Interestingly, skeleton defects noted in the sacral region, including underdeveloped ischium bones and fused sacral vertebrae (Supplementary Figure S2d–f) show similarity to congenital defects found in autosomal dominant Currarino syndrome (also known as hereditary sacral agenesis (HSA) or caudal regression syndrome) patients that have HLXB9 mutation20, 21. This evidence concerns the gene MNX1 and caudal regression sequence.