Abstract

INTRODUCTION

McArdle’s disease (McArdle 1951) (myophosphorylase deficiency, glycogen storage disease type V, OMIM 232600) is undoubtedly rare. No accurate incidence figures are available. Even large specialist muscle clinics are unlikely to see more than one new case a year. In the United Kingdom (population ~55 million), 55 patients are known to the Association for Glycogen Storage Disease (http://www.agsd.org.uk/). Despite its rarity, it is worth having some knowledge about it for two main reasons. Firstly, it is a diagnosis often considered in patients presenting with exercise induced myalgia or myoglobinuria, and it is important to know how to exclude it. Secondly, an understanding of the biochemical basis of the disease provides insight into other metabolic myopathies.

It is an autosomal recessive disorder, but in reported cases there is a higher frequency of males. The myophosphorylase gene is on chromosome 11. Many mutations have been reported, and compound heterozygotes are common (Tsujino