AbstractBackgroundGlycogen storage disease type IV (GSD‐IV) is a rare autosomal recessive disorder due to mutations in the GBE1 gene causing deficiency of the glycogen branching enzyme (GBE). Prenatal diagnosis has occasionally been performed by the measurement of the GBE activity in cultured chorionic villi (CV) cells.MethodsTwo unrelated probands with severe hypotonia at birth and death during the neonatal period were diagnosed with GSD‐IV on the basis of postmortem histological findings. DNA analysis revealed truncating GBE1 mutations in both families.ResultsPrenatal diagnosis was performed in subsequent pregnancies by determination of branching enzyme activity and DNA analysis of CV or cultured amniocytes. Detailed autopsies of the affected fetuses at 14 and 24 weeks of gestation demonstrated intracellular inclusions of abnormal glycogen characteristic of GSD‐IV.ConclusionPrenatal diagnosis of GSD‐IV by DNA analysis is highly accurate in genetically confirmed cases. Copyright © 2006 John Wiley & Sons, Ltd.