For example, mutations within the transcription factor genes T-box 4 (TBX4) and SRY-box 17 (SOX17) show enriched contribution to paediatric PAH compared to adult-onset, explaining up to 7.7% and 3.3% of paediatric cases, respectively [8,21,22]. The gene discussed is TBX4; the disease is pulmonary arterial hypertension.