A child with typical spondyloepiphyseal dysplasia congenita had a recurrent, heterozygous substitution of arginine 789 by cysteine in the triple helical domain of alpha 1 (II) chains of type II collagen. The amino substitution was due to the transition of cytosine 2913 to thymine in exon 41 of the COL2A1 gene. The amino acid substitution involved the Y position of a Gly-X-Y triplet.