Every cell of our body has a complete copy of our genetic information. Genes serve as the basic unit of heredity, providing the instructions for growth and development. Genes are composed of DNA and are housed on structures called chromosomes. There are 23 pairs of chromosomes (46 total chromosomes). The first 22 chromosome pairs hold the instructions for your body to grow, develop, and function properly. The last pair determine if you are male or female: males usually have one X and one Y chromosome while females usually have two X chromosomes.

Chromosomes are passed from parent to child. A child receives one chromosome of each pair from his or her mother's egg and one from his or her father's sperm. In this way, a child inherits half the information needed for development from each parent.

A picture of all the chromosome pairs lined up together is called a karyotype (see image below). Examination of the chromosomes provides valuable information because experts can see if there may be a structural change that may cause a genetic condition.

Normal male karyotype with the arrow pointing to the location of the PTEN gene.

Looking at karyotypes is not the only way to look for a genetic problem. The genes within each chromosome can have changes as well. These changes are too small to see under a microscope, so scientists have developed other tests to look for small changes in the sequence (pattern) of a gene. A change in the sequence of the PTEN gene may cause Bannyan-Riley-Ruvalcaba or Cowden Syndrome.

The PTEN gene is located on chromosome number 10 (see karyotype above) and functions as a tumor suppressor. Tumor suppressor genes keep cell growth in balance, ensuring that cells do not grow (divide) more than they are supposed to. Only one copy of a gene is needed to control cell growth. While one gene may be changed, the functional copy is still able to successfully control cell growth. When an individual has Bannayan-Riley-Ruvalcaba syndrome, they have an inherited change in one of their genes. Random events* that occur throughout life may cause a change in the second copy of their PTEN gene, which may make the gene not work properly. Cells with two nonworking copies of the PTEN tumor suppressor gene are at increased risk for benign and malignant cell growth. Remember, a person with BRR inherits a predisposition or an increased chance for tumor growth; they do not inherit cancer itself.

*Random events that can change our DNA are uncontrollable. Incidents causing small changes at the cellular level can occur during normal cell growth or can be caused by environmental factors such as radiation. Everyone experiences several DNA changes throughout his or her lifetime, but most are not significant enough to be noticed.

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