MUTATION IN THE COL2A1 GENE IN A PATIENT WITH HYPOCHONDROGENESIS - EXPRESSION OF MUTATED COL2A1 GENE IS ACCOMPANIED BY EXPRESSION OF GENES FOR TYPE-I PROCOLLAGEN IN CHONDROCYTES

A new dominant mutation in the COL2A1 gene was found in a 38-week-old fetus with hypochondrogenesis. Denaturing gradient gel electrophoresis was used to analyze all 44 exons coding for the triple helical domain of COL2A1 gene and the corresponding exon-intron boundaries. The tech nique detected a new sequence variation in exon 35. Sequencing of exon 35 demonstrated a single base mutation that converted the codon for g lycine at position 604 to a codon for alanine. Electrophoresis of peps in-digested collagen extracted from the diseased cartilage showed a do ublet band of the alpha 1(II) chain of type II collagen and the presen ce of alpha 1(I) and alpha 2(I) chains of type I collagen. Two-dimensi onal analysis of cyanogen bromide peptides from the type II collagen r evealed post-translational overmodification of peptides CB12, CB11, CB 8, and CB10.5, whereas peptide CB9.7 migrated normally. Microscopic ex amination of cartilage showed that the mutation altered the organizati on of the growth plate. Also, articular chondrocytes contained large c isternae of rough endoplasmic reticulum. The density of the extracellu lar matrix was reduced, and the intensity of the staining with an anti body to type II collagen was diminished. In contrast, a significant st aining with an antibody to type I collagen was observed. In situ hybri dization with cRNA probes revealed a significant level of alpha 1(I) m RNA in the cytoplasm of the patient's chondrocytes. The signal for alp ha 1(II) mRNA was about the same in control samples. The results indic ated, therefore, that the genes for both type I and type II procollage ns were simultaneously expressed in chondrocytes from the patient.