J. De Backer

Effect of Mutation Type and Location on Clinical Outcome in 1,013 Probands with Marfan Syndrome or Related Phenotypes and FBN1 Mutations: An International Study

Mutations in the fibrillin-1 (FBN1) gene cause Marfan syndrome (MFS) and have been associated with a wide range of overlapping phenotypes. Clinical care is complicated by variable age at onset and the wide range of severity of aortic features. The factors that modulate phenotypical severity, both among and within families, remain to be determined. The availability of international FBN1 mutation Universal Mutation Database (UMD-FBN1) has allowed us to perform the largest collaborative study ever reported, to investigate the correlation between the FBN1 genotype and the nature and severity of the clinical phenotype. A range of qualitative and quantitative clinical parameters (skeletal, cardiovascular, ophthalmologic, skin, pulmonary, and dural) was compared for different classes of mutation (types and locations) in 1,013 probands with a pathogenic FBN1 mutation. A higher probability of ectopia lentis was found for patients with a missense mutation substituting or producing a cysteine, when compared with other missense mutations. Patients with an FBN1 premature termination codon had a more severe skeletal and skin phenotype than did patients with an inframe mutation. Mutations in exons 24-32 were associated with a more severe and complete phenotype, including younger age at diagnosis of type I fibrillinopathy and higher probability of developing ectopia lentis, ascending aortic dilatation, aortic surgery, mitral valve abnormalities, scoliosis, and shorter survival; the majority of these results were replicated even when cases of neonatal MFS were excluded. These correlations, found between different mutation types and clinical manifestations, might be explained by different underlying genetic mechanisms (dominant negative versus haploinsufficiency) and by consideration of the two main physiological functions of fibrillin-1 (structural versus mediator of TGF beta signalling). Exon 24-32 mutations define a high-risk group for cardiac manifestations associated with severe prognosis at all ages.

Contribution of molecular analyses in diagnosing Marfan syndrome and type I fibrillinopathies: an international study of 1009 probands

Background: The diagnosis of Marfan syndrome (MFS) is usually initially based on clinical criteria according to the number of major and minor systems affected following international nosology. The number of FBN1 mutation carriers, at risk of aortic complications who would not be properly diagnosed based only on clinical grounds, is of growing importance owing to the increased availability of molecular screening. The aim of the study was to identify patients who should be considered for FBN1 mutation screening. Methods: Our international series included 1009 probands with a known FBN1 mutation. Patients were classified as either fulfilling or not fulfilling “clinical” criteria. In patients with unfulfilled “clinical” criteria, we evaluated the percentage of additional patients who became positive for international criteria when the FBN1 mutation was considered. The aortic risk was evaluated and compared in patients fulfilling or not fulfilling the “clinical” international criteria. Results: Diagnosis of MFS was possible on clinical grounds in 79% of the adults, whereas 90% fulfilled the international criteria when including the FBN1 mutation. Corresponding figures for children were 56% and 85%, respectively. Aortic dilatation occurred later in adults with unfulfilled “clinical criteria” when compared to the Marfan syndrome group (44% vs 73% at 40 years, p<0.001), but the lifelong risk for ascending aortic dissection or surgery was not significantly different in both groups. Conclusions: Because of its implications for aortic follow-up, FBN1 molecular analysis is recommended in newly suspected MFS when two systems are involved with at least one major system affected. This is of utmost importance in patients without aortic dilatation and in children.

The new Ghent criteria for Marfan syndrome: What do they change?

Faivre L, Collod‐Beroud G, Adès L, Arbustini E, Child A, Callewaert BL, Loeys B, Binquet C, Gautier E, Mayer K, Arslan‐Kirchner M, Grasso M, Beroud C, Hamroun D, Bonithon‐Kopp C, Plauchu H, Robinson PN, De Backer J, Coucke P, Francke U, Bouchot O, Wolf JE, Stheneur C, Hanna N, Detaint D, De Paepe A, Boileau C, Jondeau G. The new Ghent criteria for Marfan syndrome: what do they change?

Effect of an Abdominal Aortic Aneurysm on Wave Reflection in the Aorta

Despite extensive attention to abdominal aortic aneurysm (AAA) in the biomedical engineering community, its effect on aortic hemodynamics and arterial wave reflection has not been addressed before. We used experimental and numerical methods, relying on a realistic AAA geometry constructed from patient computer tomography scans (CT-scans), to study this issue. Pressure and flow waves were measured and simulated before and after AAA repair, and wave reflections were analyzed using linear wave separation and wave intensity analysis. With AAA, pronounced reflections were present in the pressure and flow waveforms. The reflection coefficient measured experimentally in the upper aorta was negative with AAA (-0.10) versus 0.47 without AAA. Wave intensity analysis confirmed the presence of a backward expansion wave caused by sudden expansion of the aorta; this was absent without AAA. These results were confirmed using a 1-D numerical model. A parameter study using this model demonstrated that dominant factors are diameter and compliance of the aneurysm, with larger diameters and more compliant AAA generating more negative reflections. Finally, a preliminary noninvasive study in three patients before and after AAA repair demonstrated that AAA-repair increased the reflection coefficient. In conclusion, the presence of AAA significantly alters wave reflection and hemodynamics in the aorta, with apparently measurable effects in humans.

Parameters of inflammation and infection in a community based case-control study of coronary heart disease

BACKGROUND increased levels of systemic inflammatory markers appear to be related to coronary heart disease (CHD) both in asymptomatic individuals and in subjects with established CHD. Whether these associations are related to confounding coronary risk factors or are explicable through chronic infectious conditions is not clear. OBJECTIVES (1) to determine whether subjects with stable CHD differ from normal controls in inflammatory markers (CRP, SAA and fibrinogen) and/or in serostatus of four infectious agents (Helicobacter pylori, Chlamydia pneumoniae, CMV and EBV), independent of classical coronary risk factors. (2) To determine whether these inflammatory markers are related to the serostatus against these four infectious agents either in patients with CHD or in normal subjects. METHODS in a large epidemiologic survey, 446 out of 16307 men at work, aged 35-59 years, had antecedents of myocardial infarction, CABG or PTCA or had prominent Q/QS waves on their resting ECG. They were compared with double the number (n=892) of men, matched for age, educational level and industry. Inflammatory biomarkers (CRP, fibrinogen and SAA) and antibodies against H. pylori, C. pneumoniae, CMV and EBV were measured, besides classical coronary risk factors. RESULTS in univariate analyses, cases had higher CRP, fibrinogen and SAA levels than controls, but no differences were observed in serumantibody levels to any of the infectious agents. Markers of previous infections were not related to inflammatory biomarkers. In multivariate analyses CRP was significantly different between cases and controls independent of differences in other coronary risk factors and in the use of lipid lowering drugs and antiplatelet aggregants. CONCLUSIONS in men at work with CHD, CRP levels are significantly different from controls, independent of known risk factors. No association was found between inflammatory biomarkers and positive serostatus against four infectious agents, neither in the patients nor in the healthy controls.

Clinical and mutation-type analysis from an international series of 198 probands with a pathogenic FBN1 exons 24-32 mutation.

Mutations in the FBN1 gene cause Marfan syndrome (MFS) and a wide range of overlapping phenotypes. The severe end of the spectrum is represented by neonatal MFS, the vast majority of probands carrying a mutation within exons 24–32. We previously showed that a mutation in exons 24–32 is predictive of a severe cardiovascular phenotype even in non-neonatal cases, and that mutations leading to premature truncation codons are under-represented in this region. To describe patients carrying a mutation in this so-called ‘neonatal’ region, we studied the clinical and molecular characteristics of 198 probands with a mutation in exons 24–32 from a series of 1013 probands with a FBN1 mutation (20%). When comparing patients with mutations leading to a premature termination codon (PTC) within exons 24–32 to patients with an in-frame mutation within the same region, a significantly higher probability of developing ectopia lentis and mitral insufficiency were found in the second group. Patients with a PTC within exons 24–32 rarely displayed a neonatal or severe MFS presentation. We also found a higher probability of neonatal presentations associated with exon 25 mutations, as well as a higher probability of cardiovascular manifestations. A high phenotypic heterogeneity could be described for recurrent mutations, ranging from neonatal to classical MFS phenotype. In conclusion, even if the exons 24–32 location appears as a major cause of the severity of the phenotype in patients with a mutation in this region, other factors such as the type of mutation or modifier genes might also be relevant.

Pathogenic FBN1 mutations in 146 adults not meeting clinical diagnostic criteria for Marfan syndrome: further delineation of type 1 fibrillinopathies and focus on patients with an isolated major criterion.

Mutations in the FBN1 gene cause Marfan syndrome (MFS) and have been associated with a wide range of milder overlapping phenotypes. A proportion of patients carrying a FBN1 mutation does not meet diagnostic criteria for MFS, and are diagnosed with “other type I fibrillinopathy.” In order to better describe this entity, we analyzed a subgroup of 146 out of 689 adult propositi with incomplete “clinical” international criteria (Ghent nosology) from a large collaborative international study including 1,009 propositi with a pathogenic FBN1 mutation. We focused on patients with only one major clinical criterion, [including isolated ectopia lentis (EL; 12 patients), isolated ascending aortic dilatation (17 patients), and isolated major skeletal manifestations (1 patient)] or with no major criterion but only minor criteria in 1 or more organ systems (16 patients). At least one component of the Ghent nosology, insufficient alone to make a minor criterion, was found in the majority of patients with isolated ascending aortic dilatation and isolated EL. In patients with isolated EL, missense mutations involving a cysteine were predominant, mutations in exons 24–32 were underrepresented, and no mutations leading to a premature truncation were found. Studies of recurrent mutations and affected family members of propositi with only one major clinical criterion argue for a clinical continuum between such phenotypes and classical MFS. Using strict definitions, we conclude that patients with FBN1 mutation and only one major clinical criterion or with only minor clinical criteria of one or more organ system do exist but represent only 5% of the adult cohort.

Utility of molecular analyses in the exploration of extreme intrafamilial variability in the Marfan syndrome

The diagnosis of Marfan syndrome may be hampered by the existence of very mild and atypical cases as well as by marked intrafamilial variability. In these instances, molecular analysis of the fibrillin‐1 gene (FBN1) can be helpful to identify individuals at risk. The underlying molecular mechanism for the clinical variability is presently unknown. We performed clinical and molecular studies in 36 subjects from three unrelated families. Expression studies of both FBN1 alleles were performed and related to the clinical severity. In family 1, an overlapping phenotype between Marfan syndrome (MFS) and Weill–Marchesani syndrome is presented. The diagnosis necessitated molecular studies and clinical examination in first‐degree relatives. In family 2, the young proband presented with a phenotype overlapping between MFS and the kyphoscoliotic type of Ehlers–Danlos syndrome. Follow‐up over time and identification of a FBN1 mutation allowed confirmation of the diagnosis. Mutation analysis enabled us to identify family members with mild expression. Family 3 illustrates the extensive intrafamilial variability in the clinical severity of MFS. Identification of a FBN1 mutation was helpful to identify subjects with mild expression and for the timely diagnosis in a neonate. In families 2 and 3, the relative expression of both FBN1 alleles was not related to clinical severity. We demonstrated that confirmation of the diagnosis of MFS may require detailed and repeated clinical evaluation and thorough family history taking. FBN1 mutation analysis is supportive for the diagnosis in mild and atypical presentations.

Questioning the Pathogenic Role of the GLA p.Ala143Thr “Mutation” in Fabry Disease: Implications for Screening Studies and ERT

Fabry disease is an X-linked inborn error of glycosphingolipid metabolism caused by quantitative or qualitative defects in the lysosomal enzyme alfa-Galactosidase A (aGAL A), ultimately resulting in vital organ dysfunction. Mainly the kidneys, the heart, and the central nervous system are involved. While the classical phenotype of Fabry disease is readily recognizable, screening studies have identified clinical variants. Here, we report the phenotype associated with the GLA p.Ala143Thr (c.427G>A) mutation in 12 patients aged 42-83 years. None of the patients had classical Fabry signs or symptoms as angiokeratoma, hypohidrosis, acroparesthesia, or cornea verticillata. Possible Fabry manifestations were renal failure (5/12), stroke (7/12), and left ventricular hypertrophy (5/12), but these were not necessarily attributable to the p.Ala143Thr mutation, as a cardiac biopsy in one female and left ventricular hypertrophy and kidney biopsies in two males with renal failure and microalbuminuria lacked Gb-3 deposits. The literature data on this mutation as well as data collected in the Fabry Outcome Survey (FOS) database confirm these findings. The association of renal failure, stroke, and left ventricular hypertrophy with this mutation could be the result of selection bias, as most patients were detected in screening studies.We conclude that care should be taken with attribution of vital organ dysfunction to GLA sequence alterations. In case of the p.Ala143Thr mutation, and possibly also other mutations associated with an attenuated phenotype, diagnostic tools such as biopsy and imaging should critically evaluate the relation of end-organ failure with Fabry disease, as this has important consequences for enzyme replacement therapy.

QT dispersion is not related to infarct size or inducibility in patients with coronary artery disease and life threatening ventricular arrhythmias

OBJECTIVE To relate QT parameters to infarct size and inducibility during electrophysiological studies. DESIGN Analysis of a prospective register. SETTING University hospital. PATIENTS 64 patients with coronary artery disease and documented life threatening ventricular arrhythmias. INTERVENTIONS Measurements of QT-max, QTc-max, and QT dispersion (QT-d) on a simultaneous 12 lead ECG (50 mm/s). Estimation of myocardial infarct size with radionuclide left ventricular ejection fraction (LVEF), echocardiography (left ventricular end diastolic diameter, LVEDD), and a defect score based on a quantitative stress redistribution 201-thallium perfusion study. Electrophysiological study to assess inducibility. RESULTS Mean (SD) QT parameters were: QT-max 440 (50) ms, QTc-max 475 (46) ms, and QT-d 47 (20) ms. Mean (SD) estimates of infarct size were: LVEF 34 (13)%, LVEDD 61 (9) mm, and defect score 18 (11). There was no significant correlation between any index of infarct size and QT parameters. QT parameters were not significantly different between patients with inducible (n = 57) and non-inducible arrhythmias (n = 7) (QT-max: 416 (30) v 443 (51) ms, p = 0.18; QTc-max 485 (34) v 473 (47) ms, p = 0.34; QT-d 47 (12) v 47 (21) ms, p = 0.73). Non-inducible patients had a significant lower defect score: 8 (9)v 19 (11), p = 0.02, but comparable LVEF: 38 (12)% v 34 (12)%, p = 0.58, and LVEDD: 54 (10) v 61 (8) mm, p = 0.13. CONCLUSIONS QT parameters are not influenced by infarct size and do not predict inducibility during electrophysiological study in patients with coronary artery disease and malignant ventricular arrhythmias. In contrast, the amount of scar tissue determined by perfusion imaging is strongly correlated with inducibility.