Rigid spine syndrome in Late-Onset Pompe Disease: a syndrome of paravertebral muscle hyperactivity

Abstract

Late-onset Pompe disease (LOPD) with rigid spine syndrome (RSS) is a rare phenotype. We report a Chinese man with RSS and mild proximal lower limb weakness since 15 years old.  Imaging of paravertebral muscles was normal, while electromyography showed continuous complex repetitive discharges, suggesting paravertebral muscle hyperactivity as a cause of rigidity. Unlike previous reported cases, he carried compound heterozygous GAA mutations, including the c.2238G>C, p.Trp746Cys allele, common in Chinese LOPD patients. Combined with two common pseudodeficiency alleles, his genotype predicted a more severe phenotype, as suggested by a very low acid alpha-glucosidase (GAA) activity (<0.1 µmol/L/hour) on dried blood spot test and a forced vital capacity of 40% of predicted values. Our case demonstrates the absence of genotype-phenotype correlation in LOPD patients with RSS. Continuous muscle hyperactivity could be a reason for spinal rigidity in our patient.