Identification of a mutation causing deficient BMP1/mTLD proteolytic activity in autosomal recessive osteogenesis...

Area of Science:

• Genetics
• Molecular Biology
• Biochemistry

Background:

• Osteogenesis imperfecta (OI) is a group of genetic disorders characterized by bone fragility.
• Autosomal recessive forms of OI (AR-OI) are typically caused by mutations in collagen processing genes.
• A consanguineous Egyptian family presented with severe AR-OI and umbilical hernia, suggesting a novel genetic etiology.

Purpose of the Study:

• To identify the genetic cause of severe AR-OI in a consanguineous Egyptian family.
• To investigate the role of the BMP1 gene in the pathogenesis of AR-OI.

Main Methods:

• Homozygosity mapping was performed to identify shared homozygous regions in affected siblings.
• Mutation analysis of the BMP1 gene was conducted.
• Procollagen I C-terminal propeptide (PICP) processing was analyzed in patient-derived fibroblasts.
• Functional studies involved overexpressing wild-type and mutant BMP1 (mTLD) in cell lines.

Main Results:

• A novel homozygous missense mutation (Phe249Leu) was identified in the BMP1 gene in affected individuals.
• Patient fibroblasts showed impaired PICP processing, indicating reduced BMP1 function.
• Overexpression of the mutant BMP1/mTLD protein failed to enhance proα1(I) cleavage, confirming deficient proteolytic activity.

Conclusions:

• The Phe249Leu mutation in BMP1 leads to deficient PICP proteolytic activity.
• Mutations in BMP1 are a newly identified cause of autosomal recessive osteogenesis imperfecta.
• This finding expands the genetic landscape of AR-OI and highlights BMP1's critical role in collagen maturation.