FIGURE 7.

Possible roles for laforin in malin in the formation of polyglucosan. We propose that laforin is a physiological glycogen phosphatase whose impairment leads to the structural abnormalities in glycogen described in this work and to Lafora body formation. The role of malin remains a matter of active investigation. Malin could act together with or upstream of laforin in the removal of phosphate from glycogen (a). Malin could function independently of laforin to reduce glycogen phosphorylation, such as by down-regulating the enzyme(s) responsible for glycogen phosphorylation (b). Alternatively, malin could suppress polyglucosan formation independently of glycogen phosphorylation by controlling glycogen metabolic enzymes (c), as has been proposed.