There has been intensive research and some progress in ways of modifying the underlying disease process for a number of inborn errors of metabolism. In the context of metabolic bone diseases, most progress has been made in the lysosomal storage disorders, notably mucopolysaccharidoses types I, II, and VI. However the indications for these treatments have to be carefully evaluated, as not all disease subtypes are suitable. For example, there are significant differences between mucopolysaccharidoses I-H, I-HS, and I-S. Whether or not an individual patient is suitable for any of these therapies requires careful scrutiny by multidisciplinary teams.
- Bone marrow transplantation: Most published data refer to mucopolysaccharidosis I-H, where success rates for bone marrow transplantation are in the order of 80% in appropriately selected cases.
- Enzyme replacement therapy: Exogenous administration of the defective gene product has become possible for a number of inborn errors of metabolism. In the lysosomal disorders enzyme replacement therapy is now available for the treatment of some of the mucopolysaccharidoses including type I (and its subtypes), type II, and type VI. These treatments beneficially alter the systemic manifestations of the disease (8). However, enzyme replacement therapy does not prevent the evolution of myelopathy in children with lysosomal disorders.
- Bisphosphonate therapy: Reduced bone mineral density is a characteristic of osteogenesis imperfecta and Hajdu-Cheney syndrome. A growing body of evidence supports the efficacy of cyclic intravenous bisphosphonate administration in improving bone density. It is currently unclear whether this therapy can reduce the rate of progression of basilar invagination in these conditions.