Glycogenic myopathy: A case of skeletal muscle-glycogenosis in twins

Abstract

With two adult male twins aged 29, severe muscle fatigue was noted after every effort of a rhythmical nature, which in the last 2 years had worsened and then continued unchanged. Both men are well-developed and muscular, and without either atrophy or hypertrophy. They never passed brownish or dark urine. Muscular fatigue was checked by various exercises, while in connection with ischaemic exercises exhaustion ensued much sooner than in the absence of ischaemia and with healthy controls. Neurological investigation did not reveal any abnormality in our patients. Thorough laboratory, biochemical, and biopsy investigations yielded the folllowing findings in the case of one twin (Peter E.): 1. (1) Quiescent values of serum-pyruvic acid were found to be raised; at the end of the ischaemia effort experiment the serum pyruvic acid content rose to less than twice the initial value. 2. (2) With serum lactic acid, the quiescent value was at the normal upper limit; by the end of the ischaemic effort experiment, only a slight rise was noticeable. The relatively slight increase of serum pyruvic acid and serum lactic acid levels at the end of the ischaemic effort test indicated that anaerobic breakdown of muscles glycogen was partially inhibited. Biopsy was performed on bilateral samples from the quadriceps femoris muscle. Staining with haematoxylin-eosin and the Van Gieson and Mallory methods, revealed the presence of a strikingly large number of vacuoles filled, not with neutral fats or lipid substances, but with glycogen, acid mucopolysaccharides, perhaps mixed with other substances. The amount of muscle-glycogen was found histochemically to be increased, while muscle-phosphorylase activity remained approximately normal on the histochemical slides. With one twin (Peter E.) erythrocyte glycogen concentration was normal; with the other it was slightly increased. In the case of both patients, the glycogen isolated from the red blood cells was of pathological structure. Judged by the above histological and histochemical evidence, our case stands nearest to case No. 2 of Thomson et al. [ J. Neurol. Neurosurg. Psychiat. (1963) 26: 20]. With reference to the clinical findings, effort tests and ischaemic exercises, to serological, biopsy-histological and -histochemical findings, our case can be probably placed within the “type-5” group of the glycogenosis table of Stetten and Stetten [ Physiol. Rev. (1960) 40: 505] and Thomson et al., where no enzyme deficiency has been found to occur, but where numerous partial enzyme deficiencies may be deemed responsible. However, since glycogen structure has proved to be pathological in our cases, they may constitute a new, so far unknown subgroup of “type 5”. This is the first occasion in the literature, where glycogen myopathy has been observed in twins.