Editor—The journal has previously published a letter entitled “Glycogen storage disease type II: frequency of three common mutant alleles and their associated clinical phenotypes studied in 121 patients”.1 The title of the letter has apparently led to the mistaken impression that all three of the mutations discussed (IVS1-13T→G, Δ525T, and Δexon 18) are common in the general patient population. The IVS1-13T→G mutation was found to be “common” in diverse white populations (Dutch and “non-Dutch”), confirming our previous report.2However, careful reading of the authors’ results and comments indicates that while the Δ525T and Δexon 18 mutations have a relatively high allele frequency in Dutch patients (>0.2), their frequency is much lower in patients from “non-Dutch” populations. Nonetheless, a subsequently published paper suggests that the exon 18 deletion should be preferentially screened for in non-Dutch patients,3 perpetuating the mistaken impression that Δexon 18 is very common in the general white population. We have been prompted to report our own unpublished data because of three manuscripts recently received by us for review, indicating the same misconceptions as to the frequency of the Δ525T and Δexon 18 mutations in diverse white populations. …