Gly674Arg linked with the bowed legs stature in the Schmid metaphyseal chondrodysplasia-affected Chinese lineage

To evaluate the clinical-phenotypic characteristics of Schmid metaphyseal chondrodysplasia (SMCD) inflicted by a novel missense mutation of COL10A1 gene: c.2020G > A; p.Gly674Arg.

A female child aged about 3 yrs. and 8 months was subjected to Radiograph test to validate the symptoms of SMCD. The polymorphism analysis by the next-generation sequencing (NGS) was performed using the peripheral blood DNA samples of the patient and other family inmates, including, the younger male sibling. The effect of the mutation on the non-collagenous carboxyl-terminal (NC1) domain of collagen X was studied using the SWISS-MODEL online server for trimer modelling; PROSA and PROCHECK-Ramachandran plot for structural validation; Mean Square Plot (RMSF) for structural rigidity.

Radiograph examination of lower limbs confirmed the bowed legs in both the patient and her younger brother (study groups). The inheritance of the novel missense mutation of COL10A1: c.2020G > A; p.Gly674Arg (at chromosome-6q22.1) was confirmed in the study groups from the SMCD-affected mother. The extended interactions of the mutant-Arg674 with the Ser552 and Phe589 (β strand B) in the NC1 domain of α1(X) chain monomer is more likely to intervene its trimer formation by weakening the structural rigidity of the crucial strand H compared to its wild type. This plausibly deters the collagen X synthesis inflicting the bowed legs with the altered distal ulna bone morphology in the study groups.

The inheritance of COL10A1 mutation: c.2020G > A; p.Gly674Arg has inflicted the SMCD with the characteristic bowed legs in the study groups. Radiograph and NGS could be a valid diagnostic module to initiate the treatment of SMCD.

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A novel missense COL10A1 mutation (c.2020G>A; p.Gly674Arg) of NC1 domain of collagen X preceding Schmid Metaphyseal Chondrodysplasia.

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COL10A1 mutation (p.Gly674Arg) and the disturbed trimer structure of α1(X) chain monomer of collagen X.

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COL10A1 mutation (p.Gly674Arg) and the reduced rigidity of α1(X) chain monomer of collagen X.

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The mutated NC1 domain of collagen X structure and the bowed legs stature.

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Cupping and fraying of the distal ulna bone regulated by the weakened rigidity of the α1(X) chain monomer of collagen X.

Schmid's Type of Metaphyseal Chondrodysplasia: Diagnosis and Management

OBJECTIVES

There are several types of metaphyseal chondrodysplasia and various clinical types have been differentiated. The Schmid type of metaphyseal chondrodysplasia is the most common. Diffuse metaphyseal flaring, irregularity, and growth plate widening, which are most severe in the knees, are the most striking radiological features of this disease. The Schmid type of metaphyseal dysostosis is characterized by failure of normal mineralization of the zone of provisional calcification, leading to widened physes and enlarged knobby metaphyses, effectively causing shortening of the tubular bones, splaying of the metaphyses, coxa vara, and bow legs. Orthopaedic interventions were primarily performed on the lower extremities.

METHODS

Twelve children (seven girls and five boys) aged 7-10 years were enrolled in this study. Moderate short stature was a uniform feature associated with predominant involvement of the proximal femora and bow legs resulted in the development of angular deformities. A waddling gait was a consequence of coxa vara in eight children. Valgus osteotomy of the proximal femur was planned after physeal closure for the group of children with coxa vara. Hemiepiphysiodesis was performed to re-align the genu varum in three children.

RESULTS

Other forms of metaphyseal dysostosis were ruled based on full clinical and radiographic phenotypes, with confirmation through molecular pathology. Mutations in the COL10A1 gene located on chromosome 6q21-q22.3 were confirmed. Re-alignment was accomplished in our group of patients.

CONCLUSION

The most striking clinical features of Schmid metaphyseal chondrodysplasia which appear within the first 2-3 years of life are: moderate short limbs and short stature, a waddling gait, and increasing shortness of stature with age. The Schmid type of metaphyseal chondrodysplasia is a disorder that arises from defective type X collagen, which is typically found in the hypertrophic zone of the physes. Moderate short stature and a waddling gait associated with pain are the most common clinical presentations. Osteotomies to correct bow legs are sometimes combined with lengthening procedures. Recurrence of the deformities with growth is not uncommon; therefore, hemiepiphysiodesis or stapling might be indicated in some cases.