Smith-McCort dysplasia

Smith-McCort dysplasia (SMC) is a rare autosomal recessive skeletal disorder classified as a spondyloepimetaphyseal dysplasia. It is closely related to Dyggve-Melchior-Clausen (DMC) syndrome, sharing virtually identical skeletal features but without the intellectual disability seen in DMC. The condition is caused by mutations in the DYM gene (also known as FLJ20116) on chromosome 18q21, which encodes dymeclin, a protein involved in Golgi apparatus function. A second form, Smith-McCort dysplasia type 2, has been linked to mutations in the RAB33B gene. Smith-McCort dysplasia primarily affects the skeletal system. Key clinical features include short-trunk dwarfism (disproportionate short stature), a barrel-shaped chest, short neck, and exaggerated lumbar lordosis. Radiographic hallmarks include generalized platyspondyly (flattened vertebral bodies) with a characteristic "lace-like" or double-humped appearance of the vertebral bodies, irregular iliac crests, and epiphyseal and metaphyseal irregularities of the long bones. Joint mobility may be restricted, and progressive degenerative joint disease can develop. Importantly, intelligence is normal in Smith-McCort dysplasia, which is the primary distinguishing feature from Dyggve-Melchior-Clausen syndrome. There is currently no cure or disease-specific treatment for Smith-McCort dysplasia. Management is supportive and symptomatic, focusing on orthopedic surveillance and intervention for skeletal complications such as spinal abnormalities (including possible atlantoaxial instability), hip dysplasia, and joint problems. Physical therapy may help maintain mobility. Regular monitoring by a multidisciplinary team including orthopedic specialists, geneticists, and rehabilitation professionals is recommended. Genetic counseling is important for affected families.

Common questions about Smith-McCort dysplasia