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Functional validation reveals the novel missense V419L variant in TGFBR2
associated with Loeys-Dietz syndrome (LDS) impairs canonical TGF-? signaling
#MMPMID28679693
Cousin MA
; Zimmermann MT
; Mathison AJ
; Blackburn PR
; Boczek NJ
; Oliver GR
; Lomberk GA
; Urrutia RA
; Deyle DR
; Klee EW
Cold Spring Harb Mol Case Stud
2017[Jul]; 3
(4
): ? PMID28679693
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TGF-?-related heritable connective tissue disorders are characterized by a
similar pattern of cardiovascular defects, including aortic root dilatation,
mitral valve prolapse, vascular aneurysms, and vascular dissections and exhibit
incomplete penetrance and variable expressivity. Because of the phenotypic
overlap of these disorders, panel-based genetic testing is frequently used to
confirm the clinical findings. Unfortunately in many cases, variants of uncertain
significance (VUSs) obscure the genetic diagnosis until more information becomes
available. Here, we describe and characterize the functional impact of a novel
VUS in the TGFBR2 kinase domain (c.1255G>T; p.Val419Leu), in a patient with the
clinical diagnosis of Marfan syndrome spectrum. We assessed the structural and
functional consequence of this VUS using molecular modeling, molecular dynamic
simulations, and in vitro cell-based assays. A high-quality homology-based model
of TGFBR2 was generated and computational mutagenesis followed by refinement and
molecular dynamics simulations were used to assess structural and dynamic
changes. Relative to wild type, the V419L induced conformational and dynamic
changes that may affect ATP binding, increasing the likelihood of adopting an
inactive state, and, we hypothesize, alter canonical signaling. Experimentally,
we tested this by measuring the canonical TGF-? signaling pathway activation at
two points; V419L significantly delayed SMAD2 phosphorylation by western blot and
significantly decreased TGF-?-induced gene transcription by reporter assays
consistent with known pathogenic variants in this gene. Thus, our results
establish that the V419L variant leads to aberrant TGF-? signaling and confirm
the diagnosis of Loeys-Dietz syndrome in this patient.
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