Fetal-onset severe skeletal muscle glycogenosis associated with phosphorylase-b kinase deficiency

We report on a premature newborn girl delivered after 32 weeks of gestation by cesarean section after sparse limb movements, fetal tachycardia and lat e heart rate decelerations had suggested fetal distress. Following 1 day of mechanical ventilation, adequate pulmonary gas exchange was achieved by sp ontaneous breathing. Main symptoms were virtually complete absence of spont aneous movements, increased flexor tonus of the extremities, and hypotonia of the trunk. Inability to suck or swallow required nasogastric gavage feed ing. There were no hypoglycemic episodes. Echocardiography revealed normal myocardial function. Creatine kinase was 237 U/l at 2 days of life, declini ng to normal values thereafter. Muscle biopsy revealed increased glycogen s torage with subsarcolemmal glycogen deposits and low phosphorylase-a activi ty while total phosphorylase was normal after in vitro activation, suggesti ve of phosphorylase-b kinase deficiency. No mutation was detected in exon 1 of the myophosphorylase gene. No psychomotor development was observed, and the infant died of central apnea at 3 months of age.