Nosology of fetal hypokinesia sequence based on CNS abnormalities: is there an Aase-Smith syndrome?

Aase-Smith syndrome (ASS) is usually defined as a dominantly inherited combination of arthrogryposis, Dandy-Walker malformation and cleft palate. We describe a sporadic case of foetal akinesia with abnormal fossa posterior, fitting the diagnosis of ASS, and discuss the nosology of this entity among syndromes with distal arthrogryposis. ASS shows a "hybrid" phenotype: adults with mild ASS could be classified as distal arthrogryposis, whereas severely affected newborns overlap with the Marden-Walker phenotype, which is recessively inherited. The specificity of the disorder comes from the coexistence of both forms in the same pedigree, so that ASS appears impossible to diagnose with certitude in sporadic cases. We suggest that the severe expression of ASS is only the extreme but aspecific expression of a dominantly inherited form of distal arthrogryposis. Implications for genetic counselling in distal arthrogryposis are outlined.