Frequency of glycogen storage disease type II in The Netherlands: implications for diagnosis and genetic counselling

Glycogen storage disease type II (GSD II) is an autosomal recessive myopath y, Early and late-onset phenotypes are distinguished - infantile, juvenile and adult, Three mutations in the acid a-glucosidase gene are common in the Dutch patient population: IVS1(-13F-->G), 525delT and delexon18 63% of Dut ch GSD II patients carry one or two of these mutations, and the genotype-ph enotype correlation is known, To determine the frequency of GSD II, we have screened an unselected sample of neonates for the occurrence of these thre e mutations. Based on the calculated carrier frequencies, the predicted fre quency of the disease is 1 in 40 000 divided by 1 in 138 000 for infantile G SD II and 1 in 57 000 for adult GSD II. This is about two to four times h igher than previously suggested, which is a reason to become more familiar with the presentation of GSD II in its different clinical forms and to adju st the risk assessment for genetic counselling.