Based on this evidence, the 643rd amino acid substitution from glycine to serine in the helical region was incorporated because our type III patient with OI carried a heterozygous p.Gly821Ser pathogenic variant in the COL1A1 gene, resulting in a 643rd amino acid alteration [4, 10]. The gene discussed is COL1A1; the disease is osteogenesis imperfecta.