A mutation in MBTPS2 exon 11, c.1376A>G (nucleotide: NM_015884.3, GRCh38) predicting a p.N459S substitution (protein: NP_056968.1), was confirmed by Sanger sequencing of proband DNA (Fig. 2c), segregated with OI in the pedigree (Fig. 1b) and was absent in 644 X chromosomes of unrelated Thai controls (181 females, 282 males). Here, MBTPS2 is linked to osteogenesis imperfecta.