Factor XII deficiency is inherited as an autosomal recessive disorder. Genetic diseases are determined by two genes, one received from the father and one from the mother.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
Investigators have determined that factor XII deficiency occurs due to mutations of the F12 gene located on the long arm of chromosome 5 (5q33-qter). Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Pairs of human chromosomes are numbered from 1 through 22, and an additional 23rd pair of sex chromosomes which include one X and one Y chromosome in males and two X chromosomes in females. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 5q33” refers to band 33 on the long arm of chromosome 5. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
The F12 gene creates (encodes) factor XII, which is a clotting factor. Mutations of the F12 gene lead to low levels of functional factor XII in the blood (potentially less than 1%). The exact role that factor XII plays in the clotting process and any additional effects it has on the body are not fully understood. In addition to the clotting process, factor XII is believed to play a role tissue repair and the formation of blood vessels (angiogenesis).