omy 21: the alleles don't do the same thing to every person who has it. Both reasons may be why there is such variation in children and adults with Down syndrome.The actual causative factors of Downs are still unknown. Although many theories have been developed. Some professionals believe that hormonal abnormalities, X-rays, viral infections, immunologic problems, or genetic predisposition may be the cause of the improper cell division resulting in DS. It has been known for some time that the risk of having a child with Down syndrome increases with advancing age of the mother; i.e., the older the mother, the greater the possibility that she may have a child with DS. However, most babies with Down syndrome (more than 85 percent) (Vosatka, 213) are born to mothers younger than 35 years. Some investigators reported that older fathers might also be at an increased risk of having a child with DS. An interesting note about this is that this is only the case for Down syndrome caused by the triplication of chromosome 21, the risk of DS through Robertsonian translocation actually decreases with age. Again the causes of this are not fully realized, only that the risks for triplication of chromosome 21 seem to be variable and increase exponentially with age, while Robertsonian translocation is a constant variable and seems to be hereditary. Approximately 40% to 50% are familial in that they are inherited from a cytogenetically balanced parent. (Epstien 57)Diagnosis of Down syndrome can be done either prenatally through screening and diagnostic tests, or through physical examination of the newborn. The most commonly used screening tests are the Triple Screen and the Alpha-fetoprotein Plus. (National DS Society) These tests measure quantities of various substances in the blood (alpha-fetoprotein, human chorionic gonadotropin and unconjugated estriol) and together with the woman's age, estimate her risk of having a child with DS. These screening te...
