We report the clinical, neuro-imaging, pathological and biochemical features of an Italian family in which two siblings have the Adult Polyglucosan Body Disease (APBD). APBD is a rare autosomal recessive disorder characterized by a gradually progressive involvement of both the central and peripheral nervous systems caused by the deficiency of the glycogen branching enzyme (GBE1). The two affected siblings, a 64-year-old man and his 67-year-old sister who had complained of urinary urgency and sporadic incontinence and also progressive gait difficulty for 6 and 7 years respectively, had severely impaired deep sensations on direct examination and a moderately severe symmetrical, axonal sensory-motor neuropathy on electrophysiological testing. GBE1 activity was below 25% of the normal rate in leukocytes and sural nerves. The siblings were homozygous for the novel GBE1 mutation p.N541D. All other members of the pedigree are heterozygous and manifest no symptoms, even in the very elderly. The affected siblings showed polyglucosan bodies (PBs) included within non-myelinating Schwann cells and within lymphocyte vesicles, which were positive for the autophagy markers P62 and LC3-II at immunofluorescence microscopy.