A previous Alpk3–/– C57BL/6J mouse model14 failed to recapitulate the rapidly progressive and often fatal neonatal disease that is observed in human patients.3,6 We therefore acquired and studied an alternative model, C57BL/6N Alpk3+/– mice (MRC Harwell Institute), that was created by deleting a region encompassing exon 3 (Figure S4). The gene discussed is ALPK3; the disease is glycogen storage disease VI.