Genotype-Phenotype Correlation Insights Through Molecular Modeling Analysis in a Patient with Loeys-Dietz Syndrome

Abstract

Background: Pathogenic variants within the gene encoding transforming growth factor β (TGF-β) are responsible for Loeys-Dietz syndrome (LDS), a heritable thoracic aortic disease sharing clinical features with Marfan syndrome, including craniofacial and skeletal abnormalities as well as aortic root aneurysms and dissections. In contrast to Marfan syndrome patients, who rarely develop aneurysms or dissections beyond the aortic root, LDS patients frequently exhibit vessel aneurysms in locations other than the aortic root. Here, we report the case of a 61-year-old patient who initially presented with marfanoid characteristics and an aortic root aneurysm and was presumed to have Marfan syndrome two decades ago. Later, the patient developed an abdominal aorta aneurysm, necessitating endovascular repair and stent placement. That fact raised doubts regarding the initial diagnosis of Marfan syndrome, and we decided to investigate the genetic cause of the disorder.

Methods: Genetic testing was performed using WES analysis and Sanger sequencing.

Results: The genetic analysis detected a de novo heterozygous pathogenic variant c.896G>A in exon 5 of the TGFB2 gene, resulting in the amino acid substitution p. Arg299Gln that has devastating destabilizing structural effects on 3D folding of the protein, as demonstrated by the molecular modeling study we performed. This variant is pathogenic for LDS type 4, partially consistent with the patient's clinical presentation.

Conclusions: Our case emphasizes the significance of precise clinical assessment and genetic verification in patients exhibiting marfanoid characteristics. Furthermore, our findings contribute to the understanding of the diverse clinical spectrum associated with this specific pathogenic variant of TGFB2, underscoring the importance of detailed clinical assessment in expanding knowledge of genotype-phenotype correlations. Accurate diagnosis is crucial for tailored and appropriate management of individuals with heritable thoracic aortic diseases.

Keywords: Loeys-Dietz syndrome; TGF-β2 mutations; aortic aneurysms; craniofacial anomalies; marfanoid habitus; skeletal anomalies; transforming growth factor β; vascular tortuosity.

Figure 1

Image of the patient.

Figure 2

Aortic root aneurysm of 7 cm visualized on coronography.

Figure 3

Abdominal aorta stent graft.

Figure 4

Pedigree of the patient’s family. The patient (II-2, indicated with an arrow) and his daughter (III-1) were genetically analyzed.

Figure 5

DNA sequencing findings of exon 5 of the heterozygous patient’s TGFB2 gene (NM_003238.6(TGFB2):c.896G>A (p.Arg299Gln) in comparison to a healthy control.

Figure 6

Molecular modeling of the mutant TGFB2 R299Q model. (A): Upper: The template used to show R299 in a ball and stick representation; Lower: The template and the designed model of the TGFB2 R299Q (left and right, respectively). (B): Molecular interaction of two diagrams of the R299 and the Q299, respectively. Protein residues appear in spheres (red and blue circled for acidic and basic respectively). (C): Electrostatic cloud surface calculation for both R and Q (left and right, respectively).

Figure 7

Investigation of structural integrity upon molecular dynamics simulations. Molecular dynamics (MD) simulations are a powerful computational tool used to explore the behavior and properties of molecular systems over time. One of the key applications of MD simulations is the investigation of structural integrity, which involves studying the stability and resilience of molecular structures under various conditions. This approach provides valuable insights into the physical and chemical characteristics of molecules, especially in fields such as biochemistry, materials science, and drug discovery. The model of the mutant TGFB2 299Q (magenta ribbon) was superposed to the final model upon MDs in various poses/viewpoints (orange ribbon).

Figure 8

Superposition of the wild-type TGFB2 (green ribbon) and the model of the 299Q mutated protein upon MDs. It is evident that a significant amount of the protein has been lost, which is indicative of biological loss of function. (A): Superposed models, (B): Wild and mutated 3D models of TGFB2, (C): Same as B, but close up on the binding site.