Muscle glycogenoses

There are 11 hereditary disorders of glycogen metabolism affecting muscle a lone or together with other tissues, and they cause two main clinical syndr omes: episodic, recurrent exercise intolerance with cramps, myalgia, and my oglobinuria; or fixed, often progressive weakness, Great strides have been made in our understanding of the molecular bases of these disorders, all of which show remarkable genetic heterogeneity. In contrast, the pathophysiol ogical mechanisms underlying acute muscle breakdown and chronic weakness re main unclear. Although glycogen storage diseases have been studied for deca des. new biochemical defects are still being discovered, especially in the glycolytic pathway. In addition, the pathogenesis of polyglucosan depositio n is being clarified both in traditional glycogenoses and in disorders such as Lafora's disease. In some conditions, combined dietary and exercise reg imens may be of help, and gene therapy, including recombinant enzyme replac ement, is being actively pursued. (C) 2001 John Wiley & Sons, Inc.