Sex-linked dominant
Definition
Sex-linked dominant is a rare way that a genetic trait or disorder can be passed down through families. One abnormal gene on the X chromosome can cause a sex-linked dominant disease.
Related terms and topics include:
Alternative Names
Inheritance - sex-linked dominant; Genetics - sex-linked dominant; X-linked dominant; Y-linked dominant
Information
Inheritance of a specific disease, condition, or trait depends on the type of chromosome that is affected. It can be either an autosomal chromosome or a sex chromosome. It also depends on whether the trait is dominant or recessive. Sex-linked diseases are inherited through one of the sex chromosomes, which are the X and Y chromosomes.
Dominant inheritance occurs when a variant gene from one parent can cause a disease, even though a matching gene from the other parent is normal. The variant gene dominates the gene pair.
For an X-linked dominant disorder: If the father has the variant X gene, all of his daughters will inherit the disease and none of his sons will have the disease. That is because daughters always inherit their father's X chromosome. If the mother carries the variant X gene, half of all her children (daughters and sons) will inherit the trait.
For example, if there are four children (two boys and two girls) and the mother is affected (she has one variant X and has the disease) but the father does not have the variant X gene, the expected odds are:
- Two children (one girl and one boy) will have the disease
- Two children (one girl and one boy) will not have the disease
If there are four children (two boys and two girls) and the father is affected (he has one variant X gene and has the disease) but the mother is not affected, the expected odds are:
- Two girls will have the disease
- Two boys will not have the disease
These odds do not mean that the children who inherit the variant X gene will show severe symptoms of the disease. The chance of inheritance is new with each conception, so these expected odds may not be what actually occurs in a family. Some X-linked dominant disorders are so severe that males with the genetic disorder may die before birth. Therefore, there may be an increased rate of miscarriages in the family or fewer male children than expected.
References
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Jones KL, Jones MC, Campo M. Genetics, genetic counseling, and prevention. In: Jones KL, Jones MC, Campo MD, eds. Smith's Recognizable Patterns of Human Malformation. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 2.
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Scott DA, Lee B. Patterns of genetic transmission. In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 97.
Sondheimer N. Patterns of single-gene inheritance. In: Cohn RD, Scherer SW, Hamosh A, eds. Thompson & Thompson Genetics and Genomics in Medicine. 9th ed. Philadelphia, PA: Elsevier; 2024:chap 7.