Defects in the gene COL27A1 cause a range of disorders of the skeleton and are characterized mainly by short stature, hip dislocations, abnormal curvature of the spine, and other bone abnormalities such as fusion of bones of the hands and feet. Other features can include bowing of the bones of the legs and hearing loss in some cases. The disorders associated with defects in the COL27A1 gene are inherited in an autosomal recessive manner, meaning that the patient will have two abnormal copies of the gene, each inherited by each of the parents.

The majority of patients with defects in COL27A1 have a variant that changes an amino acid in the collagen XXVII protein produced by the COL27A1 gene. This variant has been mainly observed in people from Puerto Rico and other islands of the Caribbean. Therefore, a child with short stature, hip dislocations and of Puerto Rican ancestry is highly suspected to have a diagnosis of Steel syndrome. Other patients have been reported in other parts of the world with different mutations that cause a loss of the COL27A1 protein product and can have more severe clinical manifestations.