CHST3 encodes a sulfotransferase enzyme that catalyzes sulfation of chondroitin at the 6-position of N-acetylgalactosamine residues using PAPS as a sulfate donor 123. This modification is critical for chondroitin sulfate biosynthesis, the predominant proteoglycan in cartilage and extracellular matrices. CHST3 also sulfates keratan sulfate galactose residues with lower efficiency 2 and may contribute to naive T-lymphocyte maintenance. Biallelic loss-of-function CHST3 variants cause spondyloepiphyseal dysplasia with congenital joint dislocations (CDCJD), a rare skeletal dysplasia characterized by congenital knee and elbow dislocations, short stature, progressive vertebral anomalies, kyphoscoliosis, and joint contractures 4567. Cardiac valve abnormalities and progressive hearing loss are significant clinical manifestations requiring monitoring 78. The c.776T>C mutation shows ethnic clustering in Turkish populations 5, while variants demonstrate geographic diversity across populations 9. Beyond skeletal dysplasia, CHST3 variants have been identified as potential diagnostic genes for osteoporosis and sarcopenia 10, implicating broader roles in bone and muscle metabolism. Genotype-phenotype correlation remains unclear, with both missense and nonmissense mutations producing variable clinical presentations 4.