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MTHFR is the rate-limiting enzyme in the methyl cycle, which includes the conversion of homocysteine into methionine. Defects in variants of MTHFR can therefore lead to hyperhomocysteinemia. [9] There are two common variants of MTHFR deficiency. In the more significant of the two, the individual is homozygous for the 677T polymorphism.
At nucleotide 1298 of the MTHFR, there are two possibilities: A or C. 1298A (leading to a Glu at amino acid 429) is the most common while 1298C (leading to an Ala substitution at amino acid 429) is less common. 1298AA is the "normal" homozygous, 1298AC the heterozygous, and 1298CC the homozygous for the "variant".
Pathophysiology of factor V Leiden gene mutation. Factor V Leiden is an autosomal dominant genetic condition that exhibits incomplete penetrance, i.e. not every person who has the mutation develops the disease. The condition results in a factor V variant that cannot be as easily degraded by activated protein C.
Coagulation factor V (Factor V), also less commonly known as proaccelerin or labile factor, is a protein involved in coagulation, encoded, in humans, by F5 gene. [5] In contrast to most other coagulation factors, it is not enzymatically active but functions as a cofactor . [ 5 ]
In medical genetics, compound heterozygosity is the condition of having two or more heterogeneous recessive alleles at a particular locus that can cause genetic disease in a heterozygous state; that is, an organism is a compound heterozygote when it has two recessive alleles for the same gene, but with those two alleles being different from each other (for example, both alleles might be ...
Congenital dysfibrinogenemia is most often caused by a single autosomal dominant missense mutation in the Aα, Bβ, or γ gene; rarely, it is caused by a homozygous or compound heterozygous missense mutation, a deletion, frameshift mutation, insert mutation, or splice site mutation in one of these genes.
The remaining copy of the tumor suppressor gene can be inactivated by a point mutation or via other mechanisms, resulting in a loss of heterozygosity event, and leaving no tumor suppressor gene to protect the body. Loss of heterozygosity does not imply a homozygous state (which would require the presence of two identical alleles in the cell).
The minor ("type 2") thrombophilias are much more common. Factor V Leiden is present in 5% of the population of Northern European descent, but much rarer in those of Asian or African extraction. In people with thrombosis, 10% have factor V Leiden. In those who are referred for thrombophilia testing, 30–50% have the defect.