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Multifactorial Inheritance

What is multifactorial inheritance?

Multifactorial inheritance means that many factors (multifactorial) are involved in causing a birth defect. The factors are usually both genetic and environmental, where a combination of genes from both parents, in addition to unknown environmental factors, produce the trait or condition. Often one gender (either males or females) is affected more frequently than the other in multifactorial traits. There appears to be a different threshold of expression, which means that one gender is more likely to show the problem over the other gender. For example, hip dysplasia is nine times more common in females than males.

Multifactorial traits do recur in families, because they are partly caused by genes. The chance for a multifactorial trait or condition to happen again depends upon how closely the family member with the trait is related to you. For example, the risk is higher if your brother or sister has the trait or disease, than if your first cousin has the trait or disease. Family members share a certain percentage of genes in common, depending upon their relationship. For example:

Degrees of relationship

Percentage of Genes in Common

Example

First Degree Relative

50 percent

Parents, children, siblings

Second Degree Relative

25 percent

Aunts, uncles, nieces, nephews, grandparents

Third Degree Relative

12.5 percent

First cousins

Now, if we look at a multifactorial condition, such as a neural tube defect (NTD), the chance for this birth defect to be seen in a future pregnancy would be:

As you can see, the more genes you have in common with the family member, the higher the chance for you to have a child with a similar defect.

What are some of the different types of multifactorial traits and diseases?

Examples of multifactorial traits and diseases include: height, neural tube defects, and hip dysplasia.

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