Dysspondyloenchondromatosis (DSC) associated with COL2A1 mutation: Clinical and radiological overlap with spondyloepimetaphyseal dysplasia-Strudwick type (SEMD-S)

Radiologic Features of Type II and Type XI Collagenopathies

Type II collagen is a major component of the cartilage matrix. Pathogenic variants (ie, disease-causing aberrations) in the type II collagen gene (COL2A1) lead to an abnormal structure of type II collagen, causing a large group of skeletal dysplasias termed type II collagenopathies. Because type II collagen is also located in the vitreous body of the eyes and inner ears, type II collagenopathies are commonly associated with vitreoretinal degeneration and hearing impairment. Type II collagenopathies can be radiologically divided into two major groups: the spondyloepiphyseal dysplasia congenita (SEDC) group and the Kniest-Stickler group. The SEDC group is characterized by delayed ossification of the juxtatruncal bones, including pear-shaped vertebrae. These collagenopathies comprise achondrogenesis type 2, hypochondrogenesis, SEDC, and other uncommon subtypes. The Kniest-Stickler group is characterized by disordered tubular bone growth that leads to "dumbbell" deformities. It comprises Kniest dysplasia and Stickler dysplasia type 1, whose radiographic manifestations overlap with those of type XI collagenopathies (a group of disorders due to abnormal type XI collagen) such as Stickler dysplasia types 2 and 3. This phenotypic overlap is caused by type II and type XI collagen molecules sharing part of the same connective tissues. The authors describe the diagnostic pathways to type II and type XI collagenopathies and the associated differential diagnoses. In addition, they review the clinical features and genetic bases of these conditions, which radiologists should know to participate in multidisciplinary care and translational research. Online supplemental material is available for this article. ^©RSNA, 2020.

Integrated analysis of COL2A1 variant data and classification of type II collagenopathies

The COL2A1 gene encodes the alpha-1 chain of type II procollagen. Type II collagen, comprised of three identical alpha-1 chains, is the major component of cartilage. COL2A1 gene variants are the etiologies of genetic diseases, termed type II collagenopathies, with a wide spectrum of clinical presentations. To date, at least 460 distinct COL2A1 mutations, identified in 663 independent probands, and 21 definite disorders have been reported. Nevertheless, a well-defined genotype-phenotype correlation has not been established, and few hot spots of mutation have been reported. In this study, we analyzed data of COL2A1 variants and clinical information of patients obtained from the Leiden Open Variation Database 3.0, as well as the currently available relevant literature. We determined the characteristics of the COL2A1 variants and distributions of the clinical manifestations in patients, and identified four likely genotype-phenotype correlations. Moreover, we classified 21 COL2A1-related disorders into five categories, which may assist clinicians in understanding the essence of these complex phenotypes and prompt genetic screening in clinical practice.

Longitudinal Follow-Up of Two Patients with Dysspondyloenchondromatosis due to Novel Heterozygous Mutations in COL2A1

Dysspondyloenchondromatosis (DSC) is a rare form of generalized enchondromatosis and characterized by short stature with unequal limb length, multiple enchondromas in metaphyseal and diaphyseal parts of the long tubular bones, and progressive kyphoscoliosis. Although the COL2A1 gene mutation was found to be responsible for DSC, a case of DSC with no pathogenic mutation in the COL2A1 gene has also been reported, suggesting that the condition is genetically heterogeneous. Here, we report 2 novel heterozygous mutations in COL2A1 in 2 patients with DSC. They had prenatal onset short stature with unequal limb length and generalized enchondroma-like lesions in metaphyseal and diaphyseal parts of the long tubular bones, and osteopenia. The first patient was diagnosed at 3 months of age and followed for 10.5 years. Severe lumbosacral scoliosis and recurrent fractures were observed. The second patient was diagnosed at the age of 4 years. Mild deterioration in scoliosis was observed during the 3-year-long follow-up period. However, skeletal radiography of both patients showed the improvement of enchondromatous lesions. In conclusion, we verified that the COL2A1 gene mutations are responsible for the DSC phenotype. We observed severe osteopenia and fractures which were not reported previously.