Osteogenesis Imperfecta Blue Sclerae

A 4-year-old boy presents with his fifth fracture in 3 years following a minor fall from a chair. On examination, the structure marked **A** (blue sclerae) is noted, along with triangular facies, frontal bossing, and opalescent grey-brown teeth. Skeletal survey shows generalised osteopenia, wormian bones, and platyspondyly. Genetic testing reveals a heterozygous pathogenic missense variant in COL1A1. Which of the following best explains the pathophysiology of the blue sclerae seen in this child?