Clinical, Molecular Characteristics, and Genotype-Phenotype Relationships of Metaphyseal Chondrodysplasia Type Schmid.

Metaphyseal chondrodysplasia type Schmid (MCDS), a rare skeletal disorder caused by COL10A1 mutations, exhibits significant phenotypic heterogeneity, yet genotype-phenotype correlations remain poorly defined. We aim to determine the clinical and radiographic manifestation, mutational features, and genotype-phenotype relationships by characterization of 4 patients with MCDS and literature review. The four patients presented with short stature or waddling gait, flattened vertebrae, and irregular femoral epiphyses. We identified two novel COL10A1 variants (c.1925 T > A, c.1903C > G) and reported the first case harboring both a de novo nonsense (c.2001 T > G, p.Tyr667Ter) in the non-collagenous 1 (NC1) domain and a missense (c.1438A > T, p.Ile480Leu) in the helix domain. Genotype-phenotype analysis of 124 cases previously reported and 4 new cases revealed that NC1 domain mutations were associated with an earlier onset of MCDS than non-NC1 mutations (median 12 vs. 72 months, P = 0.0014). Patients carrying a missense mutation in COL10A1 showed significantly lower height Z-scores (- 3.62 ± 1.95 vs. - 1.99 ± 1.28, P = 0.013) at first and more metaphyseal irregularities in the distal radius/ulna than those with truncating mutations (P = 0.019). Structural modeling indicated that NC1 mutations may disrupt collagen X structure via electrostatic alterations or steric clashes. These findings expand the mutational spectrum of MCDS and establish that COL10A1 genotype correlates with severity of MCDS, which will help to identify patients with severe phenotypes through molecular testing and to develop effective treatment strategies for MCDS.