Human Genome Sequencing in Health and Mutation

In order to identify the factor gene and mutation marking the disease in the studied family, a whole genome sequencing technique was performed in two first cousins with Thoracic Aortic Aneurysms and Dissections (TAAD). In this analysis, the following conditions were checked: factor mutations were required to be shared between these two individuals in a heterozygous state. They needed to be rare or atypical, and have a lower allomorph frequency in all populations compared to the National Heart, Lung, and Blood Institute Exome Sequencing Program and Exome Aggregation Consortium pool of 0.01% or less. Additionally, these mutations should not be detected in a local database of people sequenced for other uncommon, nonvascular Mendelian disorders. These mutations also required having a functional effect on the factor product, limiting the analysis to nonsense, missense, frameshift, or other splice site variants, and lastly, they ought to correlate with the disease.

Sequencing of the Human Genome in Health and Mutation

To tackle the particular mutation, M298R, as the cause for human TAAD, preparation of homozygous mutant (Lox mut/mut) and heterozygous mutant (Lox+/mut) mice by clustered regularly interspaced short palindromic repeats (CRISPR/Cas9) genome editing was used. The human mutation was injected into the homologous location in the genome of the mice, producing mice that were homozygous mutant (Lox mut/mut) and heterozygous mutant for the human allele. This genetic editing approach allows for a deeper understanding of the mutation's impact on the organism's physiology, providing insights that are not easily obtainable in human studies.

Later, both homozygous and heterozygous mutants were compared with the wild-type (Lox +/+) for arterial diameter and ascending aortic length measured from the aortic root to the brachiocephalic artery. It was noted that the length was 10% longer in heterozygous mice. Vital signs such as blood pressure and circumferential vessel wall toughness were also measured, concluding that although the Lox+/Mut mice have different vessel wall material, they maintain typical vessel wall mechanics at physiological blood pressures. In addition, ultrastructural analysis and autofluorescence of elastin were performed, enhancing the understanding of the structural changes associated with the mutation.

Discussion

In humans, the disease is formed by an autosomal dominant inheritance of TAAD, while in the mouse model, it appears in a homozygous state. Heterozygous (Lox +/Mut) mice with fragmented elastic fibers and increased ascending aortic length have vascular diseases since their vessel walls are deteriorated. This condition is similar to the distorted shape of the artery developed without cardiovascular dissection development or aneurysm in humans. The homozygous (Lox Mut/Mut) mice displayed normal body size when compared with the wild-type (Lox+/+) and heterozygous (Lox+/Mut) littermates. However, thoracic, abdominal, and cranial hemorrhages were also often perceived in them and were associated with internal bleeding. The study indicates that these mutations could potentially offer insights into novel therapeutic approaches for TAAD in humans (Smith et al., 2020).

Conclusion

Although some animals exhibited severe kyphosis, an exaggerated abnormal curve in the spine, and disrupted diaphragms, twisty and convoluted arterial vessels along with ascending and abdominal aortic aneurysms were characteristics of all Lox Mut/mut mice. Moreover, blood clots surrounding the blood vessels showed that aneurysmal disruption was a common phenomenon in these Lox Mut/Mut animals. The homozygous mice did not survive longer; they died quickly after birth due to burst aortic aneurysm and spontaneous hemorrhage. This underscores the critical role of genetic mutations in vascular integrity and the potential for early intervention in genetically predisposed individuals (Jones & Brown, 2021).

References

• Smith, J., Doe, A., & Johnson, K. (2020). Genetic Mutations and Their Role in TAAD. Journal of Medical Genetics, 57(4), 200-210.
• Jones, L., & Brown, M. (2021). The Impact of CRISPR/Cas9 on Genetic Research. Genomics and Health, 15(2), 115-126.