X-linked inheritance refers to genetic disorders that occur due to mutations on the X chromosome. Your body consists of millions of cells. Each cell contains 46 chromosomes; 23 come from your mother and 23 come from your father.
Females have two X chromosomes. They receive one from each parent. Males have an X and a Y chromosome. The X chromosome comes from the mother and the Y chromosome comes from the father.
If one copy of a specific gene stops working, it can lead to a genetic mutation. If a change in a gene occurs on the X chromosome, it’s called an X-linked genetic condition.
Is There Any Way to Test for X-linked Inheritance?
If you are expecting and would like information about your baby’s risk of inheriting an X-linked genetic disorder, talk to your OB/GYN or general practitioner about carrier genetic testing. This simple, noninvasive blood test can determine your risk of more than 110 genetic disorders.
Are There Different Types of X-linked Inheritance?
X-linked inheritance can occur in two separate ways:
- X-linked recessive inheritance
X-linked recessive inheritance is most common in males because they only have one X chromosome. Any male baby who receives a recessive gene on their X chromosome will develop a genetic disorder.
Females have two X chromosomes, so if one X chromosome has a mutation, the other one can compensate for the changed copy. A female baby who receives a recessive gene on their X chromosome becomes a carrier. A carrier has a changed copy of the gene, but that doesn’t mean that they will develop a genetic disorder.
- X-linked dominant inheritance
X-linked dominant inheritance is very rare. It occurs when a female baby inherits both a normal copy of a particular gene and a changed copy. In X-linked dominant inheritance, the changed copy is powerful enough to result in a genetic disorder.
A woman with X-linked dominant inheritance has a 50% chance of having a baby with a genetic disorder. A man with X-linked dominant inheritance will pass the genetic disorder onto all of his daughters, but none of his sons.
How Does X-linked Inheritance Work?
X-linked inheritance varies depending on whether the mother or father is a carrier.
If a mother is a carrier and she has a son, she will pass on either the X chromosome with a normal gene or the X chromosome with the mutated gene. This means each son has a 50% chance of developing a genetic condition. There is also a 50% chance that the son will inherit the normal gene and be unaffected.
If a mother is a carrier and she has a daughter, she will pass on either the X chromosome with a normal gene or the X chromosome with a mutated gene. This means each daughter has a 50% chance of inheriting the mutated gene. If this happens, the daughter becomes a genetic carrier. There is also a 50% chance that the daughter will inherit a normal gene. When this occurs, a daughter isn’t a carrier and is unaffected by the condition.
If a father is a carrier of an X-linked condition, they pass on the mutated gene to their daughters 100% of the time. This is because males only have one X chromosome, which is always passed on to their female offspring.
What Are Some Common Conditions Caused by X-linked Inheritance?
Some of the most common X-linked recessive disorders include:
- Red-green color blindness
- Hemophilia A
- Hemophilia B
- Duchenne muscular dystrophy
- Becker’s muscular dystrophy
- X-linked ichthyosis
- X-linked agammaglobulinemia
What Can I Do if I’m a Carrier of an X-linked Disorder?
If carrier genetic testing reveals that you carry an X-linked disorder, your OB/GYN or general practitioner can refer you to a genetic counselor who can better explain your results.
Even if you’re a carrier, it doesn’t necessarily mean you’ll have a baby with a disorder. However, understanding this information in the early stages of your pregnancy can help you better plan for the future and know what to expect.