Whole-exome sequencing reveals TopBP1 as a novel gene in idiopathic pulmonary arterial hypertension.
BACKGROUND
Idiopathic pulmonary arterial hypertension (IPAH) is a life-threatening disorder characterized by progressive loss of pulmonary microvessels. Although mutations in the bone morphogenetic receptor 2 (BMPR2) are found in 80% of heritable and ∼15% of patients with IPAH, their low penetrance (∼20%) suggests that other unidentified genetic modifiers are required for manifestation of the disease phenotype. Use of whole-exome sequencing (WES) has recently led to the discovery of novel susceptibility genes in heritable PAH, but whether WES can also accelerate gene discovery in IPAH remains unknown.


OBJECTIVE
To determine whether WES can help identify novel gene modifiers in patients with IPAH.


METHODS
Exome capture and sequencing was performed on genomic DNA isolated from 12 unrelated patients with IPAH lacking BMPR2 mutations. Observed genetic variants were prioritized according to their pathogenic potential using ANNOVAR.


RESULTS
A total of nine genes were identified as high-priority candidates. Our top hit was topoisomerase DNA binding II binding protein 1 (TopBP1), a gene involved in the response to DNA damage and replication stress. We found that TopBP1 expression was reduced in vascular lesions and pulmonary endothelial cells isolated from patients with IPAH. Although TopBP1 deficiency made endothelial cells susceptible to DNA damage and apoptosis in response to hydroxyurea, its restoration resulted in less DNA damage and improved cell survival.


CONCLUSIONS
WES led to the discovery of TopBP1, a gene whose deficiency may increase susceptibility to small vessel loss in IPAH. We predict that use of WES will help identify gene modifiers that influence an individual's risk of developing IPAH.
1 Division of Pulmonary and Critical Care Medicine.
Vinicio A
VA
de Jesus Perez
Ke
K
Yuan
Maria A
MA
Lyuksyutova
Frederick
F
Dewey
Mark E
ME
Orcholski
Eric M
EM
Shuffle
Maya
M
Mathur
Luke
L
Yancy
Vanessa
V
Rojas
Caiyun Grace
CG
Li
Aiqin
A
Cao
Tero-Pekka
TP
Alastalo
Nayer
N
Khazeni
Karlene A
KA
Cimprich
Atul J
AJ
Butte
Euan
E
Ashley
Roham T
RT
Zamanian
D000328:Adult; D015415:Biomarkers; D002352:Carrier Proteins / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D018450:Disease Progression; D059472:Exome / Q000235:genetics*; D065627:Familial Primary Pulmonary Hypertension; D005260:Female; D005820:Genetic Testing; D006801:Humans; D006976:Hypertension, Pulmonary / Q000175:diagnosis / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics*; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D017422:Sequence Analysis, DNA
D015415:Biomarkers; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; C110513:TOPBP1 protein, human