Heterozygous TBX4 variants cause ischiocoxopodopatellar syndrome (ICPPS; OMIM #147891), also known as small patella syndrome, whilst homozygous loss-of-function variants underlie posterior amelia with pelvic and pulmonary hypoplasia syndrome (PAPPAS; OMIM #601360). The gene discussed is TBX4; the disease is coxopodopatellar syndrome.