HOXA4 and brachyolmia: Finally, the rib and spine phenotypes associated with brachyolmia and metatropic dysplasia could be contributed to the altered expression of HOXA4 to HOXA7 as it has been shown that these genes are associated with rib and spine patterning, and alterations in expression have led to defects (Chen et al., 1998; Wellik, 2009).