Rita inherited the recessive gene from her father and became a carrier.
Since both Peter and Rita are carriers for the recessive gene, there is a 25% chance that their child could well be suffering from Tay-Sachs disease. The screening test (CVS) for fetal genetic defects confirmed that the fetus was indeed afflicted by the Tay-Sachs disease.
Rita (43 years) and Peter (46 years) have been trying to have a baby for more than 2 years, Rita has conceived now. There is sufficient documentation to show that the peak fertility period for women is between 20-24 years of age, after which it begins to decrease and this explains the delayed conception. The website www.babycentre.co.uk states that
"According to the Human Fertilisation and Embryology Authority, "At 35 you're half as fertile as when you were at 25; at 40 you're half as fertile as when you were 35". This means that it can suddenly take much longer to get pregnant when you hit your late thirties or early forties and you may have problems conceiving at all."
Another problem is that the odds of having a baby with a genetic defect increase as you get older. Figures from the Office of National Statistics for 2005, show that the risk of having a baby with a genetic abnormality such as Down's syndrome rises from 2 per 1,000 births at ages 35-39 years, to 4 per 1,000 at age 40-44 years up to 14 per 1,000 at age 45 years or over. If you're almost, or over 40, you should strongly consider genetic testing because the risk of genetic problems increases significantly.
Both Rita and Peter have crossed their peak fertility age and are therefore in the high risk category for genetic disorders. The physician, ordered for a CVS to rule out any genetic defects in the developing fetus. The genetic screening pointed to Tay-Sachs in the fetus. Prior to this genetic screening neither Peter nor Rita ever suspected that they could be carriers for the Tay-Sachs disease.
The Tay-Sachs disease is an autosomal recessive disease which is a result of mutation in both the alleles of the gene Hex-A seen in chromosome 15. As a result of the mutation, an enzyme called Hexosaminidase A is either not produced at all, or, is not produced in sufficient quantity. This insufficiency leads to an abnormal accumulation of a lipid called GM2 ganglioside in the nerve cells especially in the brain leading to progressive damage of the cells and eventual death of the cells. Children who suffer from this disease usually die before the age of five, because, by this age the nervous system is so seriously affected that it cannot support life.
Knowing that it is a recessive gene that causes the disease, is good news for the Trosack couple. A recessive gene can express itself in a particular generation only if it is present in a double dose, this occurs only if the progeny has inherited the recessive gene from both its parents. The chance of the couple passing on the recessive genes to their progeny, so as to exhibit the condition is only