XYY chromosomal syndrome, also known as XYY chromosome syndrome, is a condition in which boys are born with an extra Y chromosome. children with XYY chromosomal syndrome are often tall and have speech difficulties. xYY chromosomal syndrome was once thought to be aggressive or prone to violent crime, but this theory has been proven wrong. Birth defects, also known as congenital defects, are functional and structural abnormalities that are present at birth. About 3 to 4 percent of newborns have severe birth defects. Some birth defects are not detected until the child is growing and developing. 7.5% of children have birth defects that are not diagnosed until age 5, most of which are small malformations. Birth defects are very common, and there are considerable complications in the development of the millions of specialized cells that make up the human body from the fertilized egg. Most severe malformations can be diagnosed prenatally. The severity of birth defects varies, and most can be treated or repaired, although some birth defects can be treated in utero, but most require treatment after delivery or somewhat later. There are some anomalies that do not require treatment at all, and others that are untreatable and cause severe lifelong disability to the affected child. Although the cause of most birth defects is unknown, certain factors have been shown to increase the risk of birth defects, including nutritional deficiencies, radiation, certain drugs, alcohol consumption, maternal infections and diseases, trauma, and genetic disorders. Any factor that can cause birth defects or increase the risk of birth defects is called a teratogenic factor, and radiation, certain drugs and toxins are teratogens. Exposure to teratogens during a particular period of fetal development can cause the same birth defects in different teratogens; on the other hand, exposure to the same teratogens in different trimesters can cause different birth defects. In conclusion, pregnant women should consult their doctors before taking medication, quit smoking and alcohol, and avoid taking X-rays unless absolutely necessary. If x-rays must be taken, the pregnant woman should tell the radiologist or technician that she is pregnant so that the fetus is protected as much as possible. Infectious diseases during pregnancy can be teratogenic, especially rubella virus infection. Women of childbearing age should be vaccinated against rubella if they have not previously been infected with rubella before planning a pregnancy. Pregnant women who have neither been infected with rubella nor vaccinated against rubella should avoid contact with rubella-infected individuals. Pregnant women who have already been exposed to teratogenic factors want to check if the fetus is affected by the test. However, most pregnant women exposed to these risk factors have children with no abnormalities. Some birth defects are due to inheriting abnormal genes from both or one parent, some birth defects are due to genetic mutations, and some birth defects are due to chromosomal abnormalities, such as one extra or one less chromosome. The older a pregnant woman is, especially if she is over 35 years old, the greater the chance that her fetus will have a chromosomal abnormality. Many chromosomal abnormalities can be detected early in pregnancy.