May TGFBR1 act also as low penetrance allele in Marfan syndrome?

Diagnosis of Marfan Syndrome Following Progressive Myopia and Secondary Lens-Induced Angle Closure Crisis

Marfan syndrome (MFS) is a well-described genetic connective tissue disease that heightens the risk of cardiovascular, ocular, pulmonary, and other emergencies in affected individuals. The wide range of phenotypic presentations, spanning from mild, chronic, and asymptomatic to acute and life-threatening, can pose challenges in diagnosing MFS when disease manifestations are subtle. We report a pathogenetic variant of MFS characterized by subtle systemic findings that was identified only after the patient presented with visual changes and pain associated with angle closure, despite a medical history indicating other pathologies linked to this condition. This case underscores the importance of recognizing the varied and sometimes subtle clinical features of MFS. Vigilance in identifying the constellation of findings associated with MFS can enhance its diagnosis and treatment outcomes by enabling appropriate and timely referrals for prophylactic evaluation and care to address potentially life-threatening complications.

The Molecular Genetics of Marfan Syndrome

Marfan syndrome (MFS) is a complex connective tissue disease that is primarily characterized by cardiovascular, ocular and skeletal systems disorders. Despite its rarity, MFS severely impacts the quality of life of the patients. It has been shown that molecular genetic factors serve critical roles in the pathogenesis of MFS. FBN1 is associated with MFS and the other genes such as FBN2, transforming growth factor beta (TGF-β) receptors (TGFBR1 and TGFBR2), latent TGF-β-binding protein 2 (LTBP2) and SKI, amongst others also have their associated syndromes, however high overlap may exist between these syndromes and MFS. Abnormalities in the TGF-β signaling pathway also contribute to the development of aneurysms in patients with MFS, although the detailed molecular mechanism remains unclear. Mutant FBN1 protein may cause unstableness in elastic structures, thereby perturbing the TGF-β signaling pathway, which regulates several processes in cells. Additionally, DNA methylation of FBN1 and histone acetylation in an MFS mouse model demonstrated that epigenetic factors play a regulatory role in MFS. The purpose of the present review is to provide an up-to-date understanding of MFS-related genes and relevant assessment technologies, with the aim of laying a foundation for the early diagnosis, consultation and treatment of MFS.

Role of TGFBR1 and TGFBR2 genetic variants in Marfan syndrome

OBJECTIVE

Genetic variants in transforming growth factor beta (TGF-β) receptors type 1 (TGFBR1) and type 2 (TGFBR2) genes have been associated with different hereditary connective tissue disorders sharing thoracic aortic aneurysm and dissection (TAA/D). Mutations in both TGFBR1/2 genes have been described in patients with TAA/D and Marfan syndrome (MFS), and they are associated consistently with Loeys-Dietz syndrome. The existing literature shows discordant data resulting from mutational screening of TGFBR1/2 genes in patients with MFS. The aim of the study was to investigate the role of TGFBR1/2 genetic variants in determining and/or modulating MFS clinical phenotype.

METHODS

We investigated 75 unrelated patients with MFS referred to the Center for Marfan Syndrome and Related Disorders (Careggi University Hospital, Florence) who were subjected to FBN1 and TGFBR1/2 Sanger mutational screening.

RESULTS

Forty-seven patients with MFS (63%) carried a pathogenetic FBN1 mutation. No pathogenetic mutations were detected in TGFBR1/2 genes. Ten common polymorphisms were identified in TGFBR2 and 6 in TGFBR1. Their association with cardiovascular manifestations was evaluated. Carriers of the A allele of rs11466512, delA allele of c.383delA or delT allele of c.1256-15del1T polymorphisms had a trend toward or significantly reduced z-scores (median [interquartile range (IQR)], 2.2 [1.13-4.77]; 2.1 [1.72-3.48]; 2.5 [1.85-3.86]) with respect to homozygous patients with wild-type MFS (median [IQR], 4.20 [2.39-7.25]; 3.9 [2.19-7.00]; 3.9 [2.14-6.93]). Carriers of the A allele of the rs2276767 polymorphism showed a trend toward increased z-score (median [IQR], 4.9 [2.14-7.16]) with respect to patients with wild-type MFS (median [IQR], 3.3 [1.75-5.45]). The protective effect of TGFBR1/2 genetic score including all the 4 variants was also evaluated. Patients with MFS with two or more protective alleles included in the score had statistically significant reduced aortic z-scores (median [IQR], 2.20 [1.48-3.37]) with respect to patients with 1 or no protective alleles (median [IQR], 4.20 [2.48-7.12]; P = .007). Patients with severe aortic manifestations (aortic z-score ≥ 2 or aortic surgery) showed a significantly lower prevalence of subjects with two or more protective alleles included in the genetic score (29.7%) than patients with no or milder cardiovascular involvement (63.6%; P = .029). The genetic score protective effect on global aortic manifestations severity (aortic z-score ≥ 2 or aortic surgery) was also observed at the logistic regression analysis adjusted for the presence of FBN1 gene mutations (odds ratio, 0.21; 95% CI, 0.05-0.84; P = .028).

