Chiari malformation and tonsillar ectopia in twin brothers and father with autosomal dominant spondylo-epiphyseal dysplasia tarda.

We describe twin brothers and father with autosomal dominant spondylo-epiphyseal dysplasia (SED) tarda. The proband presented at 17 years with nystagmus and esotropia due to a severe Chiari malformation. A milder, asymptomatic Chiari I malformation was seen in his brother and tonsillar ectopia in his father. Although these malformations have not been described in patients with SED, they are relatively common in other bony abnormalities, particularly those involving the cranio-cervical junction. The concordance of the Chiari malformations or tonsillar ectopia in all three family members with SED suggests that this association is not coincidental. It seems possible that the downward displacement of the cerebellum occurs secondary to primary osseous abnormality, rather than due to a primary disturbance of embryological development. The lack of additional brain malformations in our patients is consistent with this theory.