In a more recent study, 448 index patients were screened for PAH predisposing genes; 20 patients (nine childhood-onset) from 17 unrelated families carried heterozygous mutations in the TBX4 gene, bringing the frequency of TBX4 mutations in France to 6% and 3% in childhood- and adult-onset PAH, respectively [142]. The gene discussed is TBX4; the disease is pulmonary arterial hypertension.