CRTAP (cartilage-associated protein) is essential for efficient 3-hydroxylation of prolyl residues in fibrillar collagen, particularly at Pro986 of type I collagen's α1 chain 1. CRTAP functions as a critical component of the collagen prolyl 3-hydroxylation complex, where it works together with prolyl 3-hydroxylase 1 (P3H1) and cyclophilin B (PPIB) in the endoplasmic reticulum lumen 2. Recent structural studies reveal that CRTAP facilitates a bifunctional reaction center between P3H1 and PPIB, enabling coupled collagen modification through multiple substrate binding sites 3. Biallelic CRTAP mutations cause osteogenesis imperfecta type VII, a rare autosomal recessive disorder characterized by severe early-onset bone fragility 4. Loss of CRTAP function results in absent or severely reduced Pro986 hydroxylation, leading to defective collagen maturation and impaired bone formation 1. Mechanistically, CRTAP-null osteoblasts demonstrate approximately 2-fold increased proliferation coupled with upregulated BMP2 signaling, altered cell cycle regulation, and reduced expression of cell adhesion and extracellular matrix genes 5. Type VII OI is predominantly lethal in infancy but presents with white sclerae, gracile ribs, and severe growth deficiency when survival occurs 2. Among moderate-to-severe OI cases, CRTAP mutations account for 2.9% of recessive cases 6, making it clinically significant despite its rarity.