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Several ways of promoting myelin repair in myelin disorders such as multiple sclerosis and certain types of leukodystrophies are currently being investigated. Numerous studies suggest that it is possible to repair the central nervous system (CNS) by cell transplantation or by enhancing endogenous remyelination. Investigations in animal models indicate that cell therapy results in robust anatomical and functional recovery of acute myelin lesions. These models are also used to explore and validate the role of candidate molecules to stimulate endogenous remyelination by activating the myelin competent population or providing neuroprotection. However, in view of the heterogeneity of the lesion environment in MS, it seems more likely that cell therapy alone will not be able to contribute efficiently to the repair of the lesion. Further developments should indicate whether combining multiple approaches will be more powerful to achieve global myelin repair in the CNS than applying these strategies alone.

In 14 patients with methylmalonic acidemia we studied the correlations between clinical severity (considered in terms of survival and number of acute episodes), daily tolerance to proteins (amounts of leucine, valine, methionine, threonine compatible with good health and a methylmalonic acid excretion below 4 mmol/24h), the in vivo response to vitamin B12 and the nature of the enzymatic defect. This study showed that 2 groups of patients with congenital methylmalonic acidemia may be delineated with respect to prognosis. In patients with complete methylmalonyl CoA mutase deficiency, unresponsive to vitamin B12 in vitro and in vivo, the disease begins most often in the neonatal period and evolution is severe, with frequent acute episodes. Their tolerance to precursor aminoacids is similar to the minimal need (10-15 moles i.e. a total proteic intake of 6-9 g/24 h). None of the 8 patients of this group survived for more than 3 years. Conversely, in the second group (patients with normal in vitro MMCoA mutase activity in the presence of vitamin B12 in excess) the disease begins later, evolution is less severe and tolerance to protein intake is normal or subnormal. However, in this group, in vivo response to vitamin B12 is not constant.