Bone changes in mucopolysaccharidosis VI in cats and the effects of bone marrow transplantation: mechanical testing of long bones

Mucopolysaccharidosis VI (MPS VI) is a genetic lysosomal storage disease in which a defect in aryl sulfatase B leads to accumulation of the glycosaminoglycan dermatan sulfate and abnormalities in the development of cartilage and bone. A feline model of this disease was used to evaluate the efficacy of bone marrow transplant (BMT) therapy. Long bones from MPS VI cats (N = 6) and MPS VI + BMT cats (N = 7) were compared with control cats (N = 11) and control + BMT cats (N = 5) in mechanical tests. Dissected femurs and tibias were subjected to three-point bending and a subgroup of tibias were tested with the mechanical response tissue analyzer (MRTA) in which vibration is used to measure tissue impedance. Cats with MPS VI had markedly decreased stiffness and strength in both bone (p < 0.01). There was no significant difference in the MPS VI + BMT group. In the tibias, there was also decreased stiffness and strength in the control + BMT group as compared to controls (p < 0.05). However, when cross-sectional area was used to normalize for bone size there was good correlation with strength in both femurs (r = 0.907, p < 0.01) and tibias (r = 0.915, p < 0.1), and there were no significant differences between groups in the modulus of elasticity. In the tibias, in which stiffness was measured by MRTA, there was significant correlation with three-point bending stiffness. These results indicate that, in cats with MPS VI, the decreases in stiffness and strength of long bones can be largely accounted for by the decrease in bone size (osteopenia) that is present.