Rock et al. (2008) provided an overview of the brachyolmias, a heterogeneous group of skeletal dysplasias that affect primarily the spine. Type 1 brachyolmia includes the Hobaek and Toledo (BCYM1B; 271630) forms, which are inherited in an autosomal recessive fashion. Both forms of type 1 are characterized by scoliosis, platyspondyly with rectangular and elongated vertebral bodies, overfaced pedicles, and irregular, narrow intervertebral spaces. The Toledo form is distinguished by the presence of corneal opacities and precocious calcification of the costal cartilage. Type 2 brachyolmia (BCYM2; 613678), sometimes referred to as the Maroteaux type, is also an autosomal recessive disorder, primarily distinguished from type 1 by rounded vertebral bodies and less overfaced pedicles. Some cases are associated with precocious calcification of the falx cerebri. Type 3 brachyolmia (BCYM3; 113500) is an autosomal dominant form, caused by mutation in the TRPV4 gene (605427), with severe kyphoscoliosis and flattened, irregular cervical vertebrae. Paradoxically, although the limbs are mildly shortened in all types of brachyolmia, they show minimal epiphyseal and metaphyseal abnormalities on radiographs. Type 4 brachyolmia (BCYM4; 612847) is an autosomal recessive form, caused by mutation in the PAPSS2 gene (603005), with mild epiphyseal and metaphyseal changes.