Background:
Glycogen branching enzyme (GBE) catalyzes the branching of linear glycogen chains to form soluble glycogen. A deficiency in GBE thus renders synthesized molecules (polyglucosans) insoluble. These polyglucosans precipitate in many tissues, leading to APBD.
Objective:
To report a unique presentation and infrequently reported mutation in Adult Polyglucosan Body Disease (APBD).
Results:
A 56-year-old male presented for progressive visual changes. He described initial painless discomfort with environmental light evolving to persistent visual snow, particularly upon light exposure. On exam, his cognition, cranial nerves, strength and coordination were intact. His bilateral biceps and brachioradialis reflexes were brisk. His sensory exam revealed a distal symmetric large-fiber peripheral polyneuropathy. MRI of the orbits, brain, and spinal cord revealed bilateral atrophy of the optic nerves, tracts, and optic chiasm; pontine white matter changes and extensive supratentorial leukoencephalopathy; and decreased caliber of the cervical spinal cord. A genetics panel for leukoencephalopathy revealed a pathogenic variant and likely pathogenic variant within GBE1: c.986A>C (p.Tyr329Ser) and c.2052+1G>T (splice donor), respectively.
Conclusions:
This report details an infrequently reported, likely pathogenic mutation within GBE1 with a unique initial phenotype in APBD.