3M syndrome is a rare autosomal recessive disorder that combines intrauterine growth retardation (IUGR) and postnatal growth retardation. Additionally, this syndrome is characterized by dysmorphic facial features (large head, dolichocephaly, frontal bossing, a triangular face, long philtrum and hypoplastic midface) and certain radiological abnormalities. The latter includes slender long bones and ribs, foreshortened vertebral bodies, and small pelvis. The name of this disorder comes from the initials of the three researchers (Miller, McKusik and Malvaux) who first identified it. The characteristic radiologic findings of 3M syndrome are used to rule out similar disorders such as Silver-Russel syndrome (SRS), particularly the lack of limb length asymmetry that is present in over half of those with autosomal recessive SRS. The severity of symptoms and physical features varies considerably from case to case.
Mutations leading to 3M syndrome-2 were mapped to the OBSL1 gene, which encodes a putative cytoskeletal adaptor protein. The OBSL1 gene is also involved in maintaining normal levels of CUL7, which plays a role in chondrocyte growth and proliferation. This explains the main feature of 3M syndrome; retarded growth. However, there are certain consanguineous families with 3M syndrome who have neither CUL7 nor OBSL1 mutations, which indicates that there is at least one further locus that is causing this growth disorder.