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Inherited Disorders and Birth Defects

What is a `flipped` seventh chromosone

06/26/2006

Question:

My step son has been diagnosed with a `flipped` seventh chromosone.

Is this.. or could it be Williams Syndrome??

Could you give me some information about this disorder?

Answer:

A "flipped" seventh chromosome may be referring to what is known as an inversion of chromosomal material. There are 46 chromosomes in every cell of the body. If a chromosome or piece of a chromosome is missing or duplicated, this leads to missing or extra genes. When a person has missing or extra genes, problems can develop for that person's health and development.

Each chromosome has a short arm = p (petit) and a long arm = q (next letter in the alphabet). In some chromosomes the arms are pretty equal in length, in other chromosomes (like 13, 14, and 150 the p arms are very small. In pictures (a karyotype), the p arm is always on top and the q arm is always on the bottom. The arms are separated by an area called the centromere, which is a pinched area of the chromosome.

An inversion happens when there are two breaks in one chromosome. The area between the breaks is inverted (turned around or flipped). This flipped chromosomal material is then reinserted and the areas of the breaks unite to the rest of the chromosome. If the inverted area includes the centromere it is called a pericentric inversion. If it does not, it is called a paracentric inversion.

Inversions may not cause any problems; however, if a parent has an inversion there is an increased risk for any child to receive an incorrect amount of genetic material. This can lead to babies with birth defects and/or abnormal development or an increased risk for miscarriage. Sometimes inversions can happen just in the baby and not come from either parent.

Williams syndrome is a genetic disorder that is caused by the loss of genes on chromosome #7. Most individuals with Williams syndrome are missing genetic material on chromosome #7 including the gene that makes the protein elastin (a protein which provides strength and elasticity to vessel walls.)

People with Williams syndrome have a particular facial appearance, usually have a specific type of heart defect, increased amounts of calcium, dental problems, overly friendly personality and some degree of intellectual handicap.

Researchers think that the loss (deletion) of the elastin gene is the basis for many of the physical features of Williams syndrome. Some medical and developmental problems are probably caused by deletions of additional genetic material near the elastin gene on chromosome #7. The extent of these deletions may vary among individuals.

Unless the "flipped" part of chromosome #7 in your step son has lost the part of the chromosome material that includes the elastin gene and other genes near it - your step son may not have Williams syndrome.

I would recommend that you speak to a geneticist or genetic counselor to discuss your step son's diagnosis in detail. Based on chromosome test findings, they would be able to tell you if he has William syndrome or some other type of chromosome problem. You can locate a genetics center near you at the National Society of Genetic Counselors' website 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