Exome sequencing-aided precise diagnosis of four families with type I Stickler syndrome.

BACKGROUND: Stickler syndrome is a multisystemic disorder characterized by ophthalmological and non-ophthalmological abnormalities, frequently misdiagnosed due to high clinical heterogeneity. Stickler syndrome type I (STL1) is predominantly caused by mutations in the COL2A1 gene. METHODS: Exome sequencing and co-segregation analysis were utilized to scrutinize 35 families with high myopia, and pathogenic mutations were identified. Mutant COL2A1 was overexpressed in cells for mechanistic study. A retrospective genotype-phenotype correlation analysis was further conducted. RESULTS: Two novel pathogenic mutations (c.2895+1G>C and c.3505G>A (p.Val1169Ile)) and two reported mutations (c.1597C>T (p.Arg533*) and c.1693C>T (p.Arg565Cys)) in COL2A1 were identified causing STL1. These mutations are all in the G-X-Y triplet, and c.2895+1G>C contributed to aberrant RNA splicing. COL2A1 mutants tended to form large aggregates in the endoplasmic reticulum (ER) and elevated ER stress. Additionally, mutations c.550G>A (p.Ala184Thr) and c.2806G>A (p.Gly936Ser) in COL2A1 were found in high myopia families, but were likely benign, although c.2806G>A (p.Gly936Ser) is on G-X-Y triplet. Moreover, genotype-phenotype correlation analysis revealed that mutations in exon 2 mainly contribute to retinal detachment, whereas mutations in the collagen alpha-1 chain region of COL2A1 tend to cause non-ophthalmologic symptoms. CONCLUSION: This study broadens the COL2A1 gene mutation spectrum, provides evidence for ER stress caused by pathogenic COL2A1 mutations and highlights the importance of non-ophthalmological examination in clinical diagnosis of high myopia.