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| What is a chromosome? |
| Chromosomes contain the genetic blue print of an individual and are constituted by DNA, which contain the genes that are the regulatory elements of the living being. |
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| What is a gene? |
Gene is the unit of heredity in the living organism. It is composed of DNA and it directs the physical developments and behavior of an individual. |
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| What is meant by Down syndrome? |
Down syndrome is the commonest chromosomal condition where in an individual has 47 chromosomes instead of the normal 46. This extra chromosome is contributed by chromosome 21. The 46 chromosomes are arranged as 23 pairs and instead of two chromosomes 21, individuals with Down syndrome have three chromosomes 21. These individuals will be having characteristic facial features with associated mental retardation. Down syndrome usually occurs to children born to elderly mothers (35 years and above). These children need early intervention programmes and physiotherapy from very early age.
The risk for a pregnant woman to have a baby with Down syndrome at 25 years is 1/1350 whereas the risk increases to 1/85 when she is 41 years old |
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| Can my next child develop Down syndrome? |
If you have one child with Down syndrome the risk to have recurrence in next pregnancy depends upon the type of Down syndrome. Regular type of Down syndrome (non-disjunction) is the most common type (90 -95%) and this is usually seen to children born to elderly mothers. This type can occur in children born to younger mothers also. Even though these parents of children with regular type of Down syndrome have a normal chromosomal pattern, they should undergo prenatal diagnosis for Down syndrome in next pregnancy as they have increased risk than the other couple who do not have children with chromosomal anomaly.
If the baby has a translocation down syndrome, where the chromosome 21 is attached to either chromosomes 14 or 15 then there is absolute indication to check the chromosomes of the parents as the risk for such carrier parents are comparatively high. |
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| Can we detect whether my baby is affected with Down syndrome in my next pregnancy? |
| Yes. Down syndrome can be detected by the chromosomal study of the amniotic fluid, (Fluid around the baby in the womb) at 16-18 weeks, or by studying the chorionic villi (a component of placenta) at 10-12 weeks of pregnancy. |
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| What is prenatal diagnosis? |
| Prenatal diagnosis literally means “Diagnosis before birth”. Prenatal diagnosis helps to identify the fetus at risk of genetic abnormality and provides them with accurate information about the condition, its risks and available management. As many of the genetic disorders do not have curative treatment, early diagnosis in pregnancy allows the couple to decide whether to continue the pregnancy or to terminate should a diagnosis of a serious disorder be made. To achieve this the diagnosis should be made at the earliest, not later than 20 weeks of pregnancy. |
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| Do I have increased risk of having children with deformity if I marry my cousin? |
| Yes. Cousins share 1/8th genes in common. If there is a gene abnormality in the family there is increased chance for the cousins to share them. Children born to blood relatives have increased risk to get the defective gene and hence have increased chance to have congenital malformations. |
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| I am a 38 yr old mother and I am 2 months pregnant. I have no family h/o Down syndrome or other genetic disorders. Should I consider prenatal diagnosis options? |
| Yes. As we have answered in our previous question, even though you do not have a family history of genetic disorders there is a definite increase in risk for having a baby with a chromosomal anomaly when the mother’s age is more than 35 years. Hence as your age is 38 years you should definitely resort to prenatal diagnosis, which can pick up Down syndrome as well as trisomy 13 and 18. |
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