Glycogen storage diseases (GSDs) result from the deficiency of enzymes involved in glycogen synthesis and breakdown into glucose. Mutations in the gene PHKA2 encoding phosphorylase kinase regulatory subunit alpha 2 have been linked to GSD type IXa. We describe a family with two adult brothers with neonatal hepatosplenomegaly and later onset of hearing loss, cognitive impairment, and cerebellar involvement. Whole-exome sequencing was performed on both subjects and revealed a shared hemizygous missense variant (c.A1561G; p.T521A) in exon 15 of PHKA2. The phenotype broadens the clinical and magnetic resonance imaging spectrum of GSD type IXa to include later onset neurological manifestations.
