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Inherited Disorders and Birth Defects

Extra chromosome



Just to give you a background - when I was 36 I was pregnant with my daughter. The doctors wanted to do an amniocentesis to check to make sure the baby was normal. They discovered she had an extra chromozone .... so they did a DNA test to find out which parent carried the extra chromozone. It was me. Is this a rare instance? And if so, what if any, things could have occurred to cause this? Are there any benefits? or problems associated? I am also an identical twin. My daughter is 12 years old and is a very intelligent little girl.


It is not possible to give you additional information except in general. You do not mention which chromosome is extra. Usually we have 46 chromosomes in each cell in our bodies - 44 non-sex chromosomes (called autosomes) and 2 sex chromosomes, an X and Y for males and 2 X chromosomes for females. Chromosomes carry all of our genes which tell our bodies how to develop and function.

When there is a whole extra chromosome - this usually leads to birth defects and mental retardation. The most common problem where there is an extra chromosome is Down syndrome, also called trisomy 21. Down syndrome happens in about 1 in 700 live births. There are other rare trisomies, however, these usually cause very serious problems and most children do not live very long.

Children can also be born with part of an extra chromosome. The types of problems seen can be variable and depend on how much extra chromosome material is present. Usually, too much or too little chromosome material leads to birth defects and other problems.

Sometimes, the person has what is called a translocation - where a part of one chromosome has broken off and switched places with another chromosome. In these cases, someone can be a "balanced translocation carrier" - parts of the chromosomes are rearranged, but all the chromosome material is present and functioning properly. In this case, you would not expect to see any problems for the person that has the "balanced" rearrangement.

You may want to talk to a genetic counselor or geneticist to discuss the specific extra chromosome your daughter has to receive more information about potential problems or benefits. You can locate a genetics center near you at the National Society of Genetic Counselors website listed below.

Related Resources:

National Society of Genetic Counselors Resource Center

For more information:

Go to the Inherited Disorders and Birth Defects health topic, where you can:

Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University