How is Genetic Disease Inherited?
Genetic traits can be passed through families in several distinct patterns. The most common patterns are the following:
- Dominant genetic diseases are caused by a mutation in one copy of a gene. If a parent has a dominant genetic disease, then each of that person’s children has a 50% chance of inheriting the disease. Dominant diseases can also occur spontaneously; this happens when a random mutation in one gene occurs at conception. Examples of dominant genetic diseases include Achondroplasia and Huntington disease. For some dominant genetic diseases, there may be specific DNA tests available.
- Recessive genetic diseases. When both parents are carriers of the same recessive disease, there is a 25% chance that the pregnancy will inherit the trait from both parents and have the disease, a 50% chance that the pregnancy will inherit the trait from only one parent and be a carrier, or a 25% chance that the pregnancy will not inherit the trait from either parent and will not be a carrier or have the disease.
- Sex-linked genetic diseases affect males and females differently. This is a smaller set of diseases related to gene mutations on the X or Y chromosomes. Some common examples include hemophilia and color-blindness. Depending on your family history, testing for a sex-linked genetic disease may be available.
- Multifactorial traits occur due to many complex interactions and combinations of maternal, environmental and genetic influences. The most common birth defects are members of this category, including congenital heart defects and cleft lip. Almost 1 child in 150 is born with a congenital heart defect and 1 in 500 with cleft lip. Another multifactorial condition is spina bifida, a type of an open neural tube defect. Spina bifida occurs in approximately 1 or 2 in 1000 births. Taking the vitamin folic acid (folate) helps reduce the chance of having a baby with spina bifida. In most cases predictive genetic testing is not available for multifactorial traits, however a family history assessment may provide more accurate recurrence risks.
- Chromosome abnormalities can occur in any pregnancy. Sometimes these risks are related to the parent’s age and involve extra or missing chromosomes. A second type of chromosome abnormality is a change in the structure or organization of the chromosomes. These changes include deletions (a small missing piece), inversions (a piece flipped upside down), insertions (an added piece), or translocations (exchange of pieces involving two or more chromosomes). Structural changes are not associated with maternal age. They can be passed from parent to child in many complex patterns and can be the cause of multiple unexplained miscarriages, birth defects, or apparent infertility.