Pompe disease is an inherited disorder caused by a deficiency of alpha glucosidase, encoded by the GAA gene. Lysosomal glycogen accumulates in tissues, including muscles (most notably skeletal and cardiac) and the central nervous system.
Exon 6 of the mouse Gaa (glucosidase, alpha, acid) gene was targeted with a stop codon and neomycin cassette, and flanked by loxP sites to create this 6neo (or PD) knock-out allele. Low levels of transcript are detectable, but functional protein is absent.
At birth, mice that are homozygotes are viable, normal in size, and do not display any gross physical or behavioral abnormalities. By 3 weeks of age, light microscopy (PAS staining) reveals a progressive accumulation of lysosomal glycogen in heart and skeletal muscle, and the diaphragm.
Concomitant with accumulating glycogen is a significant reduction in the number of myofibrils and signs of damaged muscle structure. Reduced mobility and progressive muscle weakness are observed by 3-4 weeks of age. By 8-9 months of age, muscle glycogen storage and progressive muscle weakness are obvious but do not become clinically evident until 12 months of age, delaying clinical assessment of treatment efficacy. Adults are fertile. These mice recapitulate key features of glycogen storage disease type II (GSDII) and provide a model for studying the underlying mechanism of GSDII.
Of note, C57BL/6NJ-Gaatm1Jhng/J mice, available as Stock No. 034609, also survive into adulthood, however they carry a mutation orthologous to one found in human IOPD making it much “closer” in genetic homology to human Pompe Disease.
