What is X-linked dominant inheritance?

X-linked dominant inheritance is a pattern of genetic inheritance that occurs when there is a dominant gene on the differential segment of the X chromosome and therefore does not appear on the Y chromosome.

Also called X-linked dominance or X-linked inheritance dominant. It is less common than X-linked recessive inheritance, and both are more common than Y-linked inheritance.

In medicine, X-linked dominant inheritance indicates that a genetic disease is transmitted to offspring through a gene located on the X chromosome and that only one allele carrying the mutation is necessary for the disease to manifest, unlike inheritance. recessive in which both alleles must carry the mutation for the disease to manifest.

It is now known that the expression of genetic traits associated with the X chromosome can vary between different individuals due to mechanisms such as autonomous cell expression, biased inactivation of the X chromosome, clonal expansion or somatic mosaicism. Because of this, within the scientific community, it has been suggested that the terms “dominant” and “recessive” have been abandoned when talking about X3-linked inheritance.

inheritance pattern

The sex chromosomes are the X chromosome and the Y chromosome. Males have the XY chromosome pair and the female sex the XX pair. X-linked dominant inheritance is therefore determined by the sex of the parent who carries the gene. Whereas male offspring always inherit one X chromosome from the mother and one Y chromosome from the father and female offspring always inherit one X chromosome from the mother and one X chromosome from the father, X-linked dominant inheritance has the following characteristics:

Males pass it on to all of their female offspring and to no male offspring. Women pass it on to half of their female offspring and half of their male offspring. All affected have at least one affected parent (dominant inheritance). Being a dominant gene, it can appear in all generations
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We can find the following situations:

Only the mother is a carrier

If the father is unaffected and only the mother carries the gene on one of the alleles, she herself will have the disease and 50% of the offspring, male or female, will inherit the gene and develop the disease. Sons and daughters have an equal chance of inheriting the gene. The other 50% of the offspring will not inherit the gene and in this case there is also no difference between male and female offspring.

Only the father is a carrier

When the father is a carrier of the X-linked gene and the mother is not, it is the father who manifests the disease. In this case, the female offspring will always receive an affected X chromosome from the father and therefore 100% of the daughters will be affected. On the contrary, none of the children will be affected by receiving the Y chromosome from the father and the X chromosome from the unaffected mother.

Both parents are carriers

If both the father and the mother carry the X chromosome with the affected gene, they both manifest the disease. In this case, the inheritance pattern determines a probability that 100% of the daughters and 50% of the sons will inherit the disease. If the mother has the affected gene on both X chromosomes (homozygous), 100% of the sons and daughters will inherit the disease as they will always receive a copy of an affected X chromosome.

associated diseases

Among the diseases associated with a dominant gene on the X chromosome we can find:

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Vitamin D-resistant hypophosphatemia (also known as vitamin D-resistant rickets) Rett syndrome Alport syndrome (also known as hereditary nephritis. Only cases due to the COL4A5 gene are X-linked) Bloch-Sulzberger syndrome (also known as pigment incontinence) Giuffrè-Tsukahara syndrome4 Focal dermal hypoplasia (also known as Goltz syndrome) Androgen insensitivity syndrome (also known as testicular feminization) Aicardi syndrome X-linked dominant erythropoietic protoporphyria Fragile X syndrome CHILD syndrome (hemidisplasia congenita with erythroderma ichthyosiform and limb defects) Lujan-Fryns syndrome (marfanoid habitus with X-linked intellectual disability) Orophaciodigital syndrome type 1 Craniofrontonasal dysplasia

Other disorders such as synesthesia are also considered X-linked dominant traits, although this has yet to be determined exactly.

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