A familial case of aortic dilatation with p.Tyr470Cys in TGFBR2 in which the phenotype included only vascular lesions

Abstract

Hereditary connective tissue diseases have different risks of aortic dissection depending on the causative gene. We report a family with no extravascular phenotype and a clinical diagnosis of familial thoracic aortic aneurysm and dissection, but genetic testing confirmed p.Tyr470Cys in TGFBR2, which is typically the responsible gene for Loeys–Dietz syndrome. Validation of the clinical diagnosis by genetic testing is warranted.

Introduction

Several genes are responsible for connective tissue diseases that cause aortic dissection, for example, FBN1, TGFBR1, and TGFBR2. There are some cases in which variants in unexpected causative genes are detected, and it is known that the risk of aortic dissection varies depending on the responsible gene. A Japanese familial case (Figure 1 a ) of nonsyndromic juvenile aortic dissection with a pathogenic variant of TGFBR2, typically known as the causative gene of Loeys–Dietz syndrome, is reported. Based on this report, we would recommend aggressive genetic testing for cases with aortic dilatation at a young age, with or without a nonvascular phenotype. Consent for publication of this report was obtained from the family members. This study was approved by the Ethics Committee of Nagoya University Graduate School of Medicine (approval number 2015-0032).

Figure 1. Clinical data of the present family. ( a ) Pedigree chart. Arrow indicates the proband. “+” indicates TGFBR2 c.1409A>G-positive, and “-” indicates TGFBR2 c.1409A>G-negative. ( b ) Contrast-enhanced 3DCT of the proband after ascending aortic replacement, showing meandering of the descending aorta and abdominal aortic aneurysm. ( c ) Sequence chromatograms of the affected family member (III-1) and control. ( d ) Head magnetic resonance angiographies of the proband’s daughters: top is III-1, and bottom is III-3. Both show marked tortuosity of the left internal carotid artery (arrows).

Case

The proband (II-1), a 38-year-old man, developed an ascending aortic dissection at age 27 years and underwent ascending aortic arch replacement. Subsequent contrast-enhanced CT also showed an aneurysm in the abdominal aorta (Figure 1b ), and vascular replacement was performed. His mother (I-2) and brother (II-4) died at ages 34 and 18 years, respectively, presumably due to aortic dissection. Because autosomal dominant inheritance was suggested, his three daughters also underwent screening echocardiography, and two of them, ages 12 (III-1) and 3 (III-3) years, were found to have mild dilation of the aortic root. Both the proband and the two daughters with aortic dilatation were of standard height and weight, and they did not show any craniofacial or skeletal characteristics of Marfan syndrome and/or Loeys–Dietz syndrome. There was no history of ophthalmology visits, and no family member had any subjective visual abnormalities. From these clinical features, familial thoracic aortic aneurysm and dissection, due to ACTA2, MYH11, or MYLK, were suspected. After appropriate genetic counselling, targeted next-generation sequencing was performed at Kazusa DNA Research Institute (Chiba, Japan) for the following genes: ACTA2, MYH11, MYLK, TGFBR1, TGFBR2, SLC2A10, COL3A1, EFEMP2, FBN1, FBN2, FLNA, SMAD3, TGFB2, and TGFB3. A missense variant of c.1409A>G (p.Tyr470Cys) in TGFBR2 (NM_003242.6) was identified in three individuals with aortic lesions, and the variant was confirmed by Sanger sequencing (Figure 1c ) by the method described below. Subsequent contrast-enhanced CT of the aorta performed on the two affected daughters showed no vasodilatation or tortuous vessels beyond the arch, including branching. Three affected members underwent head magnetic resonance angiography, which showed meandering of the left internal carotid artery in both daughters (Figure 1d ).

Variant validation method

DNA from the patients and an unrelated healthy adult male, as a control, was extracted from peripheral blood using the QIAamp DNA Blood Mini Kit (Qiagen, Hilden, Germany). The variant c.1409A>G in TGFBR2 was validated by Sanger sequencing using PrimeSTAR GXL DNA polymerase (Takara, Shiga, Japan), Big Dye Terminator 3.1 Cycle Sequencing Kit (Thermo Fisher Scientific, Waltham, MA, USA), ABI PRISM 3130xL (Applied Biosystems, Foster City, CA, USA), and the following primers: forward primer: 5’-CCAGCGTAACACCTAGCACA-3’; and reverse primer: 5’-GTTGAGCCAGAAGCTGGGAA-3’. All reagents and equipment were used according to the manufacturer’s instructions.

Discussion

Of the hereditary connective tissue diseases, pathogenic variants of TGFBR1 and TGFBR2 are known to have a higher risk of vascular disruption than variants of other causative genes. The guidelines state that the surgical criterion for the aortic diameter of cases with pathogenic variants of FBN1, the gene responsible for Marfan syndrome, is 50 mm, whereas that of cases with TGFBR1 and TGFBR2 variants is 45 mm. ¹ The clinical pitfall in cases with TGFBR1 or TGFBR2 variants is phenotypic diversity. That is, their phenotypes range from classical Loeys–Dietz syndrome with craniofacial and skeletal findings to nonsyndromic cases with vascular lesions only, as in the present case. In the TGFBR1 and TGFBR2 registries, many nonvascular phenotypes, such as hypertelorism and bifid uvula, were reported to be identified in only less than half of the cases. ^2,3 These findings suggest that being a nonsyndromic case does not indicate that the aortic lesion is not derived from a variant of TGFBR1 or TGFBR2, the highest risk genes responsible for aortic dissection.

Try470 of TGFBR2 is in a highly conserved amino acid in the STKc TGFbR2-like domain (Figure 2 a, b) (https://www.uniprot.org/), and p.Tyr470Cys is registered as “pathogenic” in ClinVar as a phenotype of “familial thoracic aortic aneurysm and aortic dissection” (rs760797386) (https://www.ncbi.nlm.nih.gov/clinvar/). In the present family, there were certainly no craniofacial or skeletal symptoms. However, pathological findings were observed in vessels other than the thoracic aorta, namely, the abdominal aorta and internal carotid artery. Similar to the previously reported several nonsyndromic cases due to TGFBR2 variants, most of which are registered as “familial thoracic aortic aneurysm and aortic dissection” in ClinVar, aneurysms of various vessels, not only in the thoracic aorta, have been identified. ⁴

Figure 2. Information about the Tyr470 residue in TGFBR2. ( a ) The Tyr470 residue is highly conserved among vertebrates. ( b ) The Tyr470 residue in the STKc TGFbR2-like domain in TGFBR2.

To conclude, we recommend that genetic testing for various responsible genes, including TGFBR1 and TGFBR2, be aggressively performed in cases with juvenile aortic dilatation, even in nonsyndromic cases, of course after appropriate genetic counselling. If a pathogenic variant of TGFBR1 or TGFBR2 is identified, systemic vascular screening should be performed.