Pulmonary arterial hypertension (PAH) in children is a progressive and often fatal disease of the lung vessels, for which no curative therapy exists. PAH may be heritable: mutations in the BMPR2-gene have been found in about 15% of children with the disease. In a national cohort of Dutch children with unexplained PAH, we identified mutations of the TBX4-gene in 30% of the cases. TBX4-mutations have previously been shown to cause Small Patella Syndrome (SPS) and, interestingly, the pediatric PAH-patients with TBX4 mutations, also appeared to have SPS. This is the first time that TBX4-mutations are reported in PAH. (By Dr. Wilhelmina S Kerstjens-Frederikse, http://jmg.bmj.com/content/early/2013/04/15/jmedgenet-2012-101152 )