To date, TBX5 has been associated with upper amelia, TBX4 with lower amelia, and WNT3, WNT7A and RSPO2 with tetra-amelia syndromes in humans (and cattle, for RSPO2) (Becker et al. 2020; Eyaid et al. 2011; Niemann et al. 2004; Kariminejad et al. 2009; Ranganath et al. 2020). The gene discussed is RSPO2; the disease is tetra-amelia.