Genotype-phenotype correlations in Marfan syndrome patients with FBN1 mutations: a cohort study on 1575 patients

Background

Marfan syndrome (MFS) is a connective tissue disorder in which several systems are affected with great phenotypic variability. Although known to be associated with pathogenic variants in the FBN1 gene, few genotype-phenotype correlations have been found in probands' studies only.

Purpose

The aim of this study is to provide survival curves and genotype-phenotype correlations in all patients with FBN1 mutations, probands and relatives.

Methods

We established survival curves and sought genotype–phenotype correlations in a population of 1575 consecutive MFS patients with pathogenic class 4 or 5 variants in the FBN1 gene. This population represents the most comprehensive clinical database worldwide on MFS.

Results

Global survival was 90% at 60 years. However, lifelong aortic event rate (either dissection or surgery) and survival were impacted by the genotype. Premature termination codons (PTC), resulting in haploinsufficiency, were associated with a shorter life expectancy and a high lifelong risk of an aortic event (83%). Interestingly, these variants were also associated with the highest risk of severe scoliosis (52%) and with a lower risk for ectopia lentis (EL) surgery (13%). Dominant negative in-frame pathogenic variants could be subdivided according to their impact on the cysteine content of fibrillin-1: cysteine loss (–Cys) was associated with high aortic risk (73%) and a higher frequency of EL surgery (43%); cysteine addition was associated with moderate aortic risk (29%) and the highest frequency of EL surgery (48%); unchanged cysteine content was associated with high aortic risk (61%) and lower frequency of EL surgery (23%). No gene-region effect was observed, except for a more severe phenotype for in-frame variants with cysteine loss within the “neonatal region”. Aortic risk was greater for males in all subgroups, and probands were more severely affected.

Conclusions

MFS genotype-phenotype correlations related to pathogenic FBN1 variants exist for aortic and extra-aortic features. This leads us to propose new tools to refine the prognosis in this population. Preventive therapy with β-blockers and restricted exercise should be proposed regardless of the aortic diameter in the high aortic risk groups (PTC and –Cys variants). These results have major consequences on genetic counseling and personalized medicine for patients carrying a FBN1 mutation. This study also improves the overall understanding of the role of FBN1 in various organs.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Fondation Coeur et Recherche, Paris, FranceFédération Française de Cardiologie, Paris, France Patients with PTC vs. in-frame mutationsDifferences within in-frame mutations

Phenotypic variability and diffuse arterial lesions in a family with Loeys-Dietz syndrome type 4

Syndromic thoracic aortic aneurysm and dissection (TAAD) can suggest Marfan, vascular Ehlers-Danlos or Loeys-Dietz (LDS) syndromes. Several of the TGFβ-pathway-related genes predispose to different types of LDS. Heterozygous loss-of-function variations in TGFβ2 have been shown to be responsible for a novel form of syndromic TAAD associated with an impairment of the mitral valve and cerebrovascular disease called Loeys-Dietz syndrome type 4 (LDS4). We report the clinical characterization of a LDS4 French family with sudden deaths and diffuse vascular lesions, caused by a frameshift mutation in TGFβ2 gene: c.[995del]; p.(Leu332TrpfsTer27). Clinical characteristics include aneurysm of aortic sinus, skeletal and cutaneous features compatible with a syndromic form of TAAD (joint hypermobility, scoliosis, and easy bruises), intracranial aneurysms and rare mitral valve involvement. Iliac aneurysms, systemic medium caliber arteries dissections, and mild developmental delay were present in the family, and have not been described in LDS4. Phenotypic variability was also an important finding, including absence of clinical vascular events at advanced age in one case. Our data expand the phenotype of LDS4: we confirm that TGFβ2 mutations are responsible for true LDS syndrome with non-specific features of connective tissue disorders and diffuse vascular lesions. Adapted vascular follow up and prevention has to be proposed for these patients.