CONCLUSIONS

In conclusion, our data reappraise the role of TGFBR1 and TGFBR2 as major genes in patients with MFS, and suggest that TGFBR1/2 genetic variants (in particular when evaluated as a burden by score) might play a role in modulating the severity of cardiovascular manifestation in MFS.

Marfan syndrome: current perspectives

Marfan syndrome (MFS) is a pleiotropic connective tissue disease inherited as an autosomal dominant trait, due to mutations in the FBN1 gene encoding fibrillin 1. It is an important protein of the extracellular matrix that contributes to the final structure of a microfibril. Few cases displaying an autosomal recessive transmission are reported in the world. The FBN1 gene, which is made of 66 exons, is located on chromosome 15q21.1. This review, after an introduction on the clinical manifestations that leads to the diagnosis of MFS, focuses on cardiovascular manifestations, pharmacological and surgical therapies of thoracic aortic aneurysm and/or dissection (TAAD), mechanisms underlying the progression of aneurysm or of acute dissection, and biomarkers associated with progression of TAADs. A Dutch group compared treatment with losartan, an angiotensin II receptor-1 blocker, vs no other additional treatment (COMPARE clinical trial). They observed that losartan reduces the aortic dilatation rate in patients with Marfan syndrome. Later on, they also reported that losartan exerts a beneficial effect on patients with Marfan syndrome carrying an FBN1 mutation that causes haploinsufficiency (quantitative mutation), while it has no significant effect on patients displaying dominant negative (qualitative) mutations. Moreover, a French group in a 3-year trial compared the administration of losartan vs placebo in patients with Marfan syndrome under treatment with beta-receptor blockers. They observed that losartan decreases blood pressure but has no effect on aortic diameter progression. Thus, beta-receptor blockers remain the gold standard therapy in patients with Marfan syndrome. Three potential biochemical markers are mentioned in this review: total homocysteine, serum transforming growth factor beta, and lysyl oxidase. Moreover, markers of oxidative stress measured in plasma, previously correlated with clinical features of Marfan syndrome, may be explored as potential biomarkers of clinical severity.

Analysis of TGFBR1*6A variant in individuals evaluated for Marfan syndrome

Marfan syndrome (MFS) and Loeys-Dietz syndrome (LDS) are genetic disorders that affect connective tissue as a result of dysregulated TGF-β signaling. MFS is most frequently caused by mutations in FBN1 whereas Loeys-Dietz syndrome results from mutations in TGFBR1 or TGFBR2. There is substantial inter- and intra-familial phenotypic variability among these disorders, suggesting the presence of genetic modifiers. Previously, a polymorphism in the TGFβR1 protein termed the TFGBR1*6A allele was found to be overrepresented in patients with MFS and was identified as a low penetrance allele with suggestion as a possible modifier. To further investigate the importance of this variant, a retrospective review of genetic and phenotypic findings was conducted for 335 patients evaluated for suspicion of MFS or related disorders. In patients with a diagnosis of MFS, the presence of the TFGBR1*6A allele was not associated with phenotypic differences. Similarly, careful phenotyping of patients who carried the TFGBR1*6A allele but did not have MFS did not identify an altered frequency of specific connective tissue features. In this small cohort, the results did not reach significance to identify the TFGBR1*6A allele as a major modifier for aortic dilation, ectopia lentis, or systemic features associated with MFS or other connective tissue disorders. © 2016 Wiley Periodicals, Inc.

New population-based exome data question the pathogenicity of some genetic variants previously associated with Marfan syndrome

Background

Marfan syndrome (MFS) is a rare autosomal dominantly inherited connective tissue disorder with an estimated prevalence of 1:5,000. More than 1000 variants have been previously reported to be associated with MFS. However, the disease-causing effect of these variants may be questionable as many of the original studies used low number of controls. To study whether there are possible false-positive variants associated with MFS, four in silico prediction tools (SIFT, Polyphen-2, Grantham score, and conservation across species) were used to predict the pathogenicity of these variant.

Results

Twenty-three out of 891 previously MFS-associated variants were identified in the ESP. These variants were distributed on 100 heterozygote carriers in 6494 screened individuals. This corresponds to a genotype prevalence of 1:65 for MFS. Using a more conservative approach (cutoff value of >2 carriers in the EPS), 10 variants affected a total of 82 individuals. This gives a genotype prevalence of 1:79 (82:6494) in the ESP. A significantly higher frequency of MFS-associated variants not present in the ESP were predicted to be pathogenic with the agreement of ≥3 prediction tools, compared to the variants present in the ESP (p = 3.5 × 10⁻¹⁵).

Conclusions

This study showed a higher genotype prevalence of MFS than expected from the phenotype prevalence in the general population. The high genotype prevalence suggests that these variants are not the monogenic cause of MFS. Therefore, caution should be taken with regard to disease stratification based on these previously reported MFS-associated variants.

The genetics and genomics of thoracic aortic disease

Genetic studies over the past several decades have helped to better elucidate the genomics and inheritance of thoracic aortic diseases. Seminal work from various researchers have identified several genetic factors and mutations that predispose to aortic aneurysms, which will aid in better screening and early intervention, resulting in better clinical outcomes. Syndromic aneurysms have been associated with Marfan syndrome, Loeys-Dietz syndrome, aneurysm osteoarthritis syndrome, arterial tortuosity syndrome, Ehlers-Danlos Syndrome, and TGFβ mutation. Mutations in MYH11, TGFβR1, TGFβR2, MYLK, and ACTA2 genes have been linked to familial non-syndromic cases, although linkage analysis is limited by incomplete penetrance and/or locus heterogeneity. This overview presents a summary of key genetic and genomic factors that are associated with thoracic aortic diseases.

High prevalence of eosinophilic esophagitis in patients with inherited connective tissue disorders

BACKGROUND

Eosinophilic esophagitis (EoE) is an emerging chronic inflammatory disease mediated by immune hypersensitization to multiple foods and strongly associated with atopy and esophageal remodeling.

OBJECTIVE

We provide clinical and molecular evidence indicating a high prevalence of EoE in patients with inherited connective tissue disorders (CTDs).

METHODS

We examined the rate of EoE among patients with CTDs and subsequently analyzed esophageal mRNA transcript profiles in patients with EoE with or without CTD features.

RESULTS

We report a cohort of 42 patients with EoE with a CTD-like syndrome, representing 0.8% of patients with CTDs and 1.3% of patients with EoE within our hospital-wide electronic medical record database and our EoE research registry, respectively. An 8-fold risk of EoE in patients with CTDs (relative risk, 8.1; 95% confidence limit, 5.1-12.9; χ(2)1 = 112.0; P < 10(-3)) was present compared with the general population. Esophageal transcript profiling identified a distinct subset of genes, including COL8A2, in patients with EoE and CTDs.

CONCLUSION

There is a remarkable association of EoE with CTDs and evidence for a differential expression of genes involved in connective tissue repair in this cohort. Thus, we propose stratification of patients with EoE and CTDs into a subset referred to as EoE-CTD.

Preventing the aortic complications of Marfan syndrome: a case-example of translational genomic medicine

The translational path from pharmacological insight to effective therapy can be a long one. We aim to describe the management of Marfan syndrome as a case-example of how pharmacological and genomic insights can contribute to improved therapy. We undertook a literature search for studies of Marfan syndrome, to identify milestones in description, understanding and therapy of the syndrome. From the studies retrieved we then weaved an evidence-based description of progress. Marfan syndrome shows considerable heterogeneity in clinical presentation. It relies on defined clinical criteria with confirmation based on FBN1 mutation testing. Surgical advances have prolonged life in Marfan syndrome. First-line prophylaxis of complications with β-adrenoceptor blockers became established on the basis that reduction of aortic pressure and heart rate would help. Over-activity of proteinases, first suggested in 1980, has since been confirmed by evidence of over-expression of matrix metalloproteinases (MMP), notably MMP-2 and MMP-9. The search for MMP inhibitors led to the evaluation of doxycycline, and both animal studies and small trials, provided early evidence that this widely used antimicrobial agent was useful. Identification of the importance of TGF-β led to evaluation of angiotensin II type I receptor (AT(1) R) blockers with highly promising results. Combination prophylactic therapy would appear rational. Pharmacological and genomic research has provided good evidence that therapy with losartan and doxycycline would prevent the aortic complications of Marfan syndrome. If on-going well designed trials confirm their efficacy, the outlook for Marfan syndrome patients would be improved considerably.