SP7 and osteogenesis imperfecta: Intriguingly, there have also been reports of pathological heterozygous mutations in SP7. Siblings with a heterozygous substitution in a highly conserved zinc finger domain of osterix (p.Glu340Ala) share low cortical density with the recessive OI, but have low bone turnover [124] rather than the high bone turnover seen in SP7 recessive OI.