Heterogeneity of Dyggve-Melchior-Clausen dwarfism.

Sibs with apparent Dyggve-Melchior-Clausen (DMC) dwarfism and normal intelligence are described. Three other familial and 3 sporadic cases with DMC dwarfism and normal intelligence are known. Twelve familial and 9 sporadic cases are known with the usual combination of DMC dwarfism and severe mental retardation. Since the two conditions appear to breed true they seem to be genetically different. We propose to name the former "Smith-McCort dwarfism" to clearly distinguish it from the DMC syndrome in which mental retardation is a constituent part. Both conditions are inherited as autosomal recessive traits. Spinal cord compression due to atlantoaxial instability is a serious and preventable complication of both disorders.