Identification and functional characterization of a novel pathogenic COL1A1 splicing variant in a Chinese family with osteogenesis imperfecta.

Osteogenesis imperfecta (OI) is a hereditary disorder primarily caused by mutations in COL1A1 or COL1A2, leading to bone fragility and deformities. Although numerous pathogenic variants have been identified, novel mutations in specific populations remain underreported, complicating diagnosis and genetic counseling. A Chinese family with mild type I OI was recruited. Whole-exome sequencing and Sanger sequencing were used to identify and validate a novel splice-site variant in COL1A1. Functional effects were assessed using two minigene constructs (pcMINI-COL1A1 and pcMINI-N-COL1A1) transfected into HEK293T cells, followed by reverse transcription-polymerase chain reaction (RT-PCR) and sequencing of transcripts. A novel heterozygous splice-site variant (c.298 + 1G>A) at the donor site of COL1A1 intron 2 was identified and found to co-segregate with the disease. Minigene assays demonstrated that this mutation induces abnormal splicing patterns, including partial and complete skipping of exon 2, resulting in frameshifted transcripts with premature termination codons. The c.298 + 1G>A variant leads to aberrant splicing and likely haploinsufficiency, consistent with a mild OI phenotype. This study expands the COL1A1 mutation spectrum and supports the use of functional assays for clarifying pathogenicity.