The use of CRISPR/Cas often unavoidably leads to typical patterns of genetic changes. Specific genetic information is often present several times in the genome of plants. This seems also to be the case with edible mushrooms. The gene scissors cut at all points where there are corresponding gene sequences. As a result, these plants show a certain pattern of genetic modification that would often be difficult, or impossible, to achieve with conventional breeding, even though no additional genes are inserted. The resulting new gene combinations are also associated with new biological properties and new risks.
In the USA, edible mushrooms were created using new genetic engineering techniques, i.e. (CRISPR/Cas), to stop cut surfaces from turning brown; the mushrooms were meant to have a longer storage and shelf-life. This was achieved by destroying the structure of a certain gene present in the fungus in several copies. Using CRISPR meant that the fungus was changed in several locations at the same time. Such a pattern of genetic change would not appear spontaneously.
The responsible US authority, APHIS, approved the mushrooms in April 2016. This was because it was, in their view, sufficient that the developers of the fungus said that no additional DNA had been inserted. No further investigations were required to check whether other substances in the mushrooms had changed. No data on unwanted changes in the genome were submitted. As a result, there is no scientific publication on how exactly the properties of these mushrooms were intentionally or unintentionally changed.
This example shows: without a legally prescribed authorisation procedure, there is insufficient data to assess the risks of eating genetically engineered organisms.
Further, it is hardly possible to develop reliable methods of identifying such foods. However, if the relevant data were available, verification methods are generally not a problem.