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

Pharmacogenetic approach to losartan in Marfan patients: a starting point to improve dosing regimen?

BACKGROUND

Losartan is under evaluation for managing Marfan patients with aortic root dilatation. Cytochrome P450 (CYP) enzymes convert losartan to E3174 active metabolite. The aim of this study is to describe the distribution of CYP2C9*2, CYP2C9*3, CYP3A4*22 and CYP3A5*3 defective alleles, according to losartan tolerance in paediatric Marfan patients.

METHODS

We genotyped 53 paediatric Marfan patients treated with losartan. The rate of aortic root dilatation was evaluated using the delta z-score variation. Differences in tolerated losartan daily doses with respect to CYP metabolic classes were assessed through the Kruskal-Wallis test.

RESULTS

The losartan daily dose spans from 0.16 to 2.50 mg/kg (median 1.10 mg/kg). As we expect from the pharmacokinetics pathway, we observe highest tolerated dose in CYP2C9 poor metabolisers (median 1.50 mg/kg, interquartile range 1.08-1.67 mg/kg); however, this difference is not statistically significant.

CONCLUSIONS

The optimal dose of angiotensin receptor blocker is not known, and no data are available about losartan pharmacogenetic profile in Marfan syndrome; we have proposed a strategy to tackle this issue based on evaluating the major genetic polymorphisms involved in the losartan conversion into active carboxylic acid metabolite. Further studies are needed to support the use of genetic polymorphisms as predictors of the right dose of losartan.

Angiotensin receptor blockers: a panacea for Marfan syndrome and related disorders?

The study of mouse models for Marfan syndrome, an autosomal dominant connective tissue disorder caused by mutations in fibrillin-1 (FBN1), has shifted our understanding of the pathogenesis of thoracic aortic aneurysm significantly. Multiple lines of evidence support the notion that dysregulation of canonical and noncanonical transforming growth factor (TGF)β signaling is the responsible pathway in this and related thoracic aortic aneurysm conditions. This exciting knowledge has opened numerous new treatment options, including antagonism of the angiotensin II receptor blocker type 1 (AT1R). In this review, we summarize the current knowledge, the first human losartan Marfan trial results and future therapeutic perspectives for aortic disease in Marfan patients.

GATA5 and endothelial nitric oxide synthase expression in the ascending aorta is related to aortic size and valve morphology

BACKGROUND

The pathogenesis of aortic dilatation in patients with congenital aortic valve anomalies is poorly understood. Recent studies suggest that alterations of gene expression may be related to ascending aortic aneurysm formation in these patients. Knockout of endothelial nitric oxide synthase (eNOS) and GATA5 is associated with bicuspid aortic valves in mice. To study the role of eNOS and GATA5 in human congenital aortic valve disease and aortic dilatation, we investigated their gene expression in aortic tissue from patients with unicuspid, bicuspid, and tricuspid aortic valves.

METHODS

Samples from 84 patients (33 tricuspid, 32 bicuspid, and 19 unicuspid) were harvested intraoperatively from the ascending aorta. GATA5 and eNOS expression was determined by real-time polymerase chain reaction.

RESULTS

GATA5 and eNOS expression in the aortic wall from patients with unicuspid aortic valves (GATA5: mean [M], 2.14; standard deviation [SD], 1.72; eNOS: M, 3.40; SD, 3.83) was significantly higher than in tricuspid aortic valves (GATA5: M, 1.12; SD, 0.80; eNOS: M, 1.00; SD, 0.74; each p < 0.05). Patients with bicuspid aortic valves (GATA5: M, 1.29, SD, 1.33; eNOS: M, 1.66; SD, 1.31) had a significantly higher eNOS expression than patients with tricuspid aortic valves (p < 0.05). The expression levels of eNOS and GATA5 correlated positively with each other and negatively with the ascending aortic diameter.

CONCLUSIONS

Our data suggest that GATA5, possibly through upregulation of eNOS, plays a role in the development of aortic dilatation in patients with unicuspid and bicuspid aortic valves. The differential gene expression in patients with unicuspid compared with bicuspid aortic valves suggests that the pathogenesis of both aortic valve anomalies may be different.

Epidemiological profile of Marfan syndrome in a general population: a national database study

OBJECTIVE

To explore the current epidemiological profile of Marfan syndrome in a general population.

PATIENTS AND METHODS

Patients who had received a diagnosis of Marfan syndrome were identified from the Taiwan National Health Insurance database records from January 1, 2000, through December 31, 2012 (average population size, 22,765,535). Cardiovascular events and interventions were identified by using the respective International Classification of Diseases codes.

RESULTS

We identified 2329 patients (58% men) with Marfan syndrome. The overall prevalence was 10.2 (95% CI, 9.8-10.7) per 100,000 individuals, with peaks at the age of 15 to 19, 10 to 14, and 20 to 24 years. The minimal birth incidence of 23.3 (95% CI, 21.7-23.3) per 100,000 individuals was estimated in those aged 20 to 29 years. The average annual mortality was 0.23% (69 deaths), mostly owing to cardiac causes (including dissection and sudden death in 40 patients, 58%). Aortic dissection occurred in 226 patients (10%; 61% men) at a mean age of 36.6±10.7 years. The probability of freedom from dissection was 99%, 80%, and 66% at the age of 20, 40, and 50 years, respectively. Of the 69 deaths and 226 dissections during the follow-up period, more than half of the cases occurred before the age of 40 years. Cardiovascular intervention was performed in 360 patients, with early mortality being higher in the emergent operation group (8%) than in the elective group (0%).

CONCLUSION

From this national cohort study, the minimal birth incidence was 23.3 per 100,000 individuals, that is, possibly 1 patient with Marfan syndrome per 4286 people. Despite medical advances, aortic dissection still occurs in about one-tenth of the patients and carries a high mortality risk. Early diagnosis and timely medical interventions are warranted.

Genetic testing for inherited ocular disease: delivering on the promise at last?

Genetic testing is of increasing clinical utility for diagnosing inherited eye disease. Clarifying a clinical diagnosis is important for accurate estimation of prognosis, facilitating genetic counselling and management of families, and in the future will direct gene-specific therapeutic strategies. Often, precise diagnosis of genetic ophthalmic conditions is complicated by genetic heterogeneity, a difficulty that the so-called 'next-generation sequencing' technologies promise to overcome. Despite considerable counselling and ethical complexities, next-generation sequencing offers to revolutionize clinical practice. This will necessitate considerable adjustment to standard practice but has the power to deliver a personalized approach to genomic medicine for many more patients and enhance the potential for preventing vision loss.