Spondyloepiphyseal Dysplasia (SED) [Q78.9]
Dr. rer. nat. Christoph Marschall
SED is a rare autosomal dominant type II collagenopathy. Affected children are of short stature, have clubfeet, a flat face and wide-spaced eyes. The head appears to rest directly on the torso. The thorax is frequently deformed and has a barrel-shaped appearance. The extremities are short, but relatively long in relation to the torso. Myopia occurs in 40% of all cases; retinal detachment is possible. Height may range from 85–135 cm in adulthood. X-ray classically shows delayed ossification.
SED is generally caused by mutations in the COL2A1 gene which lead to a deficiency in type II collagen. Mutations usually cause substitution of the amino acid glycine for serine. The substitution of glycine with an amino acid other than serine causes a more severe phenotype.