X-linked recessive inheritance

X-linked recessive inheritance is a pattern in which variants in genes on the X chromosome cause disease more often in males, while females may carry a variant without symptoms.

X chromosome: One of the two sex chromosomes in humans, carrying genes involved in many biological functions. The pattern concerns variants in genes located on this chromosome.
Allele: One of the alternative forms of a genetic sequence at a particular genomic location. An X-linked variant is an allele whose effects depend on chromosome context.
Hemophilia A: An inherited bleeding disorder caused by deficient or dysfunctional clotting factor VIII. Many cases follow X-linked recessive inheritance and illustrate its clinical pattern.
Autosomal recessive inheritance: A pattern in which disease usually occurs when both copies of an autosomal gene carry disease-associated variants. Unlike X-linked recessive inheritance, it affects males and females at similar rates.
Hemizygosity: The state of having only one copy of a particular chromosome or gene. Most males have one X-linked gene copy, so a disease-associated variant can act without a second copy.
Genetic variant: A difference in DNA sequence compared with a reference sequence or other individuals. A disease-associated variant is the inherited change underlying this pattern.
Duchenne muscular dystrophy: A progressive muscle-wasting disorder caused by pathogenic variants in the DMD gene. Its usual X-linked inheritance makes it a prominent example of affected boys and carrier females.
X-linked dominant inheritance: A pattern in which a disease-associated variant in one X-linked gene copy can cause the condition. A single variant can cause disease, unlike the usual recessive pattern described here.
X-inactivation: The process that largely silences one X chromosome in each cell of most female mammals. Uneven silencing can cause symptoms in some females who carry an X-linked variant.
Carrier (genetics): An individual who has a genetic variant associated with a condition but may not show its symptoms. Females with one disease-associated X-linked variant are often described as carriers.

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