First Genotype-Phenotype Study in TBX4 Syndrome: Gain-of-Function Mutations Causative for Lung Disease.

Despite the increased recognition of (T-BOX transcription factor 4)-associated pulmonary arterial hypertension (PAH), genotype-phenotype associations are lacking and may provide important insights. To compile and functionally characterize all variants reported to date and undertake a comprehensive genotype-phenotype analysis. We assembled a multicenter cohort of 137 patients harboring monoallelic variants and assessed the pathogenicity of missense variation ( = 42) using a novel luciferase reporter assay containing T-BOX binding motifs. We sought genotype-phenotype correlations and undertook a comparative analysis with patients with PAH with (Bone Morphogenetic Protein Receptor type 2) causal variants ( = 162) or no identified variants in PAH-associated genes ( = 741) genotyped via the National Institute for Health Research BioResource-Rare Diseases. Functional assessment of missense variants led to the novel finding of gain-of-function effects associated with older age at diagnosis of lung disease compared with loss-of-function effects ( = 0.038). Variants located in the T-BOX and nuclear localization domains were associated with earlier presentation ( = 0.005) and increased incidence of interstitial lung disease ( = 0.003). Event-free survival (death or transplantation) was shorter in the T-BOX group ( = 0.022), although age had a significant effect in the hazard model ( = 0.0461). Carriers of variants were diagnosed at a younger age ( < 0.001) and had worse baseline lung function (FEV, FVC) ( = 0.009) than the and no identified causal variant groups. We demonstrated that syndrome is not strictly the result of haploinsufficiency but can also be caused by gain of function. The pleiotropic effects of in lung disease may be in part explained by the differential effect of pathogenic mutations located in critical protein domains.