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 the father's sperm. In this way. a child inherits half of the information needed for development from each parent. A picture of all the chromosome pairs lined up together is called a karyotype (Diagram 2). Examination of the chromosomes provides valuable information because you can see if there may be a structural or numeric change that may cause a genetic condition.

Diagram 2. Normal male karyotype.

JP can occur in an individual by a brand new gene change (de novo mutation), or by a gene change that is inherit from a parent (at least half of reported cases). Regardless of how JP occurred, the individual has a chance to pass the condition on to their children.JP is inherited in an autosomal dominant fashion. Since genes come in pairs, if one of the parents has JP, there is a 50 percent chance with each pregnancy to pass on the changed gene causing JP, and a 50 percent chance not to pass the changed gene. JP can be inherited through the mother or the father and has an equal likelihood of affecting a son or a daughter Please refer to Diagram 5.

Diagram 3. This diagram shows how one gene from each parent is passed to a child. In the case above the father has one working gene, indicated by the lower case letter n, and one gene with a change, indicated by the capital letter N. The mother has two copies of normal genes. There are four possibilities of gene combinations for the child. Each child has a 50% chance
of inheriting the changed gene (N), regardless of the sex of the child.

An evaluation of your family history can determine if a pattern exists. A family tree or a pedigree is a diagram of the members of your extended family. Diagram 4 is a pedigree that demonstrates the pattern of autosomal dominant inheritance within a family.

Diagram 4. This pedigree tells us several things about this family.

1) Sue and Tom have three kids; two of whom are affected. Since Sue was affected, each of her children had a 50% chance for developing Juvenile Polyposis syndrome, but only Joe and Jim actually inherited the gene change.2) Sara did not inherit the gene change and has not developed Juvenile Polyposis. She cannot pass this gene on to her children, nor will they develop JP.3) Joe has one daughter who had a 50% chance of inheriting the gene change and developing Juvenile Polyposis syndrome. Jen did not inherit the change, will not develop JP, and cannot pass the gene change to her children.4) Kay and Jim have two children, one inherited the gene change. Tim inherited the gene change and he now has a 50% chance of passing this gene on to his children. Lori did not inherit the change and cannot pass the gene on to her children.To date, three genes have been discovered that we associated with an inherited predisposition to JP. SMAD4 and PTEN were the first two genes that were identified. SMAD4 is located on chromosome 18 and is estimated to be responsible for approximately 20 percent of JP cases. PTEN is located on chromosome 10 and may be responsible for less than 5 percent of JP cases. However, PTEN is also responsible for related conditions, such as Cowden syndrome and Bannayan-Riley-Ruvalcaba and patients with changes in this gene probably have one of these other conditions rather than JP. PTEN and SMAD4 both function as tumor suppressor genes. A tumor suppressor gene is a gene whose function is to monitor and control cell growth. BMPR1A is the most recently discovered gene associated with JP and may account for up to 25 percent of JP cases. This gene is also located on chromosome 10. Despite a close proximity with PTEN (both on l0q22-23), they do not appear to work together or share responsibilities. The true function of BMPR1A is still under investigation.Many changes within the JP genes have been identified, some of which will cause the gene to not function properly. This type of a gene change is called a mutation. Gene mutations of PTEN, SMAD4, or BMPR1A predispose a person to develop juvenile polyps within the GI tract. Researchers are working to discover additional genes associated with JP.

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