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An obligate carrier is an individual who may be clinically unaffected but who must carry a

autosomal recessive and X-linked recessive manner.[1][2]

X-linked Recessive

Inheritance

In

carriers of the recessive mutation, making them obligate carriers of this type of disease. Females acquire one X-chromosome from their father and one from their mother, and this means they can either be heterozygous for the mutated allele or homozygous. If heterozygous, she is a carrier of the mutated allele because the disease is recessive. If homozygous, she has the disease. An affected father with an X-linked recessive trait will always pass the trait on to the daughter. Therefore, all daughters of an affected male are obligate carriers. On the other hand, a carrier mother has a 50% chance of passing her mutated X-chromosome to the daughter.[3] This makes all daughters of carrier mothers possible carriers but not necessarily obligate carriers. Males cannot be obligate or possible carriers of X-linked recessive traits because they only have one X-chromosome, and so are always phenotypically affected when receiving the mutated X-chromosome from their mother.[4]

Females that are heterozygous for X-linked recessive disorders are obligate carriers, but can never be

copy number, presence of the functional copy results in a normal phenotype.[5]
Males only have one copy of any gene on the X-chromosome, and because they do not undergo X-inactivation, they only have the mutated gene. As a result, these types of diseases most commonly phenotypically affect males and rarely females.

Hemophilia

Hemophilia, or haemophilia, is an X-linked recessive disorder that impairs the body's control over blood clotting. Haemophilia A and Haemophilia B arise from mutations in the genes for factor VIII and factor IX, respectively.[6] Females with this disease are almost exclusively unaffected, obligate carriers. The mutations can be passed on to offspring by mothers and fathers, but the phenotype is only expressed in males that inherit the mutation.[7] All daughters of a hemophiliac father are obligate carriers of the disease.

Autosomal Recessive

In an autosomal recessive disease, if an individual is heterozygous for the mutant allele, they are a carrier because the disease is recessive. If homozygous, they have the disease. All offspring of an affected individual are either heterozygous or homozygous for the mutated allele. Consequently, all unaffected (heterozygous) offspring of an affected individual are obligate carriers of the disease because they will necessarily carry the mutated allele.[8]

Detection

Due to the predictable patterns of heritable disorders, techniques can be used to detect past, present, and future disease prevalence in individuals among a family. Specifically,

Genetic counselling
informs patients that may have a family history of a certain disease about their risk of disease and potential risk in their children.

References

  1. ^ "MedlinePlus: Genetics".
  2. ISBN 0-471-25154-2
    .
  3. PMID 23864971
    .
  4. PMID 22178198.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  5. PMID 1093816
    .
  6. doi:10.1055/s-0037-1615621.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  7. ^ "Heredity of hemophilia". Canadian Hemophilia Society. 11 April 2018. Retrieved 2 April 2021.
  8. ^ Tissot, Robert. "Autosomal Recessive Inheritance". Human Genetics. UIC. Retrieved 7 December 2015.
  9. ^ a b "Carrier Diagnosis". World Federation of Hemophilia. Retrieved 2 April 2021.
  10. PMID 8324863
    .
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