Certain bleeding disorders are caused by mutations found in the genes that help with blood coagulation. There are twelve different coagulation factors, or proteins, that originate from different areas in the body1. Factor XI (FXI) was used as an analytical topic within fourteen Turkish patients from ten unrelated families, all with a FXI disorder2. This experiment chose to focus on the relationship between the mutation and genotype-phenotype correlation, and how this relationship affected inheritance of the mutation in the families of the unrelated individuals in order to understand the potential morbidities brought about by the disorder.
The methods of this experiment included polymerase chain reactions, DNA sequencing analysis, and testing for activated partial thromboplastin time (aPPT)2. The polymerase chain reactions allowed for the DNA sequencing by copying and reproducing the mutation for study. The aPPT testing evaluated the time it takes for an individual’s blood to clot3, usually done in seconds, and is important when working with individuals who have clotting factor deficiencies. The use of DNA sequencing gave a more in-depth view of how these mutations arose and showed clearly that the deficiencies were created by missense, nonsense, and splice site mutations. Missense mutations alter a single base pair, nonsense mutations stop the protein production early, and a splice site mutation occurs between an exon and intron and can lead to disruptions in the RNA sequencing4.
The results of this experiment showed a very close relationship between the aPPT scores and F11 genotype. From an analysis of these results, it can be suggested that individuals who are heterozygous for the mutation have lower aPPT scores, meaning these individuals clotted faster than their homozygous counterparts. Further results showed that heterozygous patients have higher FXI levels, which agrees with the shorter aPPT time. The homozygous individual would have a deficiency of the FXI protein and therefore be more prone to bleeding.
PCR testing was used to amplify the F11 genes from the fourteen patients, and the following DNA replication showed eight separate mutations that led to the same disorder. The sequencing allowed the specific mutations to be identified and reported to the patients and their families. The sequencing showed a more direct correlation between homozygous individuals and the disorder, and the specific mutations these individuals had. The testing also showed that gene mutations are not limited to related individuals, as more than one patient had the same mutation but shared no relation. Another interesting point found that individuals who were heterozygous for a mutation may show minimal to no symptoms at all.
This experiment identified eight separate mutations that led to the same disorder in ten unrelated families, confirming that the FXI disorder follows the definition of genetic heterogeneity. This means that the mutations occurred at two or more loci and produce the same or similar genotype, without individuals having to be related5. The results of this experiment also show that the disorder is more severe in heterozygous individuals, as they produce much more of the FXI protein than their homozygous counterparts. The conclusions of this experiment indicate the necessity of genetic testing and diagnosis of possibly fatal diseases brought about by mutations, especially for control and treatment of the disorders.
Citation
1. The Blood Coagulation Process. https://www.rnceus.com/coag/coagpro.html
2. Colakoglu, S. et al. Molecular genetic analysis of the F11 gene in 14 Turkish patients with factor XI deficiency: identification of novel and recurrent mutations and their inheritance within families. Blood Transfusion 16, 105-113 (2018).
3. Partial Thromboplastin Time (PTT, aPTT). https://labtestsonline.org/tests/partial-thromboplastin-time-ptt-aptt (2021)
4. Splice-Site Mutation. National Cancer Institute; https://www.cancer.gov/publications/dictionaries/genetics-dictionary/def/splice-site-mutation
5. McGinniss, M. J., McGinniss, M. A. 10 – Carrier Screening and Heterozygote Testing. Emery and Rimoin’s Principles and Practice of Medical Genetics and Genomics, https://doi.org/10.1016/B978-0-12-812536-6.00010-9 (2019)