The Non-syndromic Familial Thoracic Aortic Aneurysms and Dissections Maps to 15q21 Locus

Background: Thoracic aortic aneurysms and dissections (TAAD) is a critical condition that often goes undiagnosed with fatal consequences. While majority of the cases are sporadic, more than 20% are inherited as a single gene disorder. The most common familial TAA is Marfan syndrome (MFS), which is primarily caused by mutations in fibrillin-1 (FBN1) gene. Patients with FBN1 mutations are at higher risk for dissection compared to other patients with similar size aneurysms.

Methods: Fifteen family members were genotyped using Affymetrix-10K genechips. A genome-wide association study was carried out using an autosomal dominant model of inheritance with incomplete penetrance. Mutation screening of all exons and exon-intron boundaries of FBN1 gene which reside near the peak Lod score was carried out by direct sequencing.

Results: The index case presented with agonizing substernal pain and was found to have TAAD by transthoracic echocardiogram. The family history was significant for 3 first degree relatives with TAA. Nine additional family members were diagnosed with TAA by echocardiography examinations. The affected individuals had no syndromic features. A genome-wide analysis of linkage mapped the disease gene to a single locus on chromosome 15q21 with a peak Lod score of 3.6 at fibrillin-1 (FBN1) gene locus (odds ratio > 4000:1 in favour of linkage), strongly suggesting that FBN1 is the causative gene. No mutation was identified within the exons and exon-intron boundaries of FBN1 gene that segregated with the disease. Haplotype analysis identified additional mutation carriers who had previously unknown status due to borderline dilation of the ascending aorta.

Conclusions: A familial non-syndromic TAAD is strongly associated with the FBN1 gene locus and has a malignant disease course often seen in MFS patients. This finding indicates the importance of obtaining detailed family history and echocardiographic screening of extended relatives of patients with non-syndromic TAAD to improve the outcome. In addition, association of non-syndromic TAAD with the Marfan disease gene locus poses the question whether secondary prevention strategies employed for Marfan syndrome patients should be applied to all patients with familial TAAD.