented by Global Report on Birth Defects (New York ) in 2006, birth defects are a global problem, but their impact is particularly severe in middle- and low income countries where more than 94 percent of the births with serious birth defects and 95 percent of the deaths of these children occur. The proportion of births with birth defects as well as the absolute number of births are much higher in middle and low-income countries than in high-income countries because of sharp differences in maternal health and other significant risk factors, including poverty, a high percentage of older mothers, a greater frequency of consanguineous marriages and the survival advantage against malaria for carriers of sickle cell, thalassemia, and glucose6-phosphate dehydrogenase (G6PD) deficiency genes. According to the data in this report, five common serious birth defects of genetic or partially genetic origin in 2001 were: (1) congenital heart defects ; (2) neural tube defects (3) the hemoglobin disorders ( thalassemia, and sickle cell disease) (4) Down syndrome (trisomy 21) and (5) glucose-6-phosphate dehydrogenase (G6PD) deficiency. Combined, these five conditions account for about 25 percent of all of birth defects of genetic or partially genetic origin.