The similarities in the phenotype between our patients and spondyloepimetaphyseal dysplasia congenita (SEMDC) and spondyloepimetaphyseal dysplasia Strudwick (SEMDS) type, indicated that these patients could have a defect in the COL2A1 gene.
We now describe the biochemical characterization of defects in alpha 1(II) collagen in three unrelated individuals with SEMD Strudwick, each of which is due to heterozygosity for a unique mutation in COL2A1.
A large inbred family with a distinct form of recessively inherited, spondyloepimetaphyseal dysplasia (SEMD) was mapped to PAPSS2 isoform located in the chromosome region of 10q23-24.
We characterized a nonsense mutation in ATPSK2 in the SEMD family and a missense mutation in the region of Atpsk2 encoding the APS kinase activity in the brachymorphic mouse.
We transfected these contructs into the COS-1 or MCT cells, and the results revealed that the HOA-related matrilin-3 mutation (T298M) leads to a high expression level of growth arrest DNA damage-inducible gene 153 (GADD153, also known as CHOP; an endoplasmic reticulum stress marker), as shown by western blot analysis and does not significantly affect protein secretion, as shown by immunofluorescence staining; however, osteochondroplasia, i.e., MED-related (R116W) and SEMD-related (C299S) mutations lead to both high levels of GADD153 expression and protein trafficking into the cytoplasm and form multiple vacuoles in cells, which in turn leads to insufficient protein secretion.
We therefore conclude that this form of SEMD probably differs from SEMDmatrilin 3 type and does not belong to the spectrum of type II collagenopathies.
Biallelic mutations in B3GALT6, encoding one of the linker region glycosyltransferases, are known to cause either spondyloepimetaphyseal dysplasia (SEMD) or a severe pleiotropic form of Ehlers-Danlos syndromes (EDS).
Mutations in ACAN result in a broad phenotypic spectrum of non-lethal skeletal dysplasias including spondyloepimetaphyseal dysplasia, spondyloepiphyseal dysplasia, familial osteochondritis dissecans and various undefined short stature syndromes associated with accelerated bone maturation.
This condition has clinical overlap with autosomal dominantly inherited SEMD with joint laxity, leptodactylic type caused by recurrent missense variants in the kinesin family member 22 gene (KIF22).