COL2A1 mutation (c.3508G>A) leads to avascular necrosis of the femoral head in a Chinese family: A case report

ER procollagen storage defect without coupled unfolded protein response drives precocious arthritis

Collagenopathies are a group of clinically diverse disorders caused by defects in collagen folding and secretion. For example, mutations in the gene encoding collagen type-II, the primary collagen in cartilage, can lead to diverse chondrodysplasias. One example is the Gly1170Ser substitution in procollagen-II, which causes precocious osteoarthritis. Here, we biochemically and mechanistically characterize an induced pluripotent stem cell-based cartilage model of this disease, including both hetero- and homozygous genotypes. We show that Gly1170Ser procollagen-II is notably slow to fold and secrete. Instead, procollagen-II accumulates intracellularly, consistent with an endoplasmic reticulum (ER) storage disorder. Likely owing to the unique features of the collagen triple helix, this accumulation is not recognized by the unfolded protein response. Gly1170Ser procollagen-II interacts to a greater extent than wild-type with specific ER proteostasis network components, consistent with its slow folding. These findings provide mechanistic elucidation into the etiology of this disease. Moreover, the easily expandable cartilage model will enable rapid testing of therapeutic strategies to restore proteostasis in the collagenopathies.

COL2A1 Mutation (c.611G>C) Leads to Early-Onset Osteoarthritis in a Chinese Family

Mutations in the gene coding collagen type II α1 chain (COL2A1) are associated with a series of human disorders mainly involving the skeletal system. Here, we describe the second family with COL2A1 mutation, c.611G>C, Gly204Ala, leading to a replacement of glycine in the core triple helical (Gly-X-Y) domain of COL2A1 gene. The replacements of glycine in every third position of the triple with other amino acids will cause failure in the structure of type II collagen. The affected family members manifested early-onset osteoarthritis involving multiple joints. We propose that the COL2A1 gene should be taken into consideration for genetic counseling for patients with hereditary premature osteoarthritis and individuals carrying this mutation should receive early interventions for osteoarthritis.

A novel mutation of COL2A1 in a large Chinese family with avascular necrosis of the femoral head

Avascular necrosis of the femoral head (ANFH) is a debilitating bone disease, characterized by collapse of the femoral head and subsequent loss of hip joint function. Heterozygous mutations in COL2A1 have been identified to cause familial ANFH. Here we report on a large Chinese family with ANFH and a novel heterozygous mutation (c.3517 G > A, p.Gly1173Ser) in exon 50 of COL2A1 in the Gly-X-Y domain. Previously, only five different COL2A1 mutations have been described in patients with familial ANFH. Therefore, our findings provide significant clues to the phenotype-genotype relationships in familial ANFH and may be helpful in clinical diagnosis. Furthermore, these results should assist further studies of the mechanisms underlying collagen diseases.

Novel variants in COL2A1 causing rare spondyloepiphyseal dysplasia congenita

Background

Spondyloepiphyseal dysplasia congenita (SEDC) is an extremely rare inherited chondrodysplasia characterized by abnormal epiphyses, short stature, and flattened vertebral bodies. We investigate the phenotypes and the disease‐associated variants of SEDC in two unrelated Chinese families.

Methods

We identified disease‐associated variants in two nonconsanguineous families with SEDC using targeted next‐generation sequencing and confirmed the variants using Sanger sequencing. We investigated the phenotypes of the patients, including clinical manifestations, bone turnover biomarkers, bone mineral density and skeletal radiographic features.

Results

Two probands were diagnosed as SEDC according to the phenotypes of disproportionately short‐trunk stature, kyphosis, lumbar lordosis and adduction deformity of hips. Radiographs revealed kyphosis and lumbar lordosis, flattened vertebral bodies, compressed femoral heads and shortening of the femurs. Bone mineral density of the probands was lower than that of age‐ and gender‐matched normal children, but bone turnover biomarker levels were within normal range. Two novel heterozygous missense variants (NM_001844.5: c.1654 G>A, NP_001835.3: p.Gly552Arg; NM_001844.5: c.3518G>T, NP_001835.3: p.Gly1173Val) in collagen type II alpha 1 chain (COL2A1) were detected in the two families, which would impair the formation of stable triple‐helical type II collagen.

Conclusions

We identified two novel disease‐associated variants in COL2A1, which led to severe SEDC. Our findings expanded the gene variant spectrum and phenotypic spectrum of extremely rare type II collagenopathies